Urban scene rendering using object description

We propose a method for the synthesis of urban areas based on a description of objects in the scene. Using Digital Elevation Models (DEM) and aerial pictures, we extract the objects in the scene and model them by simple geometric shapes. The extraction process is described for three groups of objects: buildings, roofs and trees. The reconstruction of buildings is based on a statistical approach developed within the Ariana project in which a marked point process is defined, whose points represent buildings. The marked point process is determined by two elements: a prior using interactions between points to model the knowledge we have about urban areas, and a data model to enforce coherence with respect to the DEM. For the treatment of the roofs, we adopt a strategy which consists of detecting intersection lines between roof planes. The ridges are extracted from the DEM by means of image filtering, morphological operations and a Hough transform. For the extraction of trees, we compare colour information from aerial images and height information from the DEM to select the zones of high vegetation corresponding to trees. Then, mathematical morphology techniques are used to refine the selected zones. Finally, the zones are filled according to a randomized algorithm with circles of fixed radius that model individual trees. Furthermore, in order to evaluate the previous techniques and to experiment with this object-oriented approach in image synthesis, we have developed a graphical tool allowing 3D rendering of urban scenes with the possibility to move around the scene and to interact with the environment. Tests have been conducted on DEMs of the city of Amiens kindly provided by the French Mapping Institute (IGN).