Benchmark Reference

The benchmark is the offset that aligns the GPS elevation frame with the survey elevation frame. This page covers the math (in plain language), all calibration methods, and the AGD imported-benchmark workflow.

The math, in plain English:

Your GPS antenna sees an altitude. Your survey crew shot a known elevation at a known spot. Those two numbers are usually different — by anything from a few centimeters to several meters — because GPS uses one geoid model and the survey uses another, and the RTK base station has its own offset.

The benchmark offset bridges them:

• offset = known_survey_elev − current_gps_ground_elev

Once the offset is set, the app shows you elevations in the survey frame:

• display_elev = gps_elev + offset

When the design says "cut to 247.50", the controller actually goes to:

• controller_target = design_target − offset

So the same physical altitude works in both frames.

Effect of blade height: calibration does not subtract blade height — it uses the raw GPS altitude. You lower the implement to the ground before calibrating, so the antenna reading already corresponds to ground level; the blade-on-ground convention is baked into the offset. Blade height is only subtracted during survey recording (implement raised). A wrong blade height corrupts the survey elevations (and any design built from them) — not the BM calibration itself. Always lower the implement to the ground before calibrating.

When to recalibrate:

• Loaded a survey or design from a different session.
• RTK base station moved, was replaced, or rebooted.
• Display elevation doesn't match a known reference point.
• Job was sitting overnight (frame can drift).

When NOT to recalibrate:

• Same session as the survey, same base running.
• Just rebooted the tablet but the base did not change.

In this chapter

• Calibration methods
• Saved benchmarks
• AGD imported benchmarks