FA-70383 / GIS polygon topology / Member archive

Ring vertex cleaning with snapping tolerance: closing tolerance · case 03

Rings end with a near-duplicate of their start vertex.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

Input [ring, eps] where ring is an open or closed list of integer [x, y] positions and eps >= 0. Walk the ring and drop a position whose Chebyshev distance to the last KEPT position is <= eps. Then repeatedly drop trailing kept positions within eps of the first kept position. If fewer than 3 positions remain return None, else return the kept positions closed by repeating the first.

Why this case matters

Digitised boundaries carry jitter and duplicate clicks; cleaning must not let small steps accumulate into dropped corners or leave near-closing duplicates.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
control #7	`[[80, 63], [64, 80], [47, 82], [62, 19], [80, 47], [79, 63], [80, 63]]`	`[[80, 63], [64, 80], [47, 82], [62, 19], [80, 47], [80, 63]]`	Failed

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