Extracting Windows from Terrestrial Laser Scanning

With the high density point clouds obtained with terrestrial laser scanning, detailed building facade structures, such as windows, can be recovered. There are usually only a few laser points available for windows, because window frames are small parts on walls, and window glass reflects no laser beam. Insufficient raw laser information makes it very difficult to recover reliable geometry of a window without human interaction. In this paper, we describe an approach to automatically extract windows from terrestrial point clouds. First, a segmentation process will group laser points in planar segments. Walls, doors and extrusions will be detected by applying feature constraints. Then, two detection strategies for windows are presented, depending on whether a window is covered with curtains or not. Windows which are not covered with curtains reflect no laser beam during the scanning process, and therefore cause holes on the wall segments. Laser points are available for windows which are covered with curtains, but they usually are not on the same plane as its wall and will therefore be grouped into other segments than wall segments. This again results in holes on wall segments. Holes on the wall are recognized by searching long edges from the TIN, generated for wall segments. After filtering out the holes caused by doors and extrusions, the remaining holes are believed to be caused by windows, and hence fitted to rectangles. The result from our approach is evaluated and discussed with examples of reconstructed building facades.