Abstract
In this paper the advantages of using combination of different GNSS including GPS, GLONASS and BeiDou with respect to singe GPS are presented. It was shown that an improvement of satellite conditions at the chosen measurement point due to increase of the number of visible satellites has an impact on RTK measurement errors. Additionally, it was shown that there are systematic errors in RTK measurements that can be eliminated to get more precise results of them, especially in the case of height determination.