GNSS observations at a network of permanent stations became now a complex systems offer except postprocessing also corrections sent in real time as well as the creation of virtual observation. An example of such a system is running in June 2008, the Polish Active Geodetic Network ASG EUPOS. For users was intended three services to real-time corrections, and two services for postprocessing. It is well known that measurements per- formed in real time are usually characterized by a lower accuracy than static measurements and that the accuracy of the height is less than the horizontal position. The accuracy of static measurements depends among others on the length of the vectors, the length of the observing session and the type of used receivers (L1 or L1/L2). In the paper methods of heights appointment from static GPS measurements was analyzed in the context of the technical capabilities of the ASG-EUPOS and some recommendations for such measurements. Particular attention was paid to the possibility of using to such determinations the Virtual Reference Station (VRS). Studies have shown that the procedure of height appointment with the use VRS may allow to reduce the length of observation sessions and improve accuracy compared to the results obtained from the POZGEO service. In addition, because of the short vectors between the virtual station and measured points, accuracy is not dependent on the type of used receiver (L1 or L1/L2).

21-34