Use of historical images for the documentation and the metrical study of Cultural Heritage by means of digital photogrammetric techniques

The paper is related to a multi-disciplinary project started in 1999, within a collaboration established between the University of Bologna and the Archaeological Superintendence of Pompeii. In the frame of this project was activated a rigorous survey, by the integration of different geomatic techniques (GPS, Laser Scanning, Photogrammetry, Visual Reality), of the most significant nymphaea of Ercolano and Pompeii (Naples); these are elements of remarkable archaeological and artistic value and presenting various geometric characteristics, needing a very accurate description of the decorative apparatus, often entrusted to particularly complex and rich mosaics. In particular are here described the studies conducted about the Lararium from the “House of the Skeleton” in Ercolano. This object is interesting for this kind of study because it presents some static problems and it has suffered during the excavations many interventions and changes, until the complete disassembly and successive replacement in situ. Three images of the 1927-1928 periods were chosen with the aim of creating a historical 3D model of the object, comparable with the actual model, derived by the photogrammetric survey conducted in the 2006 campaign. After an experimentation phase necessary to define the most suitable methods to perform the images calibration (single or multi photo, with the use of geometric constraints or also with the use of control points), a valid set of parameters was found and a complete model of the object was reconstructed, representive of the metric and qualitative conditions in this epoch. The dimensional comparison between the two temporal situations (historical and actual) has also permitted qualitative and quantitative considerations about the differences, offering a very important tool for the evaluation of the past restorations and useful also to plan all the future interventions.