A-B line guidance on an iPhone
Short answer
An A-B line is a straight reference line set by two points. In Tractor GPS – Field Guidance you tap A at the start of a pass and B a little way along it; the app then draws parallel passes across the field, spaced at your implement's working width.
Updated · Oran Dynamics
How to set an A-B line
- Choose the right implement on the Implements tab. Its working width sets the spacing between passes.
- On the Drive tab, drive to where the first pass starts and tap A.
- Drive straight along the pass and tap B. If the app shows a "Move" tip, drive a little further first: it needs enough distance to know your direction.
- The guideline appears through A and B, with parallel lines to the left and right at the working width. They extend across the whole field, so you don't need to drive the full length before tapping B.
Following the line
- Distance off line: the readout shows the distance to the nearest line in your width unit (metres, feet, centimetres or inches), rounded down to whole units.
- Steering arrows: one to three arrows point the way back to the line. They're white when you're within 10% of the implement width, yellow from 10 to 20%, and orange beyond 20%.
- Heading-up map: the map turns with the tractor, so the line always runs up the screen.
Moving or clearing the line
- Recentre: moved to another part of the field? The recentre button shifts the pattern so a line runs through your current position, keeping the same direction.
- Clear: the red X removes the line so you can set a new A and B.
- Saved per field: an A-B line set inside a saved field is stored with that field and that implement, and comes back when you continue the job.
Tips for a good line
- Set A and B on a stretch you know is straight, not on a headland turn.
- A short, accurate A-B beats a long wobbly one. Drive steadily between the two taps.
- Give the phone a minute or two after opening the app so the GPS settles before you tap A.
Questions
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A straight reference line defined by two points, A and B. Guidance systems use it to draw parallel passes across a field, spaced at the implement's working width, so each pass sits next to the last without gaps or overlaps.
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Yes, for a saved field: best fit, parallel to any boundary edge or a set angle, with headland passes. See field lines and headlands.
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Exactly the working width of the active implement. If you want a deliberate overlap, set the width slightly narrower than the tool.
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No. A short, straight run is enough; the lines extend across the whole field.
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- Field guidelines and headlands For a saved field, Tractor GPS – Field Guidance can lay out the guidance lines for you: best fit, parallel to any boundary edge or a set angle, ranked by number of turns, with 0–10 headland lines.
- Coverage mapping: see what you've covered Tractor GPS – Field Guidance paints worked ground on the map as you drive, in each implement's colour. Area covered counts overlaps once, jobs can be paused and continued, and everything is logged.
- Working width and overlap Why working width matters for GPS guidance, how to set it and the implement offset in Tractor GPS – Field Guidance, and how much overlap costs. Includes a free overlap calculator.
- How accurate is a phone as tractor GPS? Measured against an RTK reference, a dual-frequency iPhone is typically within 0.5–0.7 m side-to-side under open sky; older iPhones are typically within 4.9 m (GPS.gov). Which iPhones are dual-frequency, what the app adds, and when you need RTK.