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Figure 5. Meshed model for the left door 
3.1 Data Coregistration 
The quality of the registration process, which aligns the laser 
scanner data with the imagery, is a crucial factor for the aspired 
combined processing. This registration can realized if 
correspondence coordinates are available in both systems. Since 
the accurate detection and measurement of point 
correspondences can be difficult especially for the point clouds 
from laser scanning, straight lines are measured between the 
image and the laser data as corresponding elements. These lines 
are then used by a shape matching followed by a modified 
spatial resection [Klinec and Fritsch, 2003]. The algorithm 
transforms the 3D straight lines extracted from the laser data 
and the corresponding 2D image lines, which are given by two 
points, into a parameterized representation. Then the unknown 
exterior parameters of the image are determined by spatial 
resection. In order to solve the spatial resection problem, the 
least squares algorithm-using Gauss Markov Model with initial 
values of the exterior orientation parameters is implemented. 
The extraction of straight edges from laser scanner data is 
simplified, if the required line is defined by two intersecting 
planar surfaces as it is demonstrated in figure 6. The 
corresponding edges in the digital image can be extracted 
interactively or semi-automatically based on edge segmentation. 
At least three corresponding straight lines are required to obtain 
a unique solution for the spatial resection. 
3.2 Distance Image Generation 
After the camera coordinates and orientation parameters are 
registered in the laser scanner coordinate system, the 
collinearity equations are applied to generate a distance image 
based on the available point clouds. For our exemplary scene, 
the point cloud was collected from a close viewpoint resulting 
in ] cm average resolution. The distance images were generated 
with the same number of pixels of the corresponding images 
(1536x2304 pixels). 
  
Figure 6. Two intersecting planar surfaces, one of them is 
represented by grid lines for demonstrating 
purposes. 
  
Figure 7. The distance image of the left door projected on the 
corresponding image. 
For the left door of Al-Khasneh, three distance images were 
generated for the three images available from different camera 
stations. Figure 7 depicts one of these distance images projected 
on the corresponding image.