GPS auto-steering and precision agriculture
From ordinary GPS to centimetre-precise RTK guidance
An ordinary GPS receiver can determine a position with an accuracy of about one to two metres. That is fine for navigation, but far too imprecise to steer a tractor between rows of crops or to avoid overlap when spraying and fertilising. Therefore, modern agricultural machines use RTK (Real-Time Kinematic), which improves accuracy down to a couple of centimetres.
§How RTK correction works
RTK is based on a fixed reference station knowing its own position very precisely. The station compares its known position with the signal it receives from the satellites and calculates a correction for the local atmospheric disturbance. The correction is sent to the tractor's receiver, typically over the mobile network, and the tractor can thereby correct its own position to within a few centimeters. The result is tracks that lie precisely next to each other, drive after drive, without the driver having to steer manually.
§What auto-steering requires
- 01A GPS/GNSS receiver and antenna correctly mounted and calibrated to the machine's dimensions.
- 02A correction signal — either from your own base station or a subscription to a nationwide correction network.
- 03A control unit that converts position data to control outputs on the machine's control system.
- 04Mobile coverage or other data channel if correction is retrieved externally.
§Advantages in the field
Centimetre-precise guidance reduces overlap between driving lanes, which saves fuel, seed, fertilizer and pesticide. It also provides more uniform rows, less soil compaction from unnecessary double driving and relieves the driver who doesn't need to focus all the time on keeping a straight line. Data on the work performed can also be saved and used for documentation and planning for the next seasons.
§Typical sources of error
Most autopilot problems are not due to the satellite positioning itself but something more mundane: poor mobile coverage that interrupts the correction signal an antenna that has moved or become dirty incorrect equipment dimensions entered in the system or software that is not updated. Before you suspect the positioning you should therefore check connection mounting and setup.
GPS auto-steering is a good example of how the trade today combines classical mechanics with modern electronics and data connections. As a mechanic, you need to understand enough about the system to determine whether a fault is due to the machine's control, the data connection or the setup — and refer on when the problem is outside your field.