FA-70609 / GIS polygon topology / Member archive

Douglas-Peucker simplification of a topology arc: first maximum tie-break · case 04

Among equally distant vertices the last one is kept, changing the simplified shape.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Input [points, tol]: an arc as integer [x, y] positions (possibly closed, first == last). Keep both endpoints; recursively (explicit stack) find the interior vertex farthest from the SEGMENT between the current endpoints (projection clamped to the segment; distance to the point itself if the endpoints coincide), taking the first maximum; keep it and split when that distance is strictly greater than tol. Return kept positions in order.

Why this case matters

Shared arcs are simplified once so adjacent polygons stay gap-free; distance and split errors change which boundary vertices survive.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression #24	`[[0, 0], [3, 5], [4, 0], [20, 0]]`	`[[0, 0], [1, 5], [2, 0], [3, 5], [4, 0], [20, 0]]`	Failed

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