FA-70350 / GIS polygon topology / Member archive

Right-hand rule ring orientation enforcement: zero-area ring handling · case 05

Degenerate collapsed rings are reversed although they have no orientation.

Member previewVariant 5 · 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 #16	`[[[0, 0], [10, 0], [5, 0], [0, 0]]]`	`[[[0, 0], [5, 0], [10, 0], [0, 0]]]`	Failed

MEMBER ARCHIVE

The complete case is available to members.

This record includes three runnable implementations, regression fixtures, execution results, and source hashes.

Member access is invitation-based. Sign in with your invited account to inspect the sources.