Direct sensor orientation based on GPS network solutions

Direct sensor orientation, i.e. the determination of exterior orientation based on GPS and inertial measurements without the need for photogrammetric tie points, has gained considerable popularity over the last years. One pre-condition for direct sensor orientation is a correct sensor and system calibration. The calibration can only be carried out by a combination of a photogrammetric solution and a GPS/inertial solution, which is equivalent to the concept of integrated sensor orientation. In the work carried out so far, GPS has been identified as the most critical part in terms of achievable accuracy. Strategies for improving differential GPS results are available for terrestrial applications, but have not yet been used in direct and integrated sensor orientation. One of these solutions consists in using a network of reference stations rather than a single station only. In this paper we present our work on direct sensor orientation using a GPS network. After describing the related mathematical models we report the results of an experimental test. The test data were drawn from the OEEPE test “Integrated sensor orientation”. The results show, that while for many applications a network may not be necessary in case of short baselines and good GPS data, it still improves the accuracy of direct sensor orientation to some degree. More important is the fact, that our approach is able to detect gross errors in the reference station data and therefore has the potential to improve also the reliability of the results.