Technology development for GPS-Heighting in Hungary

During the last few years considerable research work was focused all over the world on the introduction of the GPS technique into heighting works. Although the accuracy of GPS-heighting is still well below that of spirit levelling can provide (at least on short to medium distances), the Iower order levelling could be a potential and promising deployment of GPS. In Hungary the research work was supported by practical considerations as well. The Hungarian Levelling Network is not fully completed, in the western part of the network only the 1st order lines had been measured some 20 years ago. The completion of the network is an important task for the next future. In September 1998 a GPS test campaign was performed within a carefully selected 2nd order levelling loop, where 34 benchmarks, selected from all the included 3rd order lines were measured. The GPS data were processed by BERNESE 4.0 and GPSurvey 2.1 softwares. The GPS-derived ellipsoidal heights had been transformed to normal heights using an improved local GPS-gravimetric geoid solution. The comparison of the levelled and "GPS-levelled" heights were shown extremly good agreement. Based on these experiences a refined technology had been elaborated, which was offered to use in the future 3rd order levelling works in Hungary. The technology had been discussed within the community of the responsible authorities, institutions and companies and had been accepted as an official technique for the future 3rd order densification of the levelling network of Hungary.