109 lines
3.6 KiB
Python
109 lines
3.6 KiB
Python
import numpy as np
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def _round_safe(coords):
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"""Round coords while ensuring successive values are less than 1 apart.
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When rounding coordinates for `line_nd`, we want coordinates that are less
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than 1 apart (always the case, by design) to remain less than one apart.
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However, NumPy rounds values to the nearest *even* integer, so:
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>>> np.round([0.5, 1.5, 2.5, 3.5, 4.5])
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array([0., 2., 2., 4., 4.])
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So, for our application, we detect whether the above case occurs, and use
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``np.floor`` if so. It is sufficient to detect that the first coordinate
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falls on 0.5 and that the second coordinate is 1.0 apart, since we assume
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by construction that the inter-point distance is less than or equal to 1
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and that all successive points are equidistant.
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Parameters
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----------
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coords : 1D array of float
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The coordinates array. We assume that all successive values are
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equidistant (``np.all(np.diff(coords) = coords[1] - coords[0])``)
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and that this distance is no more than 1
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(``np.abs(coords[1] - coords[0]) <= 1``).
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Returns
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-------
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rounded : 1D array of int
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The array correctly rounded for an indexing operation, such that no
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successive indices will be more than 1 apart.
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Examples
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--------
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>>> coords0 = np.array([0.5, 1.25, 2., 2.75, 3.5])
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>>> _round_safe(coords0)
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array([0, 1, 2, 3, 4])
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>>> coords1 = np.arange(0.5, 8, 1)
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>>> coords1
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array([0.5, 1.5, 2.5, 3.5, 4.5, 5.5, 6.5, 7.5])
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>>> _round_safe(coords1)
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array([0, 1, 2, 3, 4, 5, 6, 7])
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"""
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if (len(coords) > 1
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and coords[0] % 1 == 0.5
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and coords[1] - coords[0] == 1):
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_round_function = np.floor
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else:
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_round_function = np.round
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return _round_function(coords).astype(int)
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def line_nd(start, stop, *, endpoint=False, integer=True):
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"""Draw a single-pixel thick line in n dimensions.
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The line produced will be ndim-connected. That is, two subsequent
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pixels in the line will be either direct or diagonal neighbours in
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n dimensions.
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Parameters
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----------
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start : array-like, shape (N,)
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The start coordinates of the line.
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stop : array-like, shape (N,)
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The end coordinates of the line.
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endpoint : bool, optional
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Whether to include the endpoint in the returned line. Defaults
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to False, which allows for easy drawing of multi-point paths.
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integer : bool, optional
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Whether to round the coordinates to integer. If True (default),
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the returned coordinates can be used to directly index into an
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array. `False` could be used for e.g. vector drawing.
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Returns
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-------
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coords : tuple of arrays
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The coordinates of points on the line.
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Examples
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--------
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>>> lin = line_nd((1, 1), (5, 2.5), endpoint=False)
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>>> lin
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(array([1, 2, 3, 4]), array([1, 1, 2, 2]))
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>>> im = np.zeros((6, 5), dtype=int)
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>>> im[lin] = 1
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>>> im
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array([[0, 0, 0, 0, 0],
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[0, 1, 0, 0, 0],
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[0, 1, 0, 0, 0],
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[0, 0, 1, 0, 0],
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[0, 0, 1, 0, 0],
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[0, 0, 0, 0, 0]])
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>>> line_nd([2, 1, 1], [5, 5, 2.5], endpoint=True)
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(array([2, 3, 4, 4, 5]), array([1, 2, 3, 4, 5]), array([1, 1, 2, 2, 2]))
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"""
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start = np.asarray(start)
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stop = np.asarray(stop)
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npoints = int(np.ceil(np.max(np.abs(stop - start))))
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if endpoint:
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npoints += 1
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coords = []
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for dim in range(len(start)):
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dimcoords = np.linspace(start[dim], stop[dim], npoints, endpoint)
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if integer:
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dimcoords = _round_safe(dimcoords).astype(int)
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coords.append(dimcoords)
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return tuple(coords)
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