nx_geo_h3.nx

nx_geo_h3.nx -- LIB: GEO-018 H3-CLASS HEXAGONAL grid index in CUBE coordinates. A hex cell is (q,r,s) with q+r+s=0; the 6 neighbours are the 6 axial directions, each at grid-distance 1. THE EXCEED ANGLE (measured, integer-exact -- not asserted): hexagons tile the plane with UNIFORM adjacency. The exact squared Euclidean distance between two hex-lattice centres differing by axial (da,db) is the lattice NORM FORM N(da,db) = da^2 + da*db + db^2 -- the irrational sqrt(3) of the hex basis CANCELS, leaving a pure integer. All 6 immediate neighbours have N == 1: every adjacent hex is equidistant. A square grid's natural 8-neighbourhood instead splits into squared distance 1 (4 edge) and 2 (4 diagonal) -- NON-uniform by a factor of 2. Uniform adjacency = no direction-dependent bias in coverage / radius / flow, the H3 win over square cells. Pure integer, deterministic. (q,r) are axial cell coords; a real lon/lat first quantizes to the hex lattice. license_tier: ORIGINAL