Full text: New perspectives to save cultural heritage

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FAST ON-SITE RECONSTRUCTION AND VISUALIZATION OF ARCHAEOLOGICAL FINDS 
Konrad Schindler, Markus Grabner, Franz Leberl 
Computer Graphics and Vision 
Graz University of Technology 
Inffeldgasse 16, A-8010 Graz, Austria 
{schindl,grabner,leberl}@icg.tu-graz.ac.at 
KEY WORDS: Archaeology, Excavation, Close-Range Photogrammetry, Automatic Reconstruction, Interactive Visual 
ization 
ABSTRACT 
We report on a study carried out within the 3D MURALE project, in which the complete workflow necessary for automatic 
recording, reconstruction and interactive visualization of artefacts on archaeological excavation sites has been tested. With 
state-of-the-art technologies from digital photogrammetry, computer vision and computer graphics a prototypical pipeline 
for recording, 3D modeling and visualization of archaeological artefacts has been implemented and tried out on site on 
the excavation of Sagalassos (Turkey). The purpose of the presented work was to test the complete pipe-line in a real 
archaeologic environment and assess its usability. 
1 INTRODUCTION 
To meet the practical requirements of archaeological her 
itage recording and documentation, technology must be us 
able under field conditions on archaeological excavation 
sites. Besides being fast and easy to use, systems for pho- 
togrammetric recording and modeling as well as visualiza 
tion should interfere as little as possible with the excava 
tion work and use only equipment that can be found on 
archaeological excavations. 
We present a system which has been designed for the pur 
pose of fast on-site recording, reconstruction and local as 
well as remote visualization of archaeological finds. The 
system combines methods from photogrammetry and com 
puter vision with state-of-the-art computer graphics algo 
rithms to accomplish the task. Objects are recorded di 
rectly on site with an off-the-shelf digital camera and are 
reconstructed in an almost fully automated photogrammet- 
ric modeling process, in which the only user interaction 
is to segment the artefact to be modeled from the back 
ground. Robust algorithms for orientation, adjustment and 
dense object reconstruction are applied, which deliver ac 
curate, textured 3D object models. 
New methods for compressed adaptive multi-resolution en 
coding of large models are used to enable visualization of 
the resulting 3D models at interactive frame-rates even on 
computers with inexpensive graphics hardware. An ex 
tension of this technology allows smooth remote interac 
tion with the models via low-bandwidth connection using a 
standard Internet browser. This gives archaeologists in the 
field the possibility to instantly communicate about new 
finds with people who are not present on site. In contrast 
to existing simplification techniques object identities and 
attributes are preserved through the dynamic simplification 
process to provide a practically useful way of interaction. 
Again the processing is fully automatic. 
The proposed system has been successfully tested within 
the 3D MURALE project (Cosmas et al., 2001) on the 
Greco-Raman excavation site of Sagalassos (Turkey) dur 
ing the 2002 excavation campaign. Several artefacts have 
been recorded without any impact on the excavation rou 
tine, reconstructed on the same day using a standard laptop 
computer, and visualized on a different computer via a lo 
cal network connection. We will present the utilized work- 
flow and technology with real examples from Sagalassos. 
2 RECORDING 
A classical photogrammetric approach is used for on-site 
recording. Multiple overlapping images of the object to be 
modeled are recorded with a calibrated digital consumer 
camera. In our experiments we have used a high-quality 
SLR camera as well as a cheap consumer camera (a Canon 
D30 with a resolution of 2160x 1440 Pixels and a Nikon 
Coolpix 995 with 2048 x 1536 Pixels). The standard setup 
with fixed focus close to infinity has proven to yield sharp 
images in most practical situations. We therefore use it, 
because it provides the best accuracy and robustness. It 
should be mentioned, however, that within the 3D MU 
RALE project it has been shown that recording and re 
construction on archaeological sites is also possible with 
a completely uncalibrated digital video camera (Pollefeys 
et al., 2001). 
2.1 Camera Calibration 
Camera calibration is fully automatic. The user takes 4-6 
pictures of a planar calibration target from arbitrary, differ 
ent positions. The calibration target consists of a grid of 
circles with known positions and has a unique, easily de 
tectable marker (a black ring) in the center, which allows to 
aoutomatically establish the correspondence between im 
age points and target points. The calibration target is de 
picted in figure 1. With a calibration algorithm optimized 
for this configuration (Heikkila, 2000) a full set of camera 
parameters is recovered, i.e. the principal point, the focal 
length, two coefficients for a symmetric d^-order radial 
distortion polynome and two coefficients for a similar tan 
gential distortion polynome. Calibration is an offline pro 
cess, which needs to be carried out only once for a given, 
stable camera geometry, i.e. it is sufficient to calibrate a
	        
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