Cl PA 2003 XIX th International Symposium, 30 September - 04 October, 2003, Antalya, Turkey 
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These initial problems were rather easily solved using larger 
overlaps, which strongly reduce sliding and provide much better 
positional accuracy. Better selection of photographs depending 
on the angle of view for each side overcomes the problems of 
small deformations. Similar work with stereo pairs and a stereo 
plotter would probably had better results in terms of accuracy, 
but time for triangulation, on site photography and control 
measurements, along with manual collection of points would 
exceed 70 hours (10 pairs). Hence time and cost savings are 
obvious. 
Figure 5. Ygeia's head, scanned twice. Small deformations and 
a significant change of size and shape are noticeable. 
3.4 The special case of Kouros 
Kouros was a special case considering the volume of data, the 
size of the object (1.86 m) and the reproduction scale of 1:1. A 
plaster copy was provided by ARF (Archaeological Receipt 
Fund). Photography took place in ARF's laboratories. 
It must be noted that more complex geometries were tested (two 
statues from Bremen Museum, sized 1.4 and 1.6 meters 
respectively). Photography took place in site, but during 
processing undercuts and extending arms made modelling 
almost impossible. That’s the reason Kouros was finally 
selected for testing. 
3.4.1 Photography 
The body of Kouros is of rather simple geometry (fig. 6) but it 
is necessary to maintain characteristics in detailed parts, such as 
head and feet. Hence two different densities were used. 441 
digital photographs were acquired in two days. Ten different set 
ups of camera and projector were required in order to cover 
every part and aspect of the object. Setting up the projector so 
that the grid is dense enough and well focused, in conjunction 
with the well focused camera covering as mush of the area and 
keeping imaged grid crispy, was the most time consuming 
procedure. Since a replica of the original was used, it was quite 
easy to handle and rotate it (fig. 2). 
3.4.2 Computer Processing 
In the beginning of the processing a clear problem has risen. 
Lens distortion was not mathematically modelled within the 
software and therefore the digital model appeared curved (fig. 
6). In order to overcome this problem, distortion correction has 
to be taken into consideration prior entering the images into the 
software. 
Lens distortion forces straight lines in real world to be imaged 
as curves in the photograph. Therefore if a number of straight 
lines are photographed, then is it possible by measuring points 
on them over the image to calculate the lens distortion 
parameters (Karras et al., 2001). The straight lines of the grid, 
when projected over a flat surface should remain straight. That's 
the case with the calibration box, which has two flat panels, and 
therefore the projected grid should remain straight over each 
panel. This information can be used for a pre calibration of the 
images (Sechidis et al., 1999), which could be applied in order 
to produce new “calibrated” images. 
It must be noted that the photographs record the result of two 
lens distortion effects; one from the projector over the object 
and a second one from the camera itself. In the general case the 
combination of these two lens distortions cannot be combined 
under the single lens distortion mathematical model. Since 
development of new lens distortion models was not the purpose 
of this project, the simplified model used managed to improve 
the 3d model (fig. 6). 
The lens distortion was being calculated by the straight lines in 
the calibration image and then applied in all photographs of the 
particular set-up. 
Figure 6. Kouro's digital model prior (left) and after (centre) 
lens distortion correction, along with the 
reconstructed model from resin (right). 
For the final model 98 images were used for an equal number of 
independent surfaces. Processing the full model with one 
million points was not an easy task for the software, and 
therefore the final manipulation of small gap filling, refinement 
and stitching has been made externally. Since sliding along the 
independent parts was a clear danger, the digital model was 
measured in height, to ensure that there will be not essential 
difference. The four millimetre difference measured from the 
original (measured with tape) is negligible and cannot be 
observed even by experts. 
One million points correspond in an average density of 1.3 mm. 
Density in the head and toes was 0.7 mm, while on the body 
was up to 1.5 mm. The final file in stl format has been send for 
reconstruction. Since a number of problems have been 
confronted during this project, it is impossible to have exact 
time data. A crude estimation for a complete re-built of the 
model is about 50 workdays. 
3.4.3 Physical reconstruction 
Physical reconstruction needed extra post processing in order to 
translate data for the rapid prototyping machine (approximately