The Earth Gravitational Models (EGM) are a series of geopotential models of the Earth published by the National Geospatial-Intelligence Agency (NGA). They are used as the geoid reference in the World Geodetic System.
The NGA provides the models in two formats: as the series of numerical coefficients to the spherical harmonics which define the model, or a dataset giving the geoid height at each coordinate at a given resolution.[1]
Three model versions have been published: EGM84 with n=m=180, EGM96 with n=m=360, and EGM2008 with n=m=2160. n and m are the degree and orders of harmonic coefficients; the higher they are, the more parameters the models have, and the more precise they are. EGM2008 also contains expansions to n=2190.[1] Developmental versions of the EGM are referred to as Preliminary Gravitational Models (PGMs).[2]
Each version of EGM has its own EPSG code as a vertical datum.
- ^ a b "WGS 84 Earth Gravitational Model". earth-info.nga.mil. Archived from the original on 27 March 2013. Retrieved 30 July 2019.
- ^ Cite error: The named reference
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