Local geoid improvement using GPS and leveling data: Case study

National leveling height networks have recently been set up in Taiwan, and global positioning system (GPS) observations were carried out at the benchmarks of the networks. The purpose of this paper is to develop an improved local geoid model for Taiwan by integrating a local gravimetric geoid model with the GPS and leveling height data. To overcome the problems of datum inconsistencies and possible systematic errors in height data of different types, the least squares collocation technique was applied. The result from fit of the improved geoid model to the control data at 300 benchmarks shows that a mean accuracy of geoidal heights at a 2 cm level is obtainable.