A Concept for Assignment of Textures to Partially Occluded Faces of 3d City Models Stored in Citygml

Automatic texture mapping is an important task in enrichment of the common 3D city models. A significant part of all algorithms for automated texture mapping is the visibility checking. Nowadays most algorithms for texture extraction use visibility check based on z-buffer or polygon intersection in the image plane. Thus, the visibility of particular face is calculated for every frame independently. However, in many 3D city models some polygons are modeled which can be never visible for the camera because of e.g. neighboring buildings. In this paper we discuss how the topological relations between buildings and semantics can be used for visibility checking and texture mapping. First, the influence of the automatic 3D reconstruction on the geometry and topology of the 3D city models is discussed. Then, the strategy for enrichment of the model with information about invisible faces or their parts in neighboring buildings is presented. Further, the possibilities for storage of the geometry of touching buildings are reviewed considering the CityGML standard. Finally, two procedures for storage of the invisible faces: in the geometry and in the texture are presented.