GNSSnet.hu
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:
- installation on secure antenna and receiver location, preferably on buildings with existing communication infrastructure – most cases we chose Land Offices,
- undisturbed GNSS signal receiving – open skies with minimal blocking objects and multipath free location,
- in accordance with the local conditions a stable monumentation possibility providing stability of the marker better than ± 1 cm,
- reliable, unified protocol of data transmission.
The RINEX data of each station is continuously processed at the GNSS Analysis Center, monitoring the data quality and stability of the stations. PENC and PEN2 stations of GNSSnet.hu are part of the IGS (International GNSS Service) stations and together with three other stations (BUTE, OROS, SOPR) are part of the European EUREF network, thus their data are analysed by international processing centers, contributing to the global and European geodetic reference system maintainance. The GNSSnet.hu network is one of the infrastructure pillar of the SGO’s GNSS Service Centre, where from the raw data collected from the reference stations the central processing facility generates RINEX data for post-processing purposes and real-time corrections for the surveyor community.
K-GEO Accredited Calibration Laboratory
The K-GEO Accredited Calibration Laboratory, is being operated as a part of the Satellite Geodetic Observatory, performs the calibration of geodetic electro-optical distant measuring (EDM) instruments and GNSS receivers. The K-GEO Calibration Laboratory was accredited by the National Accreditation Authority (NAH) from 2000 to 2009, then the re-accreditation was in 2014. The Laboratory performs its calibrations in accordance with the MSZ EN ISO / IEC 17025: 2005 "General Requirements for Preparedness of Testing and Calibration Laboratories". The calibration of EDM instruments is carried out either in Gödöllő, on the National Standard Geodetic Baseline or on the "Penc Baseline" located in the SGO area. The Gödöllő baseline’s etalon distances were determined by the Finnish Geodetic Institute in 1987 and 1999 with the Väisälä interferometer, the most accurate technique currently available. The National Office of Measures (Országos Mérésügyi Hivatal, OMH, now part of the BFKH) proclaimed the National Standard Geodetic Baseline of Gödöllő in 2001 as a National Geodetic Length Standard. Calibration of small precision measuring instruments is performed in the SGO Baseline. The standard deviations of the Penc Baseline were derived from the Gödöllő Baseline with high-precision EDM instruments. The stability of both baselines’ pillars is checked regularly.
A During the EDM instrument’s calibration, we measure in every combination the oblique distances between the user point marks on the pillars. As a result of the calibration, we derive the errors of the distance measurements, ie. the difference between the measured and the correct distances, and using the least squares method we determine the adder and constants of the instrument. The measurement uncertainty associated with the values is given as the resultant extended uncertainty as required by the standard. For each instrument calibration protocols and calibration certificate are issued.
Calibration of the GNSS receivers is carried out on the top of the Observatory's main building, in a small network around the PENC permanent station pillar. Coordinates of the micro-grid are regularly determined using a high-precision EDM instrument and precise leveling. PENC permanent station data is processed on a daily basis by national and international GNSS processing centers, providing up-to-date information on PENC point stability and the smooth functioning of GNSS systems. The calibration time of the GNSS calibration is 6 hours of continuous static measurement at one point of the network. The 6 hours of measurement is separated into 12 30 minutes periods and those are processed separately. As a result of the processing, we derive the components of the 12 vectors between the receiver to be calibrated and the PENC permanent station. We estimate their mean values, the resulting extended uncertainties and the deviations from the correct value. For each instrument calibration protocols and certificate are issued. Contact: Gábor Virág,
ETRS89 -> (EOV, EOMA) transformation
The default reference frame of the global GNSS geodesy is the actual realization of the ITRS (International Terrestrial Reference System) with X,Y,Z spatial geocentric coordinates. The current realization is ITRF2014 and within the GNSS community its slightly updated version of IGS14. In Europe by definition we use ETRS89 as reference system. Its current realization is ETRF2000, which is not completely geocentric and co-rotates with the EURA tectonic plate as estimated by the ITRF2014 solution. In order to make use of the spatial XYZ coordinates for local surveying and mapping tasks, a transformation between the national HD72 reference datum (represented by the EOV coordinates) should be used. The method developed by SGO uses the national transformation defined by the OGPSH points between the ETRS89 - EOV systems. The projection in the plane is made by the EOV projection equations, and then the residual errors from the national transformation are taken into account by interpolation within the patches of the correction grid. The height transformation is performed using the INGA points and the Hungarian HGEO2000 geoid surface.
The transformation solution is available,
- for real-time field applications, where the transformation files are installed in GNSS instruments the transformation is being done in real-time using the VITEL (Real-time Transformation Process) solution, which transforms the spatial ETRS89 XYZ coordinates into the HD72/EOV and EOMA coordinates. The VITEL database is available through GNSS equipment distributors.
- for office applications, where transformation can be done on a central server, available at eht.gnssnet.hu. Data files in the appropriate format can be uploaded to the server where the transformation takes place, and then the result file can be downloaded. The transformation can be done in both directions, and can be used for anyone free of charge.