3D survey and documentation in building archaeology: The medieval church of San Niccolò in Montieri

Summary form only given. Not far from Massa-Marittima (Tuscany, Italy), stands the medieval castle of Montieri, built in 1133 by the Bishop of Volterra. In the Middle Ages, thanks to its metalbearing ores, the castle was the focus for a complex history. During the last few years, the University of Siena was involved in studying in the archaeology and architecture of the castle and the surrounding old silver mines. The last survey campaign was focused on the area so-called "La Canonica", San Niccolo ecclesiastical complex. The excavation came u p to light the existence of a church characterized by an unusual plan with six apses (the only example of its kind in Italy) [1]. During the survey an innovative image-based modelling (IBM) workflow for quick 3D acquisition in archaeology was tested. Building archaeology aims at reconstructing the history of existing building and analyzing materials, building techniques and, above all, the "vertical" stratigraphy. Therefore, during the survey of the Church, in order to get a data-set suitable for this kind of analysis, we had to provide a thorough metric analysis, for precise archaeological documentation and to better understand the development of the building. For this purpose, IBM as acquisition method was chosen. This recent technology allows a complete and detailed 3D to be obtained, in very short time and with very low budget, from a set of un-calibrated photos. The modeling process is carried out automatically by software that combines algorithms of computer vision. The automatic approach implies a lower precision in comparison with conventional scanning techniques, nevertheless, recent tests have demonstrated that it can be sufficient reliable and have already being used with success in archaeology [2]. The first step was the establishment of a local topographical network