FA-70379 / GIS polygon topology / Member archive

Ring vertex cleaning with snapping tolerance: drift anchor · case 04

A run of small steps is collapsed entirely, cutting off a corner reached gradually.

Member previewVariant 4 · 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
regression #13	`[[0, 0], [10, 0], [10, 10], [0, 10], [0, 0]]`	`[[0, 0], [2, 0], [10, 0], [10, 10], [0, 10], [0, 0]]`	Failed

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