RELATIVE GPS/GLONASS COORDINATES DETERMINATION IN URBAN AREAS - ACCURACY ANAYSIS

Our analysis was intended to evaluate the accuracy of relative GPS/GLONASS coordinates determination in urban areas from the end users' point of view. We used ASG-EUPOS (Polish Active Geodetic Network) observations as well as observations done on two points measured under conditions of limited satellite availability. To processing we used Topcon Tools software (an example of so-called commercial software). All analysis were done in local scale (baseline up to 70 km) because it was assumed that most of the surveying work takes place in within this framework. Five days of GPS/GLONASS date were processed to determine how the accuracy of derived three-dimensional relative position baselines between GNSS antennas depends on the distance between these antennas and on the duration of the GNSS observing session. It was found that the scatter in the up direction is larger than that in either of the horizontal components. Also as expected, the results indicated that RMS decreases as T increases. Somewhat unexpectedly, however, the results suggest that the computed RMS values do not vary significantly as a function of L, especially for longer session -up to one hour. The results show also that observing conditions can significantly affect the position determination accuracy. The impact of obstacles is especially visible in the case of processing short observation sessions. For longer sessions, the influence of observing conditions on the accuracy of the position determination was clearly reduced. In comparing GPS-only and GPS/GLONASS solutions, noticeable improvements especially