The use of Continuously Operating Reference Stations, both singly and as part of an active network, is widely employed in surveying, engineering and other geomatics applications, achieving high accuracy positioning even in real time. With an active network the measurements of the reference stations are processed jointly in order to model the errors and compute network RTK corrections. Due to distance dependent errors (ionospheric and tropospheric delays), single base RTK positioning accuracy decreases with increased baseline length. However, the network solution (NRTK) retains the accuracy and the time to fix ambiguities (TTFA) at a constant level. This study aims to contribute to the scientific research on real time positioning based on active networks. In Southern Spain, ERGNSS, a national CORS network that provides GNSS data for post-processing and real time single-based reference station corrections, shares territory with the Andalusian Positioning Network (RAP), a local active network. RAP provides network and single-based RTK corrections. In order to analyze the quality of real time positioning based on both networks, several tests have been performed on a sample of test points. The reference frame, the time to fix ambiguity resolution, precision, accuracy and repeatability of RTK positioning are considered as the evaluation parameters. The results confirm that the RAP network complements the precise positioning services provided by the ERGNSS network, ensuring accurate real time positioning, full coverage and reliable positioning services in the Andalusian Community. operating reference station. With a CORS network the measurements of several reference stations are processed jointly in order to model the GNSS measurement errors and to compute network RTK corrections for the coverage area of the active network. While a sparse CORS network is sufficient for datum definition, the distance among permanent stations is limited to few tens of kilometers (50 -60 km) to model the distance dependent errors. Wang et al. (2010) show that in areas where there are insufficient users to justify high densities of CORS stations, it may be possible to offer RTK services using more sparse networks.
ARTICLE INFOThe main advantages of an active network are: it requires a lower density of reference stations, it is more robust with respect to possible failures in a particular reference station, it improves work performance and it transmits a reference frame throughout the coverage area of the network. Different manufacturers provide slightly different concepts for network RTK corrections. The most widely used solutions are the FKP (Flächen-korrektur-parameter), the VRS (Virtual Reference Station) and the MAC (Master Auxiliary Concept) approach (Euler et al., 2001). Based on the latter, Leica Geosystems© offers MAX and i-MAX solutions (Takac and Zelder, 2008).