FA-70764 / GIS polygon topology / Member archive

Snapping ring vertices to a reference layer: nearest candidate · case 04

Vertices snap to the first reference vertex in range rather than the closest one.

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 #2	`[[5, 5], [8, 2], [9, 9], [5, 5]]`	`[[5, 6], [8, 2], [9, 9], [5, 6]]`	Failed

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