17 lines
503 B
Python
17 lines
503 B
Python
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def signed_area(ring):
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"""Return the signed area enclosed by a ring in linear time using the
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algorithm at: https://web.archive.org/web/20080209143651/http://cgafaq.info:80/wiki/Polygon_Area
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"""
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xs, ys = ring.coords.xy
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xs.append(xs[1])
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ys.append(ys[1])
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return sum(xs[i]*(ys[i+1]-ys[i-1]) for i in range(1, len(ring.coords)))/2.0
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def is_ccw_impl(name):
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"""Predicate implementation"""
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def is_ccw_op(ring):
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return signed_area(ring) >= 0.0
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return is_ccw_op
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