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 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).

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.