!> @addtogroup PrivateVarPar Private Variables and Parameters
!> List of private variables and parameters.
!> @addtogroup Interface Interfaces
!> List of explicitly defined interface.
!> @addtogroup Library Modules Libraries
!> List of modules containing libraries of procedures.
!> @addtogroup PublicProcedure Public Procedures
!> List of public procedures.
!> @addtogroup PrivateProcedure Private Procedures
!> List of private procedures.

!> @ingroup Library
!> @{
!> @defgroup Lib_VTK_IOLibrary Lib_VTK_IO
!> @}

!> @ingroup Interface
!> @{
!> @defgroup Lib_VTK_IOInterface Lib_VTK_IO
!> @}

!> @ingroup PrivateVarPar
!> @{
!> @defgroup Lib_VTK_IOPrivateVarPar Lib_VTK_IO
!> @}

!> @ingroup PublicProcedure
!> @{
!> @defgroup Lib_VTK_IOPublicProcedure Lib_VTK_IO
!> @}

!> @ingroup PrivateProcedure
!> @{
!> @defgroup Lib_VTK_IOPrivateProcedure Lib_VTK_IO
!> @}

!> @brief   This is a library of functions for Input and Output pure Fortran data in VTK format.
!> @details It is useful for Paraview visualization tool. Even though there are many wrappers/porting of the VTK source
!>          code (C++ code), there is not a Fortran one. This library is not a porting or a wrapper of the VTK code,
!>          but it only an exporter/importer of the VTK data format written in pure Fortran language (standard Fortran 2003 or
!>          higher) that can be used by Fortran coders (yes, there are still a lot of these brave coders...) without mixing Fortran
!>          with C++ language. Fortran is still the best language for high performance computing for scientific purpose, like CFD
!>          computing. It is necessary a tool to deal with VTK standard directly by Fortran code. The library was made to fill
!>          this empty: it is a simple Fortran module able to export native Fortran data into VTK data format and to import VTK
!>          data into a Fortran code, both in ascii and binary file format.
!>
!>          The library provides an automatic way to deal with VTK data format: all the formatting processes is nested into the
!>          library and users communicate with it by a simple API passing only native Fortran data (Fortran scalars and arrays).
!>
!>          The library is still in developing and testing, this is first usable release, but there are not all the features of
!>          the stable release (the importer is totally absent and the exporter is not complete). Surely there are a lot of bugs
!>          and the programming style is not the best, but the exporters are far-complete.
!>
!>          The supported VTK features are:
!>          - Exporters:
!>            - Legacy standard:
!>              - Structured Points;
!>              - Structured Grid;
!>              - Unstructured Grid;
!>              - Polydata (\b missing);
!>              - Rectilinear Grid;
!>              - Field (\b missing);
!>            - XML standard:
!>              - serial dataset:
!>                - Image Data (\b missing);
!>                - Polydata (\b missing);
!>                - Rectilinear Grid;
!>                - Structured Grid;
!>                - Unstructured Grid;
!>              - parallel (partitioned) dataset:
!>                - Image Data (\b missing);
!>                - Polydata (\b missing);
!>                - Rectilinear Grid;
!>                - Structured Grid;
!>                - Unstructured Grid;
!>              - composite dataset:
!>                - vtkMultiBlockDataSet;
!>          - Importers are \b missing.
!>
!>          @libvtk can handle multiple concurrent files and it is \b thread/processor-safe (meaning that can be safely used into
!>          parallel frameworks as OpenMP or MPI, see \ref SpeedUP "Parallel Frameworks Benchmarks").
!>
!>          The library is an open source project, it is distributed under the GPL v3. Anyone is interest to use, to develop or
!>          to contribute to @libvtk is welcome.
!>
!>          It can be found at: https://github.com/szaghi/Lib_VTK_IO
!>
!> @par VTK_Standard
!>      VTK, Visualization Toolkit, is an open source software that provides a powerful framework for the computer graphic, for
!>      the images processing and for 3D rendering. It is widely used in the world and so it has a very large community of users,
!>      besides the Kitware (The Kitware homepage can be found here: http://public.kitware.com) company provides professional
!>      support. The toolkit is written in C++ and a lot of porting/wrappers for Tcl/Tk, Java and Python are provided, unlucky
!>      there aren't wrappers for Fortran.
!>
!>      Because of its good features the VTK toolkit has been used to develop a large set of open source programs. For my work
!>      the most important family of programs is the scientific visualization programs. A lot of high-quality scientific
!>      visualization tool are available on the web but for me the best is ParaView: I think that it is one of the best
!>      scientific visualization program in the world and it is open source! Paraview is based on VTK.
!> @par Paraview
!>      ParaView (The ParaView homepage can be found here: http://www.paraview.org) is an open source software voted to scientific
!>      visualization and able to use the power of parallel architectures. It has an architecture client-server in order to make
!>      easy the remote visualization of very large set of data. Because it is based on VTK it inherits all VTK features. ParaView
!>      is very useful for Computational Fluid Dynamics visualizations because it provides powerful post-processing tools, it
!>      provides a very large set of importers for the most used format like Plot3D and HDF (the list is very large). It is easy to
!>      extend ParaView because it supports all the scripting language supported by VTK.
!> @note All the @libvtk functions are <b>I4P integer functions</b>: the returned integer output is 0 if the function calling has
!> been completed right while it is >0  if some errors occur (the error handling is only at its embryonic phase). Therefore the
!> functions calling must be done in the following way: \n
!> @code
!> ...
!> integer(I4P):: E_IO
!> ...
!> E_IO = VTK_INI(....
!> ... @endcode
!> @libvtk programming style is based on two main principles: <em>portable kind-precision</em> of reals and integers
!> variables and <em>dynamic dispatching</em>. Using <em>dynamic dispatching</em> @libvtk has a simple API. The user calls
!> a generic procedure (VTK_INI, VTK_GEO,...) and the library, depending on the type and number of the inputs passed, calls the
!> correct internal function (i.e. VTK_GEO for R8P real type if the input passed is R8P real type). By this interface only few
!> functions are used without the necessity of calling a different function for each different input type.
!> Dynamic dispatching is based on the internal kind-precision/rank selecting convention: Fortran 90/95 standard has introduced some
!> useful functions to achieve the portability of reals and integers precision and @libvtk uses these functions to define portable
!> kind-precision; to this aim @libvtk uses IR_Precision module.
!> @author    Stefano Zaghi
!> @version   1.1
!> @date      2013-05-23
!> @par News
!> - Added packed API and 3D(or higher) arrays for VTK_VAR_XML function: this avoids the necessity of explicit reshape of
!>   multi-dimensional arrays containing saved variables in VAR callings; the following inputs are now available:
!>   - scalar input:
!>     - input is 1D-rank array: var[1:NC_NN];
!>     - input is 3D-rank array: var[nx1:nx2,ny1:ny2,nz1:nz2];
!>   - vectorial inputs:
!>     - inputs are 1D-rank arrays: varX[1:NC_NN],varY[1:NC_NN],varZ[1:NC_NN];
!>     - inputs are 3D-rank arrays: varX[nx1:nx2,ny1:ny2,nz1:nz2],varY[nx1:nx2,ny1:ny2,nz1:nz2],varX[nx1:nx2,ny1:ny2,nz1:nz2];
!>   - 3D(or higher) vectorial inputs:
!>     - input is 1D-rank (packed API): var[1:N_COL,1:NC_NN];
!>     - input is 3D-rank (packed API): var[1:N_COL,nx1:nx2,ny1:ny2,nz1:nz2].
!> - Added packed API and 3D arrays for VTK_GEO and VTK_GEO_XML function: this avoids the necessity of explicit reshape of
!>   multi-dimensional arrays containing X, Y and Z coordinates in GEO callings; the following inputs are now available:
!>   - StructuredGrid (NN is the number of grid points, n\#1-n\#2, \#x,y,z are the domain extents):
!>     - 1D arrays of size NN: X[1:NN],Y[1:NN],Z[1:NN];
!>     - 3D arrays of size NN: X[nx1:nx2,ny1:ny2,nz1:nz2],Y[nx1:nx2,ny1:ny2,nz1:nz2],Z[nx1:nx2,ny1:ny2,nz1:nz2];
!>     - 1D array of size 3*NN (packed API): XYZ[1:3,1:NN];
!>     - 3D array of size 3*NN (packed API): XYZ[1:3,nx1:nx2,ny1:ny2,nz1:nz2].
!>   - UnStructuredGrid (NN is the number of grid points):
!>     - 1D arrays of size NN: X[1:NN],Y[1:NN],Z[1:NN];
!>     - 1D array of size 3*NN (packed API): XYZ[1:3,1:NN].
!> - Added base64 encoding format: the output format specifier of VTK_INI_XML has been changed:
!>   - output_format = 'ascii' means \b ascii data, the same as the previous version;
!>   - output_format = 'binary' means \b base64 encoded data, different from the previous version where it meant appended
!>     raw-binary data; base64 encoding was missing in the previous version;
!>   - output_format = 'raw' means \b appended \b raw-binary data, as 'binary' of the previous version;
!> - Added support for OpenMP multi-threads framework;
!> - Correct bug affecting binary output;
!> - implement concurrent multiple files IO capability;
!> - implement FieldData tag for XML files, useful for tagging dataset with global auxiliary data, e.g. time, time step, ecc;
!> - implement Parallel (Partitioned) XML files support (.pvtu,.pvts,.pvtr);
!> - implement Driver testing program for providing practical examples of @libvtk usage;
!> - added support for parallel framework, namely OpenMP (thread-safe) and MPI (process-safe).
!> @copyright GNU Public License version 3.
!> @note The supported compilers are GNU gfortran 4.7.x (or higher) and Intel Fortran 12.x (or higher). @libvtk needs a modern
!> compiler providing support for some Fortran standard 2003 features.
!> @todo \b CompleteExporter: Complete the exporters
!> @todo \b CompleteImporter: Complete the importers
!> @todo \b DocExamples: Complete the documentation of examples
!> @todo \b g95_test: Test g95 compiler
!> @bug <b>XML-Efficiency</b>: \n This is not properly a bug. There is an inefficiency when saving XML raw (binary) file. To write
!>                             raw data into XML file @libvtk uses a temporary scratch file to save binary data while saving all
!>                             formatting data to the final XML file. Only when all XML formatting data have been written the
!>                             scratch file is rewind and the binary data is saved in the final tag of XML file as \b raw
!>                             \b appended data. This approach is not efficient.
!> @ingroup Lib_VTK_IOLibrary
module Lib_VTK_IO
!-----------------------------------------------------------------------------------------------------------------------------------
USE IR_Precision                                                                ! Integers and reals precision definition.
USE Lib_Base64                                                                  ! Base64 encoding/decoding procedures.
USE, intrinsic:: ISO_FORTRAN_ENV, only: stdout=>OUTPUT_UNIT, stderr=>ERROR_UNIT ! Standard output/error logical units.
!-----------------------------------------------------------------------------------------------------------------------------------

!-----------------------------------------------------------------------------------------------------------------------------------
implicit none
private
save
! functions for VTK XML
public:: VTK_INI_XML
public:: VTK_FLD_XML
public:: VTK_GEO_XML
public:: VTK_CON_XML
public:: VTK_DAT_XML
public:: VTK_VAR_XML
public:: VTK_END_XML
! functions for VTM XML
public:: VTM_INI_XML
public:: VTM_BLK_XML
public:: VTM_WRF_XML
public:: VTM_END_XML
! functions for PVTK XML
public:: PVTK_INI_XML
public:: PVTK_GEO_XML
public:: PVTK_DAT_XML
public:: PVTK_VAR_XML
public:: PVTK_END_XML
! functions for VTK LEGACY
public:: VTK_INI
public:: VTK_GEO
public:: VTK_CON
public:: VTK_DAT
public:: VTK_VAR
public:: VTK_END
!-----------------------------------------------------------------------------------------------------------------------------------

!-----------------------------------------------------------------------------------------------------------------------------------
!> @brief Function for saving field data (global auxiliary data, eg time, step number, dataset name, etc).
!> VTK_FLD_XML is an interface to 7 different functions, there are 2 functions for real field data, 4 functions for integer one
!> and one function for open and close field data tag.
!> @remark VTK_FLD_XML must be called after VTK_INI_XML and befor VTK_GEO_XML. It must always called three times at least: 1) for
!> opening the FieldData tag, 2) for saving at least one FieldData entry and 3) for closing the FieldData tag.
!> Examples of usage are: \n
!> \b saving the time and step cicle counter of current dataset: \n
!> @code ...
!> real(R8P)::    time
!> integer(I4P):: step
!> ...
!> E_IO=VTK_FLD_XML(fld_action='open')
!> E_IO=VTK_FLD_XML(fld=time,fname='TIME')
!> E_IO=VTK_FLD_XML(fld=step,fname='CYCLE')
!> E_IO=VTK_FLD_XML(fld_action='close')
!> ... @endcode
!> @ingroup Lib_VTK_IOInterface
interface VTK_FLD_XML
  module procedure VTK_FLD_XML_OC, & ! open/close field data tag
                   VTK_FLD_XML_R8, & ! real(R8P)    scalar
                   VTK_FLD_XML_R4, & ! real(R4P)    scalar
                   VTK_FLD_XML_I8, & ! integer(I8P) scalar
                   VTK_FLD_XML_I4, & ! integer(I4P) scalar
                   VTK_FLD_XML_I2, & ! integer(I2P) scalar
                   VTK_FLD_XML_I1    ! integer(I1P) scalar
endinterface
!> @brief Function for saving mesh with different topologies in VTK-XML standard.
!> VTK_GEO_XML is an interface to 15 different functions; there are 2 functions for each of 3 topologies supported and a function
!> for closing XML pieces: one function for mesh coordinates with R8P precision and one for mesh coordinates with R4P precision.
!> @remark 1D/3D-rank arrays and packed API for any kinds \n
!> - For StructuredGrid there are 4 functions for each real kinds:
!>   - inputs are 1D-rank arrays: X[1:NN],Y[1:NN],Z[1:NN];
!>   - inputs are 3D-rank arrays: X[nx1:nx2,ny1:ny2,nz1:nz2],Y[nx1:nx2,ny1:ny2,nz1:nz2],Z[nx1:nx2,ny1:ny2,nz1:nz2];
!>   - input is 1D-rank array (packed API): XYZ[1:3,1:NN];
!>   - input is 3D-rank array (packed API): XYZ[1:3,nx1:nx2,ny1:ny2,nz1:nz2].
!> - For UnStructuredGrid there are 2 functions for each real kinds:
!>   - inputs are 1D arrays: X[1:NN],Y[1:NN],Z[1:NN];
!>   - input is 1D array (packed API): XYZ[1:3,1:NN].
!>
!> @remark VTK_GEO_XML must be called after VTK_INI_XML. It saves the mesh geometry. The inputs that must be passed
!> change depending on the topologies chosen. Not all VTK topologies have been implemented (\em polydata topologies are absent).
!> @note The XML standard is more powerful than legacy. XML file can contain more than 1 mesh with its
!> associated variables. Thus there is the necessity to close each \em pieces that compose the data-set saved in the
!> XML file. The VTK_GEO_XML called in the <em>close piece</em> format is used just to close the
!> current piece before saving another piece or closing the file. \n
!> Examples of usage are: \n
!> \b Structured grid calling: \n
!> @code ...
!> integer(I4P):: nx1,nx2,ny1,ny2,nz1,nz2,NN
!> real(R8P)::    X(1:NN),Y(1:NN),Z(1:NN)
!> ...
!> E_IO=VTK_GEO_XML(nx1,nx2,ny1,ny2,nz1,nz2,Nn,X,Y,Z)
!> ... @endcode
!> \b Rectilinear grid calling: \n
!> @code ...
!> integer(I4P):: nx1,nx2,ny1,ny2,nz1,nz2
!> real(R8P)::    X(nx1:nx2),Y(ny1:ny2),Z(nz1:nz2)
!> ...
!> E_IO=VTK_GEO_XML(nx1,nx2,ny1,ny2,nz1,nz2,X,Y,Z)
!> ... @endcode
!> \b Unstructured grid calling: \n
!> @code ...
!> integer(I4P):: Nn,Nc
!> real(R8P)::    X(1:Nn),Y(1:Nn),Z(1:Nn)
!> ...
!> E_IO=VTK_GEO_XML(Nn,Nc,X,Y,Z)
!> ... @endcode
!> \b Closing piece calling: 1n
!> @code ...
!> E_IO=VTK_GEO_XML()
!> ... @endcode
!> @ingroup Lib_VTK_IOInterface
interface VTK_GEO_XML
  module procedure VTK_GEO_XML_STRG_1DA_R8, VTK_GEO_XML_STRG_3DA_R8,  & ! real(R8P) StructuredGrid, 1D/3D Arrays
                   VTK_GEO_XML_STRG_1DAP_R8,VTK_GEO_XML_STRG_3DAP_R8, & ! real(R8P) StructuredGrid, 1D/3D Arrays packed API
                   VTK_GEO_XML_STRG_1DA_R4, VTK_GEO_XML_STRG_3DA_R4,  & ! real(R4P) StructuredGrid, 1D/3D Arrays
                   VTK_GEO_XML_STRG_1DAP_R4,VTK_GEO_XML_STRG_3DAP_R4, & ! real(R4P) StructuredGrid, 1D/3D Arrays packed API
                   VTK_GEO_XML_RECT_R8,                               & ! real(R8P) RectilinearGrid
                   VTK_GEO_XML_RECT_R4,                               & ! real(R4P) RectilinearGrid
                   VTK_GEO_XML_UNST_R8,VTK_GEO_XML_UNST_PACK_R4,      & ! real(R8P) UnstructuredGrid, standard and packed API
                   VTK_GEO_XML_UNST_R4,VTK_GEO_XML_UNST_PACK_R8,      & ! real(R4P) UnstructuredGrid, standard and packed API
                   VTK_GEO_XML_CLOSEP                                   ! closing tag "Piece" function
endinterface
!> @brief Function for saving data variable(s) in VTK-XML standard.
!> VTK_VAR_XML is an interface to 36 different functions, there are 6 functions for scalar variables, 6 functions for vectorial
!> variables and 6 functions for 3D(or higher) vectorial variables: for all of types the precision can be R8P, R4P, I8P, I4P, I2P
!> and I1P. This function saves the data variables related (cell-centered or node-centered) to geometric mesh.
!> @remark 1D/3D-rank arrays and packed API for any kinds \n
!> The inputs arrays can be passed as 1D-rank or 3D-rank and the vectorial variables can be component-separated (one for each of
!> the 3 components) or packed into one multidimensional array:
!> - scalar input:
!>   - input is 1D-rank array: var[1:NC_NN];
!>   - input is 3D-rank array: var[nx1:nx2,ny1:ny2,nz1:nz2];
!> - vectorial inputs:
!>   - inputs are 1D-rank arrays: varX[1:NC_NN],varY[1:NC_NN],varZ[1:NC_NN];
!>   - inputs are 3D-rank arrays: varX[nx1:nx2,ny1:ny2,nz1:nz2],varY[nx1:nx2,ny1:ny2,nz1:nz2],varX[nx1:nx2,ny1:ny2,nz1:nz2];
!> - 3D(or higher) vectorial inputs:
!>   - input is 1D-rank (packed API): var[1:N_COL,1:NC_NN];
!>   - input is 3D-rank (packed API): var[1:N_COL,nx1:nx2,ny1:ny2,nz1:nz2].
!>
!> @remark Note that the inputs that must be passed change depending on the data variables type.
!>
!> @note Examples of usage are: \n
!> \b Scalar data calling: \n
!> @code ...
!> integer(I4P):: NN
!> real(R8P)::    var(1:NN)
!> ...
!> E_IO=VTK_VAR_XML(NN,'Sca',var)
!> ... @endcode
!> \b Vectorial data calling: \n
!> @code ...
!> integer(I4P):: NN
!> real(R8P)::    varX(1:NN),varY(1:NN),varZ(1:NN),
!> ...
!> E_IO=VTK_VAR_XML(NN,'Vec',varX,varY,varZ)
!> ... @endcode
!> @ingroup Lib_VTK_IOInterface
interface VTK_VAR_XML
  module procedure VTK_VAR_XML_SCAL_1DA_R8,VTK_VAR_XML_SCAL_3DA_R8, & ! real(R8P)    scalar    1D/3D array
                   VTK_VAR_XML_SCAL_1DA_R4,VTK_VAR_XML_SCAL_3DA_R4, & ! real(R4P)    scalar    1D/3D array
                   VTK_VAR_XML_SCAL_1DA_I8,VTK_VAR_XML_SCAL_3DA_I8, & ! integer(I8P) scalar    1D/3D array
                   VTK_VAR_XML_SCAL_1DA_I4,VTK_VAR_XML_SCAL_3DA_I4, & ! integer(I4P) scalar    1D/3D array
                   VTK_VAR_XML_SCAL_1DA_I2,VTK_VAR_XML_SCAL_3DA_I2, & ! integer(I2P) scalar    1D/3D array
                   VTK_VAR_XML_SCAL_1DA_I1,VTK_VAR_XML_SCAL_3DA_I1, & ! integer(I1P) scalar    1D/3D array
                   VTK_VAR_XML_VECT_1DA_R8,VTK_VAR_XML_VECT_3DA_R8, & ! real(R8P)    vectorial 1D/3D arrays
                   VTK_VAR_XML_VECT_1DA_R4,VTK_VAR_XML_VECT_3DA_R4, & ! real(R4P)    vectorial 1D/3D arrays
                   VTK_VAR_XML_VECT_1DA_I8,VTK_VAR_XML_VECT_3DA_I8, & ! integer(I8P) vectorial 1D/3D arrays
                   VTK_VAR_XML_VECT_1DA_I4,VTK_VAR_XML_VECT_3DA_I4, & ! integer(I4P) vectorial 1D/3D arrays
                   VTK_VAR_XML_VECT_1DA_I2,VTK_VAR_XML_VECT_3DA_I2, & ! integer(I2P) vectorial 1D/3D arrays
                   VTK_VAR_XML_VECT_1DA_I1,VTK_VAR_XML_VECT_3DA_I1, & ! integer(I1P) vectorial 1D/3D arrays
                   VTK_VAR_XML_LIST_1DA_R8,VTK_VAR_XML_LIST_3DA_R8, & ! real(R8P)    list      1D/3D array
                   VTK_VAR_XML_LIST_1DA_R4,VTK_VAR_XML_LIST_3DA_R4, & ! real(R4P)    list      1D/3D array
                   VTK_VAR_XML_LIST_1DA_I8,VTK_VAR_XML_LIST_3DA_I8, & ! integer(I4P) list      1D/3D array
                   VTK_VAR_XML_LIST_1DA_I4,VTK_VAR_XML_LIST_3DA_I4, & ! integer(I4P) list      1D/3D array
                   VTK_VAR_XML_LIST_1DA_I2,VTK_VAR_XML_LIST_3DA_I2, & ! integer(I2P) list      1D/3D array
                   VTK_VAR_XML_LIST_1DA_I1,VTK_VAR_XML_LIST_3DA_I1    ! integer(I1P) list      1D/3D array
endinterface
!> @brief Function for saving mesh with different topologies in VTK-legacy standard.
!> VTK_GEO is an interface to 16 different functions, there are 2 functions for each of 4 different topologies actually supported:
!> one function for mesh coordinates with R8P precision and one for mesh coordinates with R4P precision.
!> @remark This function must be called after VTK_INI. It saves the mesh geometry. The inputs that must be passed change depending
!> on the topologies chosen. Not all VTK topologies have been implemented (\em polydata topologies are absent).
!> @note Examples of usage are: \n
!> \b Structured points calling: \n
!> @code ...
!> integer(I4P):: Nx,Ny,Nz
!> real(I8P)::    X0,Y0,Z0,Dx,Dy,Dz
!> ...
!> E_IO=VTK_GEO(Nx,Ny,Nz,X0,Y0,Z0,Dx,Dy,Dz)
!> ... @endcode
!> \b Structured grid calling: \n
!> @code ...
!> integer(I4P):: Nx,Ny,Nz,Nnodes
!> real(R8P)::    X(1:Nnodes),Y(1:Nnodes),Z(1:Nnodes)
!> ...
!> E_IO=VTK_GEO(Nx,Ny,Nz,Nnodes,X,Y,Z)
!> ... @endcode
!> \b Rectilinear grid calling: \n
!> @code ...
!> integer(I4P):: Nx,Ny,Nz
!> real(R8P)::    X(1:Nx),Y(1:Ny),Z(1:Nz)
!> ...
!> E_IO=VTK_GEO(Nx,Ny,Nz,X,Y,Z)
!> ... @endcode
!> \b Unstructured grid calling: \n
!> @code ...
!> integer(I4P):: NN
!> real(R4P)::    X(1:NN),Y(1:NN),Z(1:NN)
!> ...
!> E_IO=VTK_GEO(NN,X,Y,Z)
!> ... @endcode
!> @ingroup Lib_VTK_IOInterface
interface VTK_GEO
  module procedure VTK_GEO_UNST_R8,VTK_GEO_UNST_P_R8,         & ! real(R8P) UNSTRUCTURED_GRID, standard and packed API
                   VTK_GEO_UNST_R4,VTK_GEO_UNST_P_R4,         & ! real(R4P) UNSTRUCTURED_GRID, standard and packed API
                   VTK_GEO_STRP_R8,                           & ! real(R8P) STRUCTURED_POINTS
                   VTK_GEO_STRP_R4,                           & ! real(R4P) STRUCTURED_POINTS
                   VTK_GEO_STRG_1DA_R8, VTK_GEO_STRG_3DA_R8,  & ! real(R8P) STRUCTURED_GRID 1D/3D arrays
                   VTK_GEO_STRG_1DAP_R8,VTK_GEO_STRG_3DAP_R8, & ! real(R8P) STRUCTURED_GRID 1D/3D arrays, packed API
                   VTK_GEO_STRG_1DA_R4, VTK_GEO_STRG_3DA_R4,  & ! real(R4P) STRUCTURED_GRID 1D/3D arrays
                   VTK_GEO_STRG_1DAP_R4,VTK_GEO_STRG_3DAP_R4, & ! real(R4P) STRUCTURED_GRID 1D/3D arrays, packed API
                   VTK_GEO_RECT_R8,                           & ! real(R8P) RECTILINEAR_GRID
                   VTK_GEO_RECT_R4                              ! real(R4P) RECTILINEAR_GRID
endinterface
!> @brief Function for saving data variable(s) in VTK-legacy standard.
!> VTK_VAR is an interface to 8 different functions, there are 3 functions for scalar variables, 3 functions for vectorial
!> variables and 2 functions texture variables: scalar and vectorial data can be R8P, R4P and I4P data while texture variables can
!> be only R8P or R4P.
!> This function saves the data variables related to geometric mesh.
!> @remark The inputs that must be passed change depending on the data
!> variables type.
!> @note Examples of usage are: \n
!> \b Scalar data calling: \n
!> @code ...
!> integer(I4P):: NN
!> real(R4P)::    var(1:NN)
!> ...
!> E_IO=VTK_VAR(NN,'Sca',var)
!> ... @endcode
!> \b Vectorial data calling: \n
!> @code ...
!> integer(I4P):: NN
!> real(R4P)::    varX(1:NN),varY(1:NN),varZ(1:NN)
!> ...
!> E_IO=VTK_VAR('vect',NN,'Vec',varX,varY,varZ)
!> ... @endcode
!> @ingroup Lib_VTK_IOInterface
interface VTK_VAR
  module procedure VTK_VAR_SCAL_R8, & ! real(R8P)    scalar
                   VTK_VAR_SCAL_R4, & ! real(R4P)    scalar
                   VTK_VAR_SCAL_I4, & ! integer(I4P) scalar
                   VTK_VAR_VECT_R8, & ! real(R8P)    vectorial
                   VTK_VAR_VECT_R4, & ! real(R4P)    vectorial
                   VTK_VAR_VECT_I4, & ! integer(I4P) vectorial
                   VTK_VAR_TEXT_R8, & ! real(R8P)    vectorial (texture)
                   VTK_VAR_TEXT_R4    ! real(R4P)    vectorial (texture)
endinterface
!-----------------------------------------------------------------------------------------------------------------------------------

