DT EI T d 
19" century. 
— 1 I 
4 ode : 5 a T $e 
Bauakademie, originally constructed under Schinkel in the 
F igure 1: Images of the reconstructed corner of the destroyed 
  
e Apparent identity of repeated features on facades, like 
brick edges. 
e Large differences in the images due to different points 
of view. 
e Large differences in the images due to different image 
acquisition times. 
e Large differences in the images due to different 
  
  
backgrounds along edges of the discontinuous 
surfaces. 
| Feature based matching techniques may also be mentioned. But ee 
| also feature based matching approaches may fail due to one or Fig 
| more of the following reasons: 
e  Insufficiently sharp defined features 
e Apparent identity of repeated features det 
e Different distribution of features due different points par: 
of view rest 
| e Horizontal linear features are difficult to determine the 
| due to images acquired from the same height. and 
use 
othe 
2. IMAGE MATCHING part 
| bety 
To cope these challenges a few principles have to be used in | acq 
image matching techniques. One is to use a hierarchical 
matching approach. An other principle is to start from a 
building model consisting of plane faces and maximum positive 
and negative deviations from these planes. This data may be 
derived from a sketch or a preliminary CAD model. 
It is recommended to use at least pre-oriented images which 
allows an object space Least Squares Matching (LSM) (Helava 
1988). The orientation of architectural images is usually not a 
big problem and may be based on interactive measurement of a 
few control points and about 10-20 tie points per image. At | 
least two control or tie points per facade should allow the 
definition of the usually vertical projection planes. 
  
Figure 2: DSM derived from a CAD Model 
1.4 Problems of Image Matching Techniques 
Image matching seems to be a suitable solution. But the area 
based matching approach fails in a lot of situations due to one 
or more of the following reasons: 
2.1 Knowledge on the Surface Structure 
e Lack of texture on facades, especially on plastered : 
faces, The knowledge of the orientation parameters and approximate 
building boundaries allows the limitation of search areas, the 
  
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