PRECISION AND RELIABILITY OF GPS-COORDINATES OF PROJECTION CENTRES IN REAL AERIAL TRIANGULATIONS

摘要

The aim of this study was to determine the precision of GPS-coordinates of projection centres obtained in photogrammetric production in Poland. The second aim of the work was to estimate the reliability of this group of measurements in aerial triangulations performed for three scales of aerial photographs. The study was based on repeated processing of data from production blocks, in comply with conditions of a correct adjustment. Adjustments were preceded by the pre-adjustment detection of gross errors and improper division of data into GPS profiles. Production results originated from various measurement systems and adjustment softwares; and they were characterized by numerous imperfections related to functional and statistical model and being generally the result of the applied technologies. A set of 25 blocks was selected for testing, including three scales of aerial photographs: 1:13 000, 1:19 000 and 1:26 000, most frequently used in Poland. Number of photographs in one block varied from 136 to 3402, and the total number of photographs in all blocks was about 30 000. The corrected a priori standard deviation of GPS-coordinates obtained from 25 adjustments reached 10.7 cm on average. The analysis of global internal reliability of GPS-coordinate for particular scales revealed that in blocks of photographs at scale 1:13 000 the average redundancy numbers reached 0.50 for X, 0.48 for Y and 0.75 for Z coordinate. So, it can be concluded, the reliability of GPS-coordinates of projection centres in these aerial triangulations was good. For scales 1:19 000 and 1:26 000, in 9 blocks out of 15 the global redundancy numbers of horizontal GPS-coordinates were lower than 0.25.