!-----------------------------------------------------------------------------------------------------------------------------------
!> @ingroup Lib_VTK_IOPrivateVarPar
!> @{
! The library uses a small set of internal variables that are private (not accessible from the outside). The following are
! private variables.
! Parameters:
integer(I4P), parameter:: maxlen  = 500      !< Max number of characters of static string.
character(1), parameter:: end_rec = char(10) !< End-character for binary-record finalize.
integer(I4P), parameter:: ascii   = 0        !< Ascii-output-format parameter identifier.
integer(I4P), parameter:: binary  = 1        !< Base64-output-format parameter identifier.
integer(I4P), parameter:: raw     = 2        !< Raw-appended-binary-output-format parameter identifier.
integer(I4P), parameter:: bin_app = 3        !< Base64-appended-output-format parameter identifier.
! VTK file data:
type:: Type_VTK_File
  integer(I4P)::          f        = ascii !< Current output-format (initialized to ascii format).
  character(len=maxlen):: topology = ''    !< Mesh topology.
  integer(I4P)::          u        = 0_I4P !< Logical unit.
  integer(I4P)::          ua       = 0_I4P !< Logical unit for raw binary XML append file.
#ifdef HUGE
  integer(I8P)::          N_Byte   = 0_I8P !< Number of byte to be written/read.
#else
  integer(I4P)::          N_Byte   = 0_I4P !< Number of byte to be written/read.
#endif
  integer(I8P)::          ioffset  = 0_I8P !< Offset pointer.
  integer(I4P)::          indent   = 0_I4P !< Indent pointer.
  contains
    procedure:: byte_update ! Procedure for updating N_Byte and ioffset pointer.
endtype Type_VTK_File
type(Type_VTK_File), allocatable:: vtk(:)       !< Global data of VTK files [1:Nvtk].
integer(I4P)::                     Nvtk = 0_I4P !< Number of (concurrent) VTK files.
integer(I4P)::                     f    = 0_I4P !< Current VTK file index.
! VTM file data:
type:: Type_VTM_File
  integer(I4P):: u      = 0_I4P !< Logical unit.
  integer(I4P):: blk    = 0_I4P !< Block index.
  integer(I4P):: indent = 0_I4P !< Indent pointer.
endtype Type_VTM_File
type(Type_VTM_File):: vtm !< Global data of VTM files.
!> @}
!-----------------------------------------------------------------------------------------------------------------------------------
contains
  ! The library uses five auxiliary procedures that are private thus they cannot be called outside the library.
  !> @ingroup Lib_VTK_IOPrivateProcedure
  !> @{
  !> @brief Function for getting a free logic unit. The users of @libvtk does not know which is the logical
  !>        unit: @libvtk uses this information without boring the users. The logical unit used is safe-free: if the program
  !>        calling @libvtk has others logical units used @libvtk will never use these units, but will choice one that is free.
  !>@return Free_Unit
  integer function Get_Unit(Free_Unit)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(OUT), optional:: Free_Unit !< Free logic unit.
  integer::                        n1        !< Counter.
  integer::                        ios       !< Inquiring flag.
  logical::                        lopen     !< Inquiring flag.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  Get_Unit = -1
  n1=1
  do
    if ((n1/=stdout).AND.(n1/=stderr)) then
      inquire(unit=n1,opened=lopen,iostat=ios)
      if (ios==0) then
        if (.NOT.lopen) then
          Get_Unit = n1 ; if (present(Free_Unit)) Free_Unit = Get_Unit
          return
        endif
      endif
    endif
    n1=n1+1
  enddo
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction Get_Unit

  !> @brief Function for converting lower case characters of a string to upper case ones. @libvtk uses this function in
  !>        order to achieve case-insensitive: all character variables used within @libvtk functions are pre-processed by
  !>        Uppper_Case function before these variables are used. So the users can call @libvtk functions without pay attention of
  !>        the case of the keywords passed to the functions: calling the function VTK_INI with the string
  !>        <em>E_IO = VTK_INI('Ascii',...)</em> is equivalent to <em>E_IO = VTK_INI('ASCII',...)</em>.
  !>@return Upper_Case
  elemental function Upper_Case(string)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  character(len=*), intent(IN):: string     !< String to be converted.
  character(len=len(string))::   Upper_Case !< Converted string.
  integer::                      n1         !< Characters counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  Upper_Case = string
  do n1=1,len(string)
    select case(ichar(string(n1:n1)))
    case(97:122)
      Upper_Case(n1:n1)=char(ichar(string(n1:n1))-32) ! Upper case conversion
    endselect
  enddo
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction Upper_Case

  !> @brief Subroutine for updating N_Byte and ioffset pointer.
  elemental subroutine byte_update(vtk,N_Byte)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  class(Type_VTK_File), intent(INOUT):: vtk    !< Global data of VTK file.
#ifdef HUGE
  integer(I8P),         intent(IN)::    N_Byte !< Number of bytes saved.
#else
  integer(I4P),         intent(IN)::    N_Byte !< Number of bytes saved.
#endif
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  vtk%N_Byte = N_Byte
  if (vtk%f==raw) then
#ifdef HUGE
    vtk%ioffset = vtk%ioffset + BYI8P + N_Byte
#else
    vtk%ioffset = vtk%ioffset + BYI4P + N_Byte
#endif
  else
#ifdef HUGE
    vtk%ioffset = vtk%ioffset + ((N_Byte + BYI8P + 2_I8P)/3_I8P)*4_I8P
#else
    vtk%ioffset = vtk%ioffset + ((N_Byte + BYI4P + 2_I4P)/3_I4P)*4_I4P
#endif
  endif
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endsubroutine byte_update

  !> @brief Subroutine for updating (adding and removing elements into) vtk array.
  pure subroutine vtk_update(act,cf,Nvtk,vtk)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  character(*),                     intent(IN)::    act        !< Action: 'ADD' one more element, 'REMOVE' current element file.
  integer(I4P),                     intent(INOUT):: cf         !< Current file index (for concurrent files IO).
  integer(I4P),                     intent(INOUT):: Nvtk       !< Number of (concurrent) VTK files.
  type(Type_VTK_File), allocatable, intent(INOUT):: vtk(:)     !< VTK files data.
  type(Type_VTK_File), allocatable::                vtk_tmp(:) !< Temporary array of VTK files data.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  select case(Upper_Case(trim(act)))
  case('ADD')
    if (Nvtk>0_I4P) then
      allocate(vtk_tmp(1:Nvtk))
      vtk_tmp = vtk
      deallocate(vtk)
      Nvtk = Nvtk + 1
      allocate(vtk(1:Nvtk))
      vtk(1:Nvtk-1) = vtk_tmp
      deallocate(vtk_tmp)
      cf = Nvtk
    else
      Nvtk = 1_I4P
      allocate(vtk(1:Nvtk))
      cf = Nvtk
    endif
  case default
    if (Nvtk>1_I4P) then
      allocate(vtk_tmp(1:Nvtk-1))
      if (cf==Nvtk) then
        vtk_tmp = vtk(1:Nvtk-1)
      else
        vtk_tmp(1 :cf-1) = vtk(1   :cf-1)
        vtk_tmp(cf:    ) = vtk(cf+1:    )
      endif
      deallocate(vtk)
      Nvtk = Nvtk - 1
      allocate(vtk(1:Nvtk))
      vtk = vtk_tmp
      deallocate(vtk_tmp)
      cf = 1_I4P
    else
      Nvtk = 0_I4P
      if (allocated(vtk)) deallocate(vtk)
      cf = Nvtk
    endif
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endsubroutine vtk_update

  !> @brief Function for converting array of 1 character to a string of characters. It is used for writing the stream of base64
  !> encoded data.
  pure function tochar(string) result (char_string)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  character(1), intent(IN)::      string(1:)  !< Array of 1 character.
  character(size(string,dim=1)):: char_string !< String of characters.
  integer(I4P)::                  i           !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  forall(i = 1:size(string,dim=1))
     char_string(i:i) = string(i)
  endforall
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction tochar
  !> @}

  !> @brief Function for initializing VTK-XML file.
  !> The XML standard is more powerful than legacy one. It is flexible but on the other hand is (but not so more using a library
  !> like @libvtk...) complex than legacy standard. The output of XML functions is a well-formated valid XML file, at least for the
  !> ascii, binary and binary appended formats (in the raw-binary format @libvtk uses raw-binary-appended format that is not a valid
  !> XML file).
  !> Note that the XML functions have the same name of legacy functions with the suffix \em XML.
  !> @remark This function must be the first to be called.
  !> @note Supported output formats are (the passed specifier value is case insensitive):
  !> - ASCII: data are saved in ASCII format;
  !> - BINARY: data are saved in base64 encoded format;
  !> - RAW: data are saved in raw-binary format in the appended tag of the XML file;
  !> - BINARY-APPENDED: data are saved in base64 encoded format in the appended tag of the XML file.
  !> @note Supported topologies are:
  !> - RectilinearGrid;
  !> - StructuredGrid;
  !> - UnstructuredGrid.
  !> @note An example of usage is: \n
  !> @code ...
  !> integer(I4P):: nx1,nx2,ny1,ny2,nz1,nz2
  !> ...
  !> E_IO = VTK_INI_XML('BINARY','XML_RECT_BINARY.vtr','RectilinearGrid',nx1=nx1,nx2=nx2,ny1=ny1,ny2=ny2,nz1=nz1,nz2=nz2)
  !> ... @endcode
  !> Note that the file extension is necessary in the file name. The XML standard has different extensions for each
  !> different topologies (e.g. \em vtr for rectilinear topology). See the VTK-standard file for more information.
  !> @return E_IO: integer(I4P) error flag
  function VTK_INI_XML(output_format,filename,mesh_topology,cf,nx1,nx2,ny1,ny2,nz1,nz2) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  character(*), intent(IN)::            output_format !< Output format: ASCII, BINARY, RAW or BINARY-APPENDED.
  character(*), intent(IN)::            filename      !< File name.
  character(*), intent(IN)::            mesh_topology !< Mesh topology.
  integer(I4P), intent(OUT), optional:: cf            !< Current file index (for concurrent files IO).
  integer(I4P), intent(IN),  optional:: nx1           !< Initial node of x axis.
  integer(I4P), intent(IN),  optional:: nx2           !< Final node of x axis.
  integer(I4P), intent(IN),  optional:: ny1           !< Initial node of y axis.
  integer(I4P), intent(IN),  optional:: ny2           !< Final node of y axis.
  integer(I4P), intent(IN),  optional:: nz1           !< Initial node of z axis.
  integer(I4P), intent(IN),  optional:: nz2           !< Final node of z axis.
  integer(I4P)::                        E_IO          !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::               s_buffer      !< Buffer string.
  integer(I4P)::                        rf            !< Real file index.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  if (.not.ir_initialized) call IR_Init
  call vtk_update(act='add',cf=rf,Nvtk=Nvtk,vtk=vtk)
  f = rf
  if (present(cf)) cf = rf
  vtk(rf)%topology = trim(mesh_topology)
  select case(trim(Upper_Case(output_format)))
  case('ASCII')
    vtk(rf)%f = ascii
    open(unit=Get_Unit(vtk(rf)%u),file=trim(filename),form='FORMATTED',&
         access='SEQUENTIAL',action='WRITE',status='REPLACE',iostat=E_IO)
    ! writing header of file
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)'<?xml version="1.0"?>'
    if (endian==endianL) then
      s_buffer = '<VTKFile type="'//trim(vtk(rf)%topology)//'" version="0.1" byte_order="LittleEndian">'
    else
      s_buffer = '<VTKFile type="'//trim(vtk(rf)%topology)//'" version="0.1" byte_order="BigEndian">'
    endif
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer) ; vtk(rf)%indent = 2
    select case(trim(vtk(rf)%topology))
    case('RectilinearGrid','StructuredGrid')
      s_buffer = repeat(' ',vtk(rf)%indent)//'<'//trim(vtk(rf)%topology)//' WholeExtent="'//&
                 trim(str(n=nx1))//' '//trim(str(n=nx2))//' '//                             &
                 trim(str(n=ny1))//' '//trim(str(n=ny2))//' '//                             &
                 trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    case('UnstructuredGrid')
      s_buffer = repeat(' ',vtk(rf)%indent)//'<'//trim(vtk(rf)%topology)//'>'
    endselect
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer) ; vtk(rf)%indent = vtk(rf)%indent + 2
  case('RAW','BINARY-APPENDED')
    vtk(rf)%f = raw
    if (trim(Upper_Case(output_format))=='BINARY-APPENDED') vtk(rf)%f = bin_app
    open(unit=Get_Unit(vtk(rf)%u),file=trim(filename),&
         form='UNFORMATTED',access='STREAM',action='WRITE',status='REPLACE',iostat=E_IO)
    ! writing header of file
    write(unit=vtk(rf)%u,iostat=E_IO)'<?xml version="1.0"?>'//end_rec
    if (endian==endianL) then
      s_buffer = '<VTKFile type="'//trim(vtk(rf)%topology)//'" version="0.1" byte_order="LittleEndian">'
    else
      s_buffer = '<VTKFile type="'//trim(vtk(rf)%topology)//'" version="0.1" byte_order="BigEndian">'
    endif
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = 2
    select case(trim(vtk(rf)%topology))
    case('RectilinearGrid','StructuredGrid')
      s_buffer = repeat(' ',vtk(rf)%indent)//'<'//trim(vtk(rf)%topology)//' WholeExtent="'//&
                 trim(str(n=nx1))//' '//trim(str(n=nx2))//' '//                             &
                 trim(str(n=ny1))//' '//trim(str(n=ny2))//' '//                             &
                 trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    case('UnstructuredGrid')
      s_buffer = repeat(' ',vtk(rf)%indent)//'<'//trim(vtk(rf)%topology)//'>'
    endselect
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    ! opening the SCRATCH file used for appending raw binary data
    open(unit=Get_Unit(vtk(rf)%ua), form='UNFORMATTED', access='STREAM', action='READWRITE', status='SCRATCH', iostat=E_IO)
    vtk(rf)%ioffset = 0 ! initializing offset pointer
  case('BINARY')
    vtk(rf)%f = binary
    open(unit=Get_Unit(vtk(rf)%u),file=trim(filename),&
         form='UNFORMATTED',access='STREAM',action='WRITE',status='REPLACE',iostat=E_IO)
    ! writing header of file
    write(unit=vtk(rf)%u,iostat=E_IO)'<?xml version="1.0"?>'//end_rec
    if (endian==endianL) then
      s_buffer = '<VTKFile type="'//trim(vtk(rf)%topology)//'" version="0.1" byte_order="LittleEndian">'
    else
      s_buffer = '<VTKFile type="'//trim(vtk(rf)%topology)//'" version="0.1" byte_order="BigEndian">'
    endif
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = 2
    select case(trim(vtk(rf)%topology))
    case('RectilinearGrid','StructuredGrid')
      s_buffer = repeat(' ',vtk(rf)%indent)//'<'//trim(vtk(rf)%topology)//' WholeExtent="'//&
                 trim(str(n=nx1))//' '//trim(str(n=nx2))//' '//                             &
                 trim(str(n=ny1))//' '//trim(str(n=ny2))//' '//                             &
                 trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    case('UnstructuredGrid')
      s_buffer = repeat(' ',vtk(rf)%indent)//'<'//trim(vtk(rf)%topology)//'>'
    endselect
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_INI_XML

  !> @ingroup Lib_VTK_IOPrivateProcedure
  !> @{
  !> Function for open/close field data tag.
  !> @return E_IO: integer(I4P) error flag
  function VTK_FLD_XML_OC(fld_action,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  character(*), intent(IN)::           fld_action !< Field data tag action: OPEN or CLOSE tag.
  integer(I4P), intent(IN), optional:: cf         !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO       !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf         !< Real file index.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(trim(Upper_Case(fld_action)))
  case('OPEN')
    select case(vtk(rf)%f)
    case(ascii)
      write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<FieldData>' ; vtk(rf)%indent = vtk(rf)%indent + 2
    case(raw,binary,bin_app)
      write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<FieldData>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    endselect
  case('CLOSE')
    select case(vtk(rf)%f)
    case(ascii)
      vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</FieldData>'
    case(raw,binary,bin_app)
      vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</FieldData>'//end_rec
    endselect
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_FLD_XML_OC

  !> Function for saving field data (global auxiliary data, e.g. time, step number, data set name...) (R8P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_FLD_XML_R8(fld,fname,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  real(R8P),    intent(IN)::           fld      !< Field data value.
  character(*), intent(IN)::           fname    !< Field data name.
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer !< Buffer string.
  integer(I1P), allocatable::          fldp(:)  !< Packed field data.
  character(1), allocatable::          fld64(:) !< Field data encoded in base64.
  integer(I4P)::                       rf       !< Real file index.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" NumberOfTuples="1" Name="'//trim(fname)//'" format="ascii">'//&
             trim(str(n=fld))//'</DataArray>'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer)
  case(raw,bin_app)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" NumberOfTuples="1" Name="'//trim(fname)// &
             '" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = int(BYR8P,I4P))
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R8',1_I4P
    write(unit=vtk(rf)%ua,iostat=E_IO)fld
  case(binary)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" NumberOfTuples="1" Name="'//trim(fname)//'" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(BYR8P,I4P)],a2=[fld],packed=fldp)
    call b64_encode(nB=int(BYI1P,I4P),n=fldp,code=fld64) ; deallocate(fldp)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(fld64)//end_rec ; deallocate(fld64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_FLD_XML_R8

  !> Function for saving field data (global auxiliary data, e.g. time, step number, data set name...) (R4P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_FLD_XML_R4(fld,fname,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  real(R4P),    intent(IN)::           fld      !< Field data value.
  character(*), intent(IN)::           fname    !< Field data name.
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer !< Buffer string.
  integer(I1P), allocatable::          fldp(:)  !< Packed field data.
  character(1), allocatable::          fld64(:) !< Field data encoded in base64.
  integer(I4P)::                       rf       !< Real file index.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" NumberOfTuples="1" Name="'//trim(fname)//'" format="ascii">'//&
             trim(str(n=fld))//'</DataArray>'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer)
  case(raw,bin_app)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" NumberOfTuples="1" Name="'//trim(fname)// &
             '" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = int(BYR4P,I4P))
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R4',1_I4P
    write(unit=vtk(rf)%ua,iostat=E_IO)fld
  case(binary)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" NumberOfTuples="1" Name="'//trim(fname)//'" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(BYR4P,I4P)],a2=[fld],packed=fldp)
    call b64_encode(nB=int(BYI1P,I4P),n=fldp,code=fld64) ; deallocate(fldp)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(fld64)//end_rec ; deallocate(fld64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_FLD_XML_R4

  !> Function for saving field data (global auxiliary data, e.g. time, step number, data set name...) (I8P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_FLD_XML_I8(fld,fname,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I8P), intent(IN)::           fld      !< Field data value.
  character(*), intent(IN)::           fname    !< Field data name.
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer !< Buffer string.
  integer(I1P), allocatable::          fldp(:)  !< Packed field data.
  character(1), allocatable::          fld64(:) !< Field data encoded in base64.
  integer(I4P)::                       rf       !< Real file index.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int64" NumberOfTuples="1" Name="'//trim(fname)//'" format="ascii">'// &
               trim(str(n=fld))//'</DataArray>'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer)
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int64" NumberOfTuples="1" Name="'//trim(fname)// &
               '" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = int(BYI8P,I4P))
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I8',1_I4P
    write(unit=vtk(rf)%ua,iostat=E_IO)fld
  case(binary)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Int64" NumberOfTuples="1" Name="'//trim(fname)//'" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(BYI8P,I4P)],a2=[fld],packed=fldp)
    call b64_encode(nB=int(BYI1P,I4P),n=fldp,code=fld64) ; deallocate(fldp)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(fld64)//end_rec ; deallocate(fld64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_FLD_XML_I8

  !> Function for saving field data (global auxiliary data, e.g. time, step number, data set name...) (I4P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_FLD_XML_I4(fld,fname,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           fld      !< Field data value.
  character(*), intent(IN)::           fname    !< Field data name.
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer !< Buffer string.
  integer(I1P), allocatable::          fldp(:)  !< Packed field data.
  character(1), allocatable::          fld64(:) !< Field data encoded in base64.
  integer(I4P)::                       rf       !< Real file index.
  integer(I8P)::                       Nfldp    !< Dimension of fldp, packed data.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" NumberOfTuples="1" Name="'//trim(fname)//'" format="ascii">'// &
               trim(str(n=fld))//'</DataArray>'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer)
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" NumberOfTuples="1" Name="'//trim(fname)// &
               '" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = int(BYI4P,I4P))
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I4',1_I4P
    write(unit=vtk(rf)%ua,iostat=E_IO)fld
  case(binary)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" NumberOfTuples="1" Name="'//trim(fname)//'" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    Nfldp=size(transfer([int(BYI4P,I4P),fld],fldp)) ; if (allocated(fldp)) deallocate(fldp) ; allocate(fldp(1:Nfldp))
    fldp = transfer([int(BYI4P,I4P),fld],fldp)
    call b64_encode(nB=int(BYI1P,I4P),n=fldp,code=fld64) ; deallocate(fldp)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(fld64)//end_rec ; deallocate(fld64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_FLD_XML_I4

  !> Function for saving field data (global auxiliary data, e.g. time, step number, data set name...) (I2P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_FLD_XML_I2(fld,fname,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I2P), intent(IN)::           fld      !< Field data value.
  character(*), intent(IN)::           fname    !< Field data name.
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer !< Buffer string.
  integer(I1P), allocatable::          fldp(:)  !< Packed field data.
  character(1), allocatable::          fld64(:) !< Field data encoded in base64.
  integer(I4P)::                       rf       !< Real file index.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int16" NumberOfTuples="1" Name="'//trim(fname)//'" format="ascii">'// &
               trim(str(n=fld))//'</DataArray>'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer)
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int16" NumberOfTuples="1" Name="'//trim(fname)// &
               '" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = int(BYI2P,I4P))
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I2',1_I4P
    write(unit=vtk(rf)%ua,iostat=E_IO)fld
  case(binary)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Int16" NumberOfTuples="1" Name="'//trim(fname)//'" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(BYI2P,I4P)],a2=[fld],packed=fldp)
    call b64_encode(nB=int(BYI1P,I4P),n=fldp,code=fld64) ; deallocate(fldp)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(fld64)//end_rec ; deallocate(fld64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_FLD_XML_I2

  !> Function for saving field data (global auxiliary data, e.g. time, step number, data set name...) (I1P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_FLD_XML_I1(fld,fname,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I1P), intent(IN)::           fld      !< Field data value.
  character(*), intent(IN)::           fname    !< Field data name.
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer !< Buffer string.
  integer(I1P), allocatable::          fldp(:)  !< Packed field data.
  character(1), allocatable::          fld64(:) !< Field data encoded in base64.
  integer(I4P)::                       rf       !< Real file index.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" NumberOfTuples="1" Name="'//trim(fname)//'" format="ascii">'// &
               trim(str(n=fld))//'</DataArray>'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer)
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" NumberOfTuples="1" Name="'//trim(fname)// &
               '" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = int(BYI1P,I4P))
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I1',1_I4P
    write(unit=vtk(rf)%ua,iostat=E_IO)fld
  case(binary)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" NumberOfTuples="1" Name="'//trim(fname)//'" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(BYI1P,I4P)],a2=[fld],packed=fldp)
    call b64_encode(nB=int(BYI1P,I4P),n=fldp,code=fld64) ; deallocate(fldp)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(fld64)//end_rec ; deallocate(fld64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_FLD_XML_I1

  !> Function for saving mesh with \b StructuredGrid topology (R8P, 1D Arrays).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_XML_STRG_1DA_R8(nx1,nx2,ny1,ny2,nz1,nz2,NN,X,Y,Z,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           nx1      !< Initial node of x axis.
  integer(I4P), intent(IN)::           nx2      !< Final node of x axis.
  integer(I4P), intent(IN)::           ny1      !< Initial node of y axis.
  integer(I4P), intent(IN)::           ny2      !< Final node of y axis.
  integer(I4P), intent(IN)::           nz1      !< Initial node of z axis.
  integer(I4P), intent(IN)::           nz2      !< Final node of z axis.
  integer(I4P), intent(IN)::           NN       !< Number of all nodes.
  real(R8P),    intent(IN)::           X(1:)    !< X coordinates [1:NN].
  real(R8P),    intent(IN)::           Y(1:)    !< Y coordinates [1:NN].
  real(R8P),    intent(IN)::           Z(1:)    !< Z coordinates [1:NN].
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I1P), allocatable::          XYZp(:)  !< Packed coordinates data.
  character(1), allocatable::          XYZ64(:) !< X, Y, Z coordinates encoded in base64.
  character(len=maxlen)::              s_buffer !< Buffer string.
  integer(I4P)::                       rf       !< Real file index.
  integer(I4P)::                       n1       !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer) ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>' ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" NumberOfComponents="3" Name="Points" format="ascii">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer)
    do n1=1,NN
      write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//str(n=X(n1))//' '//str(n=Y(n1))//' '//str(n=Z(n1))
    enddo
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>' ; vtk(rf)%indent = vtk(rf)%indent - 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//                                                                  &
               '<DataArray type="Float64" NumberOfComponents="3" Name="Points" format="appended" offset="'// &
               trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = 3*NN*BYR8P)
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R8',3*NN
    write(unit=vtk(rf)%ua,iostat=E_IO)(X(n1),Y(n1),Z(n1),n1=1,NN)
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" NumberOfComponents="3" Name="Points" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(3*NN*BYR8P,I4P)],a2=[(X(n1),Y(n1),Z(n1),n1=1,NN)],packed=XYZp)
    call b64_encode(nB=int(BYI1P,I4P),n=XYZp,code=XYZ64) ; deallocate(XYZp)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(XYZ64)//end_rec ; deallocate(XYZ64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_XML_STRG_1DA_R8

  !> Function for saving mesh with \b StructuredGrid topology (R8P, 3D Arrays).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_XML_STRG_3DA_R8(nx1,nx2,ny1,ny2,nz1,nz2,NN,X,Y,Z,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           nx1               !< Initial node of x axis.
  integer(I4P), intent(IN)::           nx2               !< Final node of x axis.
  integer(I4P), intent(IN)::           ny1               !< Initial node of y axis.
  integer(I4P), intent(IN)::           ny2               !< Final node of y axis.
  integer(I4P), intent(IN)::           nz1               !< Initial node of z axis.
  integer(I4P), intent(IN)::           nz2               !< Final node of z axis.
  integer(I4P), intent(IN)::           NN                !< Number of all nodes.
  real(R8P),    intent(IN)::           X(nx1:,ny1:,nz1:) !< X coordinates [nx1:nx2,ny1:ny2,nz1:nz2].
  real(R8P),    intent(IN)::           Y(nx1:,ny1:,nz1:) !< Y coordinates [nx1:nx2,ny1:ny2,nz1:nz2].
  real(R8P),    intent(IN)::           Z(nx1:,ny1:,nz1:) !< Z coordinates [nx1:nx2,ny1:ny2,nz1:nz2].
  integer(I4P), intent(IN), optional:: cf                !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO              !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I1P), allocatable::          XYZp(:)           !< Packed coordinates data.
  character(1), allocatable::          XYZ64(:)          !< X, Y, Z coordinates encoded in base64.
  character(len=maxlen)::              s_buffer          !< Buffer string.
  integer(I4P)::                       rf                !< Real file index.
  integer(I4P)::                       nx,ny,nz          !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer) ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>' ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" NumberOfComponents="3" Name="Points" format="ascii">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer)
    do nz=nz1,nz2
      do ny=ny1,ny2
        do nx=nx1,nx2
          write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//&
                                                     str(n=X(nx,ny,nz))//' '//str(n=Y(nx,ny,nz))//' '//str(n=Z(nx,ny,nz))
        enddo
      enddo
    enddo
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>' ; vtk(rf)%indent = vtk(rf)%indent - 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//                                                                  &
               '<DataArray type="Float64" NumberOfComponents="3" Name="Points" format="appended" offset="'// &
               trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = 3*NN*BYR8P)
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R8',3*NN
    write(unit=vtk(rf)%ua,iostat=E_IO)(((X(nx,ny,nz),Y(nx,ny,nz),Z(nx,ny,nz),nx=nx1,nx2),ny=ny1,ny2),nz=nz1,nz2)
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" NumberOfComponents="3" Name="Points" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(3*NN*BYR8P,I4P)],a2=[(((X(nx,ny,nz),Y(nx,ny,nz),Z(nx,ny,nz),nx=nx1,nx2),ny=ny1,ny2),nz=nz1,nz2)],&
                   packed=XYZp)
    call b64_encode(nB=int(BYI1P,I4P),n=XYZp,code=XYZ64) ; deallocate(XYZp)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(XYZ64)//end_rec ; deallocate(XYZ64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_XML_STRG_3DA_R8

