return early for paths already inside

1 files changed, 6 insertions, 0 deletions

diff --git a/lib/utils/clamp_path.py b/lib/utils/clamp_path.py
index f1fc7765..f9b8991a 100644
--- a/lib/utils/clamp_path.py
+++ b/lib/utils/clamp_path.py
@@ -66,6 +66,8 @@ def find_border(polygon, point):
 def clamp_path_to_polygon(path, polygon):
     """Constrain a path to a Polygon.
 
+    The path is expected to have at least some part inside the Polygon.
+
     Description: https://gis.stackexchange.com/questions/428848/clamp-linestring-to-polygon
     """
 
@@ -76,6 +78,10 @@ def clamp_path_to_polygon(path, polygon):
     # border and returns the pieces in the same order as the original path.
     split_path = ensure_geometry_collection(LineString(path).difference(polygon.boundary))
 
+    if len(split_path.geoms) == 1:
+        # The path never intersects with the polygon, so it's entirely inside.
+        return path
+
     # Add the start and end points to avoid losing part of the path if the
     # start or end coincides with the polygon boundary
     split_path = [ShapelyPoint(start), *split_path.geoms, ShapelyPoint(end)]