Techniques for improved CityGML models

Abstract

This paper deals with some techniques that can be used to improve quality and geometric consistency of data driven 3D city models. It focuses on two practical tasks with respect to roof polygons: finding better edges and planarization. To increase the quality of edges, models are merged with true orthophotos and cadastral data. With mixed integer linear programs, the number of right angles and symmetry are maximized. Linear optimization problems also help to correct non-planar roof facets and to avoid artificial step edges within roofs. Since these methods change the positions of vertices, self-intersections of polygons have to be healed, and building walls have to be re-arranged. The techniques focus on roof geometries that can be represented in 2.5D. In general, this is true for CityGML models in level of detail 2 that do not have detailed facades or overhangs. However, techniques can also be adapted to other 2.5D modeling tasks.