Automatic generation of Pseudo Continuous LoDs for 3D polyhedral building model

This paper proposes an algorithm on the automatic generation of Pseudo-Continuous Levels-of-Detail (PCLoDs) for 3D polyhedral building model. In computer graphics the Continuous LoDs (CLoD) for terrain geometry or general objects means the number of triangles was changed by one or two triangles between two consecutive LoDs. Since the geometrical structure is inherently different between the continuous terrain and the sparse distributed 3D building models, the creation of CLoD for 3D building models is impractical. In this study, a group of connected/contacted polyhedrons with vertical wall were considered as "one building", thus the generalization could be applied on each building respectively. The most detailed polyhedral building model was created by the SMS algorithm using three-dimensional building structure lines which were measured from aerial photos. In a 3D visualization system, depend on the viewer's distance we can estimate a maximum distinguished "feature resolution". The feature resolution will be used to detect small 3D features in "one building". Two polyhedrons will be merged, if the height difference between them is smaller than the feature resolution. A wall will be eliminated if its length is smaller than the feature resolution. In order to maintain the building's principal structure, a piping process is necessary after wall collapsing. In an interactive 3D browsing system, since the distance variation is continuous while its corresponding PCLoD building model can thus be generated immediately. Experiment results demonstrate that the number of triangles was reduced as a function of logarithm of feature resolution. Additionally, the building's main structure can be preserved. Some case studies will be presented to illustrate the capability and feasibility of the proposed method either for regular or irregular type of buildings.