3D hight accuracy survey and modelling of one of aosta's anthropomorphic stelae

The Aosta Valley still preserves important traces of prehistoric and protohistoric settlements in the aeneolithic necropolises of Champrotard (Villeneuve), Montjovet and Vollein (Quart), partly associated with groups of rupestrian engravings. Megalithic monuments erected from the Neolithic Period to the Bronze Age have been found in the outskirts of Aosta, in Saint-Martin-deCorléans, in a wide area that was once used for worship purposes. The Little St-Bernard Pass "cromlech" could also date back to the same age. The Saint-Martin-de-Corleans megalithic area, on the outskirts of Aosta, was a place of worship and then of burial from the third millennium B.C. onwards, with alignments of anthropomorphic stelae, megalithic tombs and menhirs. The anthropomorphic stelae, most likely representations of gods or of ancient heroes, are reminiscent of those of the Petit Chasseur in Sion, proof of the intensity of cultural exchanges over the Great St. Bernard Pass during the whole prehistoric period. The decorations of some stelae are at present barely visible. It is just possible to see some decorated parts using a specific shaving lighting system. The aim of the archaeologists was to preserve the surface of the stelae by arranging them in sheltered areas. At the same time, it was very important to carry out a 3D high resolution survey of the decorated part of the stelae. The aim was to prevent the decoration of the stelae from being lose in the future. High resolution 3D survey systems have long existed especially for mechanical applications. High resolution prototype instruments have also been developed and used in the Cultural Heritage field in order to create accurate 3D models that are able to form a basis for reproduction, restoration and conservation purposes. Different solutions have been proposed: laser distance measurements on controlled mechanical tables, self-controlled harms, stand-alone instruments, etc. Different measuring principles have successfully been adopted: laser distance measurements, structured light, laser triangulation, etc. The common technical problems of this kind of instruments are due to the stability of the acquisition reference systems during the survey or to the need to have direct access to the object. The economic problems are due to the high costs of the instruments. A new generation of high resolution and high precision scanners have recently been introduced: these try to solve both the previously mentioned problems. At a cost of less than the usual amount for a terrestrial scanner of low accuracy and with a direct survey in a 3D reference system materialised on the object, or nearby, these new instruments (the so-called third generation scanners) allow a complete surface of convex and concave objects to be scanned avoiding the necessity of moving the object from its natural location and without heavy instrumentation. This new instrument, produced by CREAFORM, a Canadian Technological centre for reverse engineering and 3D digital solutions, is called HANDYSCAN 3D. This has been presented as the first self-positioned hand held scanner in the world. The basic idea of this instruments is very simple (it is a digital photogrammetric system), but the adopted solutions represent a true novelty from different points of view in the Cultural Heritage surveying field. The first interesting aspect is the dimension and weight of the acquisition unit which can be handled for long periods without tiring the operator and it allows the possibility of obtaining all the details, even in the case of very complex objects. The second attractive aspect is the possibility of acquiring objects of different dimensions: from small objects (e.g. rings, fragments, etc.) to very large objects (e.g. statues, large epigraphs, etc.). Finally, the third attraction is the price, which is lower than the current quotations of the less accurate terrestrial laser scanners, even considering the laptop for the storage and the visualisation of the acquired data. XXI International CIPA Symposium, 01-06 October, Athens, Greece The handling of the data can be performed using one of the well known software packages (e.g. RapidForm, 3Dmax., etc.). The acquisition can be done by a specific dedicated software created by the CREAFORM company or using a special link made by Creaform to the Geomagic Studio which can directly manage the data from the HANDYSCAN3D system. The accuracy of the acquired data, their flexible resolution and the real time check of the completeness of the acquisition phase are the best requirements for a quick and correct model approach. The paper describes the acquisition phases and the obtained resuts of a 3D HandyScan Hight accuracy survey on one of the 41 anthropomorphic stelae in the megalithic area of Saint-Martin-de-Corleans, on the outskirts of Aosta. In addition, a complete photogrammetric survey was carried out in order to check the possibility applying a realistic photo mapping of the object to the acquired 3D model. Finally, the acquired 3D high accuracy model was elaborated with a 3D surface modelling process in order to check the possibility of showing the still exsisting decorations.