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  • 计算多边形中心线

    #!/usr/bin/env python
    # -*- coding: utf-8 -*-
    from shapely.geometry import LineString
    from shapely.geometry import MultiLineString
    from scipy.spatial import Voronoi
    import numpy as np
    
    
    class Centerline(object):
        def __init__(self, inputGEOM, dist=0.5):
            self.inputGEOM = inputGEOM
            self.dist = abs(dist)
    
        def create_centerline(self):
            """
            Calculates the centerline of a polygon.
    
            Densifies the border of a polygon which is then represented
            by a Numpy array of points necessary for creating the
            Voronoi diagram. Once the diagram is created, the ridges
            located within the polygon are joined and returned.
    
            Returns:
                a MultiLinestring located within the polygon.
            """
    
            minx = int(min(self.inputGEOM.envelope.exterior.xy[0]))
            miny = int(min(self.inputGEOM.envelope.exterior.xy[1]))
            #加密边界
            border = np.array(self.densify_border(self.inputGEOM, minx, miny))
            #用边界生成Voronoi图
            vor = Voronoi(border)
            vertex = vor.vertices
    
            lst_lines = []
            for j, ridge in enumerate(vor.ridge_vertices):
                if -1 not in ridge:
                    line = LineString([
                        (vertex[ridge[0]][0] + minx, vertex[ridge[0]][1] + miny),
                        (vertex[ridge[1]][0] + minx, vertex[ridge[1]][1] + miny)])
    
                    if line.within(self.inputGEOM) and len(line.coords[0]) > 1:
                        lst_lines.append(line)
    
            return MultiLineString(lst_lines)
    
        def densify_border(self, polygon, minx, miny):
            """
            Densifies the border of a polygon by a given factor
            (by default: 0.5).
    
            The function tests the complexity of the polygons
            geometry, i.e. does the polygon have holes or not.
            If the polygon doesn't have any holes, its exterior
            is extracted and densified by a given factor. If the
            polygon has holes, the boundary of each hole as
            well as its exterior is extracted and densified
            by a given factor.
    
            Returns:
                a list of points where each point is represented
                by a list of its
                reduced coordinates.
    
            Example:
                [[X1, Y1], [X2, Y2], ..., [Xn, Yn]
            """
    
            if len(polygon.interiors) == 0:
                exterior_line = LineString(polygon.exterior)
                points = self.fixed_interpolation(exterior_line, minx, miny)
    
            else:
                exterior_line = LineString(polygon.exterior)
                points = self.fixed_interpolation(exterior_line, minx, miny)
    
                for j in range(len(polygon.interiors)):
                    interior_line = LineString(polygon.interiors[j])
                    points += self.fixed_interpolation(interior_line, minx, miny)
    
            return points
    
        def fixed_interpolation(self, line, minx, miny):
            """
            A helping function which is used in densifying
            the border of a polygon.
    
            It places points on the border at the specified distance.
            By default the distance is 0.5 (meters) which means
            that the first point will be placed 0.5 m from the
            starting point, the second point will be placed at the
            distance of 1.0 m from the first point, etc. Naturally,
            the loop breaks when the summarized distance exceeds
            the length of the line.
    
            Returns:
                a list of points where each point is represented by
                a list of its reduced coordinates.
    
            Example:
                [[X1, Y1], [X2, Y2], ..., [Xn, Yn]
            """
    
            count = self.dist
            newline = []
    
            startpoint = [line.xy[0][0] - minx, line.xy[1][0] - miny]
            endpoint = [line.xy[0][-1] - minx, line.xy[1][-1] - miny]
            newline.append(startpoint)
    
            while count < line.length:
                point = line.interpolate(count)
                newline.append([point.x - minx, point.y - miny])
                count += self.dist
    
            newline.append(endpoint)
    
            return newline
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  • 原文地址:https://www.cnblogs.com/gispathfinder/p/5791121.html
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