Instituto Brasileiro de Geografia e Estatística

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Geodesy

FAQ

(Frequently Asked Questions )

Below you find questions and answers about the geodetic reference system change. In case you have a different doubt or want further information about one of the topics,click here to send us a message.

1. What is a geodetic reference system? What is its application?

2. What is (are) the geodetic reference system(s) used in Brazil today?

3. What is (are) the difference(s) between SAD69 and SIRGAS2000?

4. What kind of problems can the coexistence of more than one system cause?

5. Is it true that the country will have only one official reference system?

6. When is the SIRGAS2000 change due?

7. Who is the adoption of only one system mandatory for?

8. While the change is not complete, in which system will the new mappings be conducted?

9. What happens to those that, upon the completion of the change process, continue adopting the old system?

10. Why does the country need only one reference system?

11. In practice, what are the advantages of adopting SIRGAS2000 instead of the other reference systems presently used?

12. What is going to change, in practice, with the adoption of the geocentric reference system?

13. Are the maps going to change?

14. Will the government provide tools for me to convert to SIRGAS2000? At what cost?



COORDINATE TRANSFORMATION

15. Are there transformation parameters between WGS84 and SIRGAS2000?

16. The results of my work should be in WGS84. Can I continue using the SAD69/WGS84 parameters published in the Resolution of the Presidency of IBGE number 23, of 21/02/89 (R.PR 23/89)?

17. Why do I obtain different results when I compare the coordinates of a geodetic station obtained from the IBGE’s data base with the same coordinates transformed in the TCGEO or ProGriD programs?


1. What is a geodetic reference system? What is its application?

It is a coordinated system used to represent geometric or physical terrestrial characteristics. In practice, it is used to obtain coordinates (latitude and longitude), which enable the representation and location of any element of the surface of the planet in maps.
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2. What is (are) the geodetic reference system(s) used in Brazil today?

Legally, there are SAD69 (South American Datum 1969) and SIRGAS2000 (Geocentric Reference System for the Americas ). There are also other systems that, though not lawful, are still used in the country.
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3. What is (are) the difference(s) between SAD69 and SIRGAS2000?

They were differently conceived. While the definition/orientation of SAD69 is topocentric, that is to say, the origin and orientation point is on the terrestrial surface, the definition/orientation of SIRGAS2000 is geocentric. That means that this system adopts a computationally estimated point in the center of the earth (geoid) as its reference.
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4. What kind of problems can the coexistence of more than one system cause?

The difficulty of aligning geographic data from several origins. For instance, for the analysis of the environmental impact a hydroelectric plant may cause, several aspects of the ecosystem of the region should be taken into account: fauna, flora, rural and urban area, roads, rivers etc. All these data must be gathered in order to build a geographical information system and, for that to happen without problems, they must be aligned to the same reference system. Data provided by SAD69 and by SIRGAS2000 are not compatible, that is, they cannot be inserted in the same map. The average distance between their coordinates (they vary depending on the location considered) is around 65 meters.
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5. Is it true that the country will have only one official reference system?

Yes. After the transition period, SIRGAS2000 will be the only geodetic reference system in the country. It is the new base for the Brazilian Geodetic System (SGB) and for the National Cartographic System (SCN).
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6. When is the SIRGAS2000 change due?

2014.
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7. Who is the adoption of only one system mandatory for?

For anyone who needs to receive or provide spatial information in relevant scales from and to the government and from and to institutions producing cartography in Brazil – in sum, for all that use or produce geographical information.
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8. While the change is not complete, in which system will the new mappings be conducted?

In SIRGAS2000.
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9. What happens to those that, upon the completion of the change process, continue adopting the old system?

They will no be able to, for example, require a revision of the limits of a property, solve any legal questioning by the old system nor provide/receive data to/from public service institutes in order to use or provide services.
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10. Why does the country need only one reference system?

In order to align geographical data, facilitating their interchange by everyone, including Brazil and the other countries that use SIRGAS2000.
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11. In practice, what are the advantages of adopting SIRGAS2000 instead of the other reference systems presently used?

