Shapely: 功能请求：添加 STRtree.nearest 函数

创建于 2019-01-07 · 5评论 · 资料来源: Toblerity/Shapely

笔记

由于 Shapely 目前仅支持 GEOS 3.4.0，因此在 GEOS 3.6.0 中添加GEOSSTRtree_nearest等其他功能会很棒。所以我试图自己添加这个功能并遇到一些问题。

问题

GEOS 源代码如下：

const GEOSGeometry *
GEOSSTRtree_nearest (geos::index::strtree::STRtree *tree,
                     const geos::geom::Geometry *g)
{
    return GEOSSTRtree_nearest_r( handle, tree, g);
}

const void* GEOSSTRtree_nearest_generic(GEOSSTRtree *tree,
                                        const void* item,
                                        const GEOSGeometry* itemEnvelope,
                                        GEOSDistanceCallback distancefn,
                                        void* userdata)
{
    return GEOSSTRtree_nearest_generic_r( handle, tree, item, itemEnvelope, distancefn, userdata);
}

然后我在 strtree.py、ctypes_declarations.py 和 test.py 中添加了代码并尝试运行测试但得到错误Segmentation fault: 11
strtree.py

from shapely.geometry.base import geom_factory
class STRtree:
    def nearest(self, geom):
        if self._n_geoms == 0:
            return None

        return geom_factory(lgeos.GEOSSTRtree_nearest(self._tree_handle, geom._geom))

ctypes_declarations.py

def prototype(lgeos, geos_version):
    if geos_version >= (3, 6, 0):
        lgeos.GEOSSTRtree_nearest.argtypes = [c_void_p, c_void_p]
        lgeos.GEOSSTRtree_nearest.restype = c_void_p

测试.py

from shapely.geometry import Point, Polygon
from shapely.strtree import STRtree

a = []
a.append(Polygon([(1,0),(2,0),(2,1),(1,1)]))
a.append(Polygon([(0,2),(1,2),(1,3),(0,3)]))
a.append(Polygon([(-1.5,0),(-2.5,0),(-2.5,-1),(-1.5,-1)]))
tree = STRtree(a)
tree.nearest(Point(0,0))

我认为我的问题是关于 ctypes 和几何之间的数据处理，所以我尝试重新实现shared_path函数，但仍然出现问题。

from shapely.geometry import LineString
from shapely.geometry.base import geom_factory
from ctypes import CDLL, c_void_p

dll = CDLL('/Users/*****/anaconda3/lib/python3.7/site-packages/shapely/.dylibs/libgeos_c.1.dylib')
shared_path = dll.GEOSSharedPaths
shared_path.restype = c_void_p
shared_path.argtypes = [c_void_p, c_void_p]
g1 = LineString([((0, 0), (1, 1)), ((-1, 0), (1, 0))])
g2 = LineString([((0, 0), (1, 1)), ((-2, 0), (1, 5))])
geom_factory(shared_path(g1._geom, g2._geom))

你能帮我解决这个问题吗，谢谢！

资料来源

FuriousRococo

👍1

最有用的评论

感谢@sgillies的建议，我认为它现在正在工作。
strtree.py

class STRtree:
    def nearest(self, geom):
        if self._n_geoms == 0:
            return None

        envelope = geom.envelope

        def callback(item1, item2, distance, userdata):
            try:
                geom1 = ctypes.cast(item1, ctypes.py_object).value
                geom2 = ctypes.cast(item2, ctypes.py_object).value
                dist = ctypes.cast(distance, ctypes.POINTER(ctypes.c_double))
                lgeos.GEOSDistance(geom1._geom, geom2._geom, dist)
                return 1
            except:
                return 0 

        item = lgeos.GEOSSTRtree_nearest_generic(self._tree_handle, ctypes.py_object(geom), envelope._geom, \
            lgeos.GEOSDistanceCallback(callback), None)
        geom = ctypes.cast(item, ctypes.py_object).value

        return geom

ctypes_declarations.py

def prototype(lgeos, geos_version):
    if geos_version >= (3, 6, 0):
        lgeos.GEOSDistanceCallback = CFUNCTYPE(c_int, c_void_p, c_void_p, c_void_p, c_void_p)

        lgeos.GEOSSTRtree_nearest_generic.argtypes = [
            c_void_p, py_object, c_void_p, lgeos.GEOSDistanceCallback, py_object]
        lgeos.GEOSSTRtree_nearest_generic.restype = c_void_p

