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Geodetic networks

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.



EOMA_3D

Field measurements of the EOMA network has stopped in 1990 without completion due to missing financial resources, and in the Transdanubia region the 3rd order network densifcation was not completed. In 1998 SGO published its height determination technology based on GPS measurements and the GPS-geoid height reference surface. Following its acceptance on the Academic level the technology was used to determine sea level heights of the new EOMA 3rd order network points relying on the simultaneous GPS measurements at the new points and at the known I. and II. order EOMA benchmarks with the help of the modified geoid surface called GPS-gravimetric geoid. Between 2000 and 2005 a total of 11 measurement campaigns in the 2-4 EOMA polygons and in the 17, 19, 20 semi-polygons were organized and as the result each settlement received a 3rd order EOMA height reference point. A total of 240 known EOMA benchmarks were included in the GPS measurement campaigns. The centered observation over the benchmarks was not a basic requirement that time, only the mm-accuracy height eccentricity determination had to be ensured. These stations represent the EOMA_3D network, which played important role to renew our real-time EOV-ETRS89 transformation solution, called VITEL.



INGA: Integrated Geodetic Base Network

The main motivation for the INGA network development is to preserve the traditional geodetic reference frames with the support of modern space geodetic techologies and to elaborate a sustainable way for the maintainance of our traditional geodetic systems with an integration approach and a lower number (less than 800 points nationwide) of reference stations, where the GPS technology used to link the systems. The INGA points were selected primarily from the I. and II. order EOMA network and, if necessary, III. order reference points were involved, which are suitable for GPS measurements, preferably providing even distribution. At the INGA points, ETRS89 (XYZ), EOMA (H), transformed EOV (y, x) and possibly gravimetric data should be available. The GPS measurement campaigns were designed to follow the 1st order re-measurement campaigns of EOMA. According to the schedule the measurements of EOMA KMO1-2 (East-Hungary 1,2 phases) were conducted between 2007 and 2009. Despite the termination of the EOMA re-levelling, former FÖMI (Hungarian abbreviation for Institute of Geodesy Cartography and Remote Sensing) decided to continue the INGA network establishment in the KMO3 area. GNSS measurements were organized in 2013-14 and with that the INGA network east from the Danube was completed. However, the INGA-KMO is not complete yet because of the selection constraints (no suitable benchmarks in certain regions) and the even distribution of points is not available and no new GNSS/EOMA benchmarks could be monumented yet. The INGA points have special legal and physical protection. While OGPSH has created a physical and mathematical relationship between the traditional horizontal EOV and the spatial ETRS89 reference systems for satellite positioning, INGA together with EOMA_3D is the primary component of the EOMA-ETRS89 connection. These points made possible for the new VITEL solution, released in 2014 to also serve the precise height transformation between GNSS and EOMA for real-time GNSS applications.



Hungarian GPS Geokinematic Reference Network (MGGA)

In 2007 we merged the National GPS Geodynamic Network and the National GPS Frame Network under the name of Hungarian GPS Geokinematic Reference Network (Hungarian abbreviation: MGGA) for extended geokinematic monitoring purposes. Since 2007 all 23 MGGA points are observed every two years (except in 2017), always at the same period of the year using the same instruments/antennae. The MGGA measurement data is regularly processed by our GNSS Analysis Center according to international standards. The processing is done together with the data of the GNSSnet.hu stations and the interpretation of those two network products will be done together.



GNSS Service Centre

The active GNSS networks are built up from continuously operating stations, optimally covering a country with 60-80 km of mean station separation. The observation data is real-time sent to an operational center, where it is processed and correction services are provided for users of cm-accuracy real time positioning needs. The installation of such a complex system requires top level infrastructure, huge hardware/software investments and qualified staff. The first Hungarian continuously operating GPS station was started its operation in 1996 on the top of the SGO main building. This time the only obstacle of the earlier operation start was the lack of a permanent Internet connection. After several years of gap the network installation was continued in 2002 and only completed in 2009 using project grants. GNSSnet.hu includes now 35 Hungarian stations, but it is extented with 19 stations from neighboring countries based on bilateral agreements in order to ensure the same positioning accuracy in the country including territories close to the state border.

At the selection of the stations we took into account the following parameters: