FA-70363 / GIS polygon topology / Member archive

Right-hand rule ring orientation enforcement: minimum ring size · case 03

Two-vertex closed "rings" pass validation.

Member previewVariant 3 · 3 implementations · 8 checks per implementation

Case contract

Input: a polygon as a list of rings (exterior first, then holes), each a list of [x, y] integer positions. Every ring must be closed (first == last) with at least 4 positions, else return None; an empty polygon is None. Exterior rings are made counter-clockwise and holes clockwise by twice-signed-area sign; a reversed ring keeps its start vertex. Zero-area rings are left untouched. Return the rewritten rings.

Why this case matters

GeoJSON writers and vector-tile encoders must emit exterior and hole rings with opposite orientation; renderers use it to decide which rings cut holes.

One recorded failure

Sample boundary fixture

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

Boundary fixture	Actual	Expected	Outcome
boundary #20	`[[[0, 0], [4, 0], [0, 0]]]`	`null`	Failed

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