mirror of
https://github.com/wassname/scikit-image.git
synced 2026-06-28 21:12:29 +08:00
Stefan van der Walt
53 lines
1.2 KiB
Python
53 lines
1.2 KiB
Python
__all__ = ['polygon_clip', 'polygon_area']
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import numpy as np
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def polygon_clip(yp, xp, 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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yp, xp : (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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y_clipped, x_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, transforms
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poly = path.Path(np.vstack((yp, xp)).T, closed=True)
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clip_rect = transforms.Bbox([[r0, c0], [r1, c1]])
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poly_clipped = poly.clip_to_bbox(clip_rect).to_polygons()[0]
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return poly_clipped[:, 0], poly_clipped[:, 1]
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def polygon_area(py, px):
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"""Compute the area of a polygon.
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Parameters
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----------
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py, px : (N,) array of float
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Polygon 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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py = np.asarray(py)
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px = np.asarray(px)
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return 0.5 * np.abs(np.sum((px[:-1] * py[1:]) - (px[1:] * py[:-1])))
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