AB-line guidance (Field Survey)

The Field Survey screen has its own steering aid for driving straight, evenly spaced parallel passes up and down a field — handy for covering a field methodically while you survey it, or just driving a tidy grid. It uses the same lightbar and arrows as contour following, so it behaves identically; only the line you follow is different. It is straight parallel passes here, instead of an elevation contour.

How it works: you mark two points to define a direction (an A-B line), and the app lays a fan of parallel lines across the field at your chosen swath spacing. It then guides you down whichever pass you are nearest, switching to the next as you move over.

The AB-line lightbar uses the same visual indicators as the Levee contour lightbar, and tapping it opens the same guidance sensitivity dialog (Full-scale deflection, On-track tolerance, Edge buffer). The settings are shared between AB-line and contour following — tune them from either screen.

To set up AB-line guidance:

1. On the Field Survey screen, set your swath width first. Tap the swath button in the sidebar to open the Swath Width dialog. Type a numeric value in your unit system (1–500 ft imperial, 1–200 m metric). The default is 40 ft in imperial; on metric, the first A-drop resets it to 15 m.
2. Drive to where you want your first pass to start and tap Set A. If you tap Set A without a valid GPS fix, the app prompts you to wait — a fix is required to anchor the A point.
3. Drive at least about 30 m (100 ft) along your intended line, then tap Set B. The two points fix the direction.
4. The app draws parallel passes across the field at the swath spacing. The pass nearest you turns active (teal); the others show in blue.

Driving the passes:

• Steer down a pass using the lightbar (lights the side you have drifted to) and the arrows (point the way to steer back) — exactly like contour following. Steer toward the arrows.
• As you finish a pass and move over toward the next one, the app auto-selects the nearest pass and switches guidance to it. You just turn around and come back; it lines you up on the adjacent pass.

Clearing or changing:

• Tap Clear AB to remove the passes and start over.
• Re-cycle the swath button any time to respace the passes; if a line is already set, the passes redraw at the new spacing.

AB-line guidance runs whenever you have a GPS fix, recording or not, so you can line up on a pass before you tap Start. It is steering help only — it does not control the blade.