For the area ground truth data in form of a 2D map provided by the German land registry office (Katasteramt) is available. This map contains the buildings with a precision of 1 cm. In addition, we obtained airborne based 3D data. Based on this data so-called reference data is generated as follows (see Figure below): The 2D map is extrapolated to 3D by vertical 3D points and fused with the 3D data from the airplane. The result is a precise 3D reference map. Using this 3D reference map, we generate ground truth poses for all 3D laser scans by matching the scans with the reference map.
(via Robotic 3D Scan Repository)