  !> Function for saving mesh with \b StructuredGrid topology (R8P, 1D Arrays, packed API).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_XML_STRG_1DAP_R8(nx1,nx2,ny1,ny2,nz1,nz2,NN,XYZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           nx1        !< Initial node of x axis.
  integer(I4P), intent(IN)::           nx2        !< Final node of x axis.
  integer(I4P), intent(IN)::           ny1        !< Initial node of y axis.
  integer(I4P), intent(IN)::           ny2        !< Final node of y axis.
  integer(I4P), intent(IN)::           nz1        !< Initial node of z axis.
  integer(I4P), intent(IN)::           nz2        !< Final node of z axis.
  integer(I4P), intent(IN)::           NN         !< Number of all nodes.
  real(R8P),    intent(IN)::           XYZ(1:,1:) !< X, Y, Z coordinates (packed API) [1:3,1:NN].
  integer(I4P), intent(IN), optional:: cf         !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO       !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I1P), allocatable::          XYZp(:)    !< Packed coordinates data.
  character(1), allocatable::          XYZ64(:)   !< X, Y, Z coordinates encoded in base64.
  character(len=maxlen)::              s_buffer   !< Buffer string.
  integer(I4P)::                       rf         !< Real file index.
  integer(I4P)::                       n1         !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer) ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>' ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" NumberOfComponents="3" Name="Points" format="ascii">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer)
    do n1=1,NN
      write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//&
                                                 str(n=XYZ(1,n1))//' '//str(n=XYZ(2,n1))//' '//str(n=XYZ(3,n1))
    enddo
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>' ; vtk(rf)%indent = vtk(rf)%indent - 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//                                                                  &
               '<DataArray type="Float64" NumberOfComponents="3" Name="Points" format="appended" offset="'// &
               trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = 3*NN*BYR8P)
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R8',3*NN
    write(unit=vtk(rf)%ua,iostat=E_IO)XYZ
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" NumberOfComponents="3" Name="Points" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(3*NN*BYR8P,I4P)],a2=reshape(XYZ,[3*NN]),packed=XYZp)
    call b64_encode(nB=int(BYI1P,I4P),n=XYZp,code=XYZ64) ; deallocate(XYZp)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(XYZ64)//end_rec ; deallocate(XYZ64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_XML_STRG_1DAP_R8

  !> Function for saving mesh with \b StructuredGrid topology (R8P, 3D Arrays, packed API).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_XML_STRG_3DAP_R8(nx1,nx2,ny1,ny2,nz1,nz2,NN,XYZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           nx1                    !< Initial node of x axis.
  integer(I4P), intent(IN)::           nx2                    !< Final node of x axis.
  integer(I4P), intent(IN)::           ny1                    !< Initial node of y axis.
  integer(I4P), intent(IN)::           ny2                    !< Final node of y axis.
  integer(I4P), intent(IN)::           nz1                    !< Initial node of z axis.
  integer(I4P), intent(IN)::           nz2                    !< Final node of z axis.
  integer(I4P), intent(IN)::           NN                     !< Number of all nodes.
  real(R8P),    intent(IN)::           XYZ(1:,nx1:,ny1:,nz1:) !< X, Y, Z coordinates (packed API).
  integer(I4P), intent(IN), optional:: cf                     !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO              !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I1P), allocatable::          XYZp(:)                !< Packed coordinates data.
  character(1), allocatable::          XYZ64(:)               !< X, Y, Z coordinates encoded in base64.
  character(len=maxlen)::              s_buffer               !< Buffer string.
  integer(I4P)::                       rf                     !< Real file index.
  integer(I4P)::                       nx,ny,nz               !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer) ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>' ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" NumberOfComponents="3" Name="Points" format="ascii">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer)
    do nz=nz1,nz2
      do ny=ny1,ny2
        do nx=nx1,nx2
          write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//&
                                                    str(n=XYZ(1,nx,ny,nz))//' '//str(n=XYZ(2,nx,ny,nz))//' '//str(n=XYZ(3,nx,ny,nz))
        enddo
      enddo
    enddo
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>' ; vtk(rf)%indent = vtk(rf)%indent - 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//                                                                  &
               '<DataArray type="Float64" NumberOfComponents="3" Name="Points" format="appended" offset="'// &
               trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = 3*NN*BYR8P)
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R8',3*NN
    write(unit=vtk(rf)%ua,iostat=E_IO)XYZ
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" NumberOfComponents="3" Name="Points" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(3*NN*BYR8P,I4P)],a2=reshape(XYZ,[3*NN]),packed=XYZp)
    call b64_encode(nB=int(BYI1P,I4P),n=XYZp,code=XYZ64) ; deallocate(XYZp)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(XYZ64)//end_rec ; deallocate(XYZ64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_XML_STRG_3DAP_R8

  !> Function for saving mesh with \b StructuredGrid topology (R4P, 1D Arrays).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_XML_STRG_1DA_R4(nx1,nx2,ny1,ny2,nz1,nz2,NN,X,Y,Z,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           nx1      !< Initial node of x axis.
  integer(I4P), intent(IN)::           nx2      !< Final node of x axis.
  integer(I4P), intent(IN)::           ny1      !< Initial node of y axis.
  integer(I4P), intent(IN)::           ny2      !< Final node of y axis.
  integer(I4P), intent(IN)::           nz1      !< Initial node of z axis.
  integer(I4P), intent(IN)::           nz2      !< Final node of z axis.
  integer(I4P), intent(IN)::           NN       !< Number of all nodes.
  real(R4P),    intent(IN)::           X(1:)    !< X coordinates [1:NN].
  real(R4P),    intent(IN)::           Y(1:)    !< Y coordinates [1:NN].
  real(R4P),    intent(IN)::           Z(1:)    !< Z coordinates [1:NN].
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer !< Buffer string.
  integer(I1P), allocatable::          XYZp(:)  !< Packed data.
  character(1), allocatable::          XYZ64(:) !< X, Y, Z coordinates encoded in base64.
  integer(I4P)::                       rf       !< Real file index.
  integer(I4P)::                       n1       !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer) ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>' ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" NumberOfComponents="3" Name="Points" format="ascii">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer)
    do n1=1,NN
      write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//str(n=X(n1))//' '//str(n=Y(n1))//' '//str(n=Z(n1))
    enddo
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>' ; vtk(rf)%indent = vtk(rf)%indent - 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//                                                                  &
               '<DataArray type="Float32" NumberOfComponents="3" Name="Points" format="appended" offset="'// &
               trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = 3*NN*BYR4P)
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R4',3*NN
    write(unit=vtk(rf)%ua,iostat=E_IO)(X(n1),Y(n1),Z(n1),n1=1,NN)
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" NumberOfComponents="3" Name="Points" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(3*NN*BYR4P,I4P)],a2=[(X(n1),Y(n1),Z(n1),n1=1,NN)],packed=XYZp)
    call b64_encode(nB=int(BYI1P,I4P),n=XYZp,code=XYZ64) ; deallocate(XYZp)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(XYZ64)//end_rec ; deallocate(XYZ64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_XML_STRG_1DA_R4

  !> Function for saving mesh with \b StructuredGrid topology (R4P, 3D Arrays).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_XML_STRG_3DA_R4(nx1,nx2,ny1,ny2,nz1,nz2,NN,X,Y,Z,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           nx1               !< Initial node of x axis.
  integer(I4P), intent(IN)::           nx2               !< Final node of x axis.
  integer(I4P), intent(IN)::           ny1               !< Initial node of y axis.
  integer(I4P), intent(IN)::           ny2               !< Final node of y axis.
  integer(I4P), intent(IN)::           nz1               !< Initial node of z axis.
  integer(I4P), intent(IN)::           nz2               !< Final node of z axis.
  integer(I4P), intent(IN)::           NN                !< Number of all nodes.
  real(R4P),    intent(IN)::           X(nx1:,ny1:,nz1:) !< X coordinates [nx1:nx2,ny1:ny2,nz1:nz2].
  real(R4P),    intent(IN)::           Y(nx1:,ny1:,nz1:) !< Y coordinates [nx1:nx2,ny1:ny2,nz1:nz2].
  real(R4P),    intent(IN)::           Z(nx1:,ny1:,nz1:) !< Z coordinates [nx1:nx2,ny1:ny2,nz1:nz2].
  integer(I4P), intent(IN), optional:: cf                !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO              !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer          !< Buffer string.
  integer(I1P), allocatable::          XYZp(:)           !< Packed data.
  character(1), allocatable::          XYZ64(:)          !< X, Y, Z coordinates encoded in base64.
  integer(I4P)::                       rf                !< Real file index.
  integer(I4P)::                       nx,ny,nz          !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer) ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>' ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" NumberOfComponents="3" Name="Points" format="ascii">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer)
    do nz=nz1,nz2
      do ny=ny1,ny2
        do nx=nx1,nx2
          write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//&
                                                     str(n=X(nx,ny,nz))//' '//str(n=Y(nx,ny,nz))//' '//str(n=Z(nx,ny,nz))
        enddo
      enddo
    enddo
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>' ; vtk(rf)%indent = vtk(rf)%indent - 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//                                                                  &
               '<DataArray type="Float32" NumberOfComponents="3" Name="Points" format="appended" offset="'// &
               trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = 3*NN*BYR4P)
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R4',3*NN
    write(unit=vtk(rf)%ua,iostat=E_IO)(((X(nx,ny,nz),Y(nx,ny,nz),Z(nx,ny,nz),nx=nx1,nx2),ny=ny1,ny2),nz=nz1,nz2)
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" NumberOfComponents="3" Name="Points" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(3*NN*BYR4P,I4P)],a2=[(((X(nx,ny,nz),Y(nx,ny,nz),Z(nx,ny,nz),nx=nx1,nx2),ny=ny1,ny2),nz=nz1,nz2)], &
                   packed=XYZp)
    call b64_encode(nB=int(BYI1P,I4P),n=XYZp,code=XYZ64) ; deallocate(XYZp)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(XYZ64)//end_rec ; deallocate(XYZ64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_XML_STRG_3DA_R4

  !> Function for saving mesh with \b StructuredGrid topology (R4P, 1D Arrays, packed API).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_XML_STRG_1DAP_R4(nx1,nx2,ny1,ny2,nz1,nz2,NN,XYZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           nx1        !< Initial node of x axis.
  integer(I4P), intent(IN)::           nx2        !< Final node of x axis.
  integer(I4P), intent(IN)::           ny1        !< Initial node of y axis.
  integer(I4P), intent(IN)::           ny2        !< Final node of y axis.
  integer(I4P), intent(IN)::           nz1        !< Initial node of z axis.
  integer(I4P), intent(IN)::           nz2        !< Final node of z axis.
  integer(I4P), intent(IN)::           NN         !< Number of all nodes.
  real(R4P),    intent(IN)::           XYZ(1:,1:) !< X, Y, Z coordinates (packed API) [1:3,1:NN].
  integer(I4P), intent(IN), optional:: cf         !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO       !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer   !< Buffer string.
  integer(I1P), allocatable::          XYZp(:)    !< Packed data.
  character(1), allocatable::          XYZ64(:)   !< X, Y, Z coordinates encoded in base64.
  integer(I4P)::                       rf         !< Real file index.
  integer(I4P)::                       n1         !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer) ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>' ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" NumberOfComponents="3" Name="Points" format="ascii">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer)
    do n1=1,NN
      write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//&
                                                 str(n=XYZ(1,n1))//' '//str(n=XYZ(2,n1))//' '//str(n=XYZ(3,n1))
    enddo
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>' ; vtk(rf)%indent = vtk(rf)%indent - 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//                                                                  &
               '<DataArray type="Float32" NumberOfComponents="3" Name="Points" format="appended" offset="'// &
               trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = 3*NN*BYR4P)
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R4',3*NN
    write(unit=vtk(rf)%ua,iostat=E_IO)XYZ
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" NumberOfComponents="3" Name="Points" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(3*NN*BYR4P,I4P)],a2=reshape(XYZ,[3*NN]),packed=XYZp)
    call b64_encode(nB=int(BYI1P,I4P),n=XYZp,code=XYZ64) ; deallocate(XYZp)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(XYZ64)//end_rec ; deallocate(XYZ64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_XML_STRG_1DAP_R4

  !> Function for saving mesh with \b StructuredGrid topology (R4P, 3D Arrays, packed API).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_XML_STRG_3DAP_R4(nx1,nx2,ny1,ny2,nz1,nz2,NN,XYZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           nx1                    !< Initial node of x axis.
  integer(I4P), intent(IN)::           nx2                    !< Final node of x axis.
  integer(I4P), intent(IN)::           ny1                    !< Initial node of y axis.
  integer(I4P), intent(IN)::           ny2                    !< Final node of y axis.
  integer(I4P), intent(IN)::           nz1                    !< Initial node of z axis.
  integer(I4P), intent(IN)::           nz2                    !< Final node of z axis.
  integer(I4P), intent(IN)::           NN                     !< Number of all nodes.
  real(R4P),    intent(IN)::           XYZ(1:,nx1:,ny1:,nz1:) !< X, Y, Z coordinates (packed API) [1:3,nx1:nx2,ny1:ny2,nz1:nz2].
  integer(I4P), intent(IN), optional:: cf                     !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO             !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer               !< Buffer string.
  integer(I1P), allocatable::          XYZp(:)                !< Packed data.
  character(1), allocatable::          XYZ64(:)               !< X, Y, Z coordinates encoded in base64.
  integer(I4P)::                       rf                     !< Real file index.
  integer(I4P)::                       nx,ny,nz               !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer) ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>' ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" NumberOfComponents="3" Name="Points" format="ascii">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer)
    do nz=nz1,nz2
      do ny=ny1,ny2
        do nx=nx1,nx2
          write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//&
                                                    str(n=XYZ(1,nx,ny,nz))//' '//str(n=XYZ(2,nx,ny,nz))//' '//str(n=XYZ(3,nx,ny,nz))
        enddo
      enddo
    enddo
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>' ; vtk(rf)%indent = vtk(rf)%indent - 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//                                                                  &
               '<DataArray type="Float32" NumberOfComponents="3" Name="Points" format="appended" offset="'// &
               trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = 3*NN*BYR4P)
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R4',3*NN
    write(unit=vtk(rf)%ua,iostat=E_IO)XYZ
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" NumberOfComponents="3" Name="Points" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(3*NN*BYR4P,I4P)],a2=reshape(XYZ,[3*NN]),packed=XYZp)
    call b64_encode(nB=int(BYI1P,I4P),n=XYZp,code=XYZ64) ; deallocate(XYZp)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(XYZ64)//end_rec ; deallocate(XYZ64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_XML_STRG_3DAP_R4

  !> Function for saving mesh with \b RectilinearGrid topology (R8P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_XML_RECT_R8(nx1,nx2,ny1,ny2,nz1,nz2,X,Y,Z,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::             nx1        !< Initial node of x axis.
  integer(I4P), intent(IN)::             nx2        !< Final node of x axis.
  integer(I4P), intent(IN)::             ny1        !< Initial node of y axis.
  integer(I4P), intent(IN)::             ny2        !< Final node of y axis.
  integer(I4P), intent(IN)::             nz1        !< Initial node of z axis.
  integer(I4P), intent(IN)::             nz2        !< Final node of z axis.
  real(R8P),    intent(IN)::             X(nx1:nx2) !< X coordinates.
  real(R8P),    intent(IN)::             Y(ny1:ny2) !< Y coordinates.
  real(R8P),    intent(IN)::             Z(nz1:nz2) !< Z coordinates.
  integer(I4P), intent(IN), optional::   cf         !< Current file index (for concurrent files IO).
  integer(I4P)::                         E_IO       !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::                s_buffer   !< Buffer string.
  integer(I1P), allocatable::            XYZp(:)    !< Packed data.
  character(1), allocatable::            XYZ64(:)   !< X, Y, Z coordinates encoded in base64.
  integer(I4P)::                         rf         !< Real file index.
  integer(I4P)::                         n1         !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer) ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Coordinates>' ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="X" format="ascii">'
    write(unit=vtk(rf)%u,fmt=FR8P, iostat=E_IO)(X(n1),n1=nx1,nx2)
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="Y" format="ascii">'
    write(unit=vtk(rf)%u,fmt=FR8P, iostat=E_IO)(Y(n1),n1=ny1,ny2)
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="Z" format="ascii">'
    write(unit=vtk(rf)%u,fmt=FR8P, iostat=E_IO)(Z(n1),n1=nz1,nz2)
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>' ; vtk(rf)%indent = vtk(rf)%indent - 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Coordinates>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Coordinates>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="X" format="appended" offset="'//&
               trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = (nx2-nx1+1)*BYR8P)
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R8',(nx2-nx1+1)
    write(unit=vtk(rf)%ua,iostat=E_IO)(X(n1),n1=nx1,nx2)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="Y" format="appended" offset="'//&
               trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = (ny2-ny1+1)*BYR8P)
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R8',(ny2-ny1+1)
    write(unit=vtk(rf)%ua,iostat=E_IO)(Y(n1),n1=ny1,ny2)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="Z" format="appended" offset="'//&
               trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = (nz2-nz1+1)*BYR8P)
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R8',(nz2-nz1+1)
    write(unit=vtk(rf)%ua,iostat=E_IO)(Z(n1),n1=nz1,nz2)
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Coordinates>'//end_rec
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Coordinates>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="X" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int((nx2-nx1+1)*BYR8P,I4P)],a2=X,packed=XYZp)
    call b64_encode(nB=int(BYI1P,I4P),n=XYZp,code=XYZ64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(XYZ64)//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="Y" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int((ny2-ny1+1)*BYR8P,I4P)],a2=Y,packed=XYZp)
    call b64_encode(nB=int(BYI1P,I4P),n=XYZp,code=XYZ64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(XYZ64)//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="Z" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int((nz2-nz1+1)*BYR8P,I4P)],a2=Z,packed=XYZp)
    call b64_encode(nB=int(BYI1P,I4P),n=XYZp,code=XYZ64) ; deallocate(XYZp)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(XYZ64)//end_rec ; deallocate(XYZ64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
    vtk(rf)%indent = vtk(rf)%indent - 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Coordinates>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_XML_RECT_R8

  !> Function for saving mesh with \b RectilinearGrid topology (R4P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_XML_RECT_R4(nx1,nx2,ny1,ny2,nz1,nz2,X,Y,Z,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::             nx1        !< Initial node of x axis.
  integer(I4P), intent(IN)::             nx2        !< Final node of x axis.
  integer(I4P), intent(IN)::             ny1        !< Initial node of y axis.
  integer(I4P), intent(IN)::             ny2        !< Final node of y axis.
  integer(I4P), intent(IN)::             nz1        !< Initial node of z axis.
  integer(I4P), intent(IN)::             nz2        !< Final node of z axis.
  real(R4P),    intent(IN)::             X(nx1:nx2) !< X coordinates.
  real(R4P),    intent(IN)::             Y(ny1:ny2) !< Y coordinates.
  real(R4P),    intent(IN)::             Z(nz1:nz2) !< Z coordinates.
  integer(I4P), intent(IN), optional::   cf         !< Current file index (for concurrent files IO).
  integer(I4P)::                         E_IO       !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::                s_buffer   !< Buffer string.
  integer(I1P), allocatable::            XYZp(:)    !< Packed data.
  character(1), allocatable::            XYZ64(:)   !< X, Y, Z coordinates encoded in base64.
  integer(I4P)::                         rf         !< Real file index.
  integer(I4P)::                         n1         !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                      trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                      trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer) ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Coordinates>' ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="X" format="ascii">'
    write(unit=vtk(rf)%u,fmt=FR4P, iostat=E_IO)(X(n1),n1=nx1,nx2)
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="Y" format="ascii">'
    write(unit=vtk(rf)%u,fmt=FR4P, iostat=E_IO)(Y(n1),n1=ny1,ny2)
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="Z" format="ascii">'
    write(unit=vtk(rf)%u,fmt=FR4P, iostat=E_IO)(Z(n1),n1=nz1,nz2)
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>' ; vtk(rf)%indent = vtk(rf)%indent - 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Coordinates>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                      trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                      trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Coordinates>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="X" format="appended" offset="'//&
               trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = (nx2-nx1+1)*BYR4P)
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R4',(nx2-nx1+1)
    write(unit=vtk(rf)%ua,iostat=E_IO)(X(n1),n1=nx1,nx2)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="Y" format="appended" offset="'//&
               trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = (ny2-ny1+1)*BYR4P)
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R4',(ny2-ny1+1)
    write(unit=vtk(rf)%ua,iostat=E_IO)(Y(n1),n1=ny1,ny2)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="Z" format="appended" offset="'//&
               trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = (nz2-nz1+1)*BYR4P)
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R4',(nz2-nz1+1)
    write(unit=vtk(rf)%ua,iostat=E_IO)(Z(n1),n1=nz1,nz2)
    vtk(rf)%indent = vtk(rf)%indent - 2  ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Coordinates>'//end_rec
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'//trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
                                                              trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
                                                              trim(str(n=nz1))//' '//trim(str(n=nz2))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Coordinates>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="X" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int((nx2-nx1+1)*BYR4P,I4P)],a2=X,packed=XYZp)
    call b64_encode(nB=int(BYI1P,I4P),n=XYZp,code=XYZ64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(XYZ64)//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="Y" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int((ny2-ny1+1)*BYR4P,I4P)],a2=Y,packed=XYZp)
    call b64_encode(nB=int(BYI1P,I4P),n=XYZp,code=XYZ64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(XYZ64)//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="Z" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int((nz2-nz1+1)*BYR4P,I4P)],a2=Z,packed=XYZp)
    call b64_encode(nB=int(BYI1P,I4P),n=XYZp,code=XYZ64) ; deallocate(XYZp)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(XYZ64)//end_rec ; deallocate(XYZ64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
    vtk(rf)%indent = vtk(rf)%indent - 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Coordinates>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_XML_RECT_R4

  !> Function for saving mesh with \b UnstructuredGrid topology (R8P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_XML_UNST_R8(NN,NC,X,Y,Z,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NN       !< Number of nodes.
  integer(I4P), intent(IN)::           NC       !< Number of cells.
  real(R8P),    intent(IN)::           X(1:NN)  !< X coordinates.
  real(R8P),    intent(IN)::           Y(1:NN)  !< Y coordinates.
  real(R8P),    intent(IN)::           Z(1:NN)  !< Z coordinates.
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer !< Buffer string.
  real(R8P), allocatable::             XYZa(:)  !< X, Y, Z coordinates.
  integer(I1P), allocatable::          XYZp(:)  !< Packed data.
  character(1), allocatable::          XYZ64(:) !< X, Y, Z coordinates encoded in base64.
  integer(I4P)::                       rf       !< Real file index.
  integer(I4P)::                       n1       !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece NumberOfPoints="'//trim(str(n=NN))//'" NumberOfCells="'//trim(str(n=NC))//'">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer) ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>' ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" NumberOfComponents="3" Name="Points" format="ascii">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer)
    do n1=1,NN
      write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//str(n=X(n1))//' '//str(n=Y(n1))//' '//str(n=Z(n1))
    enddo
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>' ; vtk(rf)%indent = vtk(rf)%indent - 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece NumberOfPoints="'//trim(str(n=NN))//'" NumberOfCells="'//trim(str(n=NC))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//                                                                  &
               '<DataArray type="Float64" NumberOfComponents="3" Name="Points" format="appended" offset="'// &
               trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = 3*NN*BYR8P)
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R8',3*NN
    write(unit=vtk(rf)%ua,iostat=E_IO)(X(n1),Y(n1),Z(n1),n1=1,NN)
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece NumberOfPoints="'//trim(str(n=NN))//'" NumberOfCells="'//trim(str(n=NC))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" NumberOfComponents="3" Name="Points" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    allocate(XYZa(1:3*NN))
    do n1 = 1,NN
      XYZa(1+(n1-1)*3:1+(n1-1)*3+2)=[X(n1),Y(n1),Z(n1)]
    enddo
    call pack_data(a1=[int(3*NN*BYR8P,I4P)],a2=XYZa,packed=XYZp) ; deallocate(XYZa)
    call b64_encode(nB=int(BYI1P,I4P),n=XYZp,code=XYZ64) ; deallocate(XYZp)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(XYZ64)//end_rec ; deallocate(XYZ64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_XML_UNST_R8

  !> Function for saving mesh with \b UnstructuredGrid topology (R8P, packed API).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_XML_UNST_PACK_R8(NN,NC,XYZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NN            !< Number of nodes.
  integer(I4P), intent(IN)::           NC            !< Number of cells.
  real(R8P),    intent(IN)::           XYZ(1:3,1:NN) !< X, Y, Z coordinates (packed API).
  integer(I4P), intent(IN), optional:: cf            !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO          !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer      !< Buffer string.
  real(R8P), allocatable::             XYZa(:)       !< X, Y, Z coordinates.
  integer(I1P), allocatable::          XYZp(:)       !< Packed data.
  character(1), allocatable::          XYZ64(:)      !< X, Y, Z coordinates encoded in base64.
  integer(I4P)::                       rf            !< Real file index.
  integer(I4P)::                       n1            !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece NumberOfPoints="'//trim(str(n=NN))//'" NumberOfCells="'//trim(str(n=NC))//'">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer) ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>' ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" NumberOfComponents="3" Name="Points" format="ascii">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer)
    do n1=1,NN
      write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//&
                                                 str(n=XYZ(1,n1))//' '//str(n=XYZ(2,n1))//' '//str(n=XYZ(3,n1))
    enddo
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>' ; vtk(rf)%indent = vtk(rf)%indent - 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece NumberOfPoints="'//trim(str(n=NN))//'" NumberOfCells="'//trim(str(n=NC))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//                                                                  &
               '<DataArray type="Float64" NumberOfComponents="3" Name="Points" format="appended" offset="'// &
               trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = 3*NN*BYR8P)
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R8',3*NN
    write(unit=vtk(rf)%ua,iostat=E_IO)XYZ
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece NumberOfPoints="'//trim(str(n=NN))//'" NumberOfCells="'//trim(str(n=NC))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" NumberOfComponents="3" Name="Points" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    allocate(XYZa(1:3*NN))
    do n1 = 1,NN
      XYZa(1+(n1-1)*3:1+(n1-1)*3+2)=XYZ(1:3,n1)
    enddo
    call pack_data(a1=[int(3*NN*BYR8P,I4P)],a2=XYZa,packed=XYZp) ; deallocate(XYZa)
    call b64_encode(nB=int(BYI1P,I4P),n=XYZp,code=XYZ64) ; deallocate(XYZp)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(XYZ64)//end_rec ; deallocate(XYZ64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_XML_UNST_PACK_R8

