FA-70620 / GIS polygon topology / Member archive

Sliver polygon detection by thinness ratio: hole perimeter · case 05

Thin rims around large holes are not flagged.

Member previewVariant 5 · 3 implementations · 8 checks per implementation

Case contract

Input [rings, threshold]: exterior then holes, closed rings in any orientation. Area = |exterior area| minus the sum of |hole areas|; perimeter = total length of all rings. If area <= 0 or perimeter == 0 return ["degenerate", 0.0]. Thinness t = 4*pi*area/perimeter**2; return ["sliver" if t < threshold else "ok", t rounded to 6 decimals].

Why this case matters

Overlay operations leave thin slivers along near-coincident boundaries; QA jobs flag them by compactness.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression #10	`["ok", 0.523599]`	`["sliver", 0.14253]`	Failed

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