如何使用Shapely提取内部多边形坐标? [英] How to extract interior polygon coordinates using Shapely?

问题描述

我是Shapely的新手(但是对此很热心)，最近我发现了一些障碍.

I am new to Shapely (but enthusiastic about it), and recently I've discovered a bit of a road bump.

我有一个要通过Fiona读取的多边形shapefile.此shapefile包含多边形和多多边形项，我需要为其内所有坐标的每个要素(即外部和/或内部)构建一个数组.值得注意的是，两个多边形项具有内部环(并且它们是有效的).

I have a polygon shapefile that I am reading in via Fiona. This shapefile contains BOTH polygon and multipolygon items and I need to build an array for each feature of all the coordinates within it (i.e. both exterior and/or interior). Notably, two of the polygon items have interior rings (and they are valid).

访问多边形/多多边形的外部坐标似乎没有问题...但是我没有为内部坐标提取任何东西.

I seem to have no problem accessing the exterior coordinates of the polygon(s)/multipolygon(s) ... but I am not pulling anything for the interior coordinates.

我是否需要在这里采用新方法(即LinearRings)...?

Do I need to take a new approach here (i.e. LinearRings)...?

def convert_polygons(inFile):

    for polys in fiona.open(inFile):
        myShape = shape(polys['geometry'])
        exterior_poly = 0
        interior_poly = 0
        if isinstance(myShape, Polygon):
            print "yes, I am a polygon"
            # count how many points for each interior polygon
            try:
                interior_poly += len(myShape.interior.coords)
            except:
                pass
            # count how many points for each exterior polygon
            exterior_poly += len(myShape.exterior.coords)
            geomArray = asarray(myShape.exterior)
            print geomArray
            print "number of interior points in polygon " + str(interior_poly)
            print "number of exterior points in polygon " + str(exterior_poly)
        elif isinstance(myShape, MultiPolygon):
            print "yes, I am a MultiPolygon"
            # count how many points for each interior polygon
            try:
                interior_poly += len(myShape.interior.coords)
            except:
                pass
            try:
                # count how many points for each exterior polygon
                exterior_poly += len(myShape.exterior.coords)
            except:
                pass
            try:
                geomArray = asarray(myShape.interior)
            except:
                pass
            try:
                geomArray = asarray(myShape.exterior)
            except:
                pass
            print geomArray
            print "number of interior points in polygon " + str(interior_poly)
            print "number of exterior points in polygon " + str(exterior_poly)

推荐答案

内圈和外圈的结构不同.对于任何多边形，总会有1个外环，其中零个或多个内环.

Interior and exterior rings are structured differently. For any polygon, there is always 1 exterior ring with zero or more interior rings.

因此，从几何结构来看，exterior是一个LinearRing对象，而interiors是一个零个或多个LinearRing对象的 list .任何LinearRing对象都将具有coords，您可以对其进行切片以使用coords[:]查看坐标列表.

So looking at the structure of a geometry, exterior is a LinearRing object, and interiors is a list of zero or more LinearRing objects. Any LinearRing object will have coords, which you can slice to see a list of the coordinates with coords[:].

以下是返回外部和内部坐标列表的字典的函数:

The following is a function that returns a dict of lists of exterior and interior coordinates:

def extract_poly_coords(geom):
    if geom.type == 'Polygon':
        exterior_coords = geom.exterior.coords[:]
        interior_coords = []
        for interior in geom.interiors:
            interior_coords += interior.coords[:]
    elif geom.type == 'MultiPolygon':
        exterior_coords = []
        interior_coords = []
        for part in geom:
            epc = extract_poly_coords(part)  # Recursive call
            exterior_coords += epc['exterior_coords']
            interior_coords += epc['interior_coords']
    else:
        raise ValueError('Unhandled geometry type: ' + repr(geom.type))
    return {'exterior_coords': exterior_coords,
            'interior_coords': interior_coords}

例如:

extract_poly_coords(myShape)

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