Feature Geometry and topology issues in trans-formation process between different geodetic reference systems

摘要

A great instrumental evolution has been noticed with the development of new technologies through the years; processing methods and spatial data analysis, among others, bringing a sensible change in cartography and related areas. The adoption of the Geocentric Reference Systems took place as a consequence of the increasing utilization of the Global Navigation Satellite System - GNSS. The adoption of the International Terrestrial Reference System - ITRS, widespread in each co ntinent as a reference system, allows a consistent integration with networks throughout the world. In Brazil, the Resolution n°1/2005 was deliberated by IBGE on February 2005, establishing the Geocentric Reference System for the Americas (SIR-GAS), which was ac complished in 2000 - SIRGAS2000 and adopted by the Brazilian Geodesic System and the National Cartographic System as the new geodesic reference system. The geodetic transformation system needs is a global reality in mapping activities. A qualitative study about the change of geodetic reference was made to indicate probable consequences that could occur in a mapping targeted to software such as Geographic In formation Systems and CAD software. These analyses were based on digital maps of cities in south ern Brazil. Some sources of positional variations were pointed out. The sources were arranged in a table according to the graphic primitives where the implications were analyzed according to the following sources of variation: a) the transformation of geodetic references; b) editing topological structure adequacy; c) conversion between vector file formats; d) mapping updates. The results showed that when transforming a mapping into a reference digital medium with some software, a range of tasks necessary to fit the data must be provided. Besides the transformation itself, format conversion, editing of topological structure and incorporating new mapping techniques that may be more or less compatible with the techniques used thus far need to be performed.