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- __all__ = ['polygon_clip', 'polygon_area']
- import numpy as np
- from .version_requirements import require
- @require("matplotlib", ">=3.3")
- def polygon_clip(rp, cp, r0, c0, r1, c1):
- """Clip a polygon to the given bounding box.
- Parameters
- ----------
- rp, cp : (K,) ndarray of double
- Row and column coordinates of the polygon.
- (r0, c0), (r1, c1) : double
- Top-left and bottom-right coordinates of the bounding box.
- Returns
- -------
- r_clipped, c_clipped : (L,) ndarray of double
- Coordinates of clipped polygon.
- Notes
- -----
- This makes use of Sutherland-Hodgman clipping as implemented in
- AGG 2.4 and exposed in Matplotlib.
- """
- from matplotlib import path, transforms
- poly = path.Path(np.vstack((rp, cp)).T, closed=True)
- clip_rect = transforms.Bbox([[r0, c0], [r1, c1]])
- poly_clipped = poly.clip_to_bbox(clip_rect).to_polygons()[0]
- return poly_clipped[:, 0], poly_clipped[:, 1]
- def polygon_area(pr, pc):
- """Compute the area of a polygon.
- Parameters
- ----------
- pr, pc : (K,) array of float
- Polygon row and column coordinates.
- Returns
- -------
- a : float
- Area of the polygon.
- """
- pr = np.asarray(pr)
- pc = np.asarray(pc)
- return 0.5 * np.abs(np.sum((pc[:-1] * pr[1:]) - (pc[1:] * pr[:-1])))
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