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math_QuaternionToAxisAngle now safe for small or close to 2pi rotations.

This commit is contained in:
Philip Eisenlohr 2010-04-29 10:01:09 +00:00
parent e8719cb6b8
commit 15e5dcf8f2
1 changed files with 10 additions and 17 deletions
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@ -1386,23 +1386,16 @@ pure function math_transpose3x3(A)
real(pReal) halfAngle, sinHalfAngle
real(pReal), dimension(4) :: math_QuaternionToAxisAngle
halfAngle=acos(Q(1))
sinHalfAngle=sin(halfAngle)
math_QuaternionToAxisAngle(1)=Q(2)/sinHalfAngle
math_QuaternionToAxisAngle(2)=Q(3)/sinHalfAngle
math_QuaternionToAxisAngle(3)=Q(4)/sinHalfAngle
! Remark: the above calculations gives problems
! for HalfAngle->0, i.e. for very small rotation angles
! and always at inrement 0 where identical orientations
! are compared in the calculation of the grainrotation;
! the correct interpretation of these special cases
! is left to the postprocessing.
! A possible integrity check would be to check for
! the unit length of the resulting axis.
math_QuaternionToAxisAngle(4)=halfAngle*2.0_pReal*inDeg
halfAngle = dacos(Q(1)) ! value range 0 to 180 deg
sinHalfAngle = dsin(halfAngle)
if (sinHalfAngle <= 1.0e-4_pReal) then ! very small rotation angle?
math_QuaternionToAxisAngle = 0.0_pReal
else
math_QuaternionToAxisAngle(1:3) = Q(2:4)/sinHalfAngle
math_QuaternionToAxisAngle(4) = halfAngle*2.0_pReal*inDeg
endif
ENDFUNCTION
!********************************************************************