Some Considerations Related to the New Realization of SAD-69 in Brazil

IBGE — the institution responsible for the Brazilian Geodetic System (BGS) worked for more than ten years in order to readjust the observables belonging to this system. This work was finished at the end of 1996. The main reason for this paper is that there is the need for complementary analysis of the results. A few aspects related to the new realization of the SAD-69 in Brazil will be shown, taking into account its accuracy and aspects related to the conversion between the new and the old realizations. For the last case, a studied was carried out by using either the seven or three parameters transformation model. A new proposal for the transformation of coordinates is presented. Further investigations should still be carried out. The analysis of the accuracy was based on 34 GPS stations, which are coincident with the conventional network, being their coordinates considered as true values. A total of 34 adjustments were carried out, in such way that the GPS baseline vectors of each one of the stations were removed in the process. The estimated coordinates were compared with the true ones. The results shown an improvement of the new realization. For a more conclusive analysis, fürther GPS stations would be required.