The Volumnis´ Hypogeum in Perugia, Italy. Application of 3D survey and modelling in archaeological sites for the analysis of deviances and deformations.

The impressive Hypogeum of the Volumnis (Ipogeo dei Volumni), prominent family from Perugia, was built in the Hellenistic period (probably III - II B.C.) of the Etruscan civilization. The tomb was discovered (1840) in original conditions with incineration urnae, still preserved and now exposed in situ which allowed Scholars to propose a genealogical tree. The monument is excavated in the soft sandstone with an anthropomorphic plan, articulated in a large atrium with a final tablinum, two alae and six lateral cellae; the atrium (3,60 x 7,30 m; h. 4,40) has a two-slopes ceiling made in a way to resemble the intrados of a wooden hut roof: therefore the entire simulated carpentry – ridge beam, rafters, joists, boards etc. are carefully carved in the rock, in a true scale; the same for the alae and tablinum which have square corbelled “wooden” coverings. The arrangement is made to give to the death’s afterlife the same comfortable setting of the house of the living people. There are a few more examples of this kind of apparatus in Italy (e.g. some Cerveteri Tombs) and in Sardinia (Puttu Codinu and others) but none made in such a realistic way. The survey was worked out by means of 3D laser scanner technology combined with topographical data obtained by means of a total station. The scan data has been acquired in difficult conditions of humidity and illumination in very short time without interfering with the affluence of tourist visits on site. In laboratory the acquired point cloud was meshed and, by means of a sequence of repeated intelligent data reduction, an organic meshed true scale model has been worked out. The research project deals with the different experimentations and approaches to obtain dimensional and geometric information from an archaeological survey worked out by means of 3D laser scanner technology. During the research process there is shown a logical path of elaboration, visualization and comparison between three different kinds of models: departing from the point cloud model, passing to the organic meshed model and finally arriving at a summarizing 3D surface model of the main ceilings. Using 3D-Laser Scanner technology combined with industrial deviation calculation procedures required a new approach in experimentation of advanced 3D modelling with extremely large input data by developing a methodology for processing colour scale images for the recognition of sensible global deformations on local elements of an ancient deteriorated structure. The analysis of deformation morphology shows surprising results: carpentry members simulate flections in stress conditions of true wooden beams in similar conditions of support, span, and loads. Many Scholars had studied the Monument and made careful surveys but none of them faced the problem in a comprehensive way and none noticed this realistic peculiarity. The deformations, in fact, are very slight and the traditional survey methods, even the optical ones, were not suitable to detect this kind of connotations of the pretended wooden ceiling. In order to fully document the whole monument with complete account of the features, researchers of the University of Ferrara together with Prof. Gennaro Tampone from the Department of “Restauro e Conservazione dei Beni Architettonici” D.I.R.E.S., University of Florence, decided to use the laser scanner methodology integrated with geological observations and survey. Detailed geometrical analysis of the scan model, for the first time, makes suspecting the presence of optical corrections in sense of enhanced perspectivity in late Etruscan funeral architecture, and allows dimension handling between repeated inaccessible points, in order to evaluate numerical series by Gaussian statistical results obtaining important information about the use of ancient dimension units. The paper focuses on the visualization of the spatial distribution, geometry and morphology of the archaeological monument and concludes with the typological study of the simulated timber structure. The investigations and the survey lead to very interesting results and conclusions such as: - Visualization of a subterranean ancient architecture with full three-dimensional control about morphology and dimension; - Updating and comparison with existing traditional surveys of the object with evidence of their limits and the new possibilities given by 3D laser scanner technology; - Handling of the 3D model of an architecture excavated by subtraction like as it was a constructed architecture; - Reconstruction of a typical carpentry of the time; - Account on the structural planning concepts and building processes of the time; - Advanced 3D-modelling methodology for deviation check of ancient buildings and the possibility to extend the used appraisal methodology to similar cases.