World Geodetic System 1984 (WGS 84)

A set of parameters, established by the U.S. Defense Mapping Agency, for determining geometric and physical geodetic relationships on a global scale.  The system includes a geocentric reference ellipsoid; a coordinate system; and a gravity field model.  The ellipsoid is essentially that of the International Union of Geodesy and Geophysics Geodetic Reference System 1980.  The coordinate system is a realization of the conventional terrestrial system, as established by the International Earth Rotation Service.  The descriptions of the GPS satellite orbits in the navigation message are referenced to WGS 84.