Guard against degenerate rings in SimplifyTopology#32
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SimonCropp merged 1 commit intoJul 10, 2026
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SimplifyRing splits a ring at its junctions and thins each arc as an open line, whose floor is two points. Nothing rechecks the reassembled ring, so a ring whose arcs all fall within the tolerance collapses below a triangle. Two polygons sharing an edge -- the case the function exists to serve -- each split into two arcs between the same junction pair and reassemble to (j0, j1, j0): three positions, zero area, an invalid linear ring under RFC 7946 3.1.6. GeoJson and WKT emit it as-is. Validate the reassembled ring and fall back to the closed-ring simplifier, whose minPoints = 4 floors it at MinimalRing exactly as the plain Simplify path already does. Both halves of the check are load-bearing: a self-touching ring can reach four positions with only two distinct vertices, which a position-count check alone waves through. The guard sits above the method switch, so it covers Douglas-Peucker and Visvalingam alike.
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SimplifyRing splits a ring at its junctions and thins each arc as an open line, whose floor is two points. Nothing rechecks the reassembled ring, so a ring whose arcs all fall within the tolerance collapses below a triangle. Two polygons sharing an edge -- the case the function exists to serve -- each split into two arcs between the same junction pair and reassemble to (j0, j1, j0): three positions, zero area, an invalid linear ring under RFC 7946 3.1.6. GeoJson and WKT emit it as-is.
Validate the reassembled ring and fall back to the closed-ring simplifier, whose minPoints = 4 floors it at MinimalRing exactly as the plain Simplify path already does. Both halves of the check are load-bearing: a self-touching ring can reach four positions with only two distinct vertices, which a position-count check alone waves through.
The guard sits above the method switch, so it covers Douglas-Peucker and Visvalingam alike.