Impiego di banche dati topografiche in ambiente GIS per la costruzione di modelli tematici 3d

The thematic maps concur to represent the variability of one or more phenomena on a territory, favoring the communication of information through georeferred synoptic frames and supplying bases for ulterior studies imprinted on the principles and methods of space analysis. The employment, in GIS environmernt, of topographical database containing information also on altimetry of the territory renders the construction of three-dimensional thematic models possible, concurring, for example, to represent the variability of one or more phenomena in reference to DTM (Digital Terrain Model) or Cad 3d features. In this paper characteristics of thematic 3d models and GIS techniques to obtain them are described, evidencing some analogies and differences in reference to the traditional 2d representation. Considering an area, that one including Vesuvio Vulcan, of which both topographical and thematic data (demographic and social economic indices, soil use, etc) are available, executed procedures within ArcGIS 9.0 for 3d models are presented. In particular, to introduce examples of different typologies of 3d thematic models, procedures to resolve some problems are illustrated in reference to: datum transformation, DTM realization, data grouping, models building.