The satellite positioning systems, without multilevel ground-based infrastructures could only provide few meter accuracy navigation solutions. The International GNSS Service (IGS) based on a global tracking network routinely delivers precise orbit solutions and maintains a global reference frame, while regional networks (e.g. the EUREF Permanent
Network, EPN) maintains the continental reference frames (e.g. ETRS89) and support the national activities with guidelines and metadata. The national infrastructures, relying on the global and regional products are
maintaining the national geodetic reference frames and delivering products and services for the positioning and scientific user groups. One of the priority tasks of the SGO is to develop national infrastructures expoliting
the capabilities of satellite geodesy. We created several network infrastructures according to the actual needs of the specific applications. Initially those infrastructures were exclusively based on the classical networks
but gradually the satellite techologies played the primari role integrating the classical technologies as well. The established networks are introduced below in chronological order.
National GPS Frame Network and National GPS Geodynamic Network
The GPS techology was first demonstrated in Hungary in 1987 in a conference, which gave a huge momentum to the planning of the national GPS infrastructure. 11 points of the National GPS Frame Network were selected and monumented as reinforced markers to the existing 3rd order points of the Unified National Projection System of Hungary (EOV). Selection and monumentation of further 12 stations was also done on outcropping rock for long-term geokinematic motion detection. The 24th station was Hungary's first permanent GPS station at the SGO, called PENC. The first joint measurement of all these points was organized in November 1991 with the support of the German IfAG (Institute für Angewandte Geodasie) - today BKG (Bundesamt für Geodasie und Kartographie). The primary goal of the campaign was Hungary's accession to the EUREF ETRS89 system. This campaign was a symbolic one, being the first in the Central-Eastern countries. All points has got official ETRS89 coordinates in 1993. The reference points are maintained (except BALL (Ballószög), which was destroyed) and they are regularly re-measured in the frame of the MGGA (Hungarian GPS Geokinematic Reference Network) campaigns.
OGPSH: National GPS Network
For surveying application of the GPS technique it is essential to establish the link between the satellite’s geocentric system and the conventionally defined geodetic coordinate systems. The optimal solution is to select appropriate points for the GPS measurements from the conventional network reference points, compute their spatial coordinates and estimate the transformation parameters using the coordinates known in both systems. The 2nd milestone (the 1st was the Frame network and the ETRS89 connection) in the development of Hungary’s GNSS infrastructure was the creation of the National GPS Network (OGPSH) between 1994 and 1998 (1994 point selection, 1995-97 GPS measurements, 1998 processing and database publication). 1153 points of the OGPSH were selected from the National Horizontal Base Network’s (EOVA) III. and IV. order reference points with approximatelly 10 km mean point distance. OGPSH had an outstanding role before the start of the active network (GNSSnet.hu), as it provided unique access to the ETRS89 reference system in field measurements. Today, its primary role is to ensure the physical background for the transformation between ETRS89 and EOV. In 2007, the ETRS89 coordinates defined in 1991 were redefined by processing GNSSnet.hu and MGGA data and the OGPSH point descriptions had been updated accordingly.