  !> Function for saving mesh with \b UnstructuredGrid topology (R4P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_XML_UNST_R4(NN,NC,X,Y,Z,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NN       !< Number of nodes.
  integer(I4P), intent(IN)::           NC       !< Number of cells.
  real(R4P),    intent(IN)::           X(1:NN)  !< X coordinates.
  real(R4P),    intent(IN)::           Y(1:NN)  !< Y coordinates.
  real(R4P),    intent(IN)::           Z(1:NN)  !< Z coordinates.
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer !< Buffer string.
  real(R4P), allocatable::             XYZa(:)  !< X, Y, Z coordinates.
  integer(I1P), allocatable::          XYZp(:)  !< Packed data.
  character(1), allocatable::          XYZ64(:) !< X, Y, Z coordinates encoded in base64.
  integer(I4P)::                       rf       !< Real file index.
  integer(I4P)::                       n1       !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece NumberOfPoints="'//trim(str(n=NN))//'" NumberOfCells="'//trim(str(n=NC))//'">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer) ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>' ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" NumberOfComponents="3" Name="Points" format="ascii">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer)
    do n1=1,NN
      write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//str(n=X(n1))//' '//str(n=Y(n1))//' '//str(n=Z(n1))
    enddo
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>' ; vtk(rf)%indent = vtk(rf)%indent - 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece NumberOfPoints="'//trim(str(n=NN))//'" NumberOfCells="'//trim(str(n=NC))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//                                                                  &
               '<DataArray type="Float32" NumberOfComponents="3" Name="Points" format="appended" offset="'// &
               trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = 3*NN*BYR4P)
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R4',3*NN
    write(unit=vtk(rf)%ua,iostat=E_IO)(X(n1),Y(n1),Z(n1),n1=1,NN)
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece NumberOfPoints="'//trim(str(n=NN))//'" NumberOfCells="'//trim(str(n=NC))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" NumberOfComponents="3" Name="Points" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    allocate(XYZa(1:3*NN))
    do n1 = 1,NN
      XYZa(1+(n1-1)*3:1+(n1-1)*3+2)=[X(n1),Y(n1),Z(n1)]
    enddo
    call pack_data(a1=[int(3*NN*BYR4P,I4P)],a2=XYZa,packed=XYZp) ; deallocate(XYZa)
    call b64_encode(nB=int(BYI1P,I4P),n=XYZp,code=XYZ64) ; deallocate(XYZp)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(XYZ64)//end_rec ; deallocate(XYZ64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_XML_UNST_R4

  !> Function for saving mesh with \b UnstructuredGrid topology (R4P, packed API).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_XML_UNST_PACK_R4(NN,NC,XYZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NN            !< Number of nodes.
  integer(I4P), intent(IN)::           NC            !< Number of cells.
  real(R4P),    intent(IN)::           XYZ(1:3,1:NN) !< X, Y, Z coordinates (packed API).
  integer(I4P), intent(IN), optional:: cf            !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO          !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer      !< Buffer string.
  real(R4P), allocatable::             XYZa(:)       !< X, Y, Z coordinates.
  integer(I1P), allocatable::          XYZp(:)       !< Packed data.
  character(1), allocatable::          XYZ64(:)      !< X, Y, Z coordinates encoded in base64.
  integer(I4P)::                       rf            !< Real file index.
  integer(I4P)::                       n1            !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece NumberOfPoints="'//trim(str(n=NN))//'" NumberOfCells="'//trim(str(n=NC))//'">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer) ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>' ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" NumberOfComponents="3" Name="Points" format="ascii">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer)
    do n1=1,NN
      write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//&
                                                 str(n=XYZ(1,n1))//' '//str(n=XYZ(2,n1))//' '//str(n=XYZ(3,n1))
    enddo
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>' ; vtk(rf)%indent = vtk(rf)%indent - 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece NumberOfPoints="'//trim(str(n=NN))//'" NumberOfCells="'//trim(str(n=NC))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//                                                                  &
               '<DataArray type="Float32" NumberOfComponents="3" Name="Points" format="appended" offset="'// &
               trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = 3*NN*BYR4P)
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R4',3*NN
    write(unit=vtk(rf)%ua,iostat=E_IO)XYZ
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece NumberOfPoints="'//trim(str(n=NN))//'" NumberOfCells="'//trim(str(n=NC))//'">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Points>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" NumberOfComponents="3" Name="Points" format="binary">'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    allocate(XYZa(1:3*NN))
    do n1 = 1,NN
      XYZa(1+(n1-1)*3:1+(n1-1)*3+2)=XYZ(1:3,n1)
    enddo
    call pack_data(a1=[int(3*NN*BYR4P,I4P)],a2=XYZa,packed=XYZp) ; deallocate(XYZa)
    call b64_encode(nB=int(BYI1P,I4P),n=XYZp,code=XYZ64) ; deallocate(XYZp)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(XYZ64)//end_rec ; deallocate(XYZ64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Points>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_XML_UNST_PACK_R4

  !> @brief Function for closing mesh block data.
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_XML_CLOSEP(cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN), optional:: cf   !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf   !< Real file index.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  vtk(rf)%indent = vtk(rf)%indent - 2
  select case(vtk(rf)%f)
  case(ascii)
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Piece>'
  case(raw,binary,bin_app)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Piece>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_XML_CLOSEP
  !> @}

  !> Function that \b must be used when unstructured grid is used, it saves the connectivity of the unstructured gird.
  !> @note The vector \b connect must follow the VTK-legacy standard. It is passed as \em assumed-shape array
  !> because its dimensions is related to the mesh dimensions in a complex way. Its dimensions can be calculated by the following
  !> equation: \f$dc = dc = \sum\limits_{i = 1}^{NC} {nvertex_i }\f$.
  !> Note that this equation is different from the legacy one. The XML connectivity convention is quite different from the
  !> legacy standard. As an example suppose we have a mesh composed by 2 cells, one hexahedron (8 vertices) and one pyramid with
  !> square basis (5 vertices) and suppose that the basis of pyramid is constitute by a face of the hexahedron and so the two cells
  !> share 4 vertices. The above equation gives \f$dc=8+5=13\f$. The connectivity vector for this mesh can be: \n
  !> first cell \n
  !> connect(1)  = 0 identification flag of \f$1^\circ\f$ vertex of 1° cell \n
  !> connect(2)  = 1 identification flag of \f$2^\circ\f$ vertex of 1° cell \n
  !> connect(3)  = 2 identification flag of \f$3^\circ\f$ vertex of 1° cell \n
  !> connect(4)  = 3 identification flag of \f$4^\circ\f$ vertex of 1° cell \n
  !> connect(5)  = 4 identification flag of \f$5^\circ\f$ vertex of 1° cell \n
  !> connect(6)  = 5 identification flag of \f$6^\circ\f$ vertex of 1° cell \n
  !> connect(7)  = 6 identification flag of \f$7^\circ\f$ vertex of 1° cell \n
  !> connect(8)  = 7 identification flag of \f$8^\circ\f$ vertex of 1° cell \n
  !> second cell \n
  !> connect(9 ) = 0 identification flag of \f$1^\circ\f$ vertex of 2° cell \n
  !> connect(10) = 1 identification flag of \f$2^\circ\f$ vertex of 2° cell \n
  !> connect(11) = 2 identification flag of \f$3^\circ\f$ vertex of 2° cell \n
  !> connect(12) = 3 identification flag of \f$4^\circ\f$ vertex of 2° cell \n
  !> connect(13) = 8 identification flag of \f$5^\circ\f$ vertex of 2° cell \n
  !> Therefore this connectivity vector convention is more simple than the legacy convention, now we must create also the
  !> \em offset vector that contains the data now missing in the \em connect vector. The offset
  !> vector for this mesh can be: \n
  !> first cell \n
  !> offset(1) = 8  => summ of nodes of \f$1^\circ\f$ cell \n
  !> second cell \n
  !> offset(2) = 13 => summ of nodes of \f$1^\circ\f$ and \f$2^\circ\f$ cells \n
  !> The value of every cell-offset can be calculated by the following equation: \f$offset_c=\sum\limits_{i=1}^{c}{nvertex_i}\f$
  !> where \f$offset_c\f$ is the value of \f$c^{th}\f$ cell and \f$nvertex_i\f$ is the number of vertices of \f$i^{th}\f$ cell.
  !> The function VTK_CON_XML does not calculate the connectivity and offset vectors: it writes the connectivity and offset
  !> vectors conforming the VTK-XML standard, but does not calculate them.
  !> The vector variable \em cell_type must conform the VTK-XML standard (see the file VTK-Standard at the
  !> Kitware homepage) that is the same of the legacy standard. It contains the
  !> \em type of each cells. For the above example this vector is: \n
  !> first cell \n
  !> cell_type(1) = 12 hexahedron type of \f$1^\circ\f$ cell \n
  !> second cell \n
  !> cell_type(2) = 14 pyramid type of \f$2^\circ\f$ cell \n
  !> @return E_IO: integer(I4P) error flag
  function VTK_CON_XML(NC,connect,offset,cell_type,idx,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC            !< Number of cells.
  integer(I4P), intent(IN)::           connect(1:)   !< Mesh connectivity.
  integer(I4P), intent(IN)::           offset(1:NC)  !< Cell offset.
  integer(I1P), intent(IN)::           cell_type(1:) !< VTK cell type.
  integer(I1P), intent(IN), optional:: idx           !< Id offset to convert Fortran (first id 1) to C (first id 0) standards.
  integer(I4P), intent(IN), optional:: cf            !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO          !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer      !< Buffer string.
  integer(I1P), allocatable::          cocp(:)       !< Packed data.
  character(1), allocatable::          coc64(:)      !< Data encoded in base64.
  integer(I1P)::                       incr          !< Actual id offset increment.
  integer(I4P)::                       rf            !< Real file index.
  integer(I4P)::                       n1            !< Counter.
  integer(I8P)::                       Ncocp         !< Dimension of cocp, packed data.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  incr = 0_I1P
  if (present(idx)) then
    incr = idx
  endif
  select case(vtk(rf)%f)
  case(ascii)
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Cells>' ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//&
                                               '<DataArray type="Int32" Name="connectivity" format="ascii">'
    write(unit=vtk(rf)%u,fmt=FI4P, iostat=E_IO)(connect(n1)+incr,n1=1,offset(NC))
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" Name="offsets" format="ascii">'
    write(unit=vtk(rf)%u,fmt=FI4P, iostat=E_IO)(offset(n1),n1=1,NC)
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" Name="types" format="ascii">'
    if (lbound(cell_type,dim=1)==ubound(cell_type,dim=1)) then
      write(unit=vtk(rf)%u,fmt=FI1P, iostat=E_IO)(cell_type(1),n1=1,NC)
    else
      write(unit=vtk(rf)%u,fmt=FI1P, iostat=E_IO)(cell_type(n1),n1=1,NC)
    endif
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>' ; vtk(rf)%indent = vtk(rf)%indent - 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Cells>'
  case(raw,bin_app)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Cells>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" Name="connectivity" format="appended" offset="'// &
               trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = offset(NC)*BYI4P)
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I4',offset(NC)
    write(unit=vtk(rf)%ua,iostat=E_IO)(connect(n1)+incr,n1=1,offset(NC))
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" Name="offsets" format="appended" offset="'// &
               trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = NC*BYI4P)
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I4',NC
    write(unit=vtk(rf)%ua,iostat=E_IO)(offset(n1),n1=1,NC)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" Name="types" format="appended" offset="'// &
               trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = NC*BYI1P)
    write(unit=vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I1',NC
    if (lbound(cell_type,dim=1)==ubound(cell_type,dim=1)) then
      write(unit=vtk(rf)%ua,iostat=E_IO)(cell_type(1),n1=1,NC)
    else
      write(unit=vtk(rf)%ua,iostat=E_IO)(cell_type(n1),n1=1,NC)
    endif
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Cells>'//end_rec
  case(binary)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Cells>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//&
                                     '<DataArray type="Int32" Name="connectivity" format="binary">'//end_rec
    Ncocp=size(transfer([int(offset(NC)*BYI4P,I4P),connect],cocp)) ; if (allocated(cocp)) deallocate(cocp) ; allocate(cocp(1:Ncocp))
    cocp = transfer([int(offset(NC)*BYI4P,I4P),connect],cocp)
    call b64_encode(nB=int(BYI1P,I4P),n=cocp,code=coc64)
    deallocate(cocp)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(coc64)//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" Name="offsets" format="binary">'//end_rec
    Ncocp=size(transfer([int(NC*BYI4P,I4P),offset],cocp)) ; if (allocated(cocp)) deallocate(cocp) ; allocate(cocp(1:Ncocp))
    cocp = transfer([int(NC*BYI4P,I4P),offset],cocp)
    call b64_encode(nB=int(BYI1P,I4P),n=cocp,code=coc64)
    deallocate(cocp)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(coc64)//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" Name="types" format="binary">'//end_rec
    if (lbound(cell_type,dim=1)==ubound(cell_type,dim=1)) then
      call pack_data(a1=[int(NC*BYI1P,I4P)],a2=[(cell_type(1),n1=1,NC)],packed=cocp)
    else
      call pack_data(a1=[int(NC*BYI1P,I4P)],a2=cell_type,packed=cocp)
    endif
    call b64_encode(nB=int(BYI1P,I4P),n=cocp,code=coc64) ; deallocate(cocp)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(coc64)//end_rec ; deallocate(coc64)
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent - 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</Cells>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_CON_XML

  !> Function that \b must be called before saving the data related to geometric mesh, this function initializes the
  !> saving of data variables indicating the \em type (node or cell centered) of variables that will be saved.
  !> @note A single file can contain both cell and node centered variables. In this case the VTK_DAT_XML function must be
  !> called two times, before saving cell-centered variables and before saving node-centered variables.
  !> Examples of usage are: \n
  !> \b Opening node piece: \n
  !> @code ...
  !> E_IO=VTK_DAT_XML('node','OPEN')
  !> ... @endcode
  !> \b Closing node piece: \n
  !> @code ...
  !> E_IO=VTK_DAT_XML('node','CLOSE')
  !> ... @endcode
  !> @return E_IO: integer(I4P) error flag
  !> @ingroup Lib_VTK_IOPublicProcedure
  function VTK_DAT_XML(var_location,var_block_action,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  character(*), intent(IN)::           var_location     !< Location of saving variables: CELL or NODE centered.
  character(*), intent(IN)::           var_block_action !< Variables block action: OPEN or CLOSE block.
  integer(I4P), intent(IN), optional:: cf               !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO             !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf               !< Real file index.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    select case(trim(Upper_Case(var_location)))
    case('CELL')
      select case(trim(Upper_Case(var_block_action)))
      case('OPEN')
        write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<CellData>' ; vtk(rf)%indent = vtk(rf)%indent + 2
      case('CLOSE')
        vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</CellData>'
      endselect
    case('NODE')
      select case(trim(Upper_Case(var_block_action)))
      case('OPEN')
        write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<PointData>' ; vtk(rf)%indent = vtk(rf)%indent + 2
      case('CLOSE')
        vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</PointData>'
      endselect
    endselect
  case(raw,binary,bin_app)
    select case(trim(Upper_Case(var_location)))
    case('CELL')
      select case(trim(Upper_Case(var_block_action)))
      case('OPEN')
        write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<CellData>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
      case('CLOSE')
        vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</CellData>'//end_rec
      endselect
    case('NODE')
      select case(trim(Upper_Case(var_block_action)))
      case('OPEN')
        write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<PointData>'//end_rec ; vtk(rf)%indent = vtk(rf)%indent + 2
      case('CLOSE')
        vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</PointData>'//end_rec
      endselect
    endselect
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_DAT_XML

  !> @ingroup Lib_VTK_IOPrivateProcedure
  !> @{

  !> Function for saving field of scalar variable (R8P, 1D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_SCAL_1DA_R8(NC_NN,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN    !< Number of cells or nodes.
  character(*), intent(IN)::           varname  !< Variable name.
  real(R8P),    intent(IN)::           var(1:)  !< Variable to be saved [1:NC_NN].
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer !< Buffer string.
  integer(I1P), allocatable::          varp(:)  !< Packed data.
  character(1), allocatable::          var64(:) !< Variable encoded in base64.
  integer(I4P)::                       rf       !< Real file index.
  integer(I4P)::                       n1       !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="'//trim(varname)//&
               '" NumberOfComponents="1" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    write(vtk(rf)%u,'('//trim(str(.true.,NC_NN+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),(' '//str(n=var(n1)),n1=1,NC_NN)
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="'//trim(varname)//&
               '" NumberOfComponents="1" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = NC_NN*BYR8P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R8',NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="'//trim(varname)//&
             '" NumberOfComponents="1" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(NC_NN*BYR8P,I4P)],a2=var,packed=varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_SCAL_1DA_R8

  !> Function for saving field of scalar variable (R8P, 3D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_SCAL_3DA_R8(NC_NN,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN         !< Number of cells or nodes.
  character(*), intent(IN)::           varname       !< Variable name.
  real(R8P),    intent(IN)::           var(1:,1:,1:) !< Variable to be saved [1:Nx,1:Ny,1:Nz].
  integer(I4P), intent(IN), optional:: cf            !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO          !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer      !< Buffer string.
  integer(I1P), allocatable::          varp(:)       !< Packed data.
  character(1), allocatable::          var64(:)      !< Variable encoded in base64.
  integer(I4P)::                       rf            !< Real file index.
  integer(I4P)::                       nx,ny,nz      !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="'//trim(varname)//&
               '" NumberOfComponents="1" format="ascii">'
    write(vtk(rf)%u,'(A)', iostat=E_IO)trim(s_buffer)
    write(vtk(rf)%u,'('//trim(str(.true.,NC_NN+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),&
                                      (((' '//str(n=var(nx,ny,nz)),nx=1,size(var,dim=1)),ny=1,size(var,dim=2)),nz=1,size(var,dim=3))
    write(vtk(rf)%u,'(A)', iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="'//trim(varname)//&
               '" NumberOfComponents="1" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = NC_NN*BYR8P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R8',NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="'//trim(varname)//&
             '" NumberOfComponents="1" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(NC_NN*BYR8P,I4P)],a2=reshape(var,[NC_NN]),packed=varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_SCAL_3DA_R8

  !> Function for saving field of scalar variable (R4P, 1D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_SCAL_1DA_R4(NC_NN,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN    !< Number of cells or nodes.
  character(*), intent(IN)::           varname  !< Variable name.
  real(R4P),    intent(IN)::           var(1:)  !< Variable to be saved [1:NC_NN].
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer !< Buffer string.
  integer(I1P), allocatable::          varp(:)  !< Packed data.
  character(1), allocatable::          var64(:) !< Variable encoded in base64.
  integer(I4P)::                       rf       !< Real file index.
  integer(I4P)::                       n1       !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="'//trim(varname)//&
               '" NumberOfComponents="1" format="ascii">'
    write(vtk(rf)%u,'(A)', iostat=E_IO)trim(s_buffer)
    write(vtk(rf)%u,'('//trim(str(.true.,NC_NN+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),(' '//str(n=var(n1)),n1=1,NC_NN)
    write(vtk(rf)%u,'(A)', iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="'//trim(varname)//&
               '" NumberOfComponents="1" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = NC_NN*BYR4P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R4',NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="'//trim(varname)//&
             '" NumberOfComponents="1" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(NC_NN*BYR4P,I4P)],a2=var,packed=varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_SCAL_1DA_R4

  !> Function for saving field of scalar variable (R4P, 3D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_SCAL_3DA_R4(NC_NN,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN         !< Number of cells or nodes.
  character(*), intent(IN)::           varname       !< Variable name.
  real(R4P),    intent(IN)::           var(1:,1:,1:) !< Variable to be saved [1:Nx,1:Ny,1:Nz].
  integer(I4P), intent(IN), optional:: cf            !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO          !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer      !< Buffer string.
  integer(I1P), allocatable::          varp(:)       !< Packed data.
  character(1), allocatable::          var64(:)      !< Variable encoded in base64.
  integer(I4P)::                       rf            !< Real file index.
  integer(I4P)::                       nx,ny,nz      !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="'//trim(varname)//&
               '" NumberOfComponents="1" format="ascii">'
    write(vtk(rf)%u,'(A)', iostat=E_IO)trim(s_buffer)
    write(vtk(rf)%u,'('//trim(str(.true.,NC_NN+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),&
                                      (((' '//str(n=var(nx,ny,nz)),nx=1,size(var,dim=1)),ny=1,size(var,dim=2)),nz=1,size(var,dim=3))
    write(vtk(rf)%u,'(A)', iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="'//trim(varname)//&
               '" NumberOfComponents="1" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = NC_NN*BYR4P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R4',NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="'//trim(varname)//&
             '" NumberOfComponents="1" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(NC_NN*BYR4P,I4P)],a2=reshape(var,[NC_NN]),packed=varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_SCAL_3DA_R4

  !> Function for saving field of scalar variable (I8P, 1D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_SCAL_1DA_I8(NC_NN,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN    !< Number of cells or nodes.
  character(*), intent(IN)::           varname  !< Variable name.
  integer(I8P), intent(IN)::           var(1:)  !< Variable to be saved [1:NC_NN].
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer !< Buffer string.
  integer(I1P), allocatable::          varp(:)  !< Packed data.
  character(1), allocatable::          var64(:) !< Variable encoded in base64.
  integer(I4P)::                       rf       !< Real file index.
  integer(I4P)::                       n1       !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int64" Name="'//trim(varname)//&
               '" NumberOfComponents="1" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    write(vtk(rf)%u,'('//trim(str(.true.,NC_NN+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),(' '//str(n=var(n1)),n1=1,NC_NN)
    write(vtk(rf)%u,'(A)',iostat=E_IO)'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int64" Name="'//trim(varname)//&
               '" NumberOfComponents="1" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = int(NC_NN*BYI8P,I4P))
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I8',NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Int64" Name="'//trim(varname)//&
             '" NumberOfComponents="1" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(NC_NN*BYI8P,I4P)],a2=var,packed=varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_SCAL_1DA_I8

  !> Function for saving field of scalar variable (I8P, 3D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_SCAL_3DA_I8(NC_NN,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN         !< Number of cells or nodes.
  character(*), intent(IN)::           varname       !< Variable name.
  integer(I8P), intent(IN)::           var(1:,1:,1:) !< Variable to be saved [1:Nx,1:Ny,1:Nz].
  integer(I4P), intent(IN), optional:: cf            !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO          !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer      !< Buffer string.
  integer(I1P), allocatable::          varp(:)       !< Packed data.
  character(1), allocatable::          var64(:)      !< Variable encoded in base64.
  integer(I4P)::                       rf            !< Real file index.
  integer(I4P)::                       nx,ny,nz      !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int64" Name="'//trim(varname)//&
               '" NumberOfComponents="1" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    write(vtk(rf)%u,'('//trim(str(.true.,NC_NN+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),&
                                      (((' '//str(n=var(nx,ny,nz)),nx=1,size(var,dim=1)),ny=1,size(var,dim=2)),nz=1,size(var,dim=3))
    write(vtk(rf)%u,'(A)',iostat=E_IO)'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int64" Name="'//trim(varname)//&
               '" NumberOfComponents="1" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = int(NC_NN*BYI8P,I4P))
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I8',NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Int64" Name="'//trim(varname)//&
             '" NumberOfComponents="1" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(NC_NN*BYI8P,I4P)],a2=reshape(var,[NC_NN]),packed=varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_SCAL_3DA_I8

  !> Function for saving field of scalar variable (I4P, 1D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_SCAL_1DA_I4(NC_NN,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN    !< Number of cells or nodes.
  character(*), intent(IN)::           varname  !< Variable name.
  integer(I4P), intent(IN)::           var(1:)  !< Variable to be saved [1:NC_NN].
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer !< Buffer string.
  integer(I1P), allocatable::          varp(:)  !< Packed data.
  character(1), allocatable::          var64(:) !< Variable encoded in base64.
  integer(I4P)::                       rf       !< Real file index.
  integer(I4P)::                       n1       !< Counter.
  integer(I8P)::                       Nvarp    !< Dimension of varp, packed data.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" Name="'//trim(varname)//&
               '" NumberOfComponents="1" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    write(vtk(rf)%u,'('//trim(str(.true.,NC_NN+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),(' '//str(n=var(n1)),n1=1,NC_NN)
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" Name="'//trim(varname)// &
               '" NumberOfComponents="1" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = NC_NN*BYI4P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I4',NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" Name="'//trim(varname)// &
             '" NumberOfComponents="1" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    Nvarp=size(transfer([int(NC_NN*BYI4P,I4P),var],varp)) ; if (allocated(varp)) deallocate(varp) ; allocate(varp(1:Nvarp))
    varp = transfer([int(NC_NN*BYI4P,I4P),var],varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_SCAL_1DA_I4

  !> Function for saving field of scalar variable (I4P, 3D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_SCAL_3DA_I4(NC_NN,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN         !< Number of cells or nodes.
  character(*), intent(IN)::           varname       !< Variable name.
  integer(I4P), intent(IN)::           var(1:,1:,1:) !< Variable to be saved [1:Nx,1:Ny,1:Nz].
  integer(I4P), intent(IN), optional:: cf            !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO          !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer      !< Buffer string.
  integer(I1P), allocatable::          varp(:)       !< Packed data.
  character(1), allocatable::          var64(:)      !< Variable encoded in base64.
  integer(I4P)::                       rf            !< Real file index.
  integer(I4P)::                       nx,ny,nz      !< Counters.
  integer(I8P)::                       Nvarp         !< Dimension of varp, packed data.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" Name="'//trim(varname)//&
               '" NumberOfComponents="1" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    write(vtk(rf)%u,'('//trim(str(.true.,NC_NN+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),&
                                      (((' '//str(n=var(nx,ny,nz)),nx=1,size(var,dim=1)),ny=1,size(var,dim=2)),nz=1,size(var,dim=3))
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" Name="'//trim(varname)// &
               '" NumberOfComponents="1" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = NC_NN*BYI4P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I4',NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" Name="'//trim(varname)// &
             '" NumberOfComponents="1" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    Nvarp=size(transfer([int(NC_NN*BYI4P,I4P),reshape(var,[NC_NN])],varp))
    if (allocated(varp)) deallocate(varp); allocate(varp(1:Nvarp))
    varp = transfer([int(NC_NN*BYI4P,I4P),reshape(var,[NC_NN])],varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_SCAL_3DA_I4

  !> Function for saving field of scalar variable (I2P, 1D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_SCAL_1DA_I2(NC_NN,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN    !< Number of cells or nodes.
  character(*), intent(IN)::           varname  !< Variable name.
  integer(I2P), intent(IN)::           var(1:)  !< Variable to be saved [1:NC_NN].
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer !< Buffer string.
  integer(I1P), allocatable::          varp(:)  !< Packed data.
  character(1), allocatable::          var64(:) !< Variable encoded in base64.
  integer(I4P)::                       rf       !< Real file index.
  integer(I4P)::                       n1       !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int16" Name="'//trim(varname)//&
               '" NumberOfComponents="1" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    write(vtk(rf)%u,'('//trim(str(.true.,NC_NN+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),(' '//str(n=var(n1)),n1=1,NC_NN)
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int16" Name="'//trim(varname)//&
               '" NumberOfComponents="1" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = NC_NN*BYI2P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I2',NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Int16" Name="'//trim(varname)//&
             '" NumberOfComponents="1" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(NC_NN*BYI2P,I4P)],a2=var,packed=varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_SCAL_1DA_I2

