python - 获取 Point 任一侧 LineString 上的顶点

Question

我有一个匀称的LineString，并定义了一个匀称的Point，它位于LineString.

如何找到LineString位于点两侧的顶点？（将线一分为二）

Answer 1

LineString在点所在的位置找到线段。然后将相应的顶点分成两组LineString。要定位线段，只需对每个线段应用点/线段相交测试。

from shapely.geometry import Point,LineString

def split(line_string, point):
    coords = line_string.coords
    j = None

    for i in range(len(coords) - 1):
        if LineString(coords[i:i + 2]).intersects(point):
           j = i
           break

    assert j is not None

    # Make sure to always include the point in the first group
    if Point(coords[j + 1:j + 2]).equals(point):
        return coords[:j + 2], coords[j + 1:]
    else:
        return coords[:j + 1], coords[j:]

Answer 2

较新版本的 Shapely ( >=1.6.0 (2017-08-21) ) 提供split可以按点分割线的功能：

from shapely.geometry import LineString, Point
from shapely.ops import split

line = LineString([(0, 0), (1, 1), (2, 1)])
point = Point(1.5, 1)
print(split(line, point))
# GEOMETRYCOLLECTION (LINESTRING (0 0, 1 1, 1.5 1), LINESTRING (1.5 1, 2 1))

---

但是，必须注意，由于精度错误，这有时无法正常工作：

line = LineString([(0, 0), (3, 2)])
point = Point(1, 2 / 3)
print(split(line, point))
# GEOMETRYCOLLECTION (LINESTRING (0 0, 3 2))
print(point.distance(line))
# 0.0

处理这个问题的一种方法是构造一个LineString包含分裂点的新的。

new_line = LineString([line.coords[0], point.coords[0], line.coords[1]])
print(split(new_line, point))
# GEOMETRYCOLLECTION (LINESTRING (0 0, 1 0.6666666666666666), LINESTRING (1 0.6666666666666666, 3 2))

或者如果您不想手动操作：

from itertools import chain

all_points_coords = chain(line.coords, point.coords)
all_points = map(Point, all_points_coords)
new_line = LineString(sorted(all_points, key=line.project))
print(split(new_line, point))
# GEOMETRYCOLLECTION (LINESTRING (0 0, 1 0.6666666666666666), LINESTRING (1 0.6666666666666666, 3 2))