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

CI PA 2003 XIX"' International Symposium, 30 September - 04 October, 2003, Antalya, Turkey
441
tion, which could serve as a basis for the physical reconstruc
tion. Using our data, a first model (1:200) has already been cre
ated while a statue at 1/10 of the original size should be built
and displayed in the Afghanistan Museum in Switzerland. Then
this model will be used to study materials and construction
techniques to be applied for the final reconstruction at full size.
Originally our interest in the computer reconstruction of the
Great Buddha was a purely scientific one. We'planned to inves
tigate if such an object could be reconstructed fully automati
cally using just amateur images taken from the Internet with
photogrammetric methods [Gruen et ah, 2002]. In this case the
main scientific challenge lies in the facts that no typical photo
grammetric information (as interior and exterior orientation pa
rameters) about these images is available and that existing
automated image analysis techniques will most probably fail
under the given circumstances. After learning about the efforts
to actually rebuild the Great Buddha we decided to get involved
in that project beyond a purely scientific approach and to con
tribute as much as we could with our technology to the success
of the work. We generated different versions of the Buddha,
depending on which algorithms and images were used: Internet,
tourist and metric images [Gruen et ah, 2003]. The results ex
tracted from the Internet and tourist images served only for sci
entific purposes. The physical reconstruction should be based
on a 3D computer model derived from the three metric images.
These photographs were acquired in Bamiyan in 1970 by Prof.
Kostka, Technical University of Graz [Kostka, 1974]. They
form the basis for a very precise, reliable and detailed recon
struction with an accuracy of 1-2 cm in relative position and
with an object resolution of about 5 cm. In order to achieve
these values we had to apply manual image measurements, as
the automatic procedures could not extract all the fine details.
In this paper we only present the results of the computer recon
struction obtained with the three metric images. For a more de
tailed technical description of the digital photogrammetric pro
cedures on all the data sets, we refer to [Gruen et al., 2002,
2003].
3.1 Phototriangulation
A contour plot of the big statue, done by Prof. Kostka [Kostka,
1974], is also available (20 cm isolines, scale 1:100). From this
plot some control points could be measured and used for the
phototriangulation. Then, using the information in [Kostka,
1974] and the control points, we achieved the first ap
proximations of the exterior and interior orientation parameters.
The final orientation of the images is achieved using a bundle
adjustment [Gruen et ah, 2002] (Figure 4).
Figure 4: The acquisition procedure (left) and the recovered
camera positions after the bundle adjustment (right).
3.2 Image coordinate measurement and point cloud
generation
Image measurements are performed with automated and manual
procedures. We first applied a commercial package (VirtuoZo)
and then our self-developed matching software for the
automated reconstruction of the statue. But, at the end, we used
manual measurements to get a very precise, reliable and
detailed 3D model of the Buddha.
2. THE METRIC IMAGES
The metric images were acquired with a TAF camera
[Finsterwalder et ah, 1968], a photo-theodolit camera that
acquires photos on 13x18 cm glass plates. The original photos
were scanned by Vexcel Imaging Inc with the ULTRA SCAN
5000 at a resolution of 10 micron. The final digitized images
resulted in 16930 x 12700 pixels each (Figure 3). Their
acquisition procedure (Figure 4, left) is known as well as the
interior parameters of the camera [Kostka, 1974]. * •
: m t :
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1 ^---7;-?
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Figure 3: The three metric images acquired by Kostka in 1970.
3. PHOTOGRAMMETRIC PROCESSING
The photogrammetric reconstruction process consists of:
• phototriangulation (calibration, orientation and bundle
adjustment),
• image coordinate measurement (automatic matching or
manual procedure) and point cloud generation,
• modeling, i.e. surface generation and texture mapping for
photo-realistic visualization.
3.2.1 Automatic measurements with commercial software
The 3D model of the Buddha statue was generated with the
VirtuoZo digital photogrammetric system. The matching
method used by VirtuoZo is a global image matching technique
based on a relaxation algorithm [VirtuoZo NT, 1999]. It uses
both grid point matching and feature point matching. The
important aspect of this matching algorithm is its smoothness
constraint satisfaction procedure. With the smoothness
constraint, poor texture areas can be bridged, assuming that the
model surface varies smoothly over the image area. Through
the VirtuoZo pre-processing module, the user can manually or
semi-automatically measure some features like ridges, edges
and regions in difficult or hidden areas. These features are used
as breaklines and planar surfaces can be interpolated, e.g.
between two parallel edges. In VirtuoZo, first the feature point
based matching method is used to compute a relative
orientation between couples of images. Then the measured
features are used to weight the smoothness constraints while the
found approximations are used in the following global
matching method [Zhang et al., 1992]. In our application, a
regular image grid with 9 pixels spacing was matched using a
patch size of 9 x 9 pixels and 4 pyramid levels. As result, a
point cloud of ca 178 000 points is obtained (Figure 5). Due to
the smoothness constraints and grid-point based matching very
small features, like the folds of the dress were filtered or
skipped.