ThinkSpatial, in conjunction with Barwon Water and the Department of Environment and Primary Industries, has developed a Geoid Correction Model (GCM) for Greater Melbourne. The GCM was completed in 2008 and was primarily used in conjunction with AUSGeoid98 to directly determine accurate Australian Height Datum (AHD) heights. A version of the GCM was also developed for AUSGeoid09, but the improved AHD accuracy provided by AUSGeoid09 means the GCM offers only a minor improvement.
Developing the GCM involved a high quality GPS survey (and associated data processing) of numerous high-stability benchmarks to obtain accurate ellipsoidal heights for the benchmarks. Approximately 100 benchmarks distributed throughout Melbourne, Geelong, the Bellarine Peninsula, and the Otway Ranges were used. The processing was carried out using the Bernese GPS Processing software to ensure the best possible results.
The processing results were used to generate a geoid correction model over the project area, which is then used to “correct” existing geoid models (e.g. AUSGeoid98). This enables surveyors (and other spatial professionals) to directly obtain accurate AHD heights from technologies such as MelbPOS.