Thomas Vögtle 
  
  
(a) (b) (c) (d) 
Figure 8: Segmentation of roof planes: (a) L-shaped hip roof, (b) flat roof, (c) complex shape, (d) hip roof; 
upper row: vegetation reduced laser scanner dDEM of buildings (see section 3.2) 
lower row: resulting segmentation of roof planes 
Before performing this intersection of two neighbouring planes it has to be verified, if there is a significant elevation 
difference at the edge of these two planes. To avoid disturbances single rejected pixels around this edge (caused by 
dormers, chimney etc.) are eliminated by a simple majority decision out of the N8 neighbourhood. In the case of 
significant elevation differences, a vertical plane has to be introduced. The position of these vertical planes can be 
estimated by an adjustment procedure based on the respective edge gradients in laser DEM. Hence, the intersection 
process provides two contour lines of the same x, y position but different elevation levels. The resulting contour lines 
and corner points built up a 3D wire frame model of the building (CAD model). This could be subsequently processed 
for various purposes, e.g. numerical applications, statistics or visualization. 
  
  
  
NV 
bii 
Figure 9: Reconstructed buildings as wireframe models in vertical and perspective view; 
test building 1 (left side) and 2 (right side), compare Figure 8 (a) and (d) 
   
  
  
  
  
  
  
  
  
  
  
The results of determination of contour lines and corner points are shown in Figure 9 as wireframe models in vertical as 
well as in perspective view. It is obvious that the geometry of the buildings has been reconstructed correctly and 
completely according to the result of the segmentation process (see section 4.1). At corner points where more than three 
detected planes intersect, ambiguous solutions occur. In this case an adjustment has to be performed regarding the 
probabilities of each plane. These probabilities have been already been estimated during segmentation process, derived 
from the membership probability of each pixel to the respective plane. On the other hand, this fact enables the 
estimation of the interior accuracy of the presented method. First experiences with building modelling in our test areas 
have resulted in an accuracy of about +/- 0.2m to 0.3m in position and about +/- 0.05m to 0.10m in elevation. 
  
932 International Archives of Photogrammetry and Remote Sensing. Vol. XXXIII, Part B3. Amsterdam 2000.