Un esperimento di visualizzazione scientifica per l'archeologia del paesaggio: la navigazione nel paesaggio virtuale

Maurizio Forte

«Archeologia e Calcolatori» 1993, 4, 137-152

Abstract

Computer simulation of natural phenomena is one of the most attractive and modern subjects for image synthesis. Simulation is the result of many processes, computed with mathematical models, which can be visually represented on a graphic screen. The synthetic image of the model generated can then be compared with other available information, and thus the image becomes an instrument for furthering knowledge. Two problems exist in the visual simulation of natural environments and 3D navigation. The first one is the construction of a reliable and detailed Digital Elevation Model (DEM or Digital Terrain Model, DTM); the second one, closely tied to ambient simulation, is terrain rendering, that is, the reproduction of the colour vision in the observer. DTM’s can be generated from isoliner or regular point data, using classical models (linear interpolation and Kriging) or fractal models (Brownian interpolation). In this example the aim is to create a landscape model (including archaeological sites) using a DTM and satellite or aerial images; these applications involve the following steps: acquisition of isolines from cartographic maps at any reasonable scale; DTM generation; digital image classification to determinate the pixel distribution map for the DTM; image synchronization (digital aerial photographs or satellite images synchronized with the DTM); texture mapping and generation of 3D images. In practical terms, the texture mapping involves the overlaying of the original image point by point on the DTM: the result is a realistic and significant landscape 3D image. This kind of simulation is especially useful to enhance the geomorphological characteristics of the landscape in connection with its evolution and the ancient settlement. Inside the image the researcher can move, navigate and explore, as in the real world. The example described concerns the Etruscan town of Marzabotto in the Reno Valley (Bologna). A realistic and representative 3D image was achieved which includes important topographical and geomorphological information about the archaeological site and the Reno Valley, the natural resources, and the correlation between the Reno river and the Etruscan town. A digital vertical aerial photography was overlayed on the DTM of this area, generated from cartographic isolines and contour lines. The processing consists of different steps: the first one is the digitisation of the aerial photograph (scale 1:30.000), in order to create a numeric input for part of the Valley of Reno, including the archaeological area and the DEM model with a topographical sample. The aerial photograph was digitised using a CCD camera and converted into a numeric format in raster file (RGB 24 bit plane, resolution 595 x 394 pixels). It was aligned with the DEM model using a regular grid with a resolution similar to the one of the digital image. Special hardware (SGI workstation) was used for the final rendering; the polygon rendering did not follow the usual texture mapping technique, but instead a geometric texturing was produced (one polygon per pixel). This technique allows a lower sampling noise (antialiasing) without heavy software interpolation. In this way the only problem is related to the dependence on the graphic library GL which is implemented either on a Silicon Graphics or RISC 6000 IBM platform.

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