CIPA 2003 XIX th International Symposium, 30 September-04 October, 2003, Antalya, Turkey 
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Figure 3. Details from photographs used during orientation and 
grid detection for surface reconstruction. 
3. TESTS ON OBJECTS 
3.1 Initial remarks 
Both scanners collect a large number of 3d points. In each case 
these points are correctly scaled, but positioned in the scanner's 
coordinate system. This means that the independent point 
clouds need to fit together and then stitched in order to produce 
a full 3d model. 
Provided there are common areas between scans, the point 
clouds are manually placed together crudely and the system can 
automatically calculated the best fit. This technique is quite 
different in photogrammetry, where the position of the 
independent models is being calculated precisely during the 
bundle adjustment and therefore points are calculated directly to 
the control point system. If a linear object is to be modelled 
using a scanner and the independent point clouds are being 
connected afterwards, it is quite possible that the final model 
might not have the exact size nor be straight enough. Therefore 
misalignment between scans is dangerous and might lead to 
erroneous models, especially since it is being applied additive. 
In this aspect photogrammetry with its homogeneous accuracy 
is advantageous. 
In any case the final points were used to create a triangulated 
surface. Optical scanner’s software supports these kinds of 
operations, but it is a closed box, in the sense that it does not 
allow import other than the processed images. Laser scanner's 
software controls the machine and can only store the points. 
Since the number of collected points is huge, another important 
feature of such software is the ability to manipulate and reduce 
points based on their importance over the surface. Points are 
erased based on their local derivatives; hence flat areas become 
sparse while irregular areas keep necessary information. 
• the fact that you need to touch the object in order to 
rotate it under the scanner, 
• the fact that the system is not portable means that the 
object has to be transferred to the scanner. 
It is quite obvious that many museums will not give away their 
exhibits and archaeologists will not be very happy seeing 
artefacts sprayed. 
On the other hand, accuracy (10 um) of the specific system is 
excellent, and the density of points unsurpassed (5 um is 
possible but noise is discouraging). 
A variety of small objects from coins to small figurines and bas- 
relief, were scanned using the laser scanner and most of them 
were reproduced using resin. 
Figure 4. Eros and Psyxi. Laser scanning, replica and final 
model, created using 15 independent point clouds. 
Figure 5. Cycladic figurine. Replica used and final model, 
created using five independent point clouds. 
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3.2 With the laser scanner 
The laser scanner procedure also seems quite straight forward, 
but there are a number of limitations and key factors.. 
Since lenses are involved, depth of field is a crucial factor. If 
the side to be scanned is quite planar with small relief there is 
no problem (fig. 5). If the object to be scanned is complicated 
with big relief (fig. 4) then two or more scans over the same 
area are necessary. The fixed focusing distance is 5 cm and the 
depth of field ±0.5cm. 
The main disadvantages are: 
• the time required to make a single scan, 
• the need to spray the object for better results, 
• the CNC's operational area sets size limitations, 
3.3 With the optical scanner 
The optical scanner is designed for fast, easy collection of 3d 
models for a wide range of sizes. It has been used to scan 
objects from 20 to 186 cm. If combined with a digital camera, 
which allows in site checking of object coverage and excessive 
gathering of photographs with no cost, the system becomes 
versatile, fast, portable and quite robust. 
Following the rule that nothing is as easy as it seems, it soon 
became apparent that if accuracy is expected the procedure must 
be exercised with extreme caution. Scanning twice the same 
object with a digital camera and a video camera revealed that 
the system was designed for speed and versatility rather than 
accuracy (fig. 5). It must be noted thought that these models 
were created within 4 and 8 hours respectively including set-up, 
photography and processing. 
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