A photogrammetric process driven by an Expert System: A new approach for underwater archaeological surveying applied to the 'Grand Ribaud F' Etruscan wreck

The present paper focuses on a new tool dedicated to the survey and the representation of archaeological and architectural heritage. The tool is based on a photogrammetric process related to an expert system that handles a knowledge base coming from the field of archaeological or architectural expertise. The system was tested on an archaeological field: the Etruscan amphora, Py4. The first step of the photogrammetric survey was presented in VAST 2001 [Drap, Long, 2001]. In this paper we present a new symbolic approach to manage the data surveyed. The use of an Expert System gives us a higher level of abstraction by the insertion of a new abstract layer between surveyed data and the model to compute. The presence of a great number of amphorae on the site of Grand Ribaud F, the Etruscan wreck located in Hyères, France, together with the archaeologist's survey needs of the wreck, led us to the development of the system. We add also a persistence mechanism for the data, structured in XML. A Web site allows access to all the excavation data. (http://GrandRibaudF.gamsau.archi.fr) The project is articulated in several phases: • Development of the theoretical model: for each identified object, a geometrical description offers a complete set of geometrical primitives, which are the only objects that can be potentially measured, and a theoretical representation of the object. • Photogrammetric measurement being highly incomplete (the object is seen only partially or is in part deteriorated), the Expert System determines the best strategy to inform all the geometrical parameters of the studied object, starting from taken measurements and the default data as defined in the architectural model and the geometrical model. • The resulting object is thus based on a theoretical model, dimensioned more or less partially by a photogrammetric measurement. At the time of the photograph exploitation, the operator can choose the number of attributes of the object, which are regarded as relevant to measure. The choice of attributes is revisable in time, for example at the time of a second series of measurements. The system can be used to position in space some objects of catalogue after a scale phase. If measurement is more complete, in addition to positioning in space, the system allows an analysis of how the measurements vary from the theoretical model and, from there, a study of these deformations or erosions. These, in turn, allow one to question the initial model. The whole developments of the project are written in Java and use the expert system Jess, available on the WEB.