Full native NGA EGM2008 GeographicLib grid: 4320 × 2161 nodes at 5 arc-minute spacing, including both poles. Model data is public domain, as documented by OSGeo PROJ-data; this is not an assertion of CC0. See ATTRIBUTION.md.
source.zip retains the existing egm/egm2008-5.zip archive; egm2008-5.pgm
is extracted byte-for-byte. Parquet retains raw uint16 pixels and float64 geoid
heights N = -108 + 0.003 × raw_value, in meters above the WGS84 ellipsoid.
This is geoid undulation, not terrain elevation: h = H + N.
Rows run north to south; columns run east from 0°. Longitude is normalized to [-180,180) in the node table. Pixel indices retain the source order. Each group contains up to 120 latitude rows; rowGroupIndex records source row ranges with exclusive rowStop. All 9,335,520 raw pixels and scaled heights are verified during conversion. Original interpolation-error estimates remain in the PGM header.
Legacy egm/ download paths remain available. Conversion and verification: ../../../scripts/prepare-reference.py. Sources, checksums and license evidence are in manifest.json. Scientific data is separate from MIT conversion code.