Transformation of ellipsoid heights to local leveling heights

The aim of this study is to evaluate the use of interpolation methods, whic h are used for digital terrain modeling, in transformation of Global Positi oning System (GPS) ellipsoid heights to local heights. To test the interpol ation methods used in this research, a set of GPS data collected in norther n Turkey, 300 km from Istanbul, is used. The data were transformed to a loc al height system using 11 different interpolation processes, classified in four types of interpolation approaches. The data set includes 109 points, w hose heights are known in both GPS and local height systems. Eighteen of th em are selected as reference points. The differences between the local and GPS heights at the remaining 91 points were recalculated by using the diffe rences at the 18 reference points. The interpolated (Or extrapolated) diffe rences were compared with the known differences for 91 points.