The Brazilian geoid model MAPGEO2004 is limited by 7°N and 35°S in latitude and 34°W and 75°W in longitude with 10' resolution. Fast Fourier Transform (FFT) technique was used to undertake the modified Stokes integral. The mean Helmert anomalies in 10'x10' grid was obtained from the existing terrestrial gravity data (IBGE, several institutions in Brazil and neighboring countries in continental area) until 2004. The free air anomalies of the KMS99 model was used in oceanic areas. The geopotential model EGM96 was used as a reference field restricted to degree and order 180. The geoid height was corrected from the zero-order term, -0.5 meter, for compatibility with the GRS80 ellipsoid, used by SIRGAS2000. The RMS difference associated with the MAPGEO2004 model was ±0.5 meter, determined from the comparison of IBGE GPS/levelling points.
The geoid model is provided in ISG format 2.0 (ISG Format Specifications), while the file in its original data format is available at the model ISG webpage.
The International Service for the Geoid (ISG) was founded in 1992 (as International Geoid Service - IGeS) and it is now an official service of the International Association of Geodesy (IAG), under the umbrella of the International Gravity Field Service (IGFS). The main activities of ISG consist in collecting, analysing and redistributing local and regional geoid models, as well as organizing international schools on the geoid determination.