By adopting the geocentric reference system, it will be possible to directly use the GPS technology (Global Positioning System), an important tool for map updates, transportation fleet control and air, sea and land navigation in real time. SIRGAS2000 will enable a higher accuracy for Brazilian territory mapping and delimitation. Moreover, the adoption of this new system by Latin America will solve a series of problems resulted from the discrepancy between the geographical coordinates obtained by GPS and those found in the maps presently used in the continent.
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12. What is going to change, in practice, with the adoption of the geocentric reference system?

The coordinates of the geographical information. As the reference system will be changed, all the coordinates will be altered following the same magnitude and direction.
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13. Are the maps going to change?

Some maps will. The changes will not be noticeable in small-scale maps, such as wall maps, in which 1 cm is equivalent to 5 km. But in larger-scale maps, such as topographic sheets and cadastral mapping, differences in coordinates will be relevant.
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14. Will the government provide tools for me to convert to SIRGAS2000? At what cost?

Yes, in the website of IBGE you can find free files and programs to help in the conversion to the new reference system such as: the SIRGAS2000 coordinates from the stations of the Brazilian Geodetic System planimetric network and the Coordinate Transformation Program – TCGEO.
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Coordinate transformation

15. Are there transformation parameters between WGS84 and SIRGAS2000?

There are not such parameters between SIRGAS2000 and WGS84 because they are practically equal, that is, DX = 0, DY = 0 and DZ = 0.
Since the establishment of GPS(Global Positioning System), its Geodetic Reference System (WGS84) has been updated three times. The purpose was to align it to ITRFyy, the most accurate ITRS realization. The latest update was named WGS84 (G1150), adopted in the GPS system since January 20th of 2002.
The SAD69 / WGS84 transformation parameters, published in the Resolution of the Presidency of IBGE number 23, of 21/02/89 (R.PR 23/89), are valid to transform the coordinates between SAD69 / WGS84 in GPS observations conducted in the period from 01/01/1987 to 01/01/1994.

WGS84 to SAD69:
DX = +66.87 m
DY = -4.37 m
DZ = +38.52 m

The SAD69 / SIRGAS2000 parameters, used in TCGeo and ProGriD (option: SAD69 Doppler Technique or GPS) and published in the Resolution of the Presidency of IBGE number 1, of 25/02/2005 (R.PR 01/05), are valid to transform the coordinates between SAD69 / WGS84 and SAD69 / SIRGAS2000 in GPS observations conducted after 1994.

SIRGAS2000(WGS84 (G1150)) to SAD69:
DX = +67.35 m
DY = -3.88 m
DZ = +38.22 m
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16. The results of my work should be in WGS84. Can I continue using the SAD69/WGS84 parameters published in the Resolution of the Presidency of IBGE number 23, of 21/02/89 (R.PR 23/89)?

As stated in the previous answer, due to the technological evolution, WGS84 has been updated three times since GPS was made available to the civil community in 1987. These updates were named WGS84(G730), WGS84(G873) and WGS84(G1150). Thus, the parameters published in the R.PR 23/89 should be used to transform results from GPS surveys conducted up to January of 1994. For surveys after this date, the parameters between SAD69/SIRGAS2000 published in the R.PR 01/05 should be used.
The difference between the old transformation parameters (R.PR 23/89 ) and the new ones (R.PR 01/05) is 0.48 m, 0.49 m and –0.30 m, to TX, TY and TZ, respectively, which is a result of the evolution of WGS84.
In order to accomplish a coordinate transformation relative to the current WGS84 (G1150), it is necessary to use the transformation parameters from the R.PR 01/05, because today the SIRGAS2000 and WGS84 (G1150) systems are compatible at a level of a few centimeters.
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17. Why do I obtain different results when I compare the coordinates of a geodetic station obtained from the IBGE’s data base with the same coordinates transformed in the TCGEO or ProGriD programs?

The coordinates available in the descriptions of the geodetic stations were not obtained through transformation parameters, but through observation adjustments. The SIRGAS2000 coordinates resulted from an adjustment conducted in 2006, while the SAD69 system coordinates resulted from a SAD69 adjustment conducted in 1996. Consequently, when the transformation by the TCGEO or ProGriD programs is conducted, a small difference is detected, in contrast with the coordinates presented in the station description.
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