Automatic room segmentation: This step is performed entirely in
the 2D projection of the xy-plane. First of all, projected candidate
walls are clustered to get a smaller number of good representative
lines for walls. Secondly, a cell complex is built from the intersections of the representative lines and its edges are weighted
according to the likelihood of being genuine walls. Diffusion
distances are then computed on the cell-graph of the complex
and they are used to drive an iterative clustering of the cells that
extracts the separate rooms.