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Title
New perspectives to save cultural heritage
Author
Altan, M. Orhan

CI PA 2003 XIX th International Symposium, 30 September - 04 October, 2003, Antalya, Turkey
508
cameras. In the case of stones, white powders that can be
sprayed on the surface and washed of with water afterwards can
be used without causing any harm to these objects.
The artifact is scanned with one end fixed by the plasticine. The
result of the measurement is directly displayed (fig. 3, left). By
rotating the object, further scans can be acquired without chang
ing the relative position of object and reference points. Usually,
5 to 7 individual views are needed to record the complete
visible surface in the first object position.
For a complete representation the individual views are merged
into a single data set. With an automatic determination of the
current sensor position, the system can transform the individual
measurements into a common object coordinate system using
the detected ATOS reference points. The result is the 3D mesh
for the first object position. The part of the artifact covered by
the plasticine must be measured subsequently in a second object
position.
Second object position. In order to allow scanning for the
second position of the object, it is turned around and the other
side is now held in the plasticine. Again, several single scans
are acquired and combined to the mesh for the second position.
Fig. 3. Left: Result of a single scan.
Right: Combination of different scans.
Now, the two meshes (first and second object position) have to
be merged into one. Since there are no common ATOS refe
rence marks available in this case, four or more common points
have to be identified interactively on the meshed surface. In
most cases, this is a very time consuming process; often it is
impossible at all. Two-dimensional points like color marks can
not be identified in the 3D views of the surfaces. After many
experiments, including the construction of swiveling clamps, it
was decided to mark four very small three-dimensional targets
on flat parts of the object. Toothpaste proved to be an ideal
material since it has the right consistency, high reflectivity and
it can be removed without any problems after the measurement
process. Thus, the identical points can be identified easily and
quickly because the tooth paste peaks’ position is known be
forehand and 3D features can be recognized easily in the mesh.
can be filled without much quality loss since the peaks are very
small and were intentionally placed in flat insignificant parts of
the object. This completes the scanning procedure, and a virtual
3D model of the object is now available (fig. 4). The whole
procedure which includes scanning, registration, meshing and
hole filling can be accomplished with the hard- and software
supplied by GOM and takes less than 45 minutes per artifact.
Fig. 4: Virtual 3D copy of a stone age artifact
3.4 Thinning methods and storage
The acquired virtual 3D model shows a very high point density
resulting in large file sizes. This density is necessary to
document the sharp edges; in parts with small and/or regular
curvature, point density can be reduced considerably, however,
without any recognizable quality loss. Using the ATOS soft
ware itself or other software products like Geomagic Studio or
qslim the mesh can be thinned intelligently. With qslim, for
example, we could often reduce the file sizes by about 50%,
with no recognizable differences when viewing the model. Of
course, the potential of thinning depends a lot on the structure of
the stone artifact’s elements. For the storage of the results the
common STL file format is used. It can be read by most 3D
viewers and 3D processing programs.
4. VISUALIZATION
4.1 3D viewers for 3D inspection
When the measurement is complete and a 3D result is stored,
archaeologists can view the data on a monitor (fig. 4). For this
purpose, a viewer is necessary which shows the 3D result. With
such a program (such as SolidView which is freeware in its
light version), anyone can view the artifact and change viewing
angles and lighting interactively. The virtual model can easily
be inspected from all sides, much in the same way as the
original stone object would be examined.
After this pre-registration which merges the two meshes to- 4.2 Edge based visualization
gether, an automatic 'Best Fit' registration improves the result
and provides the final set of data for the whole artifact as an In a diploma thesis at FH Mainz (Tschoepe 2003) an attempt
ASCII point cloud or in a polygon mesh according to the STL was made to classify and visualize local curvature on the object,
format. If there are some small insignificant holes left, these can After a triangular mesh of the object’s surface is accomplished,
easily be filled by the software. The toothpaste peaks which are every individual triangle can be furnished with an own texture
still on the mesh are cut out and removed. The resulting holes when the OBJ format is used. The computer program developed