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International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol XXXV, Part B3. Istanbul 2004 
  
The footprints from the technical feature map do not always 
cover the individual buildings. Sometimes a whole building 
block is grouped in a footprint, which is not desirable. As 
previously mentioned, there is no detection of height jump lines 
in the algorithms and consequently, units must contain as few 
height jump lines as possible. 
By cutting the raw footprints with polygons of cadastres, it is 
possible to reduce the frequency of height jump lines 
considerably. Furthermore, it is desirable to remove very small 
footprints, because the reconstruction of these is likely to fail 
due to the low resolution of the laser scanning. All footprints 
less than 50 m? are removed. 
7.2 Fixing displacements of data sets 
Unfortunately, the data sets of the technical feature map 
containing footprints and the 1x1 meter grid laser scanning are 
not aligned. The displacements are up to 1.5 meters. However, 
the displacement can be calculated numerically, by setting up a 
cost function D(x, Vai,) expressing a cost of displacing the 
footprint by x, and y;,, along the x and y axes, respectively. 
wisn 
D(x , Vas, ) = > E (£a "i Inside( Zi; oos y (5) 
disp 
i=l j=l 
where: 
® Z.ax 1S the maximum elevation in the source point 
cloud. 
*  zjisthe elevation at point (xi, yj) with / e (1,2,..,mj 
andj € {1,2,....,n}. 
e mis the number of samplings along the x axis. 
e nis the number of samplings along the y axis. 
e Inside(Z;j), qi, qi; 1$ a function that returns the input 
value z;; if the sampling point (x;, y;) is inside the 
footprint displaced by xg, and yg, . Else it returns 
Zm ax: 
The task is then to find the displacement (Xgisp, Yaisp) Which 
generates the minimum cost, which is done by displacing the 
footprint in small steps along the x and y axes in the local ares 
of the building. 
In order for the numerical displacement to be successful, it is 
important that buildings to be displaced are isolated from 
neighbouring buildings. There should be a certain gap to the 
closest neighbour (in our case a gap of 2 meters is sufficient). 
Neighbouring buildings must be grouped before the 
displacement of the group as a whole can be determined. 
8. REFERENCES 
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Faces in Very High Density Height Data. International 
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Vosselman, G. and Dijkman, S., 2001. 3D Building Model 
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Hough, P.V.C., 1962. Method and Means for Recognizing 
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Haala, N. and C. Brenner, 1997. Generation of 3D city models 
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Schindler, K. and Bauer, J., 2003. Towards Feature-Based 
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Barequet, GG. and Subodh, K., 1997. Repairing CAD Models, 
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