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- """Shapely CGA algorithms."""
- import numpy as np
- import shapely
- def signed_area(ring):
- """Return the signed area enclosed by a ring in linear time.
- Algorithm used: https://web.archive.org/web/20080209143651/http://cgafaq.info:80/wiki/Polygon_Area
- """
- coords = np.array(ring.coords)[:, :2]
- xs, ys = np.vstack([coords, coords[1]]).T
- return np.sum(xs[1:-1] * (ys[2:] - ys[:-2])) / 2.0
- def _reverse_conditioned(rings, condition):
- """Return a copy of the rings potentially reversed depending on `condition`."""
- condition = np.asarray(condition)
- if np.all(condition):
- rings = shapely.reverse(rings)
- elif np.any(condition):
- rings = np.array(rings)
- rings[condition] = shapely.reverse(rings[condition])
- return rings
- def _orient_polygon(geometry, exterior_cw=False):
- if geometry is None:
- return None
- if geometry.geom_type in ["MultiPolygon", "GeometryCollection"]:
- return geometry.__class__(
- [_orient_polygon(geom, exterior_cw) for geom in geometry.geoms]
- )
- # elif geometry.geom_type in ["LinearRing"]:
- # return reverse_conditioned(geometry, is_ccw(geometry) != ccw)
- elif geometry.geom_type == "Polygon":
- rings = np.array([geometry.exterior, *geometry.interiors])
- reverse_condition = shapely.is_ccw(rings)
- reverse_condition[0] = not reverse_condition[0]
- if exterior_cw:
- reverse_condition = np.logical_not(reverse_condition)
- if np.any(reverse_condition):
- rings = _reverse_conditioned(rings, reverse_condition)
- return geometry.__class__(rings[0], rings[1:])
- return geometry
- _orient_polygons_vectorized = np.frompyfunc(_orient_polygon, nin=2, nout=1)
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