# us_nga_README.txtThe files in this section result from the conversion of datasets originatingfrom [US NGA](http://earth-info.nga.mil)## Included grids### Worldwide: EGM96 geoid model*Source*: [NGA](http://earth-info.nga.mil/GandG/wgs84/gravitymod/egm96/egm96.html) *Format*: GeoTIFF converted from GTX *License*: Public Domain 15 minute worldwide geoid undulation grid that transforms physical heights to WGS84 ellipsoidal heights.* us_nga_egm96_15.tif### Vertical grid: EGM2008 geoid model*Source*: [NGA](http://earth-info.nga.mil/GandG/wgs84/gravitymod/egm2008/egm08_wgs84.html) *Format*: GeoTIFF converted from GTX*License*: Public Domain2.5 minute worldwide geoid undulation grid that transforms physical heights to WGS84 ellipsoidal heights.This file has been produced by [GeographicLib](https://geographiclib.sourceforge.io/html/gravity.html)using the EGM2008 gravity model and can be regenerated with the[build_egm08_25_gtx.sh](https://raw.githubusercontent.com/OSGeo/proj-datumgrid/master/world/build_egm08_25_gtx.sh) script.* us_nga_egm08_25.tif