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https://github.com/wassname/scikit-image.git
synced 2026-06-29 16:16:07 +08:00
Stefan van der Walt
32182574ec
The `clip_to_bbox` function is only available in later versions of Matplotlib, so for now inline it so that we remain compatible with v1.1.
60 lines
1.6 KiB
Python
60 lines
1.6 KiB
Python
__all__ = ['polygon_clip', 'polygon_area']
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import numpy as np
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def polygon_clip(rp, cp, r0, c0, r1, c1):
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"""Clip a polygon to the given bounding box.
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Parameters
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----------
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rp, cp : (N,) ndarray of double
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Row and column coordinates of the polygon.
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(r0, c0), (r1, c1) : double
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Top-left and bottom-right coordinates of the bounding box.
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Returns
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-------
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r_clipped, c_clipped : (M,) ndarray of double
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Coordinates of clipped polygon.
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Notes
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-----
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This makes use of Sutherland-Hodgman clipping as implemented in
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AGG 2.4 and exposed in Matplotlib.
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"""
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from matplotlib import _path, path, transforms
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# `clip_to_bbox` is included directly from Matplotlib
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# since it was only included after v1.1
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def clip_to_bbox(poly_path, bbox, inside=True):
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verts = _path.clip_path_to_rect(poly_path, bbox, inside)
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paths = [path.Path(poly) for poly in verts]
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return poly_path.make_compound_path(*paths)
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poly = path.Path(np.vstack((rp, cp)).T, closed=True)
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clip_rect = transforms.Bbox([[r0, c0], [r1, c1]])
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poly_clipped = clip_to_bbox(poly, clip_rect).to_polygons()[0]
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return poly_clipped[:, 0], poly_clipped[:, 1]
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def polygon_area(pr, pc):
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"""Compute the area of a polygon.
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Parameters
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----------
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pr, pc : (N,) array of float
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Polygon row and column coordinates.
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Returns
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-------
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a : float
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Area of the polygon.
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"""
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pr = np.asarray(pr)
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pc = np.asarray(pc)
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return 0.5 * np.abs(np.sum((pc[:-1] * pr[1:]) - (pc[1:] * pr[:-1])))
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