GPS-aerotriangulation : in observation space

Abstract

The research completed on UPS-aerial triangulation has been focused on combining of UPS and photogrammetric data in the way using GPS derived antenna coordinates, so called as "combination in position space". Thus, these antenna coordinates are used, or replaced with the normal control points on the ground, as control points which have been moved into the air. It was noticed that it is necessary to use crossing strips and introduce drift parameters into the analytical aerial triangulation estimation to compensate the shifts which are seen in these coordinates, probably caused by cycle slips in the UPS data. UPS offered a good opportunity to supplement, or completely replace, the ground control required by aerial triangulation procedures by determining the positions of an antenna onboard the aircraft, at each moment of exposure, quickly, cheaply and accurately but with crossing strips, drift parameters and stand-by GPS data, postprocessed GPS data as UPS derived antenna coordinates. This thesis offers a new method which is based on a combination of GPS dual frequency phase observations and photogrammetric measurements in a bundle estimation process, so called as "combination in observation space". Thus the new method leads to the solution of the redundancy problem facing the GPS users if the ambiguities and the point coordinates (or coordinate differences) together with the other parameters are to be solved for simultaneously. It also removes the need for cioss strips to compensate for shifts in the antenna coordinates and provides a good basis for the determination of integer ambiguities and cycle slips thereby saving a lot of effort and time. To explain this concept, the thesis reviews the UPS double differencing processes based upon phase observations and analytical aerial triangulation estimation method with emphasis being laid upon estimation using bundles. Alongside these, error sources that are likely to affect the UPS and bundle measurements are discussed and the new combination method is explained. The ability of the combined system to solve for the perspective center coordinates and the attitude of the camera onboard the aircraft, the coordinates of object points and integer ambiguities and to determine cycle slips in the way it propagates several random errors were the focus of the simulated tests carried out. The tests revealed the high potential of the combined system in relation to this. Although the system may be regarded as a reasonably sensitive method to solve for these parameters simultaneously as there are some cases where some of these parameters, especially integer ambiguities, cannot be solved for correctly or cycle slips cannot be detected. This is thought not to be a disadvantage of the method itself, but is rather due to weak geornetly or insufficient observations with the small sample used. The main conclusion from this work is that a combination of GPS and photogramrnetiy is indeed possible in observation space. The advantage in that cycle slips and integer ambiguities can be solved for (i.e. photogrammetry is contributing to GPS - not just the other way around as in the usual case) and additional photogrammetric data (in the form of cross strips) is not needed. The method has been to be successful even in the presence of severe multipath (up to 5 cm).