Today, May 6, IBGE releases a free service which, for the first time, will allow real-time access to better quality coordinates (latitude, longitude and altitude) by users of GPS equipment (Global Positioning System) connected to wireless Internet.

Called RBMC-IP, the service consists of real-time transmission, through the Internet, of observations made in 26 of the 60 continuous operation GPS stations spread all over the national territory, which belong to the Brazilian Network for Continuous Monitoring of GNSS Systems (RBMC), maintained by IBGE. When using it, a user who is on land or at sea will be able to improve from ten to one hundred times the precision of information about their position, compared to the level of precision provided by the GPS alone. For this purpose, the user needs in his GPS equipment (or notebook/PDA connected to one), besides wireless Internet, a software to apply corrections obtained from the reference stations (RBMC) to allow the access to more precise coordinates. He must also be registered on https://www.ibge.gov.br/home/geociencias/geodesia/rbmc/ntrip.Then the data in the GPS receiver will be combined with the ones transmitted by IBGE through the Internet; that will allow the access to positioning accuracy variable from some centimeters (in case of the Real-Time Relative Kinematic - RTK- technique to some decimeters (in case of the Differential Technique - DGPS - technique), instead of the nine meters provided by the GPS alone.

The data (or corrections) of RBMC will be available by means of an Internet protocol known as RTCM Networked Transport²  via Internet Protocol (NTRIP), developed by the Federal Agency for Cartography and Geodesy of Germany and widely used in Europe. NTRIP allows simultaneous connections to desktop computers, laptops and PDA’s (handheld computers) connected to wireless Internet such as, for example, GPRS or 3G modem. Before this service, RBMC had already been providing GPS data, but only for applications which did not need real-time results.

All the results obtained by RBMC-IP will be automatically put in SIRGAS2000, the reference system officially in use in Brazil since 2005.

A good example of a sector which will be benefited by this service is precision agriculture, which uses GPS to control the use of manure and pesticides in crops. Using the RBMC-IP service, through the RTK technique, the products can be applied only where they are really necessary, that is, producers will save more and, at the same time, they will benefit the environment, thus reducing aggression against the soil when pesticides are applied to crops. Use will be even wider in all the navigation applications by land and sea.

What are the advantages of RBMC-IP service for real-time applications?

So far, for the conduction of a conventional RTK survey, it was necessary to have a receiver installed in a station with known coordinates, called reference station or RTK base, a mobile receiver (rover) and a VHF communication radio to send data from the reference station to the mobile receiver.

A factor which limits the area of coverage for the conduction of RTK in this model is the reach of transmission of radio waves; if there are obstacles between the reference and the mobile receiver, the expected level of accuracy will not be reached. Besides, since the separation between the two radio channels is narrow, the signal can suffer interference from other users working in the same frequency range, thus causing reduction of  survey quality.

The RBMC-IP service through wireless Internet has replaced the connection via VHF radio. Among the advantages of this change, we can mention the following: a) GPS receivers able to conduct RTK surveys will not need special licenses to work with the NTRIP protocol, but only an Internet connection; b) a GSM/GPRS, or G3 modem, for wireless Internet access is cheaper than a VHF radio; c) it will not be necessary to keep a GPS equipment at a reference station every day, since reference stations are provided by IBGE through RBMC; d) it will not be necessary to find high locations to install the reference station and the transmitter, once the Internet reaches longer distances than the radio does; e) it will not be necessary to worry about physical obstacles, once, since the radio does not work with when there is obstruction, Internet is not affected by it; and f) with RBMC-IP working hours  will be reduced when compared to those in the conventional radio method.

How will the service work?

Data transmission will occur as follows: the GPS receiver existing in each one of the stations which compose the RBMC-IP service continuously sends messages in the RTCM method to a Caster server located in the headquarters of IBGE, in Rio de Janeiro. A user, with a client³ application, an Internet connection and a software which allows the calculation of corrected coordinates, is connected to the Caster server and chooses the RBMC-IP stations whose data or differential corrections he wishes to receive. The corrections are received by the user’s GPS and, as c a consequence, it is possible to obtain corrected positions. Currently, the Caster server of IBGE receives data from 26 stations located in the main Brazilian capitals.

However, the user will need to fill out a registration form. The request will be evaluated and a login and a password will be sent by e-mail. There will be some restraints to access in order to avoid delay of traffic in this server. This way, each user will only be allowed to access 3 of the 26 RBMC stations; if the user is connected for over 24 hours consecutively to the IBGE server, their access will be canceled; the log in and password will be valid for a maximum period of three months; 50 simultaneous accesses, at most, will be permitted.

Finally, the user’s personal computer must not be within a firewall or Proxy network, because, in this case, RBMC-IP services will not work.

What is GPS?

The Global Positioning System, popularly known as GPS is a navigation system developed in the 1980’s by the Department of Defense of the United States, at first exclusively for military means. In May 2000, the North American government started to make available the signs transmitted by GPS satellites to the community, without degradation. That has led to significant improvement in the quality of results obtained in the navigation applications in a general, thus affecting the GPS industry.

Since then, GPS has been a very useful technology for several civil applications, such as fleet control, security systems, precision agriculture, georeferencing of land elements in environmental areas, education, land, etc.

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¹RTK (Real-time Kinematic) is a survey technique based on the differential mode, in which the correction of satellite signals are transmitted in real time, from the reference station whose coordinates the user wishes to know. The accuracy reached in this survey technique is a few centimeters, mainly when high-precision GPS equipment is used.

² Radio Technical Commission for Maritime Services, a file format.

³ Such as the GNSS Internet Radio or BNC (BKG NTRIP Client).