测试.py

from shapely.geometry import Point, Polygon
from shapely.strtree import STRtree

a = []
a.append(Polygon([(1,0),(2,0),(2,1),(1,1)]))
a.append(Polygon([(0,2),(1,2),(1,3),(0,3)]))
a.append(Polygon([(-1.5,0),(-2.5,0),(-2.5,-1),(-1.5,-1)]))
a.append(Point(0,0.5))
tree = STRtree(a)
pt = tree.nearest(Point(0,0))
print(pt.wkt)

输出
POINT (0 0.5)

FuriousRococo 于 2019-01-22

🎉2 👍1

所有5条评论

嗨@FuriousRococo ，我不熟悉使用最近邻搜索功能，但看起来你大致在正确的轨道上。但是，在https://github.com/libgeos/geos/blob/master/capi/geos_c.h.in#L1824 ，我看到一个迹象表明我们需要使用通用方法，因为我们树中的项目是 Python 对象. 我认为您需要尝试一下https://github.com/libgeos/geos/blob/master/capi/geos_c.h.in#L1850 。

sgillies 于 2019-01-17

感谢@sgillies的建议，我认为它现在正在工作。
strtree.py

class STRtree:
    def nearest(self, geom):
        if self._n_geoms == 0:
            return None

        envelope = geom.envelope

        def callback(item1, item2, distance, userdata):
            try:
                geom1 = ctypes.cast(item1, ctypes.py_object).value
                geom2 = ctypes.cast(item2, ctypes.py_object).value
                dist = ctypes.cast(distance, ctypes.POINTER(ctypes.c_double))
                lgeos.GEOSDistance(geom1._geom, geom2._geom, dist)
                return 1
            except:
                return 0 

        item = lgeos.GEOSSTRtree_nearest_generic(self._tree_handle, ctypes.py_object(geom), envelope._geom, \
            lgeos.GEOSDistanceCallback(callback), None)
        geom = ctypes.cast(item, ctypes.py_object).value

        return geom

ctypes_declarations.py

def prototype(lgeos, geos_version):
    if geos_version >= (3, 6, 0):
        lgeos.GEOSDistanceCallback = CFUNCTYPE(c_int, c_void_p, c_void_p, c_void_p, c_void_p)

        lgeos.GEOSSTRtree_nearest_generic.argtypes = [
            c_void_p, py_object, c_void_p, lgeos.GEOSDistanceCallback, py_object]
        lgeos.GEOSSTRtree_nearest_generic.restype = c_void_p

测试.py

from shapely.geometry import Point, Polygon
from shapely.strtree import STRtree

a = []
a.append(Polygon([(1,0),(2,0),(2,1),(1,1)]))
a.append(Polygon([(0,2),(1,2),(1,3),(0,3)]))
a.append(Polygon([(-1.5,0),(-2.5,0),(-2.5,-1),(-1.5,-1)]))
a.append(Point(0,0.5))
tree = STRtree(a)
pt = tree.nearest(Point(0,0))
print(pt.wkt)

输出
POINT (0 0.5)

FuriousRococo 于 2019-01-22

🎉2 👍1

@FuriousRococo你想提交带有这个新功能的拉取请求吗？

snorfalorpagus 于 2019-01-23

感谢您添加 @FuriousRococo 功能。试图理解这个最近的函数时的一个问题。假设我正在尝试为某个点找到最近的道路。所以 STR 树是 MultiLineString 道路树。那么在这种情况下，是否使用从点到 MultiLineStrings 的距离投影距离给出最近的道路？还是基于到表示道路的 MultiLineStrings 质心的最小距离？谢谢！

asif-rehan 于 2020-03-18

我写了一个测试，我认为最近的函数检查 MultiLineString 中的每一行，看看最近的行是否在 MultiLineString 内。这是我的脚本@asif-rehan
测试.py

from shapely.strtree import STRtree
from shapely.geometry import Point, LineString, MultiLineString

tree_list = [LineString([[0,1],[1,1]])]
tree_list.append(MultiLineString([LineString([[0,0],[1,0]]),LineString([[0,3],[1,3]])]))
tree = STRtree(tree_list)

tree.nearest(Point(0.5,0.25)).wkt

输出
MULTILINESTRING ((0 0, 1 0), (0 3, 1 3))

FuriousRococo 于 2020-03-31

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Shapely: 功能请求：添加 STRtree.nearest 函数

笔记

问题

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