Using your phone's GPS to guide the tractor
A phone knows where it is to within a few metres. Guidance needs an inch. That is not a gap you close with a better app.
What it is
Phone apps that overlay a field map and claim to guide a pass, or a phone clamped to the dash standing in for a guidance receiver.
The numbers
- A GPS-enabled phone is typically accurate to about 4.9 m (16 ft) under open sky, per the U.S. government's own published figure.
- Guidance needs pass-to-pass error under an inch. That is a difference of more than a hundred times — not a tuning problem, a different instrument.
- The dual-frequency phones sold since 2018 do better, reaching sub-metre in good conditions. Sub-metre is still forty times too coarse to plant against.
Why it's here
Because the apps are not lying, exactly — they are being read wrong. They are coverage-mapping tools, and people hear 'GPS' and assume it is the same GPS the $14,000 kit uses.
The catch
Use it for the thing it is actually good at. A phone will honestly log where you drove, count your acres, and show you the strip you missed — all useful, all free. What it will not do is tell a steering motor where to go, and an app that offers to try will put you off the whole idea of guidance for a bad reason. The inch comes from RTK, and RTK comes from a correction stream and a receiver built to use it.
In the guide
Chapter 4 of the Autofarmation guide explains where the inch actually comes from. Autofarmation →