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Figure 1. Theatre view 
22 Photogrammetric Acquisition 
The photographs were taken in May, with criterion the 
distinctness of the restituted object. Advantages of the natural 
lighting and choice of the suitable time were considered so as to 
avoid shadows and samplings with different technical 
characteristics in order to achieve the best results during film 
development. 
The main problem during image acquisition was to find the best 
way for the photogrammetric camera's elevation. The initial 
plan was to use the WILD P31 metric camera, in combination 
with a vehicle having a suitable nacelle. The high elevation 
contrast of the monument (about 40m) with regards to the 
surface of the monument did not permit the implementation of 
the initial planning. 
The use of *a balloon" carrying a special construction for 
holding the camera, which should be lighter than WILD P31, 
was chosen as the best technical solution. For that reason, the 
FUZIFILM GA645W1 camera was chosen, which although is 
of a less format, it is five times lighter than WILD P31. 
  
Figure 2. Image acquisition from the balloon. 
The camera was raised to a height of 19m, while it was held 
vertically over the shooting point by special strips of variable 
length depending on the conditions. 
  
Figure 3. The rest for the camera with stabiliser. 
The critical part was that, concerning the geometry of the image 
acquisition. For that reason, the image centres (Nadir points) 
were marked so that the initial planning of image acquisition 
was followed. 
  
Figure 4. Image centre. 
Moreover the above marked centres were geodetically 
calculated so as to enable their use as ground control points 
(gcp's). Thus, there was a need for 36 more points, which were 
placed perimetric to the photogrammetric block. All images 
were acquired in colour. 
2.3 Geodetic network — calculation of GCP'S 
Simultaneously with the acquisition planning a set of gcp's 
were marked in advanced targets with dimensions 5cm x 5cm, 
in such a way that could be visible in the images. 
These points were coded according to the corresponding 
number of flight strip that they were depicted. The methodology 
that was followed for the measurement and their adjustment for 
the calculations of the coordinates was the same with that used 
for the polygonometric and checkpoints network. 
For the needs of the restitution, a net of points of high accuracy 
in horizontal and the vertical level should be measured and 
computed. The network covers a horizontal area of about 130m 
x 130m, while it was also extended to the outer sides of the 
monument which were included in the above surface. 
The network points, which include the trigonometric — 
polygonometric points and the gcp's, create a “grid” with a cell 
size of about 2—5m, covering the whole monument's area. 
Initially, there were established and materialised two (2) new 
trigonometric points in the monument's area. These points were 
placed along to the theatre's axis, in the lowest and highest 
level, correspondingly, covering in visibility the whole 
monument. 
The polygonometric network was drawn and materialised in 
such a way that would include all the surrounding points of the 
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