The EGM96 geopotential model has been developed by NASA, NIMA and Ohio State University. By means of this model, the geoid undulation of a point can be calculated if its latitude and longitude are known in WGS84 datum. A local geoid solution TG99 for Turkey has been developed by the General Command of Mapping in order to obtain orthometric height from GPS observation for Turkey. In this study, geoid undulations of 75 points have been obtained in an area of about 1700 km2 between the latitudes 39º 39'-40º 06' and longitudes 32º 25'-32º 57' by using EGM96, TG99 and GPS/Leveling and results were then compared. Geoid undulation differences have been obtained in the range between -12.8 cm and 61.3 cm for EGM96 and GPS/Leveling comparison and -17.2 cm and 18.2 cm for TG99 and GPS/Leveling comparison.
Nowadays, GPS is the best positioning system with its constellation, but number of GLONASS satellites increased to the required number, with launched new ones, for positioning. With recent revitalization of GLONASS, a great number of high precision GLONASS and GPS/GLONASS receivers have been produced. In this paper, baselines of two networks have been analyzed in order to assess the usability of GLONASS on global positioning. In both networks, repeatabilities of results were investigated by using GPS, GLONASS and GPS/GLONASS data. Results revealed that repeatabilities of all baselines by using GLONASS observations are not consistent when compared to the GPS and GPS/GLONASS.