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About the publication - Planialtimetric Network
The first geodetic surveys in Brazil were conducted in October of 1939 by the National Council of Geography (CNG) with the purpose of determining astronomical coordinates in cities and villages in order to update the 1:1,000,000 Brazil Chart of 1922. In 1944 the first geodetic basis was measured in the vicinities of Goiânia. That was the beginning of the systematic establishment of the Brazilian Geodetic System (SGB) in its planimetric component, through measurements of latitudes and longitudes. SGB was materialized by a set of points (pedestals, benchmarks or plates) located on the earth surface by the triangulation method and densified by the poligonation method. Such methods, named “classical”, were applied up to the mid 90s, and their equipment included theodolites and distance electronic measurers.
At the same time, in the 70s, the artificial satellites tracking operations of the American Navy’s Navy Navigation Satellite System (NNSS), also known as TRANSIT, began. That methodology was initially applied to the installation of geodetic stations in Amazon, where the classical methods were unfeasible due to the difficulties posed by the characteristics of the region.
In 1991 IBGE acquired four Global Positioning System (GPS) receivers and started using that technology in the densification of the SGB planimetric benchmarks. As a result, the GPS era started in IBGE. The first campaign, inserted in a world project known as GPS for IERS and Geodinamics (GIG91), happened in the beginning of 1991.
The implementation of RBMC (Brazilian Network for Continuous Monitoring of the GPS system) in 1996 established the concept of ‘active’ networks by means of the continuous monitoring (tracking) of the GPS satellites. All the data daily collected in the RBMC stations are automatically transferred and made available to users in the RINEX format.
The Geocentric Reference System for the Americas (SIRGAS) project includes the participation of the Latin American countries and Caribbe. In the context of the project, 2 reference networks for the continent were established, one in 1995 and the other in 2000. These scientifically accurate networks will function as a basis for the American national networks.
In the Work Group 1 workshop – Reference System –, held in August of 2006, 5 “Analysis Centers” were established with the purpose of processing, comparing and combining the GPS data from the permanent stations located in the Latin America countries and Caribbe. The activities of these centers are aimed at maintaining the SIRGAS Reference Network and at integrating this with the GNSS Service International Global Network (IGS).
State GPS Networks
The state GPS networks aim at addressing the current demands of the society, which are even more improved with the use of positioning techniques through artificial satellites. As an example of these needs of the society, law no. 10,267/01, established by INCRA, aims at georeferencing every rural property existing in Brazil, based on the Brazilian Geodetic System - SGB.
Having accomplished it, every Federation Unit will have a highly precise network, interconnected, based on the Brazilian Network of Continuous Monitoring - RBMC, the main geodetic structure of the Brazilian territory.
Thirteen state GPS networks were established up to December 2006, encompassing 18 states: São Paulo, Paraná, Minas Gerais, Mato Grosso, Mato Grosso do Sul, Santa Catarina, Rio de Janeiro, Rio Grande do Sul, Bahia, Ceará, Espírito Santo, Acre and the Northeast Region. The Northeastern network was a specific case, as it was established in a single measurement campaign, including the states of Alagoas, Sergipe, Pernambuco, Paraíba and Rio Grande do Norte.
The location of each milestone is previously selected by representatives of federal, state and municipal institutions, as a way to preserve its physical integrity, i.e., avoid shocks that could interfere in its coordinates or even destroy it.
The implementation of a state geodetic network will help in the development of the following products and information:
- design of maps and charts;
- reference for engineering works like: road construction and paving, construction of bridges, overpasses and tunnels;
- demarcation of state units, municipal units, Indian areas, preservation areas;
- land regulation;
- energy transmission;
- water supply, etc.
From 1939 up to the current date, the IBGE has been following the state-of-the-art of the geodetic science, aiming at providing Brazil with a planimetric structure compatible with the precision level provided by current technology.