How Does It Work?


WHAT IS GPS?

The GPS (Global Positioning System) operated by the U.S Department of Defence and GLONASS operated by the Russian Federation are a space-based navigation system formed from a network of satellites which determine the position of a vehicle using signals from the 32 satellites that circle the earth. These satellites travel in known orbits that allow a land based receiver to determine its own position in relation to each satellite from which it receives a signal.

The GPS antenna fitted to the machine receives continuous signals from the GPS satellites. ground based GPS receivers, at known locations across the country, receive the same signals. As their absolute location is known, they can calculate the real time position and send a position correction signal. Geostationary satellites then return the correction signal to the GPS receiver on the vehicle, and the correction can be applied to the received position.

The signals generated by GPS alone are not accurate enough for use in agriculture. Therefore, corrections must be made to GPS signals to improve their accuracy. With these correction signals we refer to the system as DGPS (Differential Global Positioning System).

GLONASS NETWORK

The Russian navigation satellite network GLONASS uses the same principle as the GPS network emitting signals at different frequencies. Some agricultural applications require a level of precision that can only be guaranteed by the joint reception of signals from both the GPS and GLONASS networks, in order to ensure adequate satellite coverage and the required correction.

To provide this capability, some of our receivers are able to process GPS and GLONASS satellite signals, offering users a higher level of "productivity insurance” than the single constellation receivers.

THERE ARE TWO MAIN DGPS CORRECTION SERVICES AVAILABLE TODAY

SBAS - The GPS (Global Positioning System) operated by the U.S Department of Defence and GLONASS operated by the SBAS-Satellite Based Augmentation System, communicate difference via geostationary satellite.

RTK - Real Time Kinematics, communicate difference directly to the vehicle via short wave radio from a local base station.

HOW ACCURATE IS GPS?

 An uncorrected GPS or GLONASS signal gives you position accuracy between 5 to 10 meters. This is more than adequate for car navigation systems, but not accurate enough for vehicle guidance in agricultural applications, where we need Pass to Pass and Year to Year accuracy and repeatability.

Pass-to-Pass accuracy measures the relative accuracy over a 15 minute interval. This is usually thought of as skip/overlap from one pass to the next when driving swaths. A New Holland receiver with pass-to-pass accuracy of +/- 2.5 cm means you get less than 2.5 cm skip or overlap, 95% of the time.

Year-to-Year accuracy is the measure of repeatable accuracy which means that you can drive the same rows a day, week, month, or year later. So, +/- 2.5 cm year-to-year accuracy means you can drive the same rows next year within 2.5 cm of this year’s rows, 95% of the time.