Physical geodesy
Geodesy is usually subdivided into geometrical geodesy, satellite geodesy and physical geodesy,
although additional subdivisions are recognized as well.
Geometrical geodesy is concerned with describing locations in terms of geometry. Consequently, coordinate systems are one of the primary products of geometrical geodesy.
Satellite geodesy is concerned with using orbiting satellites to obtain data for geodetic purposes.
Physical geodesy is concerned with determining the Earth’s gravity field, which is necessary for establishing heights. Physical Geodesy deals with the measurement and representation of the Earth's gravity field. Physical geodesy is the branch of science, which deals with the study of physical properties of the Earth’s gravity field, the geopotential.
The basic tools of physical geodesy are:
 Astronomical measurements to obtain the direction of the plumb line;
 Linear and azimuthal measure¬ments to ascertain distances and angles in a triangulation net;
 Gravimetrical measurements, which provide rather accurate values for the gravity anomaly, for the difference between gravity on the geoid and gravity on a reference surface, which is commonly assumed to be an ellipsoid of revolution.
Physical geodesy also covers the variation in coordinates due to a shift in the reference surface.
