python - 匀称的 LineString 交集是否错误？

Question

在使用 shapely 时，我遇到了一个奇怪的问题。有 2 个点 p1 和 p2，第一个属于多边形，第二个不属于。当我试图找到包含这 2 个点的 LineString 与多边形边界线的端点之间的交点时，我收到消息说没有找到交点。我想知道，这怎么可能？

from shapely.geometry import Polygon as SPolygon, Point, LineString

p1 = Point(5.414213562373095, 2.585786437626905)
p2 = Point(15.17279752753168, -7.172797527531679)

l = LineString([p1, p2])

l1 = LineString([(2, 2), (2, 6)])
l2 = LineString([(2, 6), (6, 6)])
l3 = LineString([(6, 6), (6, 2)])
l4 = LineString([(6, 2), (2, 2)])


sp = SPolygon([(2, 2), (2, 6), (6, 6), (6, 2)])

print "Polygon contains p1:", sp.contains(p1)
print "Polygon contains p2:", sp.contains(p2)

for i, line in enumerate((l1, l2, l3, l4)):
    res = l.intersects(line)
    print "Line {0} intersects l1: {1}".format(i, res) 

这里是输出:

Polygon contains p1: True
Polygon contains p2: False
Line 0 intersects l1: False
Line 1 intersects l1: False
Line 2 intersects l1: False
Line 3 intersects l1: False

Answer 1

我将 l.intersects(line) 更改为 l.intersection(line) 并且我在

处得到了一个交叉点

LINESTRING (6 6, 6 2) at Point (6, 2) 

不确定为什么 .instersects() 表现不同。

然后我四舍五入p1和p2

p1 = Point(round(5.414213562373095, 2), round(2.585786437626905, 2))
p2 = Point(round(15.17279752753168, 2), round(-7.172797527531679, 2))

我在

有 2 个路口

LINESTRING (6 6, 6 2) at POINT (6 2)
LINESTRING (6 2, 2 2) at POINT (6 2)

此修复也适用于 .intersects()(2 个正确)

Shapely 对浮点精度有点敏感，我通常可以通过舍入来解决问题。尽管这对您来说可能无法接受。