High Resolution 3d Recording and Modelling of the Bronze Age Cave “les Fraux” in Perigord (france)

The Bronze Age cave “Les Fraux” at Saint-Martin-de-Fressengeas (Dordogne, France) has been discovered in 1989. This site made of a network of galleries of several hundred meters, is a field of investigation for several researchers. This paper will focus on threedimensional contact free measurement techniques for a full 3D-documentation of the structural elements of the cave with some focus on cave art details. In this cave, most of the art is etched in the clay and follows linear, schematic and geometric designs. There are indeed several manmade depictions on the walls and other valuable remains of activity all around the cave. For the archaeologists, the documentation and recording started in 2008 should: contribute to the accurate indexing of the surveys and images of the remains and collections as well as structural elements and sculptures; guarantee the indexing compatibility of the data between the different groups of researchers involved in the excavation; ensure the georeferencing of any type of object in the different parts of the cave. Different techniques based on Terrestrial Laser Scanning (FARO Photon 80), Digital Photogrammetry (CANON EOS 5D images) and Spatial Imaging System (Trimble VX) have been used. The aim of the documentation work is to generate a geometric and photorealistic 3D model from the combination of point clouds and photogrammetric images, for both visualization and accurate documentation purposes. The underground tunnels of the cave are linked to the above terrain with surveying techniques for an accurate georeferencing. The workflow from the raw data to the final PDF-3D model will be discussed. Emphasis will also be given to the deliverables, since the huge amount of data is not directly usable by the archaeologists. * Corresponding author. 1. CONTEXT This papers deals with 3D reconstruction and visualization of a complex archaeological site. Our field of interest is the Bronze Age cave “Les Fraux” (1300 BC) located at Saint-Martin-deFressengeas (Dordogne, France). This cave has been discovered in 1989 after the collapse of an artificial lake, allowing access to a complex underground network never visited in the last 3000 years. Several researches are bringing together different specialists in charge of surveying and documentation, excavations, epigraphy, magnetic measurements in this site. Laurent Carozza is managing this archaeological project in France. Most of the art in the cave is etched in the clay and follows linear, schematic and geometric designs. There are several manmade depictions on the walls and other valuable remains of activities all around. This site, made of a network of galleries of several hundred meters, is a fantastic field of investigation for the researchers. Advances in Terrestrial Laser Scanning (TLS), as well as the performance of Imaging Systems are rapidly developing, so that a huge amount of data is usually recorded in such a project (Grussenmeyer & Hanke, 2010). The overall recording of the cave (Figure 1) is one of the main topics, since it will ensure the georeferencing of any other operation. In this context, techniques allowing three-dimensional contact free measurements have been performed for the 3D-documentation of the whole structural elements and archaeological aspects of the cave. 2. AIM OF THE DOCUMENTATION For the archaeologists, the documentation and recording work (started in 2008) shall contribute to the accurate indexing and georeferencing of the whole set of surveys and images of the remains and collections as well as structural elements and relief drawings acquired in the different parts of the cave. Furthermore, another purpose of the recording is to deliver data and models in formats that can be handled by most of the partners involved. The cave is linked to the above terrain thanks to surveying techniques, allowing accurate georeferencing in the French Geodetic Reference System. There are several constraints for the recording process, since the original entrance of the cave is unknown at this step of the research. The access for the researchers and their material to the underground tunnels of the cave is limited to a narrow and uncomfortable gallery. Due to several archaeological remains all around the cave, the movements in the cave are restricted along a path designed by the head of the project. Fixed reference points can only be International Archives of Photogrammetry, Remote Sensing and Spatial Information Sciences, Vol. XXXVIII, Part 5 Commission V Symposium, Newcastle upon Tyne, UK. 2010