A little note about portals. You seem to have not covered one case that can happen with portals. You suppose that portals are links only between the outdoor and indoor groups, while actually you can link portals between two indoor groups and maybe even two outdoors, not sure, because it is not necessary. For this case, portal directions can be a little different. See the human barn wmo or Stratholme Past for bigger reference. The direction of portals is sometimes inverted there. We are still working on the issue as we are imporving the import/export script for Blender.
