Auto-grading the ditch

The Grade screen has the map on the left, a top stats bar, the chevron indicator overlaid on the center, and a profile chart along the bottom edge. The sidebar on the left shows: Start, Hold, Nudge Up / Down, Reset, Resume, Raise / Lower.

To start grading:

1. Lower the blade so the cutting edge is at or near the ground at your starting point.
2. Tap Start in the sidebar. A red banner reads "Auto Grading Active" and the blade goes under automatic control.
3. Drive at your normal grading speed. The blade moves up or down by itself to track the design.

Start is gated to a real controller link. Start is enabled only when the tablet is paired with a Ditch Assist Control Module, the simulator is running, or the DIG module is attached. Bluetooth GNSS alone is not enough — Bluetooth is for surveying only, not for driving the blade.

Start is also GPS-gated. Tapping Start with no valid GPS fix is refused with a red SnackBar No GPS fix; tapping Start while the GPS stream has gone stale (no data for longer than the GPS Delay Timeout, default 5 s) is refused with GPS: STALE — position not updating. The simulator is exempt. This gate fires before the Pre-Start safety dialog and applies to every auto-grading mode (Ditching, Simple Grading, Tiling, Terracing, Manual, Forming).

Pre-Start safety check

The elevation mismatch check is off by default. Switch it on under Settings → PRE-START SAFETY → Elevation Mismatch Check if you want it: when you tap Start, the app then compares the design target at your current position against your live GPS elevation. If the two differ by more than the configured threshold (Elevation Mismatch Warning, default 30 in / 76 cm), a yellow Safety Check dialog titled Target Far From Current Ground appears showing the magnitude and direction (for example, "The design target here is 3.00 ft above the current ground elevation. On Start, the controller will lift the implement by roughly that amount."). Tap Start Anyway to proceed or Cancel to abort. The check catches stale benchmark offsets and designs loaded from the wrong field — but it also fires at any station where the design calls for a deep cut or fill, and whenever the machine is parked off the design line on higher or lower ground, which is why it is off by default. Manual nudge is included in the checked target, but the Auto-Nudge per-pass offset is not — on a deep-cut job with Auto-Nudge on, the warning can fire on the pass-1 Start because the check compares the final design target against the ground. Expect it, verify the benchmark, and tap Start Anyway.

Reading the chevrons

The chevron indicator in the middle of the screen is a vertical bar with arrows pointing up or down.

• Arrows pointing up → the blade is below target, the app is raising it. Drive normally — the blade is correcting.
• Arrows pointing down → the blade is above target, the app is lowering it.
• Center dot, no arrows → on grade (within ±1″).

The chevrons step in increments set by Settings → GRADING → Inches Per Chevron (default 3", or 0.25 ft in Decimal Feet mode — the label reads Feet Per Chevron there; same stored step, just a different display). At the default, one arrow appears at 1–3" off grade, two at 3–6", three at 6–9", four at 9–12"+. Tighten the slider to 0.5" and four arrows show by 2" off grade; loosen to 6" and four arrows show by 24" off grade. Below 1" off grade the arrows disappear and a green "ON GRADE" line shows instead.

The top stats bar shows:

• Current (ft) — your machine's elevation in the survey frame (GPS altitude + benchmark offset).
• Target (ft) — target elevation the blade is aiming at (includes nudge or Auto-Nudge pass offset).
• Design — un-nudged design target. Only appears when manual nudge is non-zero or Auto-Nudge is on.
• Nudge — current temporary depth offset, green = raise / red = lower.
• BM badge — green when calibrated this session, amber when restored from a prior session, grey when not calibrated; tap to open the Calibrate Elevation sheet.
• Auto Nudge toggle — a switch. The current pass and pass count appear in the sidebar's Auto-Nudge group.

Hold and release

Tap Hold to halt the hydraulics without exiting grading mode. The app sends a halt command to the controller (the blade stops in place) and stops sending new target elevations until you release. The chevrons keep updating. The Raise / Lower buttons stay live during Hold for hand-jogging. Tap Release to re-engage auto-grading.

Auto-Hold

Auto-Hold engages automatically when GPS quality drops. Triggers include:

• GPS drops out of RTK Fixed (Float / single / no fix).
• GPS positions stop updating (stale beyond the GPS Delay Timeout in Settings).
• HDOP rises above the threshold for your RTK Sensitivity setting (Mid 1.2, High 0.9). Low ignores HDOP entirely and holds only on the two conditions above.
• At Mid sensitivity, the rolling RTK-fix window dips below 70% clean.
• At High sensitivity, any degradation from a fully stable window.

If the hold stays on after the fix looks fine again, an amber pill names what it is waiting for — for example AUTO HOLD - WAITING FOR HDOP ≤ 0.9 (NOW 1.10) - SENSITIVITY MID. Releasing needs a tighter HDOP than engaging did (hysteresis, so the blade does not chatter at the line), and on Mid and High the fix window has to read Stable again. If your receiver never reaches the release figure, drop RTK Sensitivity to Low, which ignores HDOP.

Only the RTK-quality triggers (Float / single fix, HDOP, stability window) are gated by the RTK Filter (Settings → SURVEY). The GPS-stale and no-fix triggers fire auto-hold always, regardless of the RTK Filter setting — a frozen or absent GPS stream always engages hold. With RTK Filter off the blade can still chase a Float fix — not endorsed, at your own risk — but never a dead feed. Simulator mode bypasses auto-hold entirely.

Release always requires fresh GPS data first. When the RTK Filter is on, release additionally uses hysteresis — GPS quality has to recover past a tighter threshold (and stay clean across the rolling window on Mid/High) before commands resume. You'll see "HOLD — No RTK Fix" or "HOLD — GPS Stale" in the red banner; both clear automatically once the gate passes.

RTK-loss banner timing. When auto-hold engages on degraded RTK, a red banner appears in the upper third of the map after a short delay: 5 seconds by default during auto-hold (configurable via Settings → CONTROLLER → RTK Loss Timeout), or 2 seconds during a manual hold — the manual-hold timing is fixed because the operator otherwise has no visual cue that GPS dropped while they are hand-driving the blade.

Lateral distance warning. If you drift more than about 30 m from the surveyed centerline, a yellow informational banner appears reminding you that the design line was surveyed elsewhere. The banner is informational only — grading continues and the blade follows its target — but the further you wander, the less the design represents the ground under the blade.

Stop

Tap Stop to end grading. The blade halts immediately. The job auto-saves. You can drive away, switch tabs, even close the app — when you come back, the job is right where you left it.

Reset

Tap Reset in the sidebar to fully clear the current session and return to the Home screen. Reset wipes active survey points, the loaded design, graded terrain and coverage, nudge offset, breadcrumb track, and imported map overlays (KML, WMS, Image, Drain-IQ). Reset does not delete saved files — survey and design JSON remain in Documents/DitchAssist/.