The Geoid what’s it got to do with me?

Abstract

The Global Positioning System (GPS), a US Department of Defense satellite positioning system, has become a widely used measuring tool in practical surveying applications, especially in the provision of coordinate control for construction projects, small scale mapping and cadastral survey coordination. To use GPS effectively, the surveyor must be familiar with the relationships between (i) local and geocentric datums, (ii) geodetic, Australian Map Grid (AMG) and three dimensional Cartesian coordinates and (iii) heights referred to the ellipsoid, the geoid and the Australian Height Datum (AHD). These relationships, often complex, are usually expressed mathematically. The surveyor, therefore, must also be an applied mathematician - certainly by practice, if not by training. The aim of this paper is to provide an explanation of some of the mathematical theory associated with the reference surfaces and relationships mentioned above with particular attention to the geoid and GPS heighting.