FA-70774 / GIS polygon topology / Member archive

Snapping ring vertices to a reference layer: post-snap merge · case 04

Snapped rings contain repeated consecutive vertices.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Input [ring, ref, tol]: a closed ring, reference vertices and a tolerance. Each ring vertex moves to the NEAREST reference vertex within Euclidean distance tol (inclusive; ties go to the lowest reference index), otherwise stays. Consecutive identical snapped vertices merge. If the result has fewer than 4 positions or is not closed return None, else return it.

Why this case matters

Integrating new survey data with an authoritative layer snaps nearby vertices so shared boundaries become identical; snapping to the wrong vertex creates slivers.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
regression #7	`[[0, 0], [0, 0], [10, 0], [10, 10], [0, 0]]`	`[[0, 0], [10, 0], [10, 10], [0, 0]]`	Failed

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