  !> Function for saving field of scalar variable (I2P, 3D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_SCAL_3DA_I2(NC_NN,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN         !< Number of cells or nodes.
  character(*), intent(IN)::           varname       !< Variable name.
  integer(I2P), intent(IN)::           var(1:,1:,1:) !< Variable to be saved [1:Nx,1:Ny,1:Nz].
  integer(I4P), intent(IN), optional:: cf            !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO          !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer      !< Buffer string.
  integer(I1P), allocatable::          varp(:)       !< Packed data.
  character(1), allocatable::          var64(:)      !< Variable encoded in base64.
  integer(I4P)::                       rf            !< Real file index.
  integer(I4P)::                       nx,ny,nz      !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int16" Name="'//trim(varname)//&
               '" NumberOfComponents="1" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    write(vtk(rf)%u,'('//trim(str(.true.,NC_NN+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),&
                                      (((' '//str(n=var(nx,ny,nz)),nx=1,size(var,dim=1)),ny=1,size(var,dim=2)),nz=1,size(var,dim=3))
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int16" Name="'//trim(varname)//&
               '" NumberOfComponents="1" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = NC_NN*BYI2P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I2',NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Int16" Name="'//trim(varname)//&
             '" NumberOfComponents="1" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(NC_NN*BYI2P,I4P)],a2=reshape(var,[NC_NN]),packed=varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_SCAL_3DA_I2

  !> Function for saving field of scalar variable (I1P, 1D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_SCAL_1DA_I1(NC_NN,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN    !< Number of cells or nodes.
  character(*), intent(IN)::           varname  !< Variable name.
  integer(I1P), intent(IN)::           var(1:)  !< Variable to be saved [1:NC_NN].
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer !< Buffer string.
  integer(I1P), allocatable::          varp(:)  !< Packed data.
  character(1), allocatable::          var64(:) !< Variable encoded in base64.
  integer(I4P)::                       rf       !< Real file index.
  integer(I4P)::                       n1       !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" Name="'//trim(varname)//'" NumberOfComponents="1" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    write(vtk(rf)%u,'('//trim(str(.true.,NC_NN+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),(' '//str(n=var(n1)),n1=1,NC_NN)
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" Name="'//trim(varname)//&
             '" NumberOfComponents="1" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = NC_NN*BYI1P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I1',NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" Name="'//trim(varname)//&
             '" NumberOfComponents="1" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(NC_NN*BYI1P,I4P)],a2=var,packed=varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_SCAL_1DA_I1

  !> Function for saving field of scalar variable (I1P, 3D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_SCAL_3DA_I1(NC_NN,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN         !< Number of cells or nodes.
  character(*), intent(IN)::           varname       !< Variable name.
  integer(I1P), intent(IN)::           var(1:,1:,1:) !< Variable to be saved [1:Nx,1:ny,1:Nz].
  integer(I4P), intent(IN), optional:: cf            !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO          !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer      !< Buffer string.
  integer(I1P), allocatable::          varp(:)       !< Packed data.
  character(1), allocatable::          var64(:)      !< Variable encoded in base64.
  integer(I4P)::                       rf            !< Real file index.
  integer(I4P)::                       nx,ny,nz      !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" Name="'//trim(varname)//'" NumberOfComponents="1" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    write(vtk(rf)%u,'('//trim(str(.true.,NC_NN+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),&
                                      (((' '//str(n=var(nx,ny,nz)),nx=1,size(var,dim=1)),ny=1,size(var,dim=2)),nz=1,size(var,dim=3))
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" Name="'//trim(varname)//&
             '" NumberOfComponents="1" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = NC_NN*BYI1P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I1',NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" Name="'//trim(varname)//&
             '" NumberOfComponents="1" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(NC_NN*BYI1P,I4P)],a2=reshape(var,[NC_NN]),packed=varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_SCAL_3DA_I1

  !> Function for saving field of vectorial variable (R8P, 1D arrays).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_VECT_1DA_R8(NC_NN,varname,varX,varY,varZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN    !< Number of cells or nodes.
  character(*), intent(IN)::           varname  !< Variable name.
  real(R8P),    intent(IN)::           varX(1:) !< X component [1:NC_NN].
  real(R8P),    intent(IN)::           varY(1:) !< Y component [1:NC_NN].
  real(R8P),    intent(IN)::           varZ(1:) !< Z component [1:NC_NN].
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer !< Buffer string.
  real(R8P),    allocatable::          var(:)   !< X, Y, Z component.
  integer(I1P), allocatable::          varp(:)  !< Packed data.
  character(1), allocatable::          var64(:) !< Variable encoded in base64.
  integer(I4P)::                       rf       !< Real file index.
  integer(I4P)::                       n1       !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do n1=1,NC_NN
      write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//str(n=varX(n1))//' '//str(n=varY(n1))//' '//str(n=varZ(n1))
    enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = 3*NC_NN*BYR8P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R8',3*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)(varX(n1),varY(n1),varZ(n1),n1=1,NC_NN)
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    allocate(var(1:3*NC_NN))
    do n1=1,NC_NN
      var(1+(n1-1)*3:1+(n1-1)*3+2)=[varX(n1),varY(n1),varZ(n1)]
    enddo
    call pack_data(a1=[int(3*NC_NN*BYR8P,I4P)],a2=var,packed=varp) ; deallocate(var)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_VECT_1DA_R8

  !> Function for saving field of vectorial variable (R8P, 3D arrays).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_VECT_3DA_R8(NC_NN,varname,varX,varY,varZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN          !< Number of cells or nodes.
  character(*), intent(IN)::           varname        !< Variable name.
  real(R8P),    intent(IN)::           varX(1:,1:,1:) !< X component [1:Nx,1:Ny,1:Nz].
  real(R8P),    intent(IN)::           varY(1:,1:,1:) !< Y component [1:Nx,1:Ny,1:Nz].
  real(R8P),    intent(IN)::           varZ(1:,1:,1:) !< Z component [1:Nx,1:Ny,1:Nz].
  integer(I4P), intent(IN), optional:: cf             !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO           !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer       !< Buffer string.
  real(R8P),    allocatable::          var(:)         !< X, Y, Z component.
  integer(I1P), allocatable::          varp(:)        !< Packed data.
  character(1), allocatable::          var64(:)       !< Variable encoded in base64.
  integer(I4P)::                       rf             !< Real file index.
  integer(I4P)::                       nx,ny,nz,n1    !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do nz=1,size(varX,dim=3) ; do ny=1,size(varX,dim=2) ; do nx=1,size(varX,dim=1)
      write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//&
                                        str(n=varX(nx,ny,nz))//' '//str(n=varY(nx,ny,nz))//' '//str(n=varZ(nx,ny,nz))
    enddo ; enddo ; enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = 3*NC_NN*BYR8P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R8',3*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)(((varX(nx,ny,nz),varY(nx,ny,nz),varZ(nx,ny,nz),&
                                 nx=1,size(varX,dim=1)),ny=1,size(varX,dim=2)),nz=1,size(varX,dim=3))
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    allocate(var(1:3*NC_NN))
    n1 = 0_I4P
    do nz=1,size(varX,dim=3) ; do ny=1,size(varX,dim=2) ; do nx=1,size(varX,dim=1)
      n1 = n1 + 1_I4P ; var(1+(n1-1)*3:1+(n1-1)*3+2)=[varX(nx,ny,nz),varY(nx,ny,nz),varZ(nx,ny,nz)]
    enddo ; enddo ; enddo
    call pack_data(a1=[int(3*NC_NN*BYR8P,I4P)],a2=var,packed=varp) ; deallocate(var)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_VECT_3DA_R8

  !> Function for saving field of vectorial variable (R4P, 1D arrays).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_VECT_1DA_R4(NC_NN,varname,varX,varY,varZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN    !< Number of cells or nodes.
  character(*), intent(IN)::           varname  !< Variable name.
  real(R4P),    intent(IN)::           varX(1:) !< X component [1:NC_NN].
  real(R4P),    intent(IN)::           varY(1:) !< Y component [1:NC_NN].
  real(R4P),    intent(IN)::           varZ(1:) !< Z component [1:NC_NN].
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer !< Buffer string.
  real(R4P),    allocatable::          var(:)   !< X, Y, Z component.
  integer(I1P), allocatable::          varp(:)  !< Packed data.
  character(1), allocatable::          var64(:) !< Variable encoded in base64.
  integer(I4P)::                       rf       !< Real file index.
  integer(I4P)::                       n1       !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do n1=1,NC_NN
      write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//str(n=varX(n1))//' '//str(n=varY(n1))//' '//str(n=varZ(n1))
    enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = 3*NC_NN*BYR4P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R4',3*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)(varX(n1),varY(n1),varZ(n1),n1=1,NC_NN)
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    allocate(var(1:3*NC_NN))
    do n1=1,NC_NN
      var(1+(n1-1)*3:1+(n1-1)*3+2)=[varX(n1),varY(n1),varZ(n1)]
    enddo
    call pack_data(a1=[int(3*NC_NN*BYR4P,I4P)],a2=var,packed=varp) ; deallocate(var)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_VECT_1DA_R4

  !> Function for saving field of vectorial variable (R4P, 3D arrays).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_VECT_3DA_R4(NC_NN,varname,varX,varY,varZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN          !< Number of cells or nodes.
  character(*), intent(IN)::           varname        !< Variable name.
  real(R4P),    intent(IN)::           varX(1:,1:,1:) !< X component [1:Nx,1:Ny,1:Nz].
  real(R4P),    intent(IN)::           varY(1:,1:,1:) !< Y component [1:Nx,1:Ny,1:Nz].
  real(R4P),    intent(IN)::           varZ(1:,1:,1:) !< Z component [1:Nx,1:Ny,1:Nz].
  integer(I4P), intent(IN), optional:: cf             !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO           !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer       !< Buffer string.
  real(R4P),    allocatable::          var(:)         !< X, Y, Z component.
  integer(I1P), allocatable::          varp(:)        !< Packed data.
  character(1), allocatable::          var64(:)       !< Variable encoded in base64.
  integer(I4P)::                       rf             !< Real file index.
  integer(I4P)::                       nx,ny,nz,n1    !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do nz=1,size(varX,dim=3) ; do ny=1,size(varX,dim=2) ; do nx=1,size(varX,dim=1)
      write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//&
                                        str(n=varX(nx,ny,nz))//' '//str(n=varY(nx,ny,nz))//' '//str(n=varZ(nx,ny,nz))
    enddo ; enddo ; enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = 3*NC_NN*BYR4P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R4',3*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)(((varX(nx,ny,nz),varY(nx,ny,nz),varZ(nx,ny,nz),&
                                 nx=1,size(varX,dim=1)),ny=1,size(varX,dim=2)),nz=1,size(varX,dim=3))
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    allocate(var(1:3*NC_NN))
    n1 = 0_I4P
    do nz=1,size(varX,dim=3) ; do ny=1,size(varX,dim=2) ; do nx=1,size(varX,dim=1)
      n1 = n1 + 1_I4P ; var(1+(n1-1)*3:1+(n1-1)*3+2)=[varX(nx,ny,nz),varY(nx,ny,nz),varZ(nx,ny,nz)]
    enddo ; enddo ; enddo
    call pack_data(a1=[int(3*NC_NN*BYR4P,I4P)],a2=var,packed=varp) ; deallocate(var)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_VECT_3DA_R4

  !> Function for saving field of vectorial variable (I8P, 1D arrays).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_VECT_1DA_I8(NC_NN,varname,varX,varY,varZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN    !< Number of cells or nodes.
  character(*), intent(IN)::           varname  !< Variable name.
  integer(I8P), intent(IN)::           varX(1:) !< X component [1:NC_NN].
  integer(I8P), intent(IN)::           varY(1:) !< Y component [1:NC_NN].
  integer(I8P), intent(IN)::           varZ(1:) !< Z component [1:NC_NN].
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer !< Buffer string.
  integer(I8P), allocatable::          var(:)   !< X, Y, Z component.
  integer(I1P), allocatable::          varp(:)  !< Packed data.
  character(1), allocatable::          var64(:) !< Variable encoded in base64.
  integer(I4P)::                       rf       !< Real file index.
  integer(I4P)::                       n1       !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int64" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do n1=1,NC_NN
      write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//str(n=varX(n1))//' '//str(n=varY(n1))//' '//str(n=varZ(n1))
    enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int64" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = int(3*NC_NN*BYI8P,I4P))
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I8',3*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)(varX(n1),varY(n1),varZ(n1),n1=1,NC_NN)
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int64" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    allocate(var(1:3*NC_NN))
    do n1=1,NC_NN
      var(1+(n1-1)*3:1+(n1-1)*3+2)=[varX(n1),varY(n1),varZ(n1)]
    enddo
    call pack_data(a1=[int(3*NC_NN*BYI8P,I4P)],a2=var,packed=varp) ; deallocate(var)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_VECT_1DA_I8

  !> Function for saving field of vectorial variable (I8P, 3D arrays).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_VECT_3DA_I8(NC_NN,varname,varX,varY,varZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN          !< Number of cells or nodes.
  character(*), intent(IN)::           varname        !< Variable name.
  integer(I8P), intent(IN)::           varX(1:,1:,1:) !< X component [1:Nx,1:Ny,1:Nz].
  integer(I8P), intent(IN)::           varY(1:,1:,1:) !< Y component [1:Nx,1:Ny,1:Nz].
  integer(I8P), intent(IN)::           varZ(1:,1:,1:) !< Z component [1:Nx,1:Ny,1:Nz].
  integer(I4P), intent(IN), optional:: cf             !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO           !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer       !< Buffer string.
  integer(I8P), allocatable::          var(:)         !< X, Y, Z component.
  integer(I1P), allocatable::          varp(:)        !< Packed data.
  character(1), allocatable::          var64(:)       !< Variable encoded in base64.
  integer(I4P)::                       rf             !< Real file index.
  integer(I4P)::                       nx,ny,nz,n1    !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int64" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do nz=1,size(varX,dim=3) ; do ny=1,size(varX,dim=2) ; do nx=1,size(varX,dim=1)
      write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//&
                                        str(n=varX(nx,ny,nz))//' '//str(n=varY(nx,ny,nz))//' '//str(n=varZ(nx,ny,nz))
    enddo ; enddo ; enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int64" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = int(3*NC_NN*BYI8P,I4P))
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I8',3*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)(((varX(nx,ny,nz),varY(nx,ny,nz),varZ(nx,ny,nz),&
                                 nx=1,size(varX,dim=1)),ny=1,size(varX,dim=2)),nz=1,size(varX,dim=3))
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int64" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    allocate(var(1:3*NC_NN))
    n1 = 0_I4P
    do nz=1,size(varX,dim=3) ; do ny=1,size(varX,dim=2) ; do nx=1,size(varX,dim=1)
      n1 = n1 + 1_I4P ; var(1+(n1-1)*3:1+(n1-1)*3+2)=[varX(nx,ny,nz),varY(nx,ny,nz),varZ(nx,ny,nz)]
    enddo ; enddo ; enddo
    call pack_data(a1=[int(3*NC_NN*BYI8P,I4P)],a2=var,packed=varp) ; deallocate(var)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_VECT_3DA_I8

  !> Function for saving field of vectorial variable (I4P, 1D arrays).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_VECT_1DA_I4(NC_NN,varname,varX,varY,varZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN    !< Number of cells or nodes.
  character(*), intent(IN)::           varname  !< Variable name.
  integer(I4P), intent(IN)::           varX(1:) !< X component [1:NC_NN].
  integer(I4P), intent(IN)::           varY(1:) !< Y component [1:NC_NN].
  integer(I4P), intent(IN)::           varZ(1:) !< Z component [1:NC_NN].
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer !< Buffer string.
  integer(I4P), allocatable::          var(:)   !< X, Y, Z component.
  integer(I1P), allocatable::          varp(:)  !< Packed data.
  character(1), allocatable::          var64(:) !< Variable encoded in base64.
  integer(I4P)::                       rf       !< Real file index.
  integer(I4P)::                       n1       !< Counter.
  integer(I8P)::                       Nvarp    !< Dimension of varp, packed data.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do n1=1,NC_NN
      write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//str(n=varX(n1))//' '//str(n=varY(n1))//' '//str(n=varZ(n1))
    enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = 3*NC_NN*BYI4P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I4',3*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)(varX(n1),varY(n1),varZ(n1),n1=1,NC_NN)
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    allocate(var(1:3*NC_NN))
    do n1=1,NC_NN
      var(1+(n1-1)*3:1+(n1-1)*3+2)=[varX(n1),varY(n1),varZ(n1)]
    enddo
    Nvarp=size(transfer([int(3*NC_NN*BYI4P,I4P),var],varp)) ; if (allocated(varp)) deallocate(varp); allocate(varp(1:Nvarp))
    varp = transfer([int(3*NC_NN*BYI4P,I4P),var],varp) ; deallocate(var)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_VECT_1DA_I4

  !> Function for saving field of vectorial variable (I4P, 3D arrays).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_VECT_3DA_I4(NC_NN,varname,varX,varY,varZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN          !< Number of cells or nodes.
  character(*), intent(IN)::           varname        !< Variable name.
  integer(I4P), intent(IN)::           varX(1:,1:,1:) !< X component [1:Nx,1:Ny,1:Nz].
  integer(I4P), intent(IN)::           varY(1:,1:,1:) !< Y component [1:Nx,1:Ny,1:Nz].
  integer(I4P), intent(IN)::           varZ(1:,1:,1:) !< Z component [1:Nx,1:Ny,1:Nz].
  integer(I4P), intent(IN), optional:: cf             !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO           !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer       !< Buffer string.
  integer(I4P), allocatable::          var(:)         !< X, Y, Z component.
  integer(I1P), allocatable::          varp(:)        !< Packed data.
  character(1), allocatable::          var64(:)       !< Variable encoded in base64.
  integer(I4P)::                       rf             !< Real file index.
  integer(I4P)::                       nx,ny,nz,n1    !< Counters.
  integer(I8P)::                       Nvarp          !< Dimension of varp, packed data.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do nz=1,size(varX,dim=3) ; do ny=1,size(varX,dim=2) ; do nx=1,size(varX,dim=1)
      write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//&
                                        str(n=varX(nx,ny,nz))//' '//str(n=varY(nx,ny,nz))//' '//str(n=varZ(nx,ny,nz))
    enddo ; enddo ; enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = 3*NC_NN*BYI4P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I4',3*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)(((varX(nx,ny,nz),varY(nx,ny,nz),varZ(nx,ny,nz),&
                                 nx=1,size(varX,dim=1)),ny=1,size(varX,dim=2)),nz=1,size(varX,dim=3))
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    allocate(var(1:3*NC_NN))
    n1 = 0_I4P
    do nz=1,size(varX,dim=3) ; do ny=1,size(varX,dim=2) ; do nx=1,size(varX,dim=1)
      n1 = n1 + 1_I4P ; var(1+(n1-1)*3:1+(n1-1)*3+2)=[varX(nx,ny,nz),varY(nx,ny,nz),varZ(nx,ny,nz)]
    enddo ; enddo ; enddo
    Nvarp=size(transfer([int(3*NC_NN*BYI4P,I4P),var],varp)) ; if (allocated(varp)) deallocate(varp); allocate(varp(1:Nvarp))
    varp = transfer([int(3*NC_NN*BYI4P,I4P),var],varp) ; deallocate(var)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_VECT_3DA_I4

  !> Function for saving field of vectorial variable (I2P, 1D arrays).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_VECT_1DA_I2(NC_NN,varname,varX,varY,varZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN    !< Number of cells or nodes.
  character(*), intent(IN)::           varname  !< Variable name.
  integer(I2P), intent(IN)::           varX(1:) !< X component [1:NC_NN].
  integer(I2P), intent(IN)::           varY(1:) !< Y component [1:NC_NN].
  integer(I2P), intent(IN)::           varZ(1:) !< Z component [1:NC_NN].
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer !< Buffer string.
  integer(I2P), allocatable::          var(:)   !< X, Y, Z component.
  integer(I1P), allocatable::          varp(:)  !< Packed data.
  character(1), allocatable::          var64(:) !< Variable encoded in base64.
  integer(I4P)::                       rf       !< Real file index.
  integer(I4P)::                       n1       !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int16" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do n1=1,NC_NN
      write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//str(n=varX(n1))//' '//str(n=varY(n1))//' '//str(n=varZ(n1))
    enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int16" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = 3*NC_NN*BYI2P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I2',3*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)(varX(n1),varY(n1),varZ(n1),n1=1,NC_NN)
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int16" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    allocate(var(1:3*NC_NN))
    do n1=1,NC_NN
      var(1+(n1-1)*3:1+(n1-1)*3+2)=[varX(n1),varY(n1),varZ(n1)]
    enddo
    call pack_data(a1=[int(3*NC_NN*BYI2P,I4P)],a2=var,packed=varp) ; deallocate(var)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_VECT_1DA_I2

  !> Function for saving field of vectorial variable (I2P, 3D arrays).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_VECT_3DA_I2(NC_NN,varname,varX,varY,varZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN          !< Number of cells or nodes.
  character(*), intent(IN)::           varname        !< Variable name.
  integer(I2P), intent(IN)::           varX(1:,1:,1:) !< X component [1:Nx,1:Ny,1:Nz].
  integer(I2P), intent(IN)::           varY(1:,1:,1:) !< Y component [1:Nx,1:Ny,1:Nz].
  integer(I2P), intent(IN)::           varZ(1:,1:,1:) !< Z component [1:Nx,1:Ny,1:Nz].
  integer(I4P), intent(IN), optional:: cf             !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO           !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer       !< Buffer string.
  integer(I2P), allocatable::          var(:)         !< X, Y, Z component.
  integer(I1P), allocatable::          varp(:)        !< Packed data.
  character(1), allocatable::          var64(:)       !< Variable encoded in base64.
  integer(I4P)::                       rf             !< Real file index.
  integer(I4P)::                       nx,ny,nz,n1    !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int16" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do nz=1,size(varX,dim=3) ; do ny=1,size(varX,dim=2) ; do nx=1,size(varX,dim=1)
      write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//&
                                        str(n=varX(nx,ny,nz))//' '//str(n=varY(nx,ny,nz))//' '//str(n=varZ(nx,ny,nz))
    enddo ; enddo ; enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int16" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = 3*NC_NN*BYI2P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I2',3*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)(((varX(nx,ny,nz),varY(nx,ny,nz),varZ(nx,ny,nz),&
                                 nx=1,size(varX,dim=1)),ny=1,size(varX,dim=2)),nz=1,size(varX,dim=3))
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int16" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    allocate(var(1:3*NC_NN))
    n1 = 0_I4P
    do nz=1,size(varX,dim=3) ; do ny=1,size(varX,dim=2) ; do nx=1,size(varX,dim=1)
      n1 = n1 + 1_I4P ; var(1+(n1-1)*3:1+(n1-1)*3+2)=[varX(nx,ny,nz),varY(nx,ny,nz),varZ(nx,ny,nz)]
    enddo ; enddo ; enddo
    call pack_data(a1=[int(3*NC_NN*BYI2P,I4P)],a2=var,packed=varp) ; deallocate(var)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_VECT_3DA_I2

  !> Function for saving field of vectorial variable (I1P, 1D arrays).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_VECT_1DA_I1(NC_NN,varname,varX,varY,varZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN    !< Number of cells or nodes.
  character(*), intent(IN)::           varname  !< Variable name.
  integer(I1P), intent(IN)::           varX(1:) !< X component [1:NC_NN].
  integer(I1P), intent(IN)::           varY(1:) !< Y component [1:NC_NN].
  integer(I1P), intent(IN)::           varZ(1:) !< Z component [1:NC_NN].
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer !< Buffer string.
  integer(I1P), allocatable::          var(:)   !< X, Y, Z component.
  integer(I1P), allocatable::          varp(:)  !< Packed data.
  character(1), allocatable::          var64(:) !< Variable encoded in base64.
  integer(I4P)::                       rf       !< Real file index.
  integer(I4P)::                       n1       !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" Name="'//trim(varname)//'" NumberOfComponents="3" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do n1=1,NC_NN
      write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//str(n=varX(n1))//' '//str(n=varY(n1))//' '//str(n=varZ(n1))
    enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" Name="'//trim(varname)//&
             '" NumberOfComponents="3" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    vtk(rf)%N_Byte = 3*NC_NN*BYI1P
    call vtk(rf)%byte_update(N_Byte = 3*NC_NN*BYI1P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I1',3*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)(varX(n1),varY(n1),varZ(n1),n1=1,NC_NN)
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    allocate(var(1:3*NC_NN))
    do n1=1,NC_NN
      var(1+(n1-1)*3:1+(n1-1)*3+2)=[varX(n1),varY(n1),varZ(n1)]
    enddo
    call pack_data(a1=[int(3*NC_NN*BYI1P,I4P)],a2=var,packed=varp) ; deallocate(var)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_VECT_1DA_I1

  !> Function for saving field of vectorial variable (I1P, 3D arrays).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_VECT_3DA_I1(NC_NN,varname,varX,varY,varZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN          !< Number of cells or nodes.
  character(*), intent(IN)::           varname        !< Variable name.
  integer(I1P), intent(IN)::           varX(1:,1:,1:) !< X component [1:Nx,1:Ny,1:Nz].
  integer(I1P), intent(IN)::           varY(1:,1:,1:) !< Y component [1:Nx,1:Ny,1:Nz].
  integer(I1P), intent(IN)::           varZ(1:,1:,1:) !< Z component [1:Nx,1:Ny,1:Nz].
  integer(I4P), intent(IN), optional:: cf             !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO           !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer       !< Buffer string.
  integer(I1P), allocatable::          var(:)         !< X, Y, Z component.
  integer(I1P), allocatable::          varp(:)        !< Packed data.
  character(1), allocatable::          var64(:)       !< Variable encoded in base64.
  integer(I4P)::                       rf             !< Real file index.
  integer(I4P)::                       nx,ny,nz,n1    !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" Name="'//trim(varname)//'" NumberOfComponents="3" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do nz=1,size(varX,dim=3) ; do ny=1,size(varX,dim=2) ; do nx=1,size(varX,dim=1)
      write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//&
                                        str(n=varX(nx,ny,nz))//' '//str(n=varY(nx,ny,nz))//' '//str(n=varZ(nx,ny,nz))
    enddo ; enddo ; enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer=repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" Name="'//trim(varname)//&
             '" NumberOfComponents="3" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    vtk(rf)%N_Byte = 3*NC_NN*BYI1P
    call vtk(rf)%byte_update(N_Byte = 3*NC_NN*BYI1P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I1',3*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)(((varX(nx,ny,nz),varY(nx,ny,nz),varZ(nx,ny,nz),&
                                 nx=1,size(varX,dim=1)),ny=1,size(varX,dim=2)),nz=1,size(varX,dim=3))
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" Name="'//trim(varname)//&
               '" NumberOfComponents="3" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    allocate(var(1:3*NC_NN))
    n1 = 0_I4P
    do nz=1,size(varX,dim=3) ; do ny=1,size(varX,dim=2) ; do nx=1,size(varX,dim=1)
      n1 = n1 + 1_I4P ; var(1+(n1-1)*3:1+(n1-1)*3+2)=[varX(nx,ny,nz),varY(nx,ny,nz),varZ(nx,ny,nz)]
    enddo ; enddo ; enddo
    call pack_data(a1=[int(3*NC_NN*BYI1P,I4P)],a2=var,packed=varp) ; deallocate(var)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_VECT_3DA_I1

