Abstract
It is described the methodology to make the survey on a carving group chosen as a case-studio, the Fontana of Nettuno at Conegliano Veneto, with the most advanced instruments and technologies in order to acquire, to process and to manage data on the carving heritage which has a widespread diffusion on the Italian territory.
It has been used modern topographic instrument, SOKKIA Power SET2000 with target plate, to acquire control point on the carving, and the Digital Camera NIKON E2 to acquire the digital taken all around the carving. It has been compared the DTM generation by auto-correlation process with the model produced by laser scanning methodology using total station reflectorness no prism (TCRM 1101 Leica). Here are related the problems and results obtained building 3dmesh model (Digital Surface Model) to process the digital 3D orthophoto (software StereoView produced by Menci srl, distributed by NIKON). Today is mandatory to set up a project of conservation which satisfy the necessity to relate heterogeneous information, which come from different disciplines, to the decision processes: GIS can be really used as decision support system in the planning of ordinary maintenance and during the yard activity.
Particularly it has been studied how to use GIS technology to relate on a three dimensional object the analysis of the materials, the state of the art, the state of degree of the marbles and of the components of the carving, the analysis of the causes of degree, disruption, decay, weathering and deterioration.. Another topic of the research deals with the problem of the metric and costs computation, managed by GIS software (ArcInfo and ArcView - ESRI), in the cases of intervention in complex shapes like it is a carving, through 3D mapping of the degree.
Introduction
The survey of the carvings constitutes from always one of the most complex problems than survey and of representation, than still today they ask the search solutions more advanced to the aim to concur the generation in times and sustainable costs of a product always better usable.
Normally carvings have been rendered with photogrammetric restitution to points. For example the Marco Aurelio (Campidoglio - Rome). This process is but much expensive and long one. This methodology is adapted to being used in extensive way only in special cases.
This methodology has but a great limit also in the degree of usability why it cannot constitute the base and the support to the specialists: it is unavoidably necessary to arrive to the generation of models in a position to integrating geometry with the semantic content of the photography.
Survey and 3D representation of the case-studio.
The research here related has been carried out in the Laboratory of "Cartografia Numerica e GIS" of the DIIAR in the Polytechnic of Milan. It is described the methodology to make the survey, on a carving chosen as a case-studio, with the most advanced instruments. It has been used modern topographic instrument (SOKKIA Power SET2000 with target plate) and the Digital Camera NIKON E2 to acquire the digital taken all around the carving.
If we have superficial not flat, in order to obtain metric photographies it is necessary to proceed to the construction of ortophoto maps. The oriented photograms, for being projected and being rendered metric have need of the construction of a three-dimensional model on whose to carry out this projection. The difficulty for a sculpture is just in the construction of the model: or it is returned to the manual restitution for points, too much expensive, or the various ways already used in several fields for the automatic generation of models are experienced. The study of the sculpture has evidenced the limits of the research that has been started, near the Polytechnic of Milan - DIIAR and is from considering not ended as far as the generation of ortophoto digital 3D on complex models.
The algorithm of the auto-correlation that is used in the modules of the software of digital photogrammetry and that the automatic generation of leaving from the oriented models concurs has given to outcome negative in this case limit: currently on a complex model therefore it becomes impossible to auto-correlate automatically corresponding points not identifiable; it is possible only for the more formalized parts, as the flank of the horses and as the test-model wire-frame inserted in the pictures. The illustrations document to all the phases of the digital photogrammetric restitution (inner guideline, external guideline, bundle-block adjustment, model 3D and ortophoto - Figg. 1/6).
The only photogrammetric way of the generation of the surfaces has been therefore placed side by side from the experimentation and topographical implementation and currently ulteriorly developable with the technology laser-scanning, that it is giving good results.
Also in the field of the representation new experimentations are opened: given a great amount of points all round as in the case of a sculpture the programs do not succeed to construct in automatic a complex surface, as instead they make for construction of the DSM (Digital Surface Model). On the statue this operation has been partially made manually on the left side, the head and the chin. This has concurred the creation of a partial digital ortophoto.
