Luc Long

Underwater image preprocessing for automated photogrammetry in high turbidity water: An application on the Arles-Rhone XIII roman wreck in the Rhodano river, France

ROV 3D project aims at developing innovative tools which link underwater photogrammetry and acoustic measurements from an active underwater sensor. The results will be 3D high resolution surveys of underwater sites. The new means and methods developed aim at reducing the investigation time in situ, and proposing comprehensive and non-intrusive measurement tools for the studied environment. In this paper, we apply a pre-processing pipe line to increase the SIFT and SURF descriptors extraction quality in order to solve the problem of surveying an underwater archaeological wreck in a very high condition of turbidity. We work in the Rhodano river, in south of France on a roman wreck with 20 centimeters visibility. Under these conditions a standard process is not efficient and water turbidity is a real obstacle to feature extraction. Nevertheless the mission was not dedicated to an exhaustive survey of the wreck, but only a test to show and evaluate the feasibility. The results are positive even if the main problem seems now to be the time processing, indeed the poor visibility increase drastically the number of photographs.

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 archaeologists 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.

Underwater Photogrammetry for Archaeology. What Will Be the Next Step

Since 1973 archaeology and computer science have developed close ties in Marseille. Two departments (computer science and archaeology) from the French National Centre for Scientific Research (CNRS) in Marseille started working together and laid the cornerstone of the Computer Applications and Quantitative Methods in Archaeology (CAA) community. Marseille also has the advantage of being located in a very interesting place on the Mediterranean Sea and being the home to several famous laboratories, such as the French Cultural Heritage Department (DRASSM) or private companies like COMEX. In 1980 they performed a series of explorations of a deep-sea wreck with the help of COMEX and DRASSM. In this paper we present new advances in underwater photogrammetry for archaeology based on forty years of experience. The survey described in this article does not only discuss the acquisition of 3D points in difficult conditions but also linking archaeological knowledge to the surveyed geometry. This approach needed to com...

The ROV 3D Project: Deep-Sea Underwater Survey Using Photogrammetry: Applications for Underwater Archaeology

In this article, we present an approach for a deep-sea survey based on photogrammetry using a remotely operated underwater vehicle (ROV). A hybrid technique gives us real-time results, sufficient for piloting the ROV from the surface vessel and ensuring a uniform coverage of the site, as well as recording high-definition images using an onboard computer that will later provide a survey with millimetric precision. The measurements are made without any contact and are noninvasive. The time required on-site is minimal and corresponds to the time needed by the ROV to cover the zone. With the photos taken at a frame rate synchronized at 10Hz, the ROV required 2 hours to perform the experiment presented in this article: the survey of the Roman shipwreck Cap Bénat 4, at a depth of 328m. The approach presented in this work was developed in the scope of the ROV 3D project. This project, financed by the Fond Unique Interministériel (FUI) for 3 years, brings together two industrial partners and a research laboratory. Companie Maritime d’Expertise (COMEX) coordinated this project.