"""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)