Shapely geometry inheritance

08/05/2024

• Custom geometry class with Shapely geometry instance
• Defining custom class for Polygon
• shapely.geometry.Polygon has no attributes or functions to get these directly:
• segments
• vertices
• coords
• ...


• Inheritance

    import numpy as np
    from shapely import geometry
    from typing import List, Union


    class Polygon(geometry.Polygon):
        def __init__(self, *args, **kwargs):
            super().__init__(*args, **kwargs)

        def coords(self, to_list: bool = False) -> Union[List[tuple], np.ndarray]:

            coords = self.exterior.coords
            if to_list:
                return list(coords)

            return np.array(coords)

        def vertices(self) -> List[geometry.Point]:

            coords = self.coords(to_list=True)

            return [geometry.Point(c) for c in coords]

        def segments(self) -> List[geometry.LineString]:

            coords = self.coords(to_list=True)

            if len(coords) == 0:
                return []

            segments = []
            start_pt = coords[0]

            for i in range(len(coords) - 1):
                end_pt = coords[i + 1]
                segments.append(geometry.LineString([start_pt, end_pt]))
                start_pt = end_pt

            return segments
            

    if __name__ == "__main__":

        square = np.array(
            [
                [0, 0],
                [0, 1],
                [1, 1],
                [1, 0],
            ]
        )

        polygon_1 = Polygon(square)
        polygon_2 = Polygon(square + 0.5)

• Visualize properties
• polygon_1
• polygon_2
• polygon_2.vertices()
• polygon_2.segments()


• polygon_1.intersection(polygon_2).vertices()
• polygon_1.intersection(polygon_2).segments()

    Traceback (most recent call last):
    AttributeError: 'Polygon' object has no attribute 'vertices'

    Traceback (most recent call last):
    AttributeError: 'Polygon' object has no attribute 'segments'

• Trick for fixing AttributeError
• Set methods of custom Polygon to the original class

    for name, method in vars(Polygon).items():
        if callable(method) and not name.startswith('__'):
            setattr(geometry.Polygon, name, method)

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