Dense Local Azimuth-Elevation Map for the Integration of GIS Data and Camera Images

The integration of outdoor camera images with three-dimensional (3D) geographic information on the observed scene has an interest in many applications of video acquisition. To solve this data fusion problem, camera images have to be matched with the 3D geometry provided by the geographic information system (GIS). This paper proposes to use, for a camera of known geographical position, a dense local azimuth-elevation map (LAEM) derived from a gridded digital elevation model (DEM) as data representation to ease the matching operation between GIS data and the image. Such a map assigns to each regularly sampled azimuth and elevation angles pair the geographic point derived from the DEM viewed in this direction. The problem of computing the LAEM from the DEM is closed to the problem of surface rendering, for which solutions exist in computer graphics. However, rendering software cannot be used directly, since their view directions are constrained by the pin-hole camera model and apparent colour rather than position of the viewed point is assigned to the viewing direction. This paper therefore also proposes a specific algorithm for the computation of the LAEM from the DEM. A MATLAB implementation of the algorithm is also provided, which is tailored to process the DEM data set swissALTI3D from the Swiss Federal Office of Topography swisstopo.