Hardware-based Texture Extraction for Building Façades

The reconstruction of 3D city models has matured to the point where large data sets are now available. As most of the data collection methods used are based on airborne sensors like e.g. aerial laser scanning or stereo imagery, the detailed geometry and material of the building façades is typically not available. For visualisation purposes, however, the surface structure is essential to achieve a good visual impression of the respective buildings. An efficient technique to provide the missing building façades is to extract texture images from terrestrial photographs and map them to the polygonal faces of the reconstructed models. As the task of manual texture extraction and placement is very time-consuming, an automatic approach is presented in this article that utilises the rendering pipeline of modern 3D graphics cards. The problem of texture extraction can therefore be solved by using graphics algorithms that are nowadays implemented in hardware and consequently are extremely fast. Since only parts of the building or even of a façade are typically captured in one single image, self occlusions of the buildings are detected and several photographs taken from various positions are fused to generate the final texture images. In order to gain high quality textures, the lens distortion of calibrated cameras is corrected on-the-fly by the use of pixel shaders that are running on the programmable graphics processing unit.