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+# README.us_nga
+
+The files in this section result from the conversion of datasets originating
+from [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.
+
+* 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 Domain
+
+2.5 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.
+
+* egm08_25.tif