Updating Camera Location and Heading Using a Sparse Displacement Field Report LiTH-ISY-R-2318

This report describes the principles of an algorithm developed within the WITAS project [3]. The goal of the WITAS project is to build an autonomous helicopter that can navigate autonomously, using differential GPS, GIS-data of the underlying terrain (elevation models and digital orthophotographs) and a video camera. Using differential GPS and other non-visual sensory equipment, the system is able to obtain crude estimates of its position and heading direction. These estimates can be refined by matching of camera-images and the on-board GIS-data. This refinement process, however is rather time consuming, and will thus only be made every once in a while. For real-time refinement of camera position and heading, the system will iteratively update the estimates using frame to frame correspondence only. In each frame a sparse set of image displacement estimates are calculated, and from these the perspective in the current image can be found. Using the calculated perspective and knowledge of the camera parameters, new values of camera position and heading can be obtained. The resultant camera position and heading can exhibit a slow drift if the original alignment was not perfect, and thus a corrective alignment with GIS-data should be performed once every minute or so.