  !> Function for saving field of list variable (R8P, 1D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_LIST_1DA_R8(NC_NN,N_COL,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN      !< Number of cells or nodes.
  integer(I4P), intent(IN)::           N_COL      !< Number of columns.
  character(*), intent(IN)::           varname    !< Variable name.
  real(R8P),    intent(IN)::           var(1:,1:) !< Components [1:N_COL,1:NC_NN].
  integer(I4P), intent(IN), optional:: cf         !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO       !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer   !< Buffer string.
  integer(I1P), allocatable::          varp(:)    !< Packed data.
  character(1), allocatable::          var64(:)   !< Variable encoded in base64.
  integer(I4P)::                       rf         !< Real file index.
  integer(I4P)::                       n1,n2      !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do n2=1,NC_NN
      write(vtk(rf)%u,'('//trim(str(.true.,N_COL+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),&
                                                                       (' '//str(n=var(n1,n2)),n1=1,N_COL)
    enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = N_COL*NC_NN*BYR8P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R8',N_COL*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(N_COL*NC_NN*BYR8P,I4P)],a2=reshape(var,[N_COL*NC_NN]),packed=varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_LIST_1DA_R8

  !> Function for saving field of list variable (R8P, 3D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_LIST_3DA_R8(NC_NN,N_COL,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN            !< Number of cells or nodes.
  integer(I4P), intent(IN)::           N_COL            !< Number of columns.
  character(*), intent(IN)::           varname          !< Variable name.
  real(R8P),    intent(IN)::           var(1:,1:,1:,1:) !< Components [1:N_COL,1:Nx,1:Ny,1:Nz].
  integer(I4P), intent(IN), optional:: cf               !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO             !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer         !< Buffer string.
  integer(I1P), allocatable::          varp(:)          !< Packed data.
  character(1), allocatable::          var64(:)         !< Variable encoded in base64.
  integer(I4P)::                       rf               !< Real file index.
  integer(I4P)::                       nx,ny,nz,n1      !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do nz=1,size(var,dim=4) ; do ny=1,size(var,dim=3) ; do nx=1,size(var,dim=2)
      write(vtk(rf)%u,'('//trim(str(.true.,N_COL+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),&
                                                                       (' '//str(n=var(n1,nx,ny,nz)),n1=1,N_COL)
    enddo ; enddo ; enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = N_COL*NC_NN*BYR8P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R8',N_COL*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float64" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(N_COL*NC_NN*BYR8P,I4P)],a2=reshape(var,[N_COL*NC_NN]),packed=varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_LIST_3DA_R8

  !> Function for saving field of list variable (R4P, 1D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_LIST_1DA_R4(NC_NN,N_COL,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN      !< Number of cells or nodes.
  integer(I4P), intent(IN)::           N_COL      !< Number of columns.
  character(*), intent(IN)::           varname    !< Variable name.
  real(R4P),    intent(IN)::           var(1:,1:) !< Components [1:N_COL,1:NC_NN].
  integer(I4P), intent(IN), optional:: cf         !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO       !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer   !< Buffer string.
  integer(I1P), allocatable::          varp(:)    !< Packed data.
  character(1), allocatable::          var64(:)   !< Variable encoded in base64.
  integer(I4P)::                       rf         !< Real file index.
  integer(I4P)::                       n1,n2      !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do n2=1,NC_NN
      write(vtk(rf)%u,'('//trim(str(.true.,N_COL+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),&
                                                                       (' '//str(n=var(n1,n2)),n1=1,N_COL)
    enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = N_COL*NC_NN*BYR4P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R4',N_COL*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(N_COL*NC_NN*BYR4P,I4P)],a2=reshape(var,[N_COL*NC_NN]),packed=varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_LIST_1DA_R4

  !> Function for saving field of list variable (R4P, 3D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_LIST_3DA_R4(NC_NN,N_COL,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN            !< Number of cells or nodes.
  integer(I4P), intent(IN)::           N_COL            !< Number of columns.
  character(*), intent(IN)::           varname          !< Variable name.
  real(R4P),    intent(IN)::           var(1:,1:,1:,1:) !< Components [1:N_COL,1:Nx,1:Ny,1:Nz].
  integer(I4P), intent(IN), optional:: cf               !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO             !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer         !< Buffer string.
  integer(I1P), allocatable::          varp(:)          !< Packed data.
  character(1), allocatable::          var64(:)         !< Variable encoded in base64.
  integer(I4P)::                       rf               !< Real file index.
  integer(I4P)::                       nx,ny,nz,n1      !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do nz=1,size(var,dim=4) ; do ny=1,size(var,dim=3) ; do nx=1,size(var,dim=2)
      write(vtk(rf)%u,'('//trim(str(.true.,N_COL+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),&
                                                                       (' '//str(n=var(n1,nx,ny,nz)),n1=1,N_COL)
    enddo ; enddo ; enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = N_COL*NC_NN*BYR4P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'R4',N_COL*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Float32" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(N_COL*NC_NN*BYR4P,I4P)],a2=reshape(var,[N_COL*NC_NN]),packed=varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_LIST_3DA_R4

  !> Function for saving field of list variable (I8P, 1D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_LIST_1DA_I8(NC_NN,N_COL,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN      !< Number of cells or nodes.
  integer(I4P), intent(IN)::           N_COL      !< Number of columns.
  character(*), intent(IN)::           varname    !< Variable name.
  integer(I8P), intent(IN)::           var(1:,1:) !< Components [1:N_COL,1:NC_NN].
  integer(I4P), intent(IN), optional:: cf         !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO       !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer   !< Buffer string.
  integer(I1P), allocatable::          varp(:)    !< Packed data.
  character(1), allocatable::          var64(:)   !< Variable encoded in base64.
  integer(I4P)::                       rf         !< Real file index.
  integer(I4P)::                       n1,n2      !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int64" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do n2=1,NC_NN
      write(vtk(rf)%u,'('//trim(str(.true.,N_COL+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),&
                                                                       (' '//str(n=var(n1,n2)),n1=1,N_COL)
    enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int64" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = int(N_COL*NC_NN*BYI8P,I4P))
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I8',N_COL*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int64" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(N_COL*NC_NN*BYI8P,I4P)],a2=reshape(var,[N_COL*NC_NN]),packed=varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_LIST_1DA_I8

  !> Function for saving field of list variable (I8P, 3D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_LIST_3DA_I8(NC_NN,N_COL,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN            !< Number of cells or nodes.
  integer(I4P), intent(IN)::           N_COL            !< Number of columns.
  character(*), intent(IN)::           varname          !< Variable name.
  integer(I8P), intent(IN)::           var(1:,1:,1:,1:) !< Components [1:N_COL,1:Nx,1:Ny,1:Nz].
  integer(I4P), intent(IN), optional:: cf               !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO             !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer         !< Buffer string.
  integer(I1P), allocatable::          varp(:)          !< Packed data.
  character(1), allocatable::          var64(:)         !< Variable encoded in base64.
  integer(I4P)::                       rf               !< Real file index.
  integer(I4P)::                       nx,ny,nz,n1      !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int64" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do nz=1,size(var,dim=4) ; do ny=1,size(var,dim=3) ; do nx=1,size(var,dim=2)
      write(vtk(rf)%u,'('//trim(str(.true.,N_COL+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),&
                                                                       (' '//str(n=var(n1,nx,ny,nz)),n1=1,N_COL)
    enddo ; enddo ; enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int64" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = int(N_COL*NC_NN*BYI8P,I4P))
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I8',N_COL*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int64" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(N_COL*NC_NN*BYI8P,I4P)],a2=reshape(var,[N_COL*NC_NN]),packed=varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_LIST_3DA_I8

  !> Function for saving field of list variable (I4P, 1D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_LIST_1DA_I4(NC_NN,N_COL,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN      !< Number of cells or nodes.
  integer(I4P), intent(IN)::           N_COL      !< Number of columns.
  character(*), intent(IN)::           varname    !< Variable name.
  integer(I4P), intent(IN)::           var(1:,1:) !< Components [1:N_COL,1:NC_NN].
  integer(I4P), intent(IN), optional:: cf         !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO       !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer   !< Buffer string.
  integer(I1P), allocatable::          varp(:)    !< Packed data.
  character(1), allocatable::          var64(:)   !< Variable encoded in base64.
  integer(I4P)::                       rf         !< Real file index.
  integer(I4P)::                       n1,n2      !< Counters.
  integer(I8P)::                       Nvarp      !< Dimension of varp, packed data.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do n2=1,NC_NN
      write(vtk(rf)%u,'('//trim(str(.true.,N_COL+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),&
                                                                       (' '//str(n=var(n1,n2)),n1=1,N_COL)
    enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = N_COL*NC_NN*BYI4P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I4',N_COL*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    Nvarp=size(transfer([int(N_COL*NC_NN*BYI4P,I4P),reshape(var,[N_COL*NC_NN])],varp))
    if (allocated(varp)) deallocate(varp); allocate(varp(1:Nvarp))
    varp = transfer([int(N_COL*NC_NN*BYI4P,I4P),reshape(var,[N_COL*NC_NN])],varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_LIST_1DA_I4

  !> Function for saving field of list variable (I4P, 3D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_LIST_3DA_I4(NC_NN,N_COL,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN            !< Number of cells or nodes.
  integer(I4P), intent(IN)::           N_COL            !< Number of columns.
  character(*), intent(IN)::           varname          !< Variable name.
  integer(I4P), intent(IN)::           var(1:,1:,1:,1:) !< Components [1:N_COL,1:Nx,1:Ny,1:Nz].
  integer(I4P), intent(IN), optional:: cf               !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO             !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer         !< Buffer string.
  integer(I1P), allocatable::          varp(:)          !< Packed data.
  character(1), allocatable::          var64(:)         !< Variable encoded in base64.
  integer(I4P)::                       rf               !< Real file index.
  integer(I4P)::                       nx,ny,nz,n1      !< Counters.
  integer(I8P)::                       Nvarp            !< Dimension of varp, packed data.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do nz=1,size(var,dim=4) ; do ny=1,size(var,dim=3) ; do nx=1,size(var,dim=2)
      write(vtk(rf)%u,'('//trim(str(.true.,N_COL+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),&
                                                                       (' '//str(n=var(n1,nx,ny,nz)),n1=1,N_COL)
    enddo ; enddo ; enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = N_COL*NC_NN*BYI4P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I4',N_COL*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int32" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    Nvarp=size(transfer([int(N_COL*NC_NN*BYI4P,I4P),reshape(var,[N_COL*NC_NN])],varp))
    if (allocated(varp)) deallocate(varp); allocate(varp(1:Nvarp))
    varp = transfer([int(N_COL*NC_NN*BYI4P,I4P),reshape(var,[N_COL*NC_NN])],varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_LIST_3DA_I4

  !> Function for saving field of list variable (I2P, 1D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_LIST_1DA_I2(NC_NN,N_COL,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN      !< Number of cells or nodes.
  integer(I4P), intent(IN)::           N_COL      !< Number of columns.
  character(*), intent(IN)::           varname    !< Variable name.
  integer(I2P), intent(IN)::           var(1:,1:) !< Components [1:N_COL,1:NC_NN].
  integer(I4P), intent(IN), optional:: cf         !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO       !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer   !< Buffer string.
  integer(I1P), allocatable::          varp(:)    !< Packed data.
  character(1), allocatable::          var64(:)   !< Variable encoded in base64.
  integer(I4P)::                       rf         !< Real file index.
  integer(I4P)::                       n1,n2      !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int16" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do n2=1,NC_NN
      write(vtk(rf)%u,'('//trim(str(.true.,N_COL+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),&
                                                                       (' '//str(n=var(n1,n2)),n1=1,N_COL)
    enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int16" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = N_COL*NC_NN*BYI2P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I2',N_COL*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int16" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(N_COL*NC_NN*BYI2P,I4P)],a2=reshape(var,[N_COL*NC_NN]),packed=varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_LIST_1DA_I2

  !> Function for saving field of list variable (I2P, 3D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_LIST_3DA_I2(NC_NN,N_COL,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN            !< Number of cells or nodes.
  integer(I4P), intent(IN)::           N_COL            !< Number of columns.
  character(*), intent(IN)::           varname          !< Variable name.
  integer(I2P), intent(IN)::           var(1:,1:,1:,1:) !< Components [1:N_COL,1:Nx,1:Ny,1:Nz].
  integer(I4P), intent(IN), optional:: cf               !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO             !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer         !< Buffer string.
  integer(I1P), allocatable::          varp(:)          !< Packed data.
  character(1), allocatable::          var64(:)         !< Variable encoded in base64.
  integer(I4P)::                       rf               !< Real file index.
  integer(I4P)::                       nx,ny,nz,n1      !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int16" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do nz=1,size(var,dim=4) ; do ny=1,size(var,dim=3) ; do nx=1,size(var,dim=2)
      write(vtk(rf)%u,'('//trim(str(.true.,N_COL+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),&
                                                                       (' '//str(n=var(n1,nx,ny,nz)),n1=1,N_COL)
    enddo ; enddo ; enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int16" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = N_COL*NC_NN*BYI2P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I2',N_COL*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int16" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(N_COL*NC_NN*BYI2P,I4P)],a2=reshape(var,[N_COL*NC_NN]),packed=varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_LIST_3DA_I2

  !> Function for saving field of list variable (I1P, 1D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_LIST_1DA_I1(NC_NN,N_COL,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN      !< Number of cells or nodes.
  integer(I4P), intent(IN)::           N_COL      !< Number of columns.
  character(*), intent(IN)::           varname    !< Variable name.
  integer(I1P), intent(IN)::           var(1:,1:) !< Components [1:N_COL,1:NC_NN].
  integer(I4P), intent(IN), optional:: cf         !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO       !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer   !< Buffer string.
  integer(I1P), allocatable::          varp(:)    !< Packed data.
  character(1), allocatable::          var64(:)   !< Variable encoded in base64.
  integer(I4P)::                       rf         !< Real file index.
  integer(I4P)::                       n1,n2      !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do n2=1,NC_NN
      write(vtk(rf)%u,'('//trim(str(.true.,N_COL+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),&
                                                                       (' '//str(n=var(n1,n2)),n1=1,N_COL)
    enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = N_COL*NC_NN*BYI1P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I1',N_COL*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(N_COL*NC_NN*BYI1P,I4P)],a2=reshape(var,[N_COL*NC_NN]),packed=varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_LIST_1DA_I1

  !> Function for saving field of list variable (I1P, 3D array).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_XML_LIST_3DA_I1(NC_NN,N_COL,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN            !< Number of cells or nodes.
  integer(I4P), intent(IN)::           N_COL            !< Number of columns.
  character(*), intent(IN)::           varname          !< Variable name.
  integer(I1P), intent(IN)::           var(1:,1:,1:,1:) !< Components [1:N_COL,1:Nx,1:Ny,1:Nz].
  integer(I4P), intent(IN), optional:: cf               !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO             !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer         !< Buffer string.
  integer(I1P), allocatable::          varp(:)          !< Packed data.
  character(1), allocatable::          var64(:)         !< Variable encoded in base64.
  integer(I4P)::                       rf               !< Real file index.
  integer(I4P)::                       nx,ny,nz,n1      !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="ascii">'
    write(vtk(rf)%u,'(A)',iostat=E_IO)trim(s_buffer)
    do nz=1,size(var,dim=4) ; do ny=1,size(var,dim=3) ; do nx=1,size(var,dim=2)
      write(vtk(rf)%u,'('//trim(str(.true.,N_COL+1))//'A)',iostat=E_IO)repeat(' ',vtk(rf)%indent),&
                                                                       (' '//str(n=var(n1,nx,ny,nz)),n1=1,N_COL)
    enddo ; enddo ; enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'
  case(raw,bin_app)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="appended" offset="'//trim(str(.true.,vtk(rf)%ioffset))//'"/>'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call vtk(rf)%byte_update(N_Byte = N_COL*NC_NN*BYI1P)
    write(vtk(rf)%ua,iostat=E_IO)vtk(rf)%N_Byte,'I1',N_COL*NC_NN
    write(vtk(rf)%ua,iostat=E_IO)var
  case(binary)
    s_buffer = repeat(' ',vtk(rf)%indent)//'<DataArray type="Int8" Name="'//trim(varname)//'" NumberOfComponents="'// &
               trim(str(.true.,N_COL))//'" format="binary">'
    write(vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    call pack_data(a1=[int(N_COL*NC_NN*BYI1P,I4P)],a2=reshape(var,[N_COL*NC_NN]),packed=varp)
    call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent+2)//tochar(var64)//end_rec ; deallocate(var64)
    write(vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</DataArray>'//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_XML_LIST_3DA_I1
  !> @}

  !> @brief Function for finalizing the VTK-XML file.
  !> @note An example of usage is: \n
  !> @code ...
  !> E_IO = VTK_END_XML()
  !> ... @endcode
  !> @return E_IO: integer(I4P) error flag
  !> @ingroup Lib_VTK_IOPublicProcedure
  function VTK_END_XML(cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(INOUT), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                          E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(2)::                          var_type !< Varable type = R8,R4,I8,I4,I2,I1.
  real(R8P),    allocatable::             v_R8(:)  !< R8 vector for IO in AppendData.
  real(R4P),    allocatable::             v_R4(:)  !< R4 vector for IO in AppendData.
  integer(I8P), allocatable::             v_I8(:)  !< I8 vector for IO in AppendData.
  integer(I4P), allocatable::             v_I4(:)  !< I4 vector for IO in AppendData.
  integer(I2P), allocatable::             v_I2(:)  !< I2 vector for IO in AppendData.
  integer(I1P), allocatable::             v_I1(:)  !< I1 vector for IO in AppendData.
  integer(I1P), allocatable::             varp(:)  !< Packed data.
  character(1), allocatable::             var64(:) !< Variable encoded in base64.
  integer(I4P)::                          rf       !< Real file index.
  integer(I8P)::                          Nvarp    !< Dimension of varp, packed data.
#ifdef HUGE
  integer(I8P)::                          N_v      !< Vector dimension.
  integer(I8P)::                          n1       !< Counter.
#else
  integer(I4P)::                          N_v      !< Vector dimension.
  integer(I4P)::                          n1       !< Counter.
#endif
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    vtk(rf)%indent = vtk(rf)%indent - 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</'//trim(vtk(rf)%topology)//'>'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)'</VTKFile>'
  case(raw,bin_app)
    vtk(rf)%indent = vtk(rf)%indent - 2
    write(unit  =vtk(rf)%u, iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</'//trim(vtk(rf)%topology)//'>'//end_rec
    if (vtk(rf)%f==raw) then
      write(unit  =vtk(rf)%u, iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<AppendedData encoding="raw">'//end_rec
    else
      write(unit  =vtk(rf)%u, iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<AppendedData encoding="base64">'//end_rec
    endif
    write(unit  =vtk(rf)%u, iostat=E_IO)'_'
    endfile(unit=vtk(rf)%ua,iostat=E_IO)
    rewind(unit =vtk(rf)%ua,iostat=E_IO)
    do
      read(unit=vtk(rf)%ua,iostat=E_IO,end=100)vtk(rf)%N_Byte,var_type,N_v
      select case(var_type)
      case('R8')
        allocate(v_R8(1:N_v))
        read(unit =vtk(rf)%ua,iostat=E_IO)(v_R8(n1),n1=1,N_v)
        if (vtk(rf)%f==raw) then
          write(unit=vtk(rf)%u,iostat=E_IO)int(vtk(rf)%N_Byte,I4P),(v_R8(n1),n1=1,N_v)
        else
          call pack_data(a1=[int(vtk(rf)%N_Byte,I4P)],a2=v_R8,packed=varp)
          call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
          write(unit=vtk(rf)%u,iostat=E_IO)tochar(var64) ; deallocate(var64)
        endif
        deallocate(v_R8)
      case('R4')
        allocate(v_R4(1:N_v))
        read(unit =vtk(rf)%ua,iostat=E_IO)(v_R4(n1),n1=1,N_v)
        if (vtk(rf)%f==raw) then
          write(unit=vtk(rf)%u,iostat=E_IO)int(vtk(rf)%N_Byte,I4P),(v_R4(n1),n1=1,N_v)
        else
          call pack_data(a1=[int(vtk(rf)%N_Byte,I4P)],a2=v_R4,packed=varp)
          call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
          write(unit=vtk(rf)%u,iostat=E_IO)tochar(var64) ; deallocate(var64)
        endif
        deallocate(v_R4)
      case('I8')
        allocate(v_I8(1:N_v))
        read(unit =vtk(rf)%ua,iostat=E_IO)(v_I8(n1),n1=1,N_v)
        if (vtk(rf)%f==raw) then
          write(unit=vtk(rf)%u,iostat=E_IO)int(vtk(rf)%N_Byte,I4P),(v_I8(n1),n1=1,N_v)
        else
          call pack_data(a1=[int(vtk(rf)%N_Byte,I4P)],a2=v_I8,packed=varp)
          call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
          write(unit=vtk(rf)%u,iostat=E_IO)tochar(var64) ; deallocate(var64)
        endif
        deallocate(v_I8)
      case('I4')
        allocate(v_I4(1:N_v))
        read(unit =vtk(rf)%ua,iostat=E_IO)(v_I4(n1),n1=1,N_v)
        if (vtk(rf)%f==raw) then
          write(unit=vtk(rf)%u,iostat=E_IO)int(vtk(rf)%N_Byte,I4P),(v_I4(n1),n1=1,N_v)
        else
          Nvarp=size(transfer([int(vtk(rf)%N_Byte,I4P),v_I4],varp)) ; if (allocated(varp)) deallocate(varp); allocate(varp(1:Nvarp))
          varp = transfer([int(vtk(rf)%N_Byte,I4P),v_I4],varp)
          call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
          write(unit=vtk(rf)%u,iostat=E_IO)tochar(var64) ; deallocate(var64)
        endif
        deallocate(v_I4)
      case('I2')
        allocate(v_I2(1:N_v))
        read(unit =vtk(rf)%ua,iostat=E_IO)(v_I2(n1),n1=1,N_v)
        if (vtk(rf)%f==raw) then
          write(unit=vtk(rf)%u,iostat=E_IO)int(vtk(rf)%N_Byte,I4P),(v_I2(n1),n1=1,N_v)
        else
          call pack_data(a1=[int(vtk(rf)%N_Byte,I4P)],a2=v_I2,packed=varp)
          call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
          write(unit=vtk(rf)%u,iostat=E_IO)tochar(var64) ; deallocate(var64)
        endif
        deallocate(v_I2)
      case('I1')
        allocate(v_I1(1:N_v))
        read(unit =vtk(rf)%ua,iostat=E_IO)(v_I1(n1),n1=1,N_v)
        if (vtk(rf)%f==raw) then
          write(unit=vtk(rf)%u,iostat=E_IO)int(vtk(rf)%N_Byte,I4P),(v_I1(n1),n1=1,N_v)
        else
          call pack_data(a1=[int(vtk(rf)%N_Byte,I4P)],a2=v_I1,packed=varp)
          call b64_encode(nB=int(BYI1P,I4P),n=varp,code=var64) ; deallocate(varp)
          write(unit=vtk(rf)%u,iostat=E_IO)tochar(var64) ; deallocate(var64)
        endif
        deallocate(v_I1)
      case default
        E_IO = 1
        write (stderr,'(A)')' bad var_type = '//var_type
        write (stderr,'(A)')' N_Byte = '//trim(str(n=vtk(rf)%N_Byte))//' N_v = '//trim(str(n=N_v))
        return
      endselect
    enddo
    100 continue
    write(unit=vtk(rf)%u,iostat=E_IO)end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</AppendedData>'//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)'</VTKFile>'//end_rec
    close(unit=vtk(rf)%ua,iostat=E_IO)
  case(binary)
    vtk(rf)%indent = vtk(rf)%indent - 2
    write(unit=vtk(rf)%u,iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</'//trim(vtk(rf)%topology)//'>'//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)'</VTKFile>'//end_rec
  endselect
  close(unit=vtk(rf)%u,iostat=E_IO)
  call vtk_update(act='remove',cf=rf,Nvtk=Nvtk,vtk=vtk)
  f = rf
  if (present(cf)) cf = rf
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_END_XML

  !> The VTK_VTM_XML function is used for initializing a VTM (VTK Multiblocks) XML file that is a wrapper to a set of VTK-XML files.
  !> @return E_IO: integer(I4P) error flag
  !> @ingroup Lib_VTK_IOPublicProcedure
  function VTM_INI_XML(filename) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  character(*), intent(IN):: filename !< File name of output VTM file.
  integer(I4P)::             E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::    s_buffer !< Buffer string.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  if (.not.ir_initialized) call IR_Init
  if (endian==endianL) then
    s_buffer='<VTKFile type="vtkMultiBlockDataSet" version="1.0" byte_order="LittleEndian">'
  else
    s_buffer='<VTKFile type="vtkMultiBlockDataSet" version="1.0" byte_order="BigEndian">'
  endif
  open(unit=Get_Unit(vtm%u),file=trim(filename),form='FORMATTED',access='SEQUENTIAL',action='WRITE',status='REPLACE',iostat=E_IO)
  write(unit=vtm%u,fmt='(A)',iostat=E_IO)'<?xml version="1.0"?>'
  write(unit=vtm%u,fmt='(A)',iostat=E_IO)trim(s_buffer) ; vtm%indent = 2
  write(unit=vtm%u,fmt='(A)',iostat=E_IO)repeat(' ',vtm%indent)//'<vtkMultiBlockDataSet>' ; vtm%indent = vtm%indent + 2
  vtm%blk = -1
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTM_INI_XML

  !> The VTM_BLK_XML function is used for opening or closing a block level of a VTM file.
  !> @return E_IO: integer(I4P) error flag
  !> @ingroup Lib_VTK_IOPublicProcedure
  function VTM_BLK_XML(block_action) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  character(*), intent(IN):: block_action !< Block action: OPEN or CLOSE block.
  integer(I4P)::             E_IO         !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  select case(trim(Upper_Case(block_action)))
  case('OPEN')
    vtm%blk = vtm%blk + 1
    write(unit=vtm%u,fmt='(A)',iostat=E_IO)repeat(' ',vtm%indent)//'<Block index="'//trim(str(.true.,vtm%blk))//'">'
    vtm%indent = vtm%indent + 2
  case('CLOSE')
    vtm%indent = vtm%indent - 2 ; write(unit=vtm%u,fmt='(A)',iostat=E_IO)repeat(' ',vtm%indent)//'</Block>'
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTM_BLK_XML

  !> The VTM_WRF_XML function is used for saving the list of VTK-XML wrapped files by the actual block of the mutliblock VTM file.
  !> @return E_IO: integer(I4P) error flag
  !> @ingroup Lib_VTK_IOPublicProcedure
  function VTM_WRF_XML(flist) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  character(*), intent(IN):: flist(:) !< List of VTK-XML wrapped files.
  integer(I4P)::             E_IO     !< Input/Output inquiring flag: 0 if IO is done, > 0 if IO is not done.
  integer(I4P)::             f        !< File counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  do f=1,size(flist)
    write(unit=vtm%u,fmt='(A)',iostat=E_IO)repeat(' ',vtm%indent)//'<DataSet index="'//trim(str(.true.,f-1))//'" file="'// &
                                           adjustl(trim(flist(f)))//'"/>'
  enddo
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTM_WRF_XML

  !> Function for finalizing open file, it has not inputs, @libvtk manages the file unit without the
  !> user's action.
  !> @return E_IO: integer(I4P) error flag
  !> @ingroup Lib_VTK_IOPublicProcedure
  function VTM_END_XML() result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P):: E_IO !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  vtm%indent = vtm%indent - 2
  write(unit=vtm%u,fmt='(A)',iostat=E_IO)repeat(' ',vtm%indent)//'</vtkMultiBlockDataSet>'
  write(unit=vtm%u,fmt='(A)',iostat=E_IO)'</VTKFile>'
  close(unit=vtm%u)
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTM_END_XML

