FA-70519 / GIS polygon topology / Member archive

Simple ring validity diagnosis: closing edge adjacency · case 04

Every valid ring is reported as self-intersecting.

Member previewVariant 4 · 3 implementations · 8 checks per implementation

Case contract

Input: one ring as a list of integer [x, y]. Report the first failing check in this order: fewer than 4 positions "too_few_points"; first != last "not_closed"; two cyclically consecutive equal vertices "repeated_point"; a vertex where the boundary reverses direction along a line (collinear with a negative dot product of the incoming and outgoing edge, checked cyclically) "spike"; any two non-adjacent edges sharing a point (crossing, touching or collinear overlap) "self_intersection"; otherwise "valid".

Why this case matters

Topology validators run before editing, overlay and publishing; a wrong diagnosis sends users to fix the wrong vertex or lets broken rings through.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
boundary #6	`"self_intersection"`	`"valid"`	Failed

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