Transformation of ellipsoid heights to local leveling heights

The aim of this study is to evaluate the use of interpolation methods, which are used for digital terrain modeling, in transformation of Global Positioning System (GPS) ellipsoid heights to local heights. To test the interpolation methods used in this research, a set of GPS data collected in northern Turkey, 300 km from Istanbul, is used. The data were transformed to a local height system using 11 different interpolation processes, classified in four types of interpolation approaches. The data set includes 109 points, whose heights are known in both GPS and local height systems. Eighteen of them are selected as reference points. The differences between the local and GPS heights at the remaining 91 points were recalculated by using the differences at the 18 reference points. The interpolated (or extrapolated) differences were compared with the known differences for 91 points.