Earth Gravitational Model

WGS84 combines the old GRS 80 with the then-latest data, namely available Doppler, satellite laser ranging, and Very Long Baseline Interferometry (VLBI) observations, and a new least squares method called collocation.

[3] It allowed for a model with n=m=180 to be defined, providing a raster for every half degree (30', 30 minute) of latitude and longitude of the world.

[5] EGM96 from 1996 is the result of a collaboration between the National Imagery and Mapping Agency (NIMA), the NASA Goddard Space Flight Center (GSFC), and the Ohio State University.

In addition, there have been major efforts to improve NIMA's existing 30' mean anomaly database through contributions over various countries in Asia.

The official Earth Gravitational Model EGM2008 has been publicly released by the National Geospatial-Intelligence Agency (NGA) EGM Development Team.

Among other new data sources, the GRACE satellite mission provided a very high resolution model of the global gravity.

That introduces an error of up to 0.3 mm because of 16 bit quantisation, using lossless float GeoTIFF or original .gsb files is a good idea.