Undersökning av kvaliteten av bytet av geodetiskt referenssystem i Ljusdals kommun : Jämförelse mellan passivt och aktivt referensnätverk

Sammanfattning: The municipality of Ljusdal changed geodetic reference system from RT R10 2,5 gon V 0:–15 to the new system SWEREF 99. The technical management had an intent to test the quality of the transformation of coordinates which became the purpose of this thesis. A comparison between the formerly known coordinates and plane coordinates, measured at the same points, was carried out.   The equipment in use consisted of a GNSS-receiver of the type Leica GX 1230+GNSS and an antenna of the type Leica AX 1203+GNSS. It was an ambition to manage to measure as many as possible of all the geodetic network points which were located in the densely built-up area of the village of Ljusdal. The measurement efforts were accomplished at 37 points and was pursued during the summer and autumn 2011.   119 series of measurement were accomplished. The result was a weighted average and its standard uncertainty for the coordinates N and E for all of the 37 points. These weighted average values were subtracted by the known value which resulted in a coordinate difference for N, E and radially for all of the 37 points. A root mean square (RMS) value was determined for all coordinate differences in N, E and radially. RMS for the N-coordinates was 9 mm, for the E coordinates it was 11 mm and radially, RMS was 14 mm. That radial RMS value was just slightly bigger than the uncertainty attached to the network RTK-method used in the project. All RMS values are low compared to their analogue data in previous studies.   There were two distinguishing features in results of the survey campaign. Firstly, there was a systematic error in the direction southwest. Secondly, surprisingly low values for the standard uncertainty were achieved. If there was a slight damage on the tripod, that may be an explanation of the systematic error. That could have been detected if the calibration would have been carried out at many more occasions and if the results of the calibration would have been treated in a more rigorous way. One special circumstance may explain the low standard uncertainties – the survey campaign was allowed to take longer time than is usual in professional surveying. Many attempts to measure a point were disrupted due to bad constellation of the GNSS-satellites on the sky. These unsuccessful attempts were resumed at many times. Survey data from four of the points showed big coordinate differences for one direction in all or most of the series of measurement. These four points may have been subjected to deformation.   There are strong reasons to assert that the coordinate transformation of the municipality of Ljusdal gave a good result.