Feasibility of Facade Footprint Extraction from Mobile Laser Scanning Data

Terrestrial laser scanning provides valuable information for building outlining, facade detection and building reconstruction. Especially mobile laser scanning (MLS) is considered as well suited to collect 3D point clouds from building facades along road corridors for large areas. However, the completeness of facade representation in MLS has to be investigated in order to be able to draw conclusions about the usability of this kind of data sets for further applications such as building facade modelling. We investigate the detection rates of a fully automatic point cloud processing method for extracting building facades from MLS. The point cloud is segmented into planar regions, from which vertical structures are extracted. The detection rate is assessed by comparing the detected facade footprints with visible building outlines extracted from a digital cadastre map. The completeness of the extraction is investigated regarding the facade structure, length and the distance of the facades to the vehicle trajectory. It was found that the representation of facades extracted from MLS and the cadastral map might differ if very short facade parts (<2 m) representing jutties are present on the ground level floor. This leads to an underestimation of completeness. Moreover, it can be shown that there is a direct relationship between further characteristics, e. g. that long facades and facades near to the vehicle are more likely to be detected than others. Facades with a length between 10 m and 20m reach a completeness of 74%. Most facades are found in a distance of 10-20 m from the vehicle where the completeness ranges from 71% to 50%. The low completeness can be explained by occlusions from moving objects and vegetation, the facade structure, orientation and its complexity. The comparison with digital cadastral data shows that MLS is not that well suited for the detection of building facades as one might expect.