Machine Autosteer

Firstly we must define what we mean by "machine autosteer". In this context it is any technology that provides vehicles or implements with automated steering and positioning in the landscape. It is useful in farming because it can reduce the overlap between passes of machines, thereby cutting down on energy and time wasted as well as expensive chemicals and fertilizers. It can also relieve drivers from the stress of driving very precisely for many hours and enables operations to continue when visibility is poor or at night.

Satellite guidance in general

Before concentrating on CTF, we will provide some information on satellite systems in general.

If operators want to improve "pass to pass" accuracy, there are many satellite-based guidance systems that will deliver this and Trimble provides an excellent web-based tutorial which explains how they work.

Equally valuable is the Only Guidance site, which gives a good grounding in guidance systems and autosteer.

The best pass to pass accuracy provided by free satellite signals is limited to ± 30 cm, but subscription services will provide ± 10 cm (e.g. Omnistar HP or John Deere SF2). Pass to pass accuracy is only what it says though; it will not re-position machines in exactly the same place every time they are taken into the field. This is because pass to pass accuracies with these systems are only guaranteed if your next pass is within about 15 minutes. Outside this time constraint, the error could be much larger and none of these "satellite-based correction signals" are capable of bringing machines back to exactly the same place year in year out. So, they are okay if you just want pass to pass accuracy, but they are unsuitable for CTF.

Satellite guidance for CTF

For controlled traffic we need a very particular type of guidance – it has to be one that steers machines very precisely as well as keeping them in exactly the same tracks from one year to the next. Only Real Time Kinematic (RTK) guidance is capable of doing this and must be used for CTF. RTK is a correction signal delivered from physical or virtual earth-bound base or reference stations, in conjunction with satellites. It is capable of delivering ± 2 cm pass to pass and absolute positioning accuracy. Virtual reference stations are referred to as Continuously Operating Reference Stations (CORS). The signals from these are generally delivered via mobile phone technology while those from physical RTK stations are via a radio.


This page provides links to a wide range of commercial satellite guidance providers, many of whom offer an RTK solution, which is essential for controlled traffic, but don't assume these providers will know about CTF; at the moment only a few of them will but we hope that will change. Links are also provided to information about free satellite-based correction signals, which are suitable only for pass to pass accuracy within a timescale and not absolute or repeatable positioning. Further information about guidance technologies is provided as part of membership, for which you can apply on the Membership page.

Correction signals provided by public funded agencies

EGNOS - the European Space Agency’s free correction signal containing information on the reliability and accuracy of the positioning signals sent out by the Global Positioning System (GPS) and the Global Orbiting Navigation Satellite System (GLONASS). This is capable of positioning to around 2 m accuracy.

Galileo - the European Space Agency’s equivalent of GPS and GLONASS, due to be completed by 2013. This array, together with EGNOS, will provide a free correction signal with a claimed positioning accuracy of around 1 m compared with the present 2 m.

Correction signals from commercial suppliers

The following is a list of suppliers of satellite guidance, support and associated equipment. Please visit their sites to see what they offer. This list does not claim to be exhaustive, just those we have discovered. Their inclusion does not imply endorsement.


CORS information for Great Britain and Ireland

Satellite and RTK base-station corrections

Omnistar - commercial provider of free and subscription correction signals
Navcom – commercial provider of free and subscription correction signals
RTK Solutions
John Deere Autotrac
Hemisphere GPS (formerly Beeline Technologies)
Precision Decisions
AS Communications
RTK Farming
Soil Essentials