degToDirForGriddedWindUv

vertexRotDeg is the instanced-vertex rotation (after per-phase atan2(u,-v) → unit vectors → mix → atan2), same as com.xweather.mapsgl.layers.tile.EncodedTileLayer returns for SampleExpression.ENCODED_WIND_UV. Maps to compass-from-north for degToDir glyphs (north-up map).