Connectivity and RTK GPS

Why centimetres matter in the row

Standard satellite positioning is fine for mapping a field but not for steering a hoe a few centimetres from a crop stem. RTK, short for real-time kinematic, sharpens the fix by comparing satellite signals with those received at a base station of known position and sending corrections to the machine as it works. In a 2014 Applied Engineering in Agriculture field test on an autonomous tractor, Carballido and colleagues recorded a mean standard deviation of 1.43 cm with RTK against 2.55 cm with satellite-delivered RTX corrections, and the tractor tracked straight lines closely with both. Ask each robot maker what positioning accuracy its weeding or seeding tools assume, and which correction methods the machine accepts.

Base station, network or satellite corrections

Corrections can reach a robot in several ways, and each brings its own dependencies. A base station on your own farm gives control but needs a secure mounting, power and a radio link to the fields. Network services stream corrections over the mobile network, which removes the hardware but ties positioning to signal strength. Satellite-delivered services avoid both, usually with some loss of precision. Galileo's High Accuracy Service, declared operational by EUSPA in January 2023, offers free corrections worldwide with typical horizontal accuracy below 25 cm, delivered through the Galileo E6-B signal and over the internet. That level suits scouting and mapping better than in-row weeding, so match the service to the job.

Map mobile coverage before the robot arrives

Many robots send position, status and alarms to an app, and some take corrections over the same mobile connection, so a weak signal can halt work as well as silence alerts. Walk or drive the fields with a phone on each network before you buy, noting where data drops out, especially in valleys, beside woodland and among tall crops late in the season. Share that map with the maker and ask what the machine does when it loses its link: stop, finish the row or return to a safe point. A mast-mounted antenna, a signal booster or a private radio link can fill gaps, but each needs its own installation work and a check that it is permitted.

Keep data flowing when the signal drops

Plan the data side as carefully as the positioning. Ask how much the robot stores on board while offline, how it catches up when the signal returns and which files you can export without the maker's cloud, such as field boundaries, task maps and treatment logs. Find out whether firmware updates need a fast connection in the yard, and schedule them away from busy weeks. For machines such as the Small Robot Company Tom or the Kilter Ax-1, also ask whether maps made on one farm can be moved to another, since contractors and neighbours may share a robot. A clear answer on offline behaviour is worth more than a long list of connected features.

Sources and further reading

• Comparison of Positional Accuracy between RTK and RTX GNSS Based on the Autonomous Agricultural Vehicles under Field Conditions — Applied Engineering in Agriculture (ASABE).
  Field test of an autonomous tractor comparing base-station RTK with satellite-delivered RTX positioning accuracy.
• Galileo High Accuracy Service goes live! — EU Agency for the Space Programme (EUSPA).
  Launch notice for Galileo's free worldwide correction service, with typical accuracy, delivery channels and intended uses.

Common questions

Is RTK correction a subscription service?

It can be. Network correction services are commonly sold as subscriptions, often per receiver, while your own base station is mainly an upfront cost plus upkeep. Satellite-delivered services vary in price, so compare the total over the years you expect to run the robot.

Can several robots share one RTK base station?

Often, yes, provided they use compatible correction formats and links, and the fields sit within the working range the equipment maker specifies. Check compatibility before adding a second brand of machine, because mixed fleets sometimes need separate receivers or correction subscriptions.