Geodetic Datum

A specifically oriented reference ellipsoid. Typically, eight parameters are required to define a geodetic datum: two to specify the dimensions of the ellipsoid, three to specify the location of its center with respect to the earths centre of mass, and three to specify the orientation of the ellipsoid with respect to the average spin axis of the earth and the Geodetic Height. The height of a point above an ellipsoidal reference surface. Also known as ellipsoidal height. The difference between the geodetic height of a point and its orthometric height is equal to the geoidal height.