Automatic aerotriangulation with frame and three-line imagery

In this paper an approach for automatic aerotriangulation (AAT) is presented, which is designed for frame and three-line imagery. We will focus on the extraction of conjugate points, because the geometric differences in geometry of frame and three-line imagery can be considered as well-known and are only different modules at the implementation stage. Our approach uses point features and a coarse-to-fine strategy based on image pyramids. To extract conjugate points we employ feature-based matching of image pairs on all pyramid levels. After matching all overlapping pairs of images, manifold conjugate point tuples are generated and checked for geometric consistency individually as well as in their local neighborhood. Subsequently, the exterior orientation parameters for the whole block are calculated on each pyramid level in a robust bundle adjustment together with 3D-coordinates for the conjugate point tuples in an arbitrary reference system. This information serves as initial values on the next lower pyramid level. Control information is not necessary a priori, but can be introduced at any stage of processing. The approach has been tested with various imagery. A few hundred well distributed conjugate points were extracted in all cases. In particular, a large number of many-ray points, which are essential for a stable block geometry was detected. The standard deviation of all image coordinates lies between 0,3 and 0,4 pixels. These results constitute a proof-of-concept and demonstrate the feasibility of the presented approach.