Ellipsoidal Height

Ellipsoidal height (h) is the vertical distance from a point to the reference ellipsoid, measured along the ellipsoidal normal. It is the height GNSS delivers directly, since satellite positioning is referenced to the WGS 84 ellipsoid, and it is purely geometric: it carries no relation to gravity or to mean sea level. Ellipsoidal height differs from orthometric height (H), the height above the geoid, by the geoid undulation N, through h = H + N. Converting GNSS ellipsoidal heights to the orthometric heights used on charts and for water flow requires a geoid model. The two can differ by tens of meters.