A Geoid for the Australian Capital Territory

Abstract AUSGE0ID93 is a national grid of geoid-ellipsoid separations (N values). When differences in N from AUSGE0ID93 are subtracted from differences in ellipsoidal height from GPS surveys, the resulting differences in orthometric height frequently approach 3rd Order levelling accuracy. However, in areas of rapid changing terrain, the results may be less accurate. It was believed that this was due to the absence of terrain data in AUSGE0ID93. The ACT region was chosen to test this hypothesis and at the same time produce a grid of improved N values approximately 4 times denser than AUSGEOID93.