Documentation of the Palmyrene Tower-Tombs in Syria ... 
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when each image was introduced with separate interior orientation. The only way to proceed was leaving the motor zoom at its initial 
position and introducing one single set ot interior orientation parameters. Images from the réseau camera served as reference images. 
It can be concluded that a digital non-metric camera (especially when it is equipped with a motor zoom) is suitable for certain duties 
only and when high precision is not of main interest. The error in the object points was 4 cm (RMS). The effort of measuring 
reference points via a geodetic survey may not be justified in this case. It turned out that even the geometric constraints could not 
help to improve the results. A suitable digital camera should have a fixed focus and should be calibrated in advance [Brail, 2000]. 
3.4 Stereoplotting 
The production of 20 facade maps at scale 1 : 50 
was done with the analytical plotter DSR 11. The 
“old-fashioned” analytical plotter was chosen for 
reasons of reliability and existing operator 
experience. However, one of the results of this 
project is that digital stereoplotting will be 
applicable for future projects, too. 
Stereoplotting becomes possible if an orientated 
stereo pair of two overlapping images is 
available (stereo model). With the analytical 
plotter the stereo model can be seen in 3D. 
Digital systems use polarization systems for the 
same purpose and the operator needs polarized 
glasses for observing the screen that displays the 
stereo model. 
The operator is able to move around in the stereo 
model with a 3D-cursor, digitizing points, lines 
and polygons on the object. 
It was intended to measure all visible elements 
on each facade. The result of this task was a raw 
facade map. Figure 2a shows as an example the 
southern facade of the tower-tomb of Elahbel. 
The stereo restitution was done by photo- 
grammetrists. Generally they do not have 
profound archaeological knowledge. As a result 
the raw facade maps reflect only a geometric 
interpretation of the stereo model. Therefore it 
was necessary that a subsequent archaeoogical 
interpretation was done by an archaeologist. This resulted in a manually drawn facade map showing extracted features which are 
archaeologically relevant. For example, after this step it is possible to distinguish reconstructed parts of the building from original 
ones. Figure 2b gives an example of a final facade map (tower of Elahbel, southern facade). 
3.5 Digital surface models 
Two different ways have been investigated to create a digital surface model (DSM) of a facade. The capability of the tool TopoSurf 
from Phodis was examined first. The basic data for this examination was a stereo-pair of the southern facade of the tower of Elahbel 
captured with the analog camera TMK.6. Because of the distinctive texture of the building high quality was expected for the 
automatically DSM calculation. The only manual step was the measurement of the different edges of the tower. Unfortunately 
problems turned out by handling the program TopoSurf. Calculation was possible only without regarding the polygons of the edges. 
Besides the coordinate resolution was limited to 10 cm by the software. This problem is caused by the fact that Phodis was created to 
analyse aerial views only. It might be possible to change the scale of the coordinate space to get a higher resolution on the surface, 
but this was not pursued further. The results of the automatic calculation of a DSM with TopoSurf were not satisfying. The second 
approach was to calculate the DSM from convergent images with Pictran. After getting rid of some problems with the software we 
got a useful DSM. In contrast to TopoSurf the software Pictran was designed for terrestrial and close-range applications and turned 
out to be much more suitable in the actual case [Priimm 2001]. 
3.6 Orthoimage production 
An orthoimage can be defined as a pictoral depiction of an object derived from photography in such a way that there are no 
displacements caused by imaging effects. An orthoimage is hence equivalent to a planimetric map except that, instead of lines and 
symbols, image tonal variations convey the information [Anderson, Mikhail 1998]. 
Orthoimage production is widely used with aerial images. Here the X and Y axes of a terrain reference system define the plane onto 
which the orthoimage is projected. This plane is in fact always predefined in aerial applications. For terrestrial and close range 
applications such a predefinition does not exist. Here projection planes are related to individual objects and can be orientated 
anywhere in the three dimensional space. 
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