An Introduction To GPS The GPS (Global Positioning System) network operated by the U.S. department of Defence and the GLONASS network
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).
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 This 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 receive with pass-to-pass accuracy of +/-2.5cm means you get less than +/-2.5cm skip or overlap, 95% of the time. Year-To-Year Accuracy This is the measure of repeatable accuracy which means that you can drive the same rows a day week, month or even a year later. To summarise this +/-2.5cm year-to-year accuracy means you can drive the same rows next year within +/-2.5cm of this year’s rows, 95% of the time. 13
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 correction signal. Geostationary satellites then return the correction signal
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
to the GPS receiver on the vehicle, and the correction can be applied to the received position.
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 visible satellite. The signals generated by GPS alone are not accurate enough for use in agriculture. Therefore, corrections
How Accurate Is GPS An uncorrected GPS or GLONASS signal gives you position accuracy between 5-10 meters. This is more
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