Efficient Break Line Extraction and Cad Data Generation to Historical Wall Using Surface Flatness

Recently, laser scanning has been receiving greater attention as a useful tool for real-time 3D data acquisition, and various applications such as city modelling, DTM generation and 3D modelling of cultural heritage sites have been proposed. However, robust filtering systems for distinguishing onand off-terrain points from 3D point-cloud data collected by an airborne laser scanner still have many issues. In particular, the filtering of 3D point-cloud data collected by a terrestrial laser scanner has severe problems caused by a large number of occlusions, few deep points, and due to the presence of windows, building walls, and so on. Addressing these issues, a robust filtering and break-line detection method using surface flatness has been developed by the authors in 2004. However, the method requires CAD-data generation. This becomes a particularly serious problem in break-line utilization for various objects. In order to perform CAD-data generation, an efficient CAD-data generation method is described in this paper.