Costruzione di modelli digitali dell’isola di Procida a partire da dati cartografici eterogenei

In GIS applications on marine and coastal environment, models concerning both bathymetric and topographic representation are necessary: nautical charts and territorial maps are particularly useful because the first supply the morphology of sea bottom and the second the relief of mainland. Integration between these different data is possible only when files in object are referenced to the same datum, same representation, same coordinates system. These conditions are not satisfied: nautical charts produced by IIM (Istituto Idrografico della Marina) are generally in Direct Mercator Representation, while maps produced by IGM (Istituto Geografico Militare) as well as by local Administrations, are in Universal Transverse of Mercator; for consequence direct layers overlay is not possible. Also the construction of 2,5 models, such as TINs (Triangulated Irregular Networks) and DEM (Digital Elevation Models), requires uniformity about datum, cartographic representation and coordinate system. In this paper operations to obtain 2 and 2,5 models of Procida isle and surrounding sea bottom are illustrated: two maps, one in scale 1:25.000 produced by IGM, the other in scale 1:30.000 by IIM, have been used. Both two raster files are georeferred and their elements concerning altimetry are vectorised. Reduced all data to the same cartographic representation (Gauss), TIN and DEM have been constructed. More detailed models have been realised using one fair sheet and one map produced by Province of Naples in scale 1:5.000. TINs and DEMs for GIS applications have been obtained, so to represent sea bottom and territorial morphology of the whole isle (medium scale) or of a part of it (large scale).