The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences. Vol. XXXVII. Part B3b. Beijing 2008 
Figure 13: 3D Model merging protrusion and excluding indenta 
tions 
6 DISCUSSION 
In this paper an automatic approach for reconstructing models in 
three levels of detail is proposed based on LIDAR data. The mod 
eling approach deals with buildings which are formed by combi 
nation of flat roof, gabled roof as well as hipped roof segments. 
The example used in the previous section to illustrate our devel 
oped algorithms shows that our concept for building reconstruc 
tion works quite well. A strength of this projection based ap 
proach is its robustness and that it is quite fast because projection 
into 2D space reduce the algorithmic complexity significantly. 
(a) Building reconstruction be- (b) Building reconstruction after 
fore adjusting the nodes adjusting the nodes 
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els by analysis of aerial images, digital surface models and exist 
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Figure 14: Another example for projection based building mod 
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ACKNOWLEDGEMENT 
The authors are grateful to the BMBF for supporting this research 
within the project “ Automated Object Extraction from Airborne 
Laser Scanning Data ”. 
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