RECONSTRUCTION OF HISTORICAL GEODETIC SYSTEMS FOR THEIR IMPLEMENTATION IN REPROJECTION ALGORITHMS

Historical cartography is an important source of geographic information for diachronic studies. The Italian geodetic datum from the second half of the 20th century are well known and used, while the reference systems used previously do not have a certain documentation also because they were developed by the military geographical institute, which at the time was a uniquely military body with the related problems of confidentiality.The reconstruction of the datum of each single historical map is a fundamental process, in order to be able to correctly compare historical information with the current ones, but it is complex because of the scarce information available on the type of datum and cartographic projection used for the production of the map.The reconstruction of the ancient morphology of an area, such as that of 1893 Forma urbis map or the pre-reclamation maps of Agro Pontino, is of fundamental importance for various studies on geomorphological changes of the territory, including, for example, the reconstruction of diverted and/or covered watercourses.Many of the Italian historical maps have been referred to the ellipsoid of Bessel with different orientations that in many cases are the same used previously or simultaneously for public purposes including, in particular, the drafting of the cadastral cartography.