Geodesy is the discipline that deals with the measurement and representation of the earth, including its gravity field, in a three-dimensional time varying space. It consists of three main sub disciplines:
Geodesy uses a variety of measuring techniques and systems and is practiced by personnel that may be categorized into scientists, engineers, technicians, and auxiliary personnel (IAG, NRC definitions; from Geodesy: The Concepts, 1986).
Geodesy is an interdisciplinary science which uses space borne and airborne remotely sensed, and ground-based measurements to precisely determine position and velocity of points or objects at the surface or orbiting the planet, within a realized terrestrial reference system, and to apply these knowledge to a variety of scientific and engineering applications, using mathematics, physics, astronomy, and computer science. (Ohio State University)