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

CIP A 2003 XIX th International Symposium, 30 September - 04 October, 2003, Antalya, Turkey
507
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2. OBJECTS AND MATERIALS
The stone artifacts from Rheinhessen which were studied up to
now were all manufactured from local raw materials like quartz,
different kinds of Devonian quartzite and Tertiarien quartzite,
by hard hammer percussion. That means in general, one rock is
hit by another. Normally, a well rounded cobble is used as a
hammer stone. The rock from which the flakes are removed is
called core. The striking products are the flakes. The best angle
for striking stones is under 90°. All flakes have two sides. The
dorsal surface represents the outside of the core when the flake
was made (which may show cortex or negatives from other
flakes removed before as well). The other side of a flake is
called the ventral surface. This is the old inner side of the core.
Just below the striking platform, which is the surface where the
hammer stone struck the core and knocked off the flake, you
find on the ventral side the bulb of percussion which represents
the energy waves of the flaking blow as they spread into the
core. On the whole ventral surface you find wallner waves
(ripple marks) which radiate in series of progressively larger
arcs from the point of percussion up to the opposite (distal) end
of the flake. These waves show the striking direction. On the
cores you find the negatives of the flakes which have been
removed. The ripple marks in these negatives also allow an
analysis of the striking direction and the technique which was
used. A normal byproduct from striking stones are small (less
than 1,5 cm long) flakes, which are called chips. These small
flakes indicate stone striking activities on a site.
Since the first appearance of stone artifacts 2,5 mio. years ago
in Africa, the striking technique became step by step more
complex. One example for a more complex striking technique is
the hand axe, which appears for the first time 1,5 mio. years ago
in Africa. The next big step in the development of the stone
striking technique is the Levallois technique which is associated
with the Middle Palaeolithic. The blade technique is linked with
modern humans and is about 40.000 years old. Flakes and
blades can be transformed by retouching into different tools like
side- and end scrapers, knifes or points. Cores can also be trans
formed by further treatment to core tools. Detailed analyses of
flake and core surfaces give indications on the technical abilities
of our prehistoric ancestors.
3. 3D SCANNING
3.1 General remarks
As the objects themselves cannot be examined by all interested
parties, very good digital representations have to be made
available. In the case of the complicated stone artifacts con
cerned, this demands a high resolution 3D documentation which
comprises the complete surface which consists of sharp edges
and larger areas which are relatively flat. Since enormous
quantities of objects have to be documented, the method will
only be acceptable if it works fast and efficiently.
3.2 Selection of an appropriate scanner
Both 3D scanners already owned by i3mainz, a Mensi S25 and a
Leica Cyrax 2500, were not suited for the task since they are
designed for much larger objects. Therefore, a new scanner
featuring sufficient accuracy and resolution for small object
spaces had to be acquired. The ATOS II system, produced by
GOM mbH (GOM, 2003), was chosen from a large list of
possible candidates with similar features for sub-meter object
spaces (i3mainz, 2003).
A main advantage of the system is
its modular design which allows
various fields of view between about
1 dm 3 and 1 m 3 when certain com
ponents (base, lenses) are exchang
ed. For the stone age tools, the
ATOS II is used in a version that
allows to scan a measuring volume
of 250 x 250 x 200 mm 3 . Fringes are
projected onto the object’s surface
(fig. 2b) and recorded by two CCD
cameras which are located at both
ends of a 600 mm base. The
software computes 3D coordinates
for up to 1.3 million object points
from the camera images with an
accuracy of about 0.01 mm. The
scanner has a weight of about 4 kg
and can be mounted on different
types of tripods (fig. 1).
Fig. 1: The ATOS II on a heavy tripod
3.3 Scanning procedure
First object position. The ATOS sensor head mounted on a
tripod can easily be positioned relative to the stone age artifact
which is fixed in special plasticine on a wooden block, where
the adhesive ATOS reference points are attached (fig. 2b).
During the measurement different fringe patterns are projected
onto the artifact (fig. 2b) for some seconds each which are cap
tured by two integrated cameras at either side of the sensor base
(fig. 1). Within some more seconds the ATOS software calcu
lates precise 3D coordinates of up to 1.3 million object points.
Fig. 2a: A typical stone artifact.
Fig. 2b: The artifact held in position by plasticine
on the base block carrying the ATOS reference points.
Fringe patterns are projected for measurement.
During the scan the software checks the ambient illumination
and possible relative movements between scanner and object
because these can have an influence on the accuracy of the
measurement. If one of these checks indicates problems, the
software gives a warning and the scan can be repeated. Because
of the critical influences of light and stability, the best place for
measurements based on light pattern triangulation is a dark
room with a solid floor. Surface reflectivity may cause
problems, too. If the material is too shiny or transparent, the
projected fringe patterns may not be identified correctly by the