GeoidEval computes the height of the geoid above the WGS84 ellipsoid using interpolation in a grid of values for the earth gravity models, EGM84, or EGM96, EGM2008. The RMS error in the interpolated height is about 1 mm. Give the position in terms of latitude and longitude, for example (these all refer to the position of Timbuktu):
16.776 -3.009 16d47' -3d1' W3°0'34" N16°46'33" 3:0:34W 16:46:33NThe coordinates can also be given in UTM, UPS, or MGRS coordinates (see the documentation on the GeoConvert utility).
GeoidEval, which is a simple wrapper of the GeographicLib::Geoid class, is one of the utilities provided with GeographicLib. This web interface illustrates a subset of its capabilities. If you wish to use GeoidEval directly, download and compile GeographicLib. A description of the methods is given here.