In the first phase of our method we extract a set of planar
patches from the input 3D point clouds that correspond to
candidate walls. We first grow planar regions in the 3D point
cloud, and to keep only segments which potentially correspond to
candidate walls, we select only those regions that are classified as
vertical. A lightweight 3D occlusion check is used to further prune
the vertical patches, discarding those that have a low unoccluded
vertical extent