  !> @brief Function for initializing parallel (partitioned) VTK-XML file.
  !> @return E_IO: integer(I4P) error flag
  !> @ingroup Lib_VTK_IOPublicProcedure
  function PVTK_INI_XML(filename,mesh_topology,tp,cf,nx1,nx2,ny1,ny2,nz1,nz2) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  character(*), intent(IN)::            filename      !< File name.
  character(*), intent(IN)::            mesh_topology !< Mesh topology.
  character(*), intent(IN)::            tp            !< Type of geometry representation (Float32, Float64, ecc).
  integer(I4P), intent(OUT), optional:: cf            !< Current file index (for concurrent files IO).
  integer(I4P), intent(IN),  optional:: nx1           !< Initial node of x axis.
  integer(I4P), intent(IN),  optional:: nx2           !< Final node of x axis.
  integer(I4P), intent(IN),  optional:: ny1           !< Initial node of y axis.
  integer(I4P), intent(IN),  optional:: ny2           !< Final node of y axis.
  integer(I4P), intent(IN),  optional:: nz1           !< Initial node of z axis.
  integer(I4P), intent(IN),  optional:: nz2           !< Final node of z axis.
  integer(I4P)::                        E_IO          !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::               s_buffer      !< Buffer string.
  integer(I4P)::                        rf            !< Real file index.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  if (.not.ir_initialized) call IR_Init
  call vtk_update(act='add',cf=rf,Nvtk=Nvtk,vtk=vtk)
  f = rf
  if (present(cf)) cf = rf
  vtk(rf)%topology = trim(mesh_topology)
  open(unit=Get_Unit(vtk(rf)%u),file=trim(filename),&
       form='FORMATTED',access='SEQUENTIAL',action='WRITE',status='REPLACE',iostat=E_IO)
  write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)'<?xml version="1.0"?>'
  if (endian==endianL) then
    s_buffer = '<VTKFile type="'//trim(vtk(rf)%topology)//'" version="0.1" byte_order="LittleEndian">'
  else
    s_buffer = '<VTKFile type="'//trim(vtk(rf)%topology)//'" version="0.1" byte_order="BigEndian">'
  endif
  write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer) ; vtk(rf)%indent = 2
  select case(trim(vtk(rf)%topology))
  case('PRectilinearGrid')
    s_buffer = repeat(' ',vtk(rf)%indent)//'<'//trim(vtk(rf)%topology)//' WholeExtent="'//&
               trim(str(n=nx1))//' '//trim(str(n=nx2))//' '//                             &
               trim(str(n=ny1))//' '//trim(str(n=ny2))//' '//                             &
               trim(str(n=nz1))//' '//trim(str(n=nz2))//'" GhostLevel="#">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer) ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<PCoordinates>' ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<PDataArray type="'//trim(tp)//'"/>'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<PDataArray type="'//trim(tp)//'"/>'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<PDataArray type="'//trim(tp)//'"/>'
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</PCoordinates>'
  case('PStructuredGrid')
    s_buffer = repeat(' ',vtk(rf)%indent)//'<'//trim(vtk(rf)%topology)//' WholeExtent="'//&
               trim(str(n=nx1))//' '//trim(str(n=nx2))//' '//                             &
               trim(str(n=ny1))//' '//trim(str(n=ny2))//' '//                             &
               trim(str(n=nz1))//' '//trim(str(n=nz2))//'" GhostLevel="#">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer) ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<PPoints>' ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<PDataArray type="'//trim(tp)//'" NumberOfComponents="3" Name="Points"/>'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer)
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</PPoints>'
  case('PUnstructuredGrid')
    s_buffer = repeat(' ',vtk(rf)%indent)//'<'//trim(vtk(rf)%topology)//' GhostLevel="0">'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer) ; vtk(rf)%indent = vtk(rf)%indent + 2
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<PPoints>' ; vtk(rf)%indent = vtk(rf)%indent + 2
    s_buffer = repeat(' ',vtk(rf)%indent)//'<PDataArray type="'//trim(tp)//'" NumberOfComponents="3" Name="Points"/>'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer)
    vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</PPoints>'
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction PVTK_INI_XML

  !> Function for saving piece geometry source for parallel (partitioned) VTK-XML file.
  !> @return E_IO: integer(I4P) error flag
  !> @ingroup Lib_VTK_IOPublicProcedure
  function PVTK_GEO_XML(source,cf,nx1,nx2,ny1,ny2,nz1,nz2) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  character(*), intent(IN)::           source   !< Source file name containing the piece data.
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P), intent(IN), optional:: nx1      !< Initial node of x axis.
  integer(I4P), intent(IN), optional:: nx2      !< Final node of x axis.
  integer(I4P), intent(IN), optional:: ny1      !< Initial node of y axis.
  integer(I4P), intent(IN), optional:: ny2      !< Final node of y axis.
  integer(I4P), intent(IN), optional:: nz1      !< Initial node of z axis.
  integer(I4P), intent(IN), optional:: nz2      !< Final node of z axis.
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer !< Buffer string.
  integer(I4P)::                       rf       !< Real file index.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case (vtk(rf)%topology)
  case('PRectilinearGrid','PStructuredGrid')
    s_buffer = repeat(' ',vtk(rf)%indent)//'<Piece Extent="'// &
               trim(str(n=nx1))//' '//trim(str(n=nx2))//' '// &
               trim(str(n=ny1))//' '//trim(str(n=ny2))//' '// &
               trim(str(n=nz1))//' '//trim(str(n=nz2))//'" Source="'//trim(source)//'"/>'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer)
  case('PUnstructuredGrid')
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<Piece Source="'//trim(source)//'"/>'
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction PVTK_GEO_XML

  !> Function that \b must be called before saving the data related to geometric mesh, this function initializes the
  !> saving of data variables indicating the \em type (node or cell centered) of variables that will be saved.
  !> @ingroup Lib_VTK_IOPublicProcedure
  function PVTK_DAT_XML(var_location,var_block_action,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  character(*), intent(IN)::           var_location     !< Location of saving variables: CELL or NODE centered.
  character(*), intent(IN)::           var_block_action !< Variables block action: OPEN or CLOSE block.
  integer(I4P), intent(IN), optional:: cf               !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO             !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf               !< Real file index.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(trim(Upper_Case(var_location)))
  case('CELL')
    select case(trim(Upper_Case(var_block_action)))
    case('OPEN')
      write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<PCellData>' ; vtk(rf)%indent = vtk(rf)%indent + 2
    case('CLOSE')
      vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</PCellData>'
    endselect
  case('NODE')
    select case(trim(Upper_Case(var_block_action)))
    case('OPEN')
      write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'<PPointData>' ; vtk(rf)%indent = vtk(rf)%indent + 2
    case('CLOSE')
      vtk(rf)%indent = vtk(rf)%indent - 2 ; write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</PPointData>'
    endselect
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction PVTK_DAT_XML

  !> Function for saving variable associated to nodes or cells geometry.
  !> @return E_IO: integer(I4P) error flag
  !> @ingroup Lib_VTK_IOPublicProcedure
  function PVTK_VAR_XML(varname,tp,cf,Nc) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  character(*), intent(IN)::           varname  !< Variable name.
  character(*), intent(IN)::           tp       !< Type of data representation (Float32, Float64, ecc).
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P), intent(IN), optional:: Nc       !< Number of components of variable.
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer !< Buffer string.
  integer(I4P)::                       rf       !< Real file index.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  if (present(Nc)) then
    s_buffer = repeat(' ',vtk(rf)%indent)//'<PDataArray type="'//trim(tp)//'" Name="'//trim(varname)//&
               '" NumberOfComponents="'//trim(str(.true.,Nc))//'"/>'
  else
    s_buffer = repeat(' ',vtk(rf)%indent)//'<PDataArray type="'//trim(tp)//'" Name="'//trim(varname)//'"/>'
  endif
  write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(s_buffer)
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction PVTK_VAR_XML

  !> @brief Function for finalizing the parallel (partitioned) VTK-XML file.
  !> @return E_IO: integer(I4P) error flag
  !> @ingroup Lib_VTK_IOPublicProcedure
  function PVTK_END_XML(cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(INOUT), optional:: cf   !< Current file index (for concurrent files IO).
  integer(I4P)::                          E_IO !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                          rf   !< Real file index.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  vtk(rf)%indent = vtk(rf)%indent - 2
  write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)repeat(' ',vtk(rf)%indent)//'</'//trim(vtk(rf)%topology)//'>'
  write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)'</VTKFile>'
  close(unit=vtk(rf)%u,iostat=E_IO)
  call vtk_update(act='remove',cf=rf,Nvtk=Nvtk,vtk=vtk)
  f = rf
  if (present(cf)) cf = rf
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction PVTK_END_XML

  !> @brief Function for initializing VTK-legacy file.
  !> @remark This function must be the first to be called.
  !> @note An example of usage is: \n
  !> @code ...
  !> E_IO=VTK_INI('Binary','example.vtk','VTK legacy file','UNSTRUCTURED_GRID')
  !> ... @endcode
  !> @return E_IO: integer(I4P) error flag
  !> @ingroup Lib_VTK_IOPublicProcedure
  function VTK_INI(output_format,filename,title,mesh_topology,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  character(*), intent(IN)::            output_format !< Output format: ASCII or RAW.
  character(*), intent(IN)::            filename      !< Name of file.
  character(*), intent(IN)::            title         !< Title.
  character(*), intent(IN)::            mesh_topology !< Mesh topology.
  integer(I4P), intent(OUT), optional:: cf            !< Current file index (for concurrent files IO).
  integer(I4P)::                        E_IO          !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                        rf            !< Real file index.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  if (.not.ir_initialized) call IR_Init
  call vtk_update(act='add',cf=rf,Nvtk=Nvtk,vtk=vtk)
  f = rf
  if (present(cf)) cf = rf
  vtk(rf)%topology = trim(mesh_topology)
  select case(trim(Upper_Case(output_format)))
  case('ASCII')
    vtk(rf)%f = ascii
    open(unit=Get_Unit(vtk(rf)%u),file=trim(filename),form='FORMATTED',&
         access='SEQUENTIAL',action='WRITE',status='REPLACE',iostat=E_IO)
    ! writing header of file
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)'# vtk DataFile Version 3.0'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(title)
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)trim(Upper_Case(output_format))
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)'DATASET '//trim(vtk(rf)%topology)
  case('RAW')
    vtk(rf)%f = raw
    open(unit=Get_Unit(vtk(rf)%u),file=trim(filename),&
         form='UNFORMATTED',access='STREAM',action='WRITE',status='REPLACE',iostat=E_IO)
    ! writing header of file
    write(unit=vtk(rf)%u,iostat=E_IO)'# vtk DataFile Version 3.0'//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)trim(title)//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)trim(Upper_Case(output_format))//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)'DATASET '//trim(vtk(rf)%topology)//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_INI

  !> @ingroup Lib_VTK_IOPrivateProcedure
  !> @{
  !> Function for saving mesh with \b STRUCTURED_POINTS topology (R8P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_STRP_R8(Nx,Ny,Nz,X0,Y0,Z0,Dx,Dy,Dz,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           Nx   !< Number of nodes in x direction.
  integer(I4P), intent(IN)::           Ny   !< Number of nodes in y direction.
  integer(I4P), intent(IN)::           Nz   !< Number of nodes in z direction.
  real(R8P),    intent(IN)::           X0   !< X coordinate of origin.
  real(R8P),    intent(IN)::           Y0   !< Y coordinate of origin.
  real(R8P),    intent(IN)::           Z0   !< Z coordinate of origin.
  real(R8P),    intent(IN)::           Dx   !< Space step in x direction.
  real(R8P),    intent(IN)::           Dy   !< Space step in y direction.
  real(R8P),    intent(IN)::           Dz   !< Space step in z direction.
  integer(I4P), intent(IN), optional:: cf   !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf   !< Real file index.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    write(vtk(rf)%u,'(A)',iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))
    write(vtk(rf)%u,'(A)',iostat=E_IO)'ORIGIN '//trim(str(n=X0))//' '//trim(str(n=Y0))//' '//trim(str(n=Z0))
    write(vtk(rf)%u,'(A)',iostat=E_IO)'SPACING '//trim(str(n=Dx))//' '//trim(str(n=Dy))//' '//trim(str(n=Dz))
  case(raw)
    write(vtk(rf)%u,iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))//end_rec
    write(vtk(rf)%u,iostat=E_IO)'ORIGIN '//trim(str(n=X0))//' '//trim(str(n=Y0))//' '//trim(str(n=Z0))//end_rec
    write(vtk(rf)%u,iostat=E_IO)'SPACING '//trim(str(n=Dx))//' '//trim(str(n=Dy))//' '//trim(str(n=Dz))//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_STRP_R8

  !> Function for saving mesh with \b STRUCTURED_POINTS topology (R4P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_STRP_R4(Nx,Ny,Nz,X0,Y0,Z0,Dx,Dy,Dz,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           Nx   !< Number of nodes in x direction.
  integer(I4P), intent(IN)::           Ny   !< Number of nodes in y direction.
  integer(I4P), intent(IN)::           Nz   !< Number of nodes in z direction.
  real(R4P),    intent(IN)::           X0   !< X coordinate of origin.
  real(R4P),    intent(IN)::           Y0   !< Y coordinate of origin.
  real(R4P),    intent(IN)::           Z0   !< Z coordinate of origin.
  real(R4P),    intent(IN)::           Dx   !< Space step in x direction.
  real(R4P),    intent(IN)::           Dy   !< Space step in y direction.
  real(R4P),    intent(IN)::           Dz   !< Space step in z direction.
  integer(I4P), intent(IN), optional:: cf   !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf   !< Real file index.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    write(vtk(rf)%u,'(A)',iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))
    write(vtk(rf)%u,'(A)',iostat=E_IO)'ORIGIN '//trim(str(n=X0))//' '//trim(str(n=Y0))//' '//trim(str(n=Z0))
    write(vtk(rf)%u,'(A)',iostat=E_IO)'SPACING '//trim(str(n=Dx))//' '//trim(str(n=Dy))//' '//trim(str(n=Dz))
  case(raw)
    write(vtk(rf)%u,iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))//end_rec
    write(vtk(rf)%u,iostat=E_IO)'ORIGIN '//trim(str(n=X0))//' '//trim(str(n=Y0))//' '//trim(str(n=Z0))//end_rec
    write(vtk(rf)%u,iostat=E_IO)'SPACING '//trim(str(n=Dx))//' '//trim(str(n=Dy))//' '//trim(str(n=Dz))//end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_STRP_R4

  !> Function for saving mesh with \b STRUCTURED_GRID topology (R8P, 1D arrays).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_STRG_1DA_R8(Nx,Ny,Nz,NN,X,Y,Z,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           Nx       !< Number of nodes in x direction.
  integer(I4P), intent(IN)::           Ny       !< Number of nodes in y direction.
  integer(I4P), intent(IN)::           Nz       !< Number of nodes in z direction.
  integer(I4P), intent(IN)::           NN       !< Number of all nodes.
  real(R8P),    intent(IN)::           X(1:)    !< X coordinates [1:NN].
  real(R8P),    intent(IN)::           Y(1:)    !< Y coordinates [1:NN].
  real(R8P),    intent(IN)::           Z(1:)    !< Z coordinates [1:NN].
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf       !< Real file index.
  integer(I4P)::                       n1       !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    write(vtk(rf)%u,'(A)',iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))
    write(vtk(rf)%u,'(A)',iostat=E_IO)'POINTS '//trim(str(.true.,NN))//' double'
    do n1=1,NN
      write(vtk(rf)%u,'(A)',iostat=E_IO)str(n=X(n1))//' '//str(n=Y(n1))//' '//str(n=Z(n1))
    enddo
  case(raw)
    write(vtk(rf)%u,iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))//end_rec
    write(vtk(rf)%u,iostat=E_IO)'POINTS '//trim(str(.true.,NN))//' double'//end_rec
    write(vtk(rf)%u,iostat=E_IO)(X(n1),Y(n1),Z(n1),n1=1,NN)
    write(vtk(rf)%u,iostat=E_IO)end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_STRG_1DA_R8

  !> Function for saving mesh with \b STRUCTURED_GRID topology (R8P, 1D arrays, packed API).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_STRG_1DAP_R8(Nx,Ny,Nz,NN,XYZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           Nx         !< Number of nodes in x direction.
  integer(I4P), intent(IN)::           Ny         !< Number of nodes in y direction.
  integer(I4P), intent(IN)::           Nz         !< Number of nodes in z direction.
  integer(I4P), intent(IN)::           NN         !< Number of all nodes.
  real(R8P),    intent(IN)::           XYZ(1:,1:) !< X, Y and Z coordinates [1:3,1:NN].
  integer(I4P), intent(IN), optional:: cf         !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO       !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf         !< Real file index.
  integer(I4P)::                       n1         !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    write(vtk(rf)%u,'(A)',iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))
    write(vtk(rf)%u,'(A)',iostat=E_IO)'POINTS '//trim(str(.true.,NN))//' double'
    do n1=1,NN
      write(vtk(rf)%u,'(A)',iostat=E_IO)str(n=XYZ(1,n1))//' '//str(n=XYZ(2,n1))//' '//str(n=XYZ(3,n1))
    enddo
  case(raw)
    write(vtk(rf)%u,iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))//end_rec
    write(vtk(rf)%u,iostat=E_IO)'POINTS '//trim(str(.true.,NN))//' double'//end_rec
    write(vtk(rf)%u,iostat=E_IO)XYZ
    write(vtk(rf)%u,iostat=E_IO)end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_STRG_1DAP_R8

  !> Function for saving mesh with \b STRUCTURED_GRID topology (R8P, 3D arrays).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_STRG_3DA_R8(Nx,Ny,Nz,NN,X,Y,Z,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           Nx          !< Number of nodes in x direction.
  integer(I4P), intent(IN)::           Ny          !< Number of nodes in y direction.
  integer(I4P), intent(IN)::           Nz          !< Number of nodes in z direction.
  integer(I4P), intent(IN)::           NN          !< Number of all nodes.
  real(R8P),    intent(IN)::           X(1:,1:,1:) !< X coordinates [1:Nx,1:Ny,1:Nz].
  real(R8P),    intent(IN)::           Y(1:,1:,1:) !< Y coordinates [1:Nx,1:Ny,1:Nz].
  real(R8P),    intent(IN)::           Z(1:,1:,1:) !< Z coordinates [1:Nx,1:Ny,1:Nz].
  integer(I4P), intent(IN), optional:: cf          !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO        !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf          !< Real file index.
  integer(I4P)::                       n1,n2,n3    !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    write(vtk(rf)%u,'(A)',iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))
    write(vtk(rf)%u,'(A)',iostat=E_IO)'POINTS '//trim(str(.true.,NN))//' double'
    do n3=1,Nz
      do n2=1,Ny
        do n1=1,Nx
          write(vtk(rf)%u,'(A)',iostat=E_IO)str(n=X(n1,n2,n3))//' '//str(n=Y(n1,n2,n3))//' '//str(n=Z(n1,n2,n3))
        enddo
      enddo
    enddo
  case(raw)
    write(vtk(rf)%u,iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))//end_rec
    write(vtk(rf)%u,iostat=E_IO)'POINTS '//trim(str(.true.,NN))//' double'//end_rec
    write(vtk(rf)%u,iostat=E_IO)(((X(n1,n2,n3),Y(n1,n2,n3),Z(n1,n2,n3),n1=1,Nx),n2=1,Ny),n3=1,Nz)
    write(vtk(rf)%u,iostat=E_IO)end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_STRG_3DA_R8

  !> Function for saving mesh with \b STRUCTURED_GRID topology (R8P, 3D arrays, packed API).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_STRG_3DAP_R8(Nx,Ny,Nz,NN,XYZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           Nx               !< Number of nodes in x direction.
  integer(I4P), intent(IN)::           Ny               !< Number of nodes in y direction.
  integer(I4P), intent(IN)::           Nz               !< Number of nodes in z direction.
  integer(I4P), intent(IN)::           NN               !< Number of all nodes.
  real(R8P),    intent(IN)::           XYZ(1:,1:,1:,1:) !< X, Y and Z coordinates [1:3,1:Nx,1:Ny,1:Nz].
  integer(I4P), intent(IN), optional:: cf               !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO             !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf               !< Real file index.
  integer(I4P)::                       n1,n2,n3         !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    write(vtk(rf)%u,'(A)',iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))
    write(vtk(rf)%u,'(A)',iostat=E_IO)'POINTS '//trim(str(.true.,NN))//' double'
    do n3=1,Nz
      do n2=1,Ny
        do n1=1,Nx
         write(vtk(rf)%u,'(A)',iostat=E_IO)str(n=XYZ(1,n1,n2,n3))//' '//str(n=XYZ(2,n1,n2,n3))//' '//str(n=XYZ(3,n1,n2,n3))
        enddo
      enddo
    enddo
  case(raw)
    write(vtk(rf)%u,iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))//end_rec
    write(vtk(rf)%u,iostat=E_IO)'POINTS '//trim(str(.true.,NN))//' double'//end_rec
    write(vtk(rf)%u,iostat=E_IO)XYZ
    write(vtk(rf)%u,iostat=E_IO)end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_STRG_3DAP_R8

  !> Function for saving mesh with \b STRUCTURED_GRID topology (R4P, 1D arrays).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_STRG_1DA_R4(Nx,Ny,Nz,NN,X,Y,Z,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           Nx       !< Number of nodes in x direction.
  integer(I4P), intent(IN)::           Ny       !< Number of nodes in y direction.
  integer(I4P), intent(IN)::           Nz       !< Number of nodes in z direction.
  integer(I4P), intent(IN)::           NN       !< Number of all nodes.
  real(R4P),    intent(IN)::           X(1:)    !< X coordinates [1:NN].
  real(R4P),    intent(IN)::           Y(1:)    !< Y coordinates [1:NN].
  real(R4P),    intent(IN)::           Z(1:)    !< Z coordinates [1:NN].
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf       !< Real file index.
  integer(I4P)::                       n1       !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    write(vtk(rf)%u,'(A)',iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))
    write(vtk(rf)%u,'(A)',iostat=E_IO)'POINTS '//trim(str(.true.,NN))//' float'
    do n1=1,NN
      write(vtk(rf)%u,'(A)',iostat=E_IO)str(n=X(n1))//' '//str(n=Y(n1))//' '//str(n=Z(n1))
    enddo
  case(raw)
    write(vtk(rf)%u,iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))//end_rec
    write(vtk(rf)%u,iostat=E_IO)'POINTS '//trim(str(.true.,NN))//' float'//end_rec
    write(vtk(rf)%u,iostat=E_IO)(X(n1),Y(n1),Z(n1),n1=1,NN)
    write(vtk(rf)%u,iostat=E_IO)end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_STRG_1DA_R4

  !> Function for saving mesh with \b STRUCTURED_GRID topology (R4P, 1D arrays, packed API).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_STRG_1DAP_R4(Nx,Ny,Nz,NN,XYZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           Nx         !< Number of nodes in x direction.
  integer(I4P), intent(IN)::           Ny         !< Number of nodes in y direction.
  integer(I4P), intent(IN)::           Nz         !< Number of nodes in z direction.
  integer(I4P), intent(IN)::           NN         !< Number of all nodes.
  real(R4P),    intent(IN)::           XYZ(1:,1:) !< X, Y and Z coordinates [1:3,1:NN].
  integer(I4P), intent(IN), optional:: cf         !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO       !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf         !< Real file index.
  integer(I4P)::                       n1         !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    write(vtk(rf)%u,'(A)',iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))
    write(vtk(rf)%u,'(A)',iostat=E_IO)'POINTS '//trim(str(.true.,NN))//' float'
    do n1=1,NN
      write(vtk(rf)%u,'(A)',iostat=E_IO)str(n=XYZ(1,n1))//' '//str(n=XYZ(2,n1))//' '//str(n=XYZ(3,n1))
    enddo
  case(raw)
    write(vtk(rf)%u,iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))//end_rec
    write(vtk(rf)%u,iostat=E_IO)'POINTS '//trim(str(.true.,NN))//' float'//end_rec
    write(vtk(rf)%u,iostat=E_IO)XYZ
    write(vtk(rf)%u,iostat=E_IO)end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_STRG_1DAP_R4

  !> Function for saving mesh with \b STRUCTURED_GRID topology (R4P, 3D arrays).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_STRG_3DA_R4(Nx,Ny,Nz,NN,X,Y,Z,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           Nx          !< Number of nodes in x direction.
  integer(I4P), intent(IN)::           Ny          !< Number of nodes in y direction.
  integer(I4P), intent(IN)::           Nz          !< Number of nodes in z direction.
  integer(I4P), intent(IN)::           NN          !< Number of all nodes.
  real(R4P),    intent(IN)::           X(1:,1:,1:) !< X coordinates [1:Nx,1:Ny,1:Nz].
  real(R4P),    intent(IN)::           Y(1:,1:,1:) !< Y coordinates [1:Nx,1:Ny,1:Nz].
  real(R4P),    intent(IN)::           Z(1:,1:,1:) !< Z coordinates [1:Nx,1:Ny,1:Nz].
  integer(I4P), intent(IN), optional:: cf          !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO        !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf          !< Real file index.
  integer(I4P)::                       n1,n2,n3    !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    write(vtk(rf)%u,'(A)',iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))
    write(vtk(rf)%u,'(A)',iostat=E_IO)'POINTS '//trim(str(.true.,NN))//' float'
    do n3=1,Nz
      do n2=1,Ny
        do n1=1,Nx
          write(vtk(rf)%u,'(A)',iostat=E_IO)str(n=X(n1,n2,n3))//' '//str(n=Y(n1,n2,n3))//' '//str(n=Z(n1,n2,n3))
        enddo
      enddo
    enddo
  case(raw)
    write(vtk(rf)%u,iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))//end_rec
    write(vtk(rf)%u,iostat=E_IO)'POINTS '//trim(str(.true.,NN))//' float'//end_rec
    write(vtk(rf)%u,iostat=E_IO)(((X(n1,n2,n3),Y(n1,n2,n3),Z(n1,n2,n3),n1=1,Nx),n2=1,Ny),n3=1,Nz)
    write(vtk(rf)%u,iostat=E_IO)end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_STRG_3DA_R4

  !> Function for saving mesh with \b STRUCTURED_GRID topology (R4P, 3D arrays, packed API).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_STRG_3DAP_R4(Nx,Ny,Nz,NN,XYZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           Nx               !< Number of nodes in x direction.
  integer(I4P), intent(IN)::           Ny               !< Number of nodes in y direction.
  integer(I4P), intent(IN)::           Nz               !< Number of nodes in z direction.
  integer(I4P), intent(IN)::           NN               !< Number of all nodes.
  real(R4P),    intent(IN)::           XYZ(1:,1:,1:,1:) !< X, Y and Z coordinates [1:3,1:Nx,1:Ny,1:Nz].
  integer(I4P), intent(IN), optional:: cf               !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO             !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf               !< Real file index.
  integer(I4P)::                       n1,n2,n3         !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    write(vtk(rf)%u,'(A)',iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))
    write(vtk(rf)%u,'(A)',iostat=E_IO)'POINTS '//trim(str(.true.,NN))//' float'
    do n3=1,Nz
      do n2=1,Ny
        do n1=1,Nx
         write(vtk(rf)%u,'(A)',iostat=E_IO)str(n=XYZ(1,n1,n2,n3))//' '//str(n=XYZ(2,n1,n2,n3))//' '//str(n=XYZ(3,n1,n2,n3))
        enddo
      enddo
    enddo
  case(raw)
    write(vtk(rf)%u,iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))//end_rec
    write(vtk(rf)%u,iostat=E_IO)'POINTS '//trim(str(.true.,NN))//' float'//end_rec
    write(vtk(rf)%u,iostat=E_IO)XYZ
    write(vtk(rf)%u,iostat=E_IO)end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_STRG_3DAP_R4

