mirror of
https://github.com/wassname/scikit-image.git
synced 2026-06-28 01:00:23 +08:00
Stefan van der Walt
62 lines
1.7 KiB
Python
62 lines
1.7 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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if np.all(poly_clipped[-1] == poly_clipped[-2]):
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poly_clipped = poly_clipped[:-1]
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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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