Self-intersecting polygon

Geometry

Bowtie/overlapping rings make area and containment undefined.

Detection

turf.kinks returns intersection points.

Mitigation

  • Repair upstream (buffer(0) / make-valid)
  • Reject and flag rather than silently fill

Affected conversions

  • PolygonH3 (intersects)
  • PolygonH3 (fully-contained)