The Mean Sea Level (MSL) is calculated by subtracting the calculated offset from the WGS84 ellipsoidal height. With this four values, a height offset is calculated using Bi-cubic interpolation. To calculate the height offset, the four points nearest to the current position are retrieved from the geoid file. The EGM2008 model can be used to calculate the height offset between the WGS84 ellipsoidal height and the Mean Sea Level (MSL) on any place on the globe. The EGM2008 geoid model (image courtesy of NGA). The EGM2008 model has a cell size of 1.0 x 1.0 minute, resulting in a grid of 10801 rows x 21600 columns containing 4 byte IEEE float values defining the difference between the WGS84 ellipsoid height and Mean Sea Level (MSL).
National Geospatial-Intelligence Agency (NGA) EGM Development Team. It is the successor of EGM96 and EGM84 and it is supplied by the U.S. EGM2008 is short for Earth Gravitational Model 2008.
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