nx_geo_union.nx

nx_geo_union.nx -- LIB: GEO-016 POLYGON UNION + INTERSECTION MEASURE (set algebra on areas). The union of two convex polygons is generally NON-convex, so it is not produced by a single Sutherland-Hodgman clip. Instead we compute the exact set MEASURE by inclusion-exclusion: area(A u B) = area(A) + area(B) - area(A n B) composing GEO-010 (geo_area2, integer-exact shoelace) and GEO-015 (geo_poly_clip, Sutherland-Hodgman intersection). HONEST SCOPE: this returns the union/intersection COVERAGE MEASURE (doubled area in microdeg^2), not the union BOUNDARY polygon -- which is exactly what geofence coverage / overlap scoring needs ("how much of region A is also covered by region B?"). EXCEED ANGLE: every term is integer arithmetic over microdegree coords -> deterministic, no float drift in the inclusion-exclusion (where chained float set-ops accumulate error). geo_iou_permil adds a sovereign Jaccard overlap score (intersection/union, per-mille) for geofence dedup/matching. Convention: polygons = flat [lat0,lon0,...]; the SECOND polygon (b) is the clip and must be CONVEX+CCW. license_tier: ORIGINAL