Shapely: Split LineString at arbitrary point along edge

Question

I'm trying to split a Shapely LineString at the nearest point to some other coordinate. I can get the closest point on the line using project and interpolate but I am unable to split the line at this point as it is not a vertex.

I need to split the line along the edge, not snapped to the nearest vertex, so that the nearest point becomes a new vertex on the line.

Here's what I've done so far:

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

line = LineString([(0, 0), (5,8)])
point = Point(2,3)

# Find coordinate of closest point on line to point
d = line.project(point)
p = line.interpolate(d)
print(p)
# >>> POINT (1.910112359550562 3.056179775280899)

# Split the line at the point
result = split(line, p)
print(result)
# >>> GEOMETRYCOLLECTION (LINESTRING (0 0, 5 8))

Thanks!

score 9 · Answer 1 · answered May 15 '18 at 09:10

As it turns out the answer I was looking for was outlined in the documentation as the cut method:

def cut(line, distance):
    # Cuts a line in two at a distance from its starting point
    if distance <= 0.0 or distance >= line.length:
        return [LineString(line)]
    coords = list(line.coords)
    for i, p in enumerate(coords):
        pd = line.project(Point(p))
        if pd == distance:
            return [
                LineString(coords[:i+1]),
                LineString(coords[i:])]
        if pd > distance:
            cp = line.interpolate(distance)
            return [
                LineString(coords[:i] + [(cp.x, cp.y)]),
                LineString([(cp.x, cp.y)] + coords[i:])]

Now I can use the projected distance to cut the LineString:

...
d = line.project(point)
# print(d) 3.6039927920216237

cut(line, d)
# LINESTRING (0 0, 1.910112359550562 3.056179775280899)
# LINESTRING (1.910112359550562 3.056179775280899, 5 8)

Shapely: Split LineString at arbitrary point along edge

1 Answers1