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CIPA 2003 XIX th International Symposium, 30 September - 04 October, 2003, Antalya, Turkey 
3.2 Problems that can be solved by readjusting the 
stereomodel 
3.2.1 Problems due to innacurate planimetry or DEM errors 
Erros in the DEM are shown most of the times very clearly in 
the orthophoto. One extreme value or a spike in the DEM may 
cause the whole result to be disturbed. By editing the parallax 
value of a single matched point or for a group of matched points 
this may be corrected. 
3.2.2 Problems due to doors and windows in the wall 
When making a DEM and an orthophoto of a wall, it may occur 
that parts of the images that are used, show the surface that is 
behind the wall. In some cases this is another wall, in other 
cases this may be the air. Either way, this causes large spikes in 
the DEM. The figures below show the effect of the spikes in the 
orthoimage. 
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1:jm 
Figure 7. Example of a DEM with spikes and the according 
orthophoto 
In the areas where spikes occur, the matched values are given 
the same height as the parts of the wall that surround the area. 
Off course, the part of the image that displays the inner part of 
the window will be shown deformed in the orthophoto, or as a 
double image, but the wall of which we want to obtain the 
orthophotoplan is no longer influenced by them. 
Figure 8. The DEM corrected for spikes and the according 
orthophoto. 
4. CONCLUSION 
The total outcome of the project is 14 orthophotoplans, made of 
30 stereopairs. The main part of the inner side of the transept is 
on 9 plans and the 5 remaining cover parts of the outside. No 
plans could be made of the chancel. 
The full coverage of the transept was not possible due to the 
inclination of some stereopairs in combination with the quality 
of some of the GCP. 
The reason why no plans are made for the chancel is the way 
the photographs were taken for this part. Where the stereopairs 
for the transept followed the modular structure of the building, 
this is not the case in the chancel. This means that for walls that 
are in different planes, a different stereopair is needed. In april 
2003 a new project on this site started, in which plans for the 
chancel will be made, and where the photograps are taken 
perpendicular to the walls, and follow the modular structure of 
the chancel. This project is done under commission of the 
Buildingsagency of the Belgian federal government