The second phase densification of the EUREF network in Finland

摘要

The Finnish Geodetic Institute (FGI) carried out the first phase of the EUREF densification in 1996-97. The densification consists of 100 points, which were used to establish the new Finnish coordinate frame EUREF-FIN. 19 points of the EUREF-FIN network were accepted as official EUREF-points in the meeting of the EUREF sub commission in Prague, June 5, 1999. These points consist of 12 FinnRef stations; five GPS-observation pillars close to tide gauges and two triangulation points. The observations of the FinnRef network were used in the Finnish densification measurement. The results of a network adjustment were published in 2000. The second phase of the densification, comprising 344 points, were measured during the years 1998-1999 and the data processed in 2000. The points of the second phase, intended as easily used starting points for surveying and mapping, are mostly 2nd and 3rd order triangulation points of the National Land Survey, or precise levelling points of the FGI. Thus we bring the precise EUREF co-ordinates within everybody's reach over the whole territory of Finland. The new points were connected to the FinnRef stations and in many cases to the EUREF-FIN stations. The nominal observation time at the second phase observation stations was 6 hours. The common adjustment of the whole network gave the following estimate for RMS accuracy of the coordinates: ±4 mm, ±4 mm, ±6 mm for latitude, longitude and height, respectively. The results of the densification was published in 2001 in Finnish in the series of the FGI. Using the EUREF-FIN coordinates and the coordinates of the I-order triangulation stations in ED50 and ED87 systems the 7-parameter transformation was derived between these systems. The residuals of the solutions show the distortion of the I-order triangulation network clearly. Because the National Grid Coordinate system (kkj) is based on the ED50 adjustment of the I-order triangulation network the same distortions are introduced to kkj. The FGI and the National Land Survey has worked out a recommendation for using the EUREF-FIN frame in the national mapping purposes. The next recommendation will concern about the use of the UTM projection and the transformation of the grid coordinates from kkj to EUREF-FIN.