CIPA 2003 XIX"' international Symposium, 30 September - 04 October, 2003. Antalva. Turkey 
20 work hours). The huge rapid prototyping machine used was 
designed for this particular project. It incorporates three laser 
beams working simultaneously and a large basin full of resin 
(fig. 7). Although the model was made hollow, the machine was 
working continuously for five days. 
The first test over the head only, showed that the precision of 
the rapid prototyping was better than the digital model and 
therefore edges from the triangles were visible in the surface of 
the reconstructed model. Modifications over the existing 
software overcame this problem and the final model created was 
continuous. 
Figure 7. Kouros during reproduction in the basin. The three 
blue laser beams are clearly visible. 
4. COMPARISON OF SYSTEMS 
Although the two systems are complimentary rather than 
competitive, a comparison has been made using the only object, 
which could be scanned by both. The test object was Athina's 
bas-relief, sized 31.1 x 53.7 cm. 
The objective of this test was the evaluation of optical scanner's 
accuracy. Accuracy does not necessarily include occlusion 
problems and missing information. In this particular case optical 
scanner performed better in this aspect. 
Since the acclaimed accuracy of the laser scanner is much better 
than the expected from the optical scanner, it is quite safe to use 
laser’s 3d model as reference. The comparison has been done 
using the corresponding METR1S module and purpose built 
software (fig. 8). The connection between independent scans is 
apparent in some areas, but it should be noted that in this case 
the lens distortion has not been taken in consideration, hence 
deteriorating results. 
Optical 
Laser 
Independent scans/photos 
15 
30 
Post processing [days] 
2 
30 
Density [mm] 
1 
0.1 to 0.05 
Number of points in final 
model 
162000 
115000 
RMS/accuracy [mm] 
0.22 
0.01 
(acclaimed) 
Mean [mm] 
0.04 
- 
Max. residual [mm] 
0.6 
- 
Table 1. Comparison of methods over Athina's 3d model. 
Table 1 reveals that the procedure with the laser scanner is 
much slower. The number of points used in final models is 
misleading. It seems that the density of points of the optical 
scanner is better, but this is only due to the fact that the vast 
number of points accumulated with the laser scanner were 
reduced for obvious reasons. A denser grid with optical scanner 
would have been possible, provided the projector have been 
positioned closer to the object. 0.5 mm of even denser is 
feasible, but in such case the post processing time rises rapidly. 
Mean difference of 0.04 mm, shows that practically there is no 
systematic error. RMS error of 0.22 mm, which is the criterion 
for the goodness of the model, reveals that there is certain 
smoothing of the surface due to the inability of the relative 
sparse points to model the object. In any case though, the 
difference is not noticeable just by observing the model. 
In order to fully cover the comparison, it should be mentioned 
that the laser scanner is six times more expensive than the 
optical one. 
Figure 8. Athina's bas-relief. 3D model (left) and accuracy tests 
with raster (centre) and vector (right) visualization. 
5. RESULTS AND DISCUSSION 
Laser scanner on 
CNC 
Optical scanner 
Black surfaces 
- 
Difficult 
White surfaces 
Excellent 
Excellent 
Open space 
- 
- 
Max. Object size 
[cm] 
50x50x20 
Unknown 
Min. Object size 
[cm] 
Limited only by 
accuracy 
10x10x10 
Objects that 
shouldn't be touched 
Feasible 
Portability 
Portable 
Complicated 
geometry 
Very good 
Difficult 
Accuracy [mm] 
0.01 
>0.22 (tested) 
Density [mm] 
>0.02 
>0.7 
(0.4 expected) 
Processing time 
10 x optical 
approx. 
Investment cost 
6 x optical 
Table 2. Comparison of methods. Optical scanner's accuracy 
and density depend on camera and projector's 
distance respectively. 
The two systems are complementary since each one covers 
different spectrum of objects, at least in terms of size. Laser 
scanner is excellent for small objects that require high accuracy 
and density, while the optical scanner can accommodate larger 
objects, where accuracy and density are not as important, or 
relatively to the object’s size still very small.