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2. OBJECT DESCRIPTION
The two gold quiver or “Gorythes” belongs to what is
known as “Amazones’s gold”, a choice of prestigious
objects illustrating one crucial moment of wandering
Eurasian steppes people’s history (southern of the Ural,
Kazakhstan, China), renewing the traditional forms of
Scythes art.
All the exposed objects came from regional Rostov and
ethnographic Azov Museum in Russia.
3. METHODOLOGY
The digitalisation of these objects was carried out with
the Minolta VI900 scanner. Combining digital
photogrammetry and laser scanning allows to reach a
high degree of efficiency. The high quality required for
object documentation did not permit the unique use of
digital photogrammetry and stereo matching. At that
time, our measurements were carried out by digital
photogrammetry, with restitution of digital surfaces
models (DSM) and orthophotos at original scale. Time
and infrastructures necessary to capture information
and their edition was considerable and thus, did not
allow to apply these techniques to secondary order
objects. In fact, photogrammetry implies high value
added work combined with strong matching algorithm
for precise surface reconstruction. Even if there are
systems that use feature extraction or image matching
process, they are limited in precision for close-range
surface editing.
Figure 2: Digitalization was carried out by leaving the
object while removing the principal protective glass.
For that reason and combined with the constraints of
not accessing the objects, it was decided to use a close
range laser scanner able to reach sub- millimetre
resolution. Then, a methodology of surface comparison
was established for archeological and historical
interpretation. The question was to determine wether or
not these two gold quivers were hand-made or issued
from a same mould.
3.1 Data acquisition:
Digitalisation is made by leaving the object while
removing the principal protective glass and then start
the survey with the laser scanner. The acquisition
process is not affecting the quiver since the laser beam
is not of sufficient energy to alter the object surface.
Several measurement are made form different viewing
angles in order to cover all the quiver. Each part were
measured by seventeen to twenty scans with 320.000
points each.
Meanwhile the laser scanner acquisition, the system is
able to take a picture stored as a textured photo, and
then draped over the object for visualization purposes.
These textures of high-resolution were acquired with a
digital camera Sinar P, equipped with a numerical back
PowerPhase FX which can reach up to 150 millions
pixels by image.
The reconstruction of this man made object is rather
complex since its reduced dimension of nearly one
meter, and also with the large amount of sculpted
reliefs. Hence, It is necessary to use subsampling
algorithms (reduce amounts of measurements)
generated by these digitalizations and proceed to
transformations on the regulated mathematical surfaces
(TIN). This is done by filtering the scatter plot for
removing noise and polluted measurements. Finally,
we obtain a set of cloud points which need to be
registrated.
3.2 Global registration:
A second step is to reference all the scans to build a
complete object. This task was done with the
commercial software Polygon Edit Tool from Minolta
delivered with the scanner. The latter proceed to
registration with morphological rules to combine
different scans and thus, construct the entire object.
Indeed, the quivers were measured with an accuracy
close to an half-millimetre. If needed, some control
points may be acquired to help the registration process
and to reference one model to another. We chose to
study the quivers matrice by matrice since a global
curvature difference was noticed. Thus the registration
process was fine tuned locally.
Photographic images digitised in high resolution are
then applied to the geometrical model for realization of
photorealists models or 1/1 scale orthophotos