In order to restrict our method to architectural structures of
interest, we only consider vertical regions as potential wall
patches. Thus, we only consider patches for which jn vupjoϵ,
where the patch normal n is computed using Principal Component
Analysis (PCA). This effectively rules out other flat structures like
tables. We also discard small cluttering patches for which the
horizontal extent (i.e., the longer of the two horizontal sides of
their OBB) is smaller than 40 cm.