The determination of orthometric heights using the global positioning system (GPS) requires the knowledge of the geoid height. However, in general, the precision of the available geoid models is not in the same level as that capable of being obtained by GPS leveling. Therefore, in order to use GPS for heightening, some additional efforts have to be taken into account. In general, the solution for local applications has been based on the use of GPS leveling, geoid model and leveling network, by using integration technique. The selection of a suitable set of polynomial parameters and the definition of the best geoidal model, together to the detection of data points with abnormal values are the main practical problems. A case study based on data set collected in Presidente Prudente, at Sao Paulo State, Brazil, will be presented in this paper. Some details of the GPS data collection and processing as well as of the selection of the polynomial parameters and geoidal model based in statistical analysis will be described. The results have shown RMS of the order of 40 mm.
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