  !> Function for saving mesh with \b RECTILINEAR_GRID topology (R8P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_RECT_R8(Nx,Ny,Nz,X,Y,Z,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           Nx       !< Number of nodes in x direction.
  integer(I4P), intent(IN)::           Ny       !< Number of nodes in y direction.
  integer(I4P), intent(IN)::           Nz       !< Number of nodes in z direction.
  real(R8P),    intent(IN)::           X(1:Nx)  !< X coordinates.
  real(R8P),    intent(IN)::           Y(1:Ny)  !< Y coordinates.
  real(R8P),    intent(IN)::           Z(1:Nz)  !< Z coordinates.
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf       !< Real file index.
  integer(I4P)::                       n1       !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    write(vtk(rf)%u,'(A)',iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))
    write(vtk(rf)%u,'(A)',iostat=E_IO)'X_COORDINATES '//trim(str(.true.,Nx))//' double'
    do n1=1,Nx
      write(vtk(rf)%u,'(A)',iostat=E_IO)str(n=X(n1))
    enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)'Y_COORDINATES '//trim(str(.true.,Ny))//' double'
    do n1=1,Ny
      write(vtk(rf)%u,'(A)',iostat=E_IO)str(n=Y(n1))
    enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)'Z_COORDINATES '//trim(str(.true.,Nz))//' double'
    do n1=1,Nz
      write(vtk(rf)%u,'(A)',iostat=E_IO)str(n=Z(n1))
    enddo
  case(raw)
    write(vtk(rf)%u,iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))//end_rec
    write(vtk(rf)%u,iostat=E_IO)'X_COORDINATES '//trim(str(.true.,Nx))//' double'//end_rec
    write(vtk(rf)%u,iostat=E_IO)X
    write(vtk(rf)%u,iostat=E_IO)end_rec
    write(vtk(rf)%u,iostat=E_IO)'Y_COORDINATES '//trim(str(.true.,Ny))//' double'//end_rec
    write(vtk(rf)%u,iostat=E_IO)Y
    write(vtk(rf)%u,iostat=E_IO)end_rec
    write(vtk(rf)%u,iostat=E_IO)'Z_COORDINATES '//trim(str(.true.,Nz))//' double'//end_rec
    write(vtk(rf)%u,iostat=E_IO)Z
    write(vtk(rf)%u,iostat=E_IO)end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_RECT_R8

  !> Function for saving mesh with \b RECTILINEAR_GRID topology (R4P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_RECT_R4(Nx,Ny,Nz,X,Y,Z,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           Nx       !< Number of nodes in x direction.
  integer(I4P), intent(IN)::           Ny       !< Number of nodes in y direction.
  integer(I4P), intent(IN)::           Nz       !< Number of nodes in z direction.
  real(R4P),    intent(IN)::           X(1:Nx)  !< X coordinates.
  real(R4P),    intent(IN)::           Y(1:Ny)  !< Y coordinates.
  real(R4P),    intent(IN)::           Z(1:Nz)  !< Z coordinates.
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf       !< Real file index.
  integer(I4P)::                       n1       !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    write(vtk(rf)%u,'(A)',iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))
    write(vtk(rf)%u,'(A)',iostat=E_IO)'X_COORDINATES '//trim(str(.true.,Nx))//' float'
    do n1=1,Nx
      write(vtk(rf)%u,'(A)',iostat=E_IO)str(n=X(n1))
    enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)'Y_COORDINATES '//trim(str(.true.,Ny))//' float'
    do n1=1,Ny
      write(vtk(rf)%u,'(A)',iostat=E_IO)str(n=Y(n1))
    enddo
    write(vtk(rf)%u,'(A)',iostat=E_IO)'Z_COORDINATES '//trim(str(.true.,Nz))//' float'
    do n1=1,Nz
      write(vtk(rf)%u,'(A)',iostat=E_IO)str(n=Z(n1))
    enddo
  case(raw)
    write(vtk(rf)%u,iostat=E_IO)'DIMENSIONS '//trim(str(.true.,Nx))//' '//trim(str(.true.,Ny))//' '//trim(str(.true.,Nz))//end_rec
    write(vtk(rf)%u,iostat=E_IO)'X_COORDINATES '//trim(str(.true.,Nx))//' float'//end_rec
    write(vtk(rf)%u,iostat=E_IO)X
    write(vtk(rf)%u,iostat=E_IO)end_rec
    write(vtk(rf)%u,iostat=E_IO)'Y_COORDINATES '//trim(str(.true.,Ny))//' float'//end_rec
    write(vtk(rf)%u,iostat=E_IO)Y
    write(vtk(rf)%u,iostat=E_IO)end_rec
    write(vtk(rf)%u,iostat=E_IO)'Z_COORDINATES '//trim(str(.true.,Nz))//' float'//end_rec
    write(vtk(rf)%u,iostat=E_IO)Z
    write(vtk(rf)%u,iostat=E_IO)end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_RECT_R4

  !> Function for saving mesh with \b UNSTRUCTURED_GRID topology (R8P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_UNST_R8(NN,X,Y,Z,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NN       !< Number of nodes.
  real(R8P),    intent(IN)::           X(1:)    !< X coordinates of all nodes [1:NN].
  real(R8P),    intent(IN)::           Y(1:)    !< Y coordinates of all nodes [1:NN].
  real(R8P),    intent(IN)::           Z(1:)    !< Z coordinates of all nodes [1:NN].
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf       !< Real file index.
  integer(I4P)::                       n1       !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)'POINTS '//str(.true.,NN)//' double'
    do n1=1,NN
      write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)str(n=X(n1))//' '//str(n=Y(n1))//' '//str(n=Z(n1))
    enddo
  case(raw)
    write(unit=vtk(rf)%u,iostat=E_IO)'POINTS '//str(.true.,NN)//' double'//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)(X(n1),Y(n1),Z(n1),n1=1,NN)
    write(unit=vtk(rf)%u,iostat=E_IO)end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_UNST_R8

  !> Function for saving mesh with \b UNSTRUCTURED_GRID topology (R8P, packed API).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_UNST_P_R8(NN,XYZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NN         !< Number of nodes.
  real(R8P),    intent(IN)::           XYZ(1:,1:) !< X, Y and Z coordinates of all nodes [1:3,1:NN].
  integer(I4P), intent(IN), optional:: cf         !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO       !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf         !< Real file index.
  integer(I4P)::                       n1         !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)'POINTS '//str(.true.,NN)//' double'
    do n1=1,NN
      write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)str(n=XYZ(1,n1))//' '//str(n=XYZ(2,n1))//' '//str(n=XYZ(3,n1))
    enddo
  case(raw)
    write(unit=vtk(rf)%u,iostat=E_IO)'POINTS '//str(.true.,NN)//' double'//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)XYZ
    write(unit=vtk(rf)%u,iostat=E_IO)end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_UNST_P_R8

  !> Function for saving mesh with \b UNSTRUCTURED_GRID topology (R4P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_UNST_R4(NN,X,Y,Z,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NN       !< number of nodes.
  real(R4P),    intent(IN)::           X(1:)    !< X coordinates of all nodes [1:NN].
  real(R4P),    intent(IN)::           Y(1:)    !< Y coordinates of all nodes [1:NN].
  real(R4P),    intent(IN)::           Z(1:)    !< Z coordinates of all nodes [1:NN].
  integer(I4P), intent(IN), optional:: cf       !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO     !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf       !< Real file index.
  integer(I4P)::                       n1       !< counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)'POINTS '//str(.true.,NN)//' float'
    do n1=1,NN
      write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)str(n=X(n1))//' '//str(n=Y(n1))//' '//str(n=Z(n1))
    enddo
  case(raw)
    write(unit=vtk(rf)%u,iostat=E_IO)'POINTS '//str(.true.,NN)//' float'//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)(X(n1),Y(n1),Z(n1),n1=1,NN)
    write(unit=vtk(rf)%u,iostat=E_IO)end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_UNST_R4

  !> Function for saving mesh with \b UNSTRUCTURED_GRID topology (R4P, packed API).
  !> @return E_IO: integer(I4P) error flag
  function VTK_GEO_UNST_P_R4(NN,XYZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NN         !< number of nodes.
  real(R4P),    intent(IN)::           XYZ(1:,1:) !< X, Y and Z coordinates of all nodes [1:3,1:NN].
  integer(I4P), intent(IN), optional:: cf         !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO       !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf         !< Real file index.
  integer(I4P)::                       n1         !< counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)'POINTS '//str(.true.,NN)//' float'
    do n1=1,NN
      write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)str(n=XYZ(1,n1))//' '//str(n=XYZ(2,n1))//' '//str(n=XYZ(3,n1))
    enddo
  case(raw)
    write(unit=vtk(rf)%u,iostat=E_IO)'POINTS '//str(.true.,NN)//' float'//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)XYZ
    write(unit=vtk(rf)%u,iostat=E_IO)end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_GEO_UNST_P_R4
  !> @}

  !> Function that \b must be used when unstructured grid is used, it saves the connectivity of the unstructured gird.
  !> @note The vector \b connect must follow the VTK-legacy standard. It is passed as \em assumed-shape array
  !> because its dimensions is related to the mesh dimensions in a complex way. Its dimensions can be calculated by the following
  !> equation: \f$dc = NC + \sum\limits_{i = 1}^{NC} {nvertex_i }\f$
  !> where \f$dc\f$ is connectivity vector dimension and \f$nvertex_i\f$ is the number of vertices of \f$i^{th}\f$ cell. The VTK-
  !> legacy standard for the mesh connectivity is quite obscure at least at first sight. It is more simple analyzing an example.
  !> Suppose we have a mesh composed by 2 cells, one hexahedron (8 vertices) and one pyramid with square basis (5 vertices) and
  !> suppose that the basis of pyramid is constitute by a face of the hexahedron and so the two cells share 4 vertices.
  !> The above equation !> gives \f$dc=2+8+5=15\f$. The connectivity vector for this mesh can be: \n
  !> first cell \n
  !> connect(1)  = 8  number of vertices of \f$1^\circ\f$ cell \n
  !> connect(2)  = 0  identification flag of \f$1^\circ\f$ vertex of 1° cell \n
  !> connect(3)  = 1  identification flag of \f$2^\circ\f$ vertex of 1° cell \n
  !> connect(4)  = 2  identification flag of \f$3^\circ\f$ vertex of 1° cell \n
  !> connect(5)  = 3  identification flag of \f$4^\circ\f$ vertex of 1° cell \n
  !> connect(6)  = 4  identification flag of \f$5^\circ\f$ vertex of 1° cell \n
  !> connect(7)  = 5  identification flag of \f$6^\circ\f$ vertex of 1° cell \n
  !> connect(8)  = 6  identification flag of \f$7^\circ\f$ vertex of 1° cell \n
  !> connect(9)  = 7  identification flag of \f$8^\circ\f$ vertex of 1° cell \n
  !> second cell \n
  !> connect(10) = 5  number of vertices of \f$2^\circ \f$cell \n
  !> connect(11) = 0  identification flag of \f$1^\circ\f$ vertex of 2° cell \n
  !> connect(12) = 1  identification flag of \f$2^\circ\f$ vertex of 2° cell \n
  !> connect(13) = 2  identification flag of \f$3^\circ\f$ vertex of 2° cell \n
  !> connect(14) = 3  identification flag of \f$4^\circ\f$ vertex of 2° cell \n
  !> connect(15) = 8  identification flag of \f$5^\circ\f$ vertex of 2° cell \n
  !> Note that the first 4 identification flags of pyramid vertices as the same of the first 4 identification flags of
  !> the hexahedron because the two cells share this face. It is also important to note that the identification flags start
  !> form $0$ value: this is impose to the VTK standard. The function VTK_CON does not calculate the connectivity vector: it
  !> writes the connectivity vector conforming the VTK standard, but does not calculate it.
  !> The vector variable \em cell_type must conform the VTK-legacy standard (see the file VTK-Standard at the
  !> Kitware homepage). It contains the
  !> \em type of each cells. For the above example this vector is: \n
  !> first cell \n
  !> cell_type(1) = 12 hexahedron type of \f$1^\circ\f$ cell \n
  !> second cell \n
  !> cell_type(2) = 14 pyramid type of \f$2^\circ\f$ cell \n
  !> @return E_IO: integer(I4P) error flag
  !> @ingroup Lib_VTK_IOPublicProcedure
  function VTK_CON(NC,connect,cell_type,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC              !< Number of cells.
  integer(I4P), intent(IN)::           connect(:)      !< Mesh connectivity.
  integer(I4P), intent(IN)::           cell_type(1:NC) !< VTK cell type.
  integer(I4P), intent(IN), optional:: cf              !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO            !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer        !< Buffer string.
  integer(I4P)::                       ncon            !< Dimension of connectivity vector.
  integer(I4P)::                       rf              !< Real file index.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  ncon = size(connect,1)
  select case(vtk(rf)%f)
  case(ascii)
    write(unit=vtk(rf)%u,fmt='(A,2'//FI4P//')',iostat=E_IO)'CELLS ',NC,ncon
    write(unit=vtk(rf)%u,fmt=FI4P,             iostat=E_IO)connect
    write(unit=vtk(rf)%u,fmt='(A,'//FI4P//')', iostat=E_IO)'CELL_TYPES ',NC
    write(unit=vtk(rf)%u,fmt=FI4P,             iostat=E_IO)cell_type
  case(raw)
    write(s_buffer,      fmt='(A,2'//FI4P//')',iostat=E_IO)'CELLS ',NC,ncon
    write(unit=vtk(rf)%u,                      iostat=E_IO)trim(s_buffer)//end_rec
    write(unit=vtk(rf)%u,                      iostat=E_IO)connect
    write(unit=vtk(rf)%u,                      iostat=E_IO)end_rec
    write(s_buffer,      fmt='(A,'//FI4P//')', iostat=E_IO)'CELL_TYPES ',NC
    write(unit=vtk(rf)%u,                      iostat=E_IO)trim(s_buffer)//end_rec
    write(unit=vtk(rf)%u,                      iostat=E_IO)cell_type
    write(unit=vtk(rf)%u,                      iostat=E_IO)end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_CON

  !> Function that \b must be called before saving the data related to geometric mesh, this function initializes the
  !> saving of data variables indicating the \em type (node or cell centered) of variables that will be saved.
  !> @note A single file can contain both cell and node centered variables. In this case the VTK_DAT function must be
  !> called two times, before saving cell-centered variables and before saving node-centered variables.
  !> Examples of usage are: \n
  !> \b Node piece: \n
  !> @code ...
  !> E_IO=VTK_DAT(50,'node')
  !> ... @endcode
  !> \b Cell piece: \n
  !> @code ...
  !> E_IO=VTK_DAT(50,'cell')
  !> ... @endcode
  !> @return E_IO: integer(I4P) error flag
  !> @ingroup Lib_VTK_IOPublicProcedure
  function VTK_DAT(NC_NN,var_location,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN        !< Number of cells or nodes of field.
  character(*), intent(IN)::           var_location !< Location of saving variables: cell for cell-centered, node for node-centered.
  integer(I4P), intent(IN), optional:: cf           !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO         !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer     !< Buffer string.
  integer(I4P)::                       rf           !< Real file index.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    select case(trim(Upper_Case(var_location)))
    case('CELL')
      write(unit=vtk(rf)%u,fmt='(A,'//FI4P//')',iostat=E_IO)'CELL_DATA ',NC_NN
    case('NODE')
      write(unit=vtk(rf)%u,fmt='(A,'//FI4P//')',iostat=E_IO)'POINT_DATA ',NC_NN
    endselect
  case(raw)
    select case(trim(Upper_Case(var_location)))
    case('CELL')
      write(s_buffer,fmt='(A,'//FI4P//')',iostat=E_IO)'CELL_DATA ',NC_NN
      write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    case('NODE')
      write(s_buffer,fmt='(A,'//FI4P//')',iostat=E_IO)'POINT_DATA ',NC_NN
      write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    endselect
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_DAT

  !> @ingroup Lib_VTK_IOPrivateProcedure
  !> @{
  !> Function for saving field of scalar variable (R8P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_SCAL_R8(NC_NN,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN        !< Number of nodes or cells.
  character(*), intent(IN)::           varname      !< Variable name.
  real(R8P),    intent(IN)::           var(1:NC_NN) !< Variable to be saved.
  integer(I4P), intent(IN), optional:: cf           !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO         !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf           !< Real file index.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)'SCALARS '//trim(varname)//' double 1'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)'LOOKUP_TABLE default'
    write(unit=vtk(rf)%u,fmt=FR8P, iostat=E_IO)var
  case(raw)
    write(unit=vtk(rf)%u,iostat=E_IO)'SCALARS '//trim(varname)//' double 1'//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)'LOOKUP_TABLE default'//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)var
    write(unit=vtk(rf)%u,iostat=E_IO)end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_SCAL_R8

  !> Function for saving field of scalar variable (R4P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_SCAL_R4(NC_NN,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN        !< Number of nodes or cells.
  character(*), intent(IN)::           varname      !< Variable name.
  real(R4P),    intent(IN)::           var(1:NC_NN) !< Variable to be saved.
  integer(I4P), intent(IN), optional:: cf           !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO         !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf           !< Real file index.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)'SCALARS '//trim(varname)//' float 1'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)'LOOKUP_TABLE default'
    write(unit=vtk(rf)%u,fmt=FR4P, iostat=E_IO)var
  case(raw)
    write(unit=vtk(rf)%u,iostat=E_IO)'SCALARS '//trim(varname)//' float 1'//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)'LOOKUP_TABLE default'//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)var
    write(unit=vtk(rf)%u,iostat=E_IO)end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_SCAL_R4

  !> Function for saving field of scalar variable (I4P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_SCAL_I4(NC_NN,varname,var,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN        !< Number of nodes or cells.
  character(*), intent(IN)::           varname      !< Variable name.
  integer(I4P), intent(IN)::           var(1:NC_NN) !< Variable to be saved.
  integer(I4P), intent(IN), optional:: cf           !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO         !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf           !< Real file index.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)'SCALARS '//trim(varname)//' int 1'
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)'LOOKUP_TABLE default'
    write(unit=vtk(rf)%u,fmt=FI4P, iostat=E_IO)var
  case(raw)
    write(unit=vtk(rf)%u,iostat=E_IO)'SCALARS '//trim(varname)//' int 1'//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)'LOOKUP_TABLE default'//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)var
    write(unit=vtk(rf)%u,iostat=E_IO)end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_SCAL_I4

  !> Function for saving field of vectorial variable (R8P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_VECT_R8(vec_type,NC_NN,varname,varX,varY,varZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  character(*), intent(IN)::           vec_type      !< Vector type: vect = generic vector , norm = normal vector.
  integer(I4P), intent(IN)::           NC_NN         !< Number of nodes or cells.
  character(*), intent(IN)::           varname       !< Variable name.
  real(R8P),    intent(IN)::           varX(1:NC_NN) !< X component of vector.
  real(R8P),    intent(IN)::           varY(1:NC_NN) !< Y component of vector.
  real(R8P),    intent(IN)::           varZ(1:NC_NN) !< Z component of vector.
  integer(I4P), intent(IN), optional:: cf            !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO          !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf            !< Real file index.
  integer(I8P)::                       n1            !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    select case(Upper_Case(trim(vec_type)))
    case('VECT')
      write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)'VECTORS '//trim(varname)//' double'
    case('NORM')
      write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)'NORMALS '//trim(varname)//' double'
    endselect
    write(unit=vtk(rf)%u,fmt='(3'//FR8P//')',iostat=E_IO)(varX(n1),varY(n1),varZ(n1),n1=1,NC_NN)
  case(raw)
    select case(Upper_Case(trim(vec_type)))
    case('VECT')
      write(unit=vtk(rf)%u,iostat=E_IO)'VECTORS '//trim(varname)//' double'//end_rec
    case('NORM')
      write(unit=vtk(rf)%u,iostat=E_IO)'NORMALS '//trim(varname)//' double'//end_rec
    endselect
    write(unit=vtk(rf)%u,iostat=E_IO)(varX(n1),varY(n1),varZ(n1),n1=1,NC_NN)
    write(unit=vtk(rf)%u,iostat=E_IO)end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_VECT_R8

  !> Function for saving field of vectorial variable (R4P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_VECT_R4(vec_type,NC_NN,varname,varX,varY,varZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  character(*), intent(IN)::           vec_type      !< Vector type: vect = generic vector , norm = normal vector.
  integer(I4P), intent(IN)::           NC_NN         !< Number of nodes or cells.
  character(*), intent(IN)::           varname       !< Variable name.
  real(R4P),    intent(IN)::           varX(1:NC_NN) !< X component of vector.
  real(R4P),    intent(IN)::           varY(1:NC_NN) !< Y component of vector.
  real(R4P),    intent(IN)::           varZ(1:NC_NN) !< Z component of vector.
  integer(I4P), intent(IN), optional:: cf            !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO          !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf            !< Real file index.
  integer(I8P)::                       n1            !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    select case(Upper_Case(trim(vec_type)))
    case('vect')
      write(unit=vtk(rf)%u,fmt='(A)',          iostat=E_IO)'VECTORS '//trim(varname)//' float'
    case('norm')
      write(unit=vtk(rf)%u,fmt='(A)',          iostat=E_IO)'NORMALS '//trim(varname)//' float'
    endselect
    write(unit=vtk(rf)%u,fmt='(3'//FR4P//')',iostat=E_IO)(varX(n1),varY(n1),varZ(n1),n1=1,NC_NN)
  case(raw)
    select case(Upper_Case(trim(vec_type)))
    case('vect')
      write(unit=vtk(rf)%u,iostat=E_IO)'VECTORS '//trim(varname)//' float'//end_rec
    case('norm')
      write(unit=vtk(rf)%u,iostat=E_IO)'NORMALS '//trim(varname)//' float'//end_rec
    endselect
    write(unit=vtk(rf)%u,iostat=E_IO)(varX(n1),varY(n1),varZ(n1),n1=1,NC_NN)
    write(unit=vtk(rf)%u,iostat=E_IO)end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_VECT_R4

  !> Function for saving field of vectorial variable (I4P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_VECT_I4(NC_NN,varname,varX,varY,varZ,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN         !< Number of nodes or cells.
  character(*), intent(IN)::           varname       !< Variable name.
  integer(I4P), intent(IN)::           varX(1:NC_NN) !< X component of vector.
  integer(I4P), intent(IN)::           varY(1:NC_NN) !< Y component of vector.
  integer(I4P), intent(IN)::           varZ(1:NC_NN) !< Z component of vector.
  integer(I4P), intent(IN), optional:: cf            !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO          !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                       rf            !< Real file index.
  integer(I8P)::                       n1            !< Counter.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    write(unit=vtk(rf)%u,fmt='(A)',iostat=E_IO)'VECTORS '//trim(varname)//' int'
    write(unit=vtk(rf)%u,fmt='(3'//FI4P//')',iostat=E_IO)(varX(n1),varY(n1),varZ(n1),n1=1,NC_NN)
  case(raw)
    write(unit=vtk(rf)%u,iostat=E_IO)'VECTORS '//trim(varname)//' int'//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)(varX(n1),varY(n1),varZ(n1),n1=1,NC_NN)
    write(unit=vtk(rf)%u,iostat=E_IO)end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_VECT_I4

  !> Function for saving texture variable (R8P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_TEXT_R8(NC_NN,dimm,varname,textCoo,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN                   !< Number of nodes or cells.
  integer(I4P), intent(IN)::           dimm                    !< Texture dimensions.
  character(*), intent(IN)::           varname                 !< Variable name.
  real(R8P),    intent(IN)::           textCoo(1:NC_NN,1:dimm) !< Texture.
  integer(I4P), intent(IN), optional:: cf                      !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO              !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer                !< Buffer string.
  integer(I4P)::                       rf                      !< Real file index.
  integer(I8P)::                       n1,n2                   !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    write(unit=vtk(rf)%u,fmt='(A,1X,'//FI4P//',1X,A)',iostat=E_IO)'TEXTURE_COORDINATES '//trim(varname),dimm,' double'
    write(s_buffer,fmt='(I1)',iostat=E_IO)dimm
    s_buffer='('//trim(s_buffer)//FR4P//')'
    write(unit=vtk(rf)%u,fmt=trim(s_buffer),iostat=E_IO)((textCoo(n1,n2),n2=1,dimm),n1=1,NC_NN)
  case(raw)
    write(s_buffer,fmt='(A,1X,'//FI4P//',1X,A)',iostat=E_IO)'TEXTURE_COORDINATES '//trim(varname),dimm,' double'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)((textCoo(n1,n2),n2=1,dimm),n1=1,NC_NN)
    write(unit=vtk(rf)%u,iostat=E_IO)end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_TEXT_R8

  !> Function for saving texture variable (R4P).
  !> @return E_IO: integer(I4P) error flag
  function VTK_VAR_TEXT_R4(NC_NN,dimm,varname,textCoo,cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  !! Function for saving texture variable (R4P).
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(IN)::           NC_NN                   !< Number of nodes or cells.
  integer(I4P), intent(IN)::           dimm                    !< Texture dimensions.
  character(*), intent(IN)::           varname                 !< Variable name.
  real(R4P),    intent(IN)::           textCoo(1:NC_NN,1:dimm) !< Texture.
  integer(I4P), intent(IN), optional:: cf                      !< Current file index (for concurrent files IO).
  integer(I4P)::                       E_IO              !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  character(len=maxlen)::              s_buffer                !< Buffer string.
  integer(I4P)::                       rf                      !< Real file index.
  integer(I8P)::                       n1,n2                   !< Counters.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  select case(vtk(rf)%f)
  case(ascii)
    write(unit=vtk(rf)%u,fmt='(A,1X,'//FI4P//',1X,A)',iostat=E_IO)'TEXTURE_COORDINATES '//trim(varname),dimm,' float'
    write(s_buffer,fmt='(I1)',iostat=E_IO)dimm
    s_buffer='('//trim(s_buffer)//FR4P//')'
    write(unit=vtk(rf)%u,fmt=trim(s_buffer),iostat=E_IO)((textCoo(n1,n2),n2=1,dimm),n1=1,NC_NN)
  case(raw)
    write(s_buffer,fmt='(A,1X,'//FI4P//',1X,A)',iostat=E_IO)'TEXTURE_COORDINATES '//trim(varname),dimm,' float'
    write(unit=vtk(rf)%u,iostat=E_IO)trim(s_buffer)//end_rec
    write(unit=vtk(rf)%u,iostat=E_IO)((textCoo(n1,n2),n2=1,dimm),n1=1,NC_NN)
    write(unit=vtk(rf)%u,iostat=E_IO)end_rec
  endselect
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_VAR_TEXT_R4
  !> @}

  !>Function for finalizing open file,  it has not inputs, @libvtk manages the file unit without the
  !>user's action.
  !> @note An example of usage is: \n
  !> @code ...
  !> E_IO=VTK_END()
  !> ... @endcode
  !> @return E_IO: integer(I4P) error flag
  !> @ingroup Lib_VTK_IOPublicProcedure
  function VTK_END(cf) result(E_IO)
  !---------------------------------------------------------------------------------------------------------------------------------
  implicit none
  integer(I4P), intent(INOUT), optional:: cf   !< Current file index (for concurrent files IO).
  integer(I4P)::                          E_IO !< Input/Output inquiring flag: $0$ if IO is done, $> 0$ if IO is not done.
  integer(I4P)::                          rf   !< Real file index.
  !---------------------------------------------------------------------------------------------------------------------------------

  !---------------------------------------------------------------------------------------------------------------------------------
  E_IO = -1_I4P
  rf = f
  if (present(cf)) then
    rf = cf ; f = cf
  endif
  close(unit=vtk(rf)%u,iostat=E_IO)
  call vtk_update(act='remove',cf=rf,Nvtk=Nvtk,vtk=vtk)
  f = rf
  if (present(cf)) cf = rf
  return
  !---------------------------------------------------------------------------------------------------------------------------------
  endfunction VTK_END
endmodule Lib_VTK_IO