broad topographic network of the area. The measurements were 
performed by using the modern electronic geodetic station 
Leica TC1100. The geometric correction (Hellenic Projection 
Reference System — EGSA 87) was performed with the aid of 
the trigonometric network. A total of fourteen (14) reference 
stations were calculated, measuring angles and distances in four 
time periods. 
As far it concerns the checkpoints and the gcp's network, each 
point was measured from three reference stations at least, 
measuring the angle and the distance simultaneously. Thus, the 
final accuracy of the coordinates (ox, oy, oh) corresponded to 
that of the scale map 1:50. 
The total number of the observation was processed and adjusted 
to the polygonometric network, using the least square method, 
ensuring thus the necessary accuracy and homogenity of the 
results. For the network solution, 2419 measurements were 
performed, 348 of which concerned the polygonometric 
network (14 reference stations at total), while the rest of them 
(2071) concerned the solution of check points (476 points at 
total). 
Figure 5. Network adjustment 
As a-priori errors the 50 cc were considered for the angles and 
the 0.5cm for the distances. It should be noted that the whole 
network distances were less than 20m, justifying thus the 
accuracy mentioned above. The network solution was 
performed with the least limitations, holding one top and one 
azimuth constants. The solution gave an a-posteriori error of 
1.4, which was absolutely acceptable. The corrections of the 
temporary coordinates were in the order of a few cm, while the 
final accuracy of the top coordinates was better than 5mm. 
For the adjustment of the whole network, the trigonometric 
points were considered constant during its solution, keeping the 
coordinates of their adjustment. As a-priori errors the 70 cc 
were considered for the angles and the 0.5cm for the distances. 
The a-posteriori error of 1.18, which resulted from the network 
solution justified this choice. The final accuracy achieved was 
in the order of a few mm. 
2.4 Digitisation and image orientation 
The film digitisation (scanning) was performed at the 
photogrammetric Scanner Station Leica Helava DSW100, with 
a pixel size of 12.5m. This resolution corresponds to 0.2cm per 
pixel in the mentioned image scale. Thus, the necessary image 
spatial resolution was kept for the needs of photogrammetric 
processing. 
The stereoscopic model orientations were performed at the 
photogrammetric digital station Leica Helava DPW770 and 
DVP. The models were orientated either monoscopic or 
stereoscopic with a mean square error of 1-2cm. It should be 
noted that special attention was given during the orientation to 
the peculiar geometry of each object that was captured, while 
the procedure was tested in several points with in-sity 
observations. 
2.5 3-Digital Object Model (DOM) 
The issue for the 3-D digital model was its full structure in a 
Cad environment, which should contain the whole elevation 
information of the Theatre's environment. This in conjunction 
with the 3-D graphical delineation of the preserved parts, would 
constitute the Theatre's model in space. 
A robotic system of automatic point's collector was used 
(Cyrax 2500 Laser Scanner) providing high density and 
accuracy, a fact that it would be impossible due to the complex 
construction if ground based observation was used. 
   
Figure 6. View of Cyrax at the Monument area. 
Cyrax 2500 is a Laser Scanner. Through the laser scanning 
technology it accomplishes accurate and detailed plotting of the 
scanning area and its transfer to a PC. Each laser palm receives 
a wide range of measurements, while integrated optical 
encoders record the reflection angles. The potentiality of Cyrax 
in combination with the ease of its operation and the reduction 
of time measurement determined a wide range of applications. 
Its most important technical details which led to the decision to 
use it, are: 
e Connection to a laptop (in field) 
e Range up to 150m 
e Field scanning width of 40? 
e Hundred of thousand points in 5-15 min 
e 6mm point accuracy at 50m 
*  -Immresolution (point cloud) 
e 6mm point diameter at 50m. 
The Monument characteristics with the steep slope alterations, 
the huge marble volume that constitute the stage, isolated areas 
with detailed restoration and epigraphs, created very difficult 
conditions for the successful use of traditional surveying and 
documentation approaches. 
Twenty (20) reference stations were used in order to cover the 
whole area. For each scanning, each point distance did not 
exceed that of 50-60m so that the final accuracy of the model 
would be desirable (less than 6mm). 
106 
  
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