Role of tie points in integrated sensor orientation for photogrammetric map compilation

Direct measurement of exterior orientation parameters has been a challenge in photogrammetry for many years. Direct sensor orientation using a calibrated GPS/INS system can potentially eliminate the need for ground control points and aerial triangulation, and consequently, result in a great reduction in the cost and time of aerial photogrammetry. Previous studies have shown that, compared to conventional aerial triangulation, direct sensor orientation yields larger errors in the image and object space. It has also been shown that including a number of tie points within an integrated orientation approach can result in a reduction of errors in the image space. In this paper, the influence of the number and distribution of tie points on integrated orientation is investigated. Experiments with various numbers of tie points regularly as well as randomly distributed are presented. Results indicate that an increase in the number of tie points up to one point per model results in a considerable reduction of the errors in the image space.