Proceedings Article | 22 July 2019
KEYWORDS: 3D modeling, 3D acquisition, Composites, Iron, Gold, Silver, Photography, X-ray technology, Natural surfaces, Stereoscopy
The Agris Helmet is a masterpiece of the Celtic art made in the middle of the 4th century A.D. It has been found near Agris, France, in 1981 during an archeological dig under the supervision of José Gomez-de-Soto. This composite object is made of an iron cap covered with bands of bronze. The bronze is itself covered with pure gold leaf, with embedded coral decorations attached using silver rivets. The Helmet was discovered with one cheek guard which had similar materials and designs. Considering this information, the cap would have been used for display rather than worn in battle.
The helmet, discovered in pieces, was restored in Mainz during the 1980th and is now held by the Musée d'Angoulême in Angoulême (France).
The present project led jointly by the AOROC department of the ENS and the C2RMF and supported by PSL, was an opportunity to make complementary work on the Helmet to document it thoroughly.
Our aim was threefold. Firstly, we wanted to document the Helmet in such a way that future studies would be doable even without physical access to the original piece. Then, we were willing to search the best 3D technique and practice for this complex piece. The level of details and the brilliant aspect of the surface were the perfect challenges for our 3D systems. In addition to these technics, we wanted to enhance the knowledge about the object (material and technical identification) and provide new data for archaeology and art history.
We began the study with a complete photographic coverage of the Helmet thus highlighting every single visible detail on its surface. In order to go further concerning the structure of the object itself, we chose to use X-Ray technology. This method allowed us to see behind the surface and understood the organization and construction of the Helmet.
Furthermore, multiple techniques of photogrammetric imaging and 3D digitalization were used to obtain the best set of data. Leadingly, we performed a photogrammetric coverage under artificial lights followed by another under natural light. Thereafter, we used two 3D scanners technologies, one based on structured light and the second based on laser technology. The resulting 3D models were compared in precision and acquisition convenience (simplicity of devices and acquisition time).
While the photogrammetric models were perfect to easily visualize the texture and color of the object, its degree of precision left something to be desired.
On the contrary, the 3D models obtained by scanning technologies were effective for the purpose of getting complete metric and volumetric values.
For the study of the Helmet, the high-resolution models provided information about tools marks and other traces of the production techniques. Moreover, mesh comparing provided new data for the matching of supposedly identical items on the surface. The results of those studies were particularly instructive for the historians of the Celtic period and gave new possibilities to the researches for the work on this precious object.
