initial commit

billinglayer/python/shapely/algorithms/cga.py

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+import numpy as np
+
+import shapely
+
+
+def signed_area(ring):
+    """Return the signed area enclosed by a ring in linear time using the
+    algorithm at: 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 is_ccw_impl(name=None):
+    """Predicate implementation"""
+
+    def is_ccw_op(ring):
+        return signed_area(ring) >= 0.0
+
+    if shapely.geos_version >= (3, 7, 0):
+        return shapely.is_ccw
+    else:
+        return is_ccw_op