GPS Accuracy Definitions

Pass-to-Pass accuracy measures the relative accuracy over a 15 minute interval, usually thought of as guess row error when driving rows, or skip/overlap from one pass to the next when driving swaths. A Trimble GPS receiver with pass-to-pass accuracy of +/- 10 cm means you get less than 10 cm skip or overlap, 95% of the time.

Year-to-Year accuracy is the measure of repeatable accuracy that you can drive the same rows a day, week, month, or year later. So, a +/- 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.

Differential GPS (DGPS) with Beacon correction

The vehicle with a GPS antenna receives GPS signals from the GPS satellite constellation. The Beacon receiver, at a known location, receives GPS signals. The beacon generates an equation that changes the location of where the GPS satellites say it is, to where it knows it is, and then sends the equation known as the 'correction message' to the GPS antenna on the vehicle, which then applies the correction.

Differential GPS with EGNOS & OmniSTAR correction

The vehicle with a GPS antenna receives GPS signals from the GPS satellite constellation. EGNOS (Europe only) and OmniSTAR services have many GPS receivers at known reference locations that send the correction messages to control stations which then uplink the message to a geostationary satellite (EGNOS or OmniSTAR). The geostationary satellite (EGNOS or OmniSTAR) then sends the correction message to the GPS antenna on the vehicle, which applies the correction

RTK (REAL TIME KINEMATIC) GPS Guidance

This is a highly precise technique that results in 2.5 cm year-to-year accuracy. RTK GPS requires two specialized GPS receivers and two radios. One GPS receiver is set up as a base station within a 11 km radius of the field you are working so it can send the correction message to the roving receiver. Both receivers collect extra data from the GPS satellites, known as L2 Band, that enables better precision.