PHOTOGRAMMETRIC MODELLING OF THE EXCAVATIONS AT TEICHOS DYMAION FROM DIGITAL IMAGES

• K. Klein, G. Sakas (Fraunhofer Institute for Computer Graphics, Fraunhoferstr. 5, 64283 Darmstadt, Germany)
• M. Gazis (Hellenic Ministry of Culture, 62 Panachaikou str., 262 24 Patra, Greece)

Archaeological excavation is a destructive process, which ideally unveils a wealth of useful physical finds, but irreversibly discards the exact spatial relationship between the finds and the site. Partially, this information is archived in the archaeological record in the form of sketches and measurements. However, this is often not sufficient to imagine the spatial relationships afterwards, in particular when different depth layers are involved. For archaeologists who were not able to physically visit the site during the excavation, the interpretation of the finds can be difficult.

In this paper, we propose a method of augmenting the conventional sketches and measurements with a 3d model of the site, which is reconstructed from multiple uncalibrated digital photographs of the site. Using photogrammetric reconstruction methods, the 3d geometry of the site is obtained semi-automatically. Additionally, the colour information is extracted from the photographs and texture mapped onto the model surface yielding a photorealistic impression of the final model.

The difference of a photorealistic model to conventional sketches can be compared with the advantage of a terrain model over a map: one can much easier get an impression of "being there" and of what the original site looks like by viewing the model from arbitrary positions. In the archaeological context, this alone can already yield additional hypotheses for the interpretation of finds without actually visiting the excavation site. Moreover, models from different phases of the excavation and from different depth layers can be combined, so that the scientist can interactively repeat the excavation in a virtual environment. All kinds of meta-information can be added to this model, like chronological classification of the excavated parts, references to finds, and additional archaeometric results.

Another important application area of the method presented here is the field of education and advertisement for tourists visiting the site. Here, visitors can get an overview of the site before the visit, learn about the important aspects, have a "virtual walkthrough", and can access additional multimedia content linked with the 3d geometry, especially finds that are displayed in museums far away from the excavation site.

In a first practical evaluation, the proposed method was used in the excavation site of Teichos Dymaion where the middle part of the main wall and the adjacent excavated region have been reconstructed from 53 digital photographs. The model covers a region of approximately 25 x 20 x 7 meters. The result serves as part of the documentation and will be completed as the excavation continues. The test shows the practical applicability of photogrammetric modeling to archaeological excavation sites.

With the proposed method, the geometric situation of archaeological finds is conserved for future generations of archaeologists who will be able to interpret it in a possibly different scientific context as well as in the original spatial context