FA-70352 / GIS polygon topology / Member archive

Right-hand rule ring orientation enforcement: start-preserving reversal · case 02

Reoriented rings come out unclosed.

Member previewVariant 2 · 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
control #1	`[[[42, 44], [-19, 64], [50, -21], [53, -16]], [[-10, -10], [-10, -4], [-6, -4], [-6, -10], [-10, -10]], [[-4, -10], [-4, -4], [0, -4], [0, -10], [-4, -10]]]`	`[[[53, -16], [42, 44], [-19, 64], [50, -21], [53, -16]], [[-10, -10], [-10, -4], [-6, -4], [-6, -10], [-10, -10]], [[-4, -10], [-4, -4], [0, -4], [0, -10], [-4, -10]]]`	Failed

MEMBER ARCHIVE

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