GNSS/Levelling

GNSS/Levelling is a geodetic technique used to determine the orthometric height (height above the geoid) of a station by combining geometric heights (ellipsoidal heights) from satellite positioning with a high-accuracy gravimetric geoid model. While GNSS (Global Navigation Satellite System) provide a purely geometric height relative to a reference ellipsoid, traditional levelling measures the physical height difference relative to the Earth’s gravity field. The relationship connecting these three height types is H=h-N, where H is the orthometric height, h is the GNSS ellipsoidal height, and N is the geoid undulation or geoid height which is the separation between the ellipsoid and the geoid.