GNSS Antenna Height — How to Measure It Correctly
Setup Guide
GNSS Antenna Height — How to Measure It Correctly Every Time
Incorrect antenna height is the single most common cause of elevation errors in GNSS surveying and construction GPS. This guide covers everything you need to know — vertical vs slope height, quick-release adapters, base station setup, and what happens when you get it wrong.
In this guide
Overview
Why Antenna Height Matters So Much
The GNSS receiver calculates the position of its antenna phase center — not the point on the ground you are measuring. SiteWorks subtracts the antenna height to compute the ground elevation. If the antenna height is wrong by even a small amount, every single elevation you collect is wrong by exactly that amount.
| Antenna height error | Effect on all collected data |
|---|---|
| 10 mm (0.01 m) error | Every elevation off by 10 mm — at the limit of RTK accuracy |
| 30 mm (0.03 m) error | Significant error — will cause rework on fine grade work |
| 32 mm (~1.25 in) | Exact height of a Trimble quick-release adapter — common mistake when forgotten |
| 100 mm (0.1 m) error | Catastrophic for grade work — entire site elevation is wrong |
△ This error is invisible until you checkRTK Fixed status does not validate your antenna height. You can have a perfect Fixed solution and still have wrong elevations if the antenna height is entered incorrectly. Always check into a known control point after setting up.
Rover
Rover Antenna Height — Range Pole
The rover antenna height is the vertical distance from the tip of the range pole (the point touching the ground) to the antenna reference point (ARP) of the receiver — which is the bottom of the receiver for most Trimble smart antennas.
1
Read the pole height from the pole graduations
- Most Trimble range poles are graduated in 10 cm increments. The most common working height is 2.000 m.
- Read the height directly from the pole where the locking collar is set.
- Always verify the locking collar is fully tightened — a partially extended section can give a false reading.
2
Measure to the correct point on the receiver
- For Trimble smart antennas (R750, R780, SPS986, R12i): measure to the bottom of the receiver — the flat face that sits on the mount adapter.
- Do NOT measure to the top of the receiver or to the center of the unit.
- The ARP location is shown in the receiver documentation — when in doubt, check the receiver datasheet.
3
Use vertical height — not slope height
- Always enter vertical height in SiteWorks unless you are explicitly measuring slope height and the software asks for it.
- Vertical height = the straight-up distance from the ground point to the ARP.
- Slope height = the slant distance along the pole. Entering slope height in a vertical height field causes errors equal to the difference, which increases with pole tilt.
Quick Release
Quick-Release Adapters — The Most Common Mistake
△ This mistake is extremely commonThe Trimble quick-release (QR) adapter adds approximately 32 mm (1.25 inches) of height between the pole and the receiver. If you enter the pole height but forget the QR, every elevation you collect will be wrong by 32 mm.
1
Measure to the bottom of the quick-release — not the receiver
- When using a quick-release adapter, measure the pole height to the bottom of the quick-release adapter, not to the bottom of the receiver.
- SiteWorks automatically adds the known quick-release height offset when you indicate a QR is in use.
- Do NOT add the QR height manually and also check the QR box — that would double-count it.
2
Tell SiteWorks a quick-release is in use
- In SiteWorks, when entering the antenna height, there is a checkbox or toggle for "Quick Release in use" (or similar wording).
- Enable this when a QR adapter is physically on the pole.
- SiteWorks will display a QR icon on the map screen to confirm it is accounting for the adapter.
- Each time the antenna height is changed, verify this setting is still correct.
💡 Check the icon on the SiteWorks map screenWhen quick-release is enabled, SiteWorks shows a small QR icon next to the antenna height in the info bar. If you see it, the offset is being applied. If you do not see it but a QR is physically on the pole, your heights are wrong — go update the antenna height settings.
Base Station
Base Station Antenna Height
The base station antenna height is the vertical distance from the control point benchmark to the antenna reference point of the base receiver. This measurement must be precise — a base height error affects every measurement made by every rover connected to that base.
1
Measure from the benchmark nail or monument
- Use a tape measure. Measure vertically from the top of the benchmark nail (or the defined measurement point on the monument) to the bottom of the base receiver or antenna.
- Be precise — measure to the nearest millimeter. Even 5 mm matters on precision work.
- If using a fixed-height tripod or T-bar: the height is constant between setups — record it once and mark it clearly on the equipment.
2
Identify the correct measurement point on the base receiver
- For Trimble R750, R780, SPS986 as a base: measure to the bottom face of the receiver body.
- For external Zephyr antennas: measure to the base of the antenna ground plane — the flat bottom of the Zephyr disk.
- Trimble provides specific ARP diagrams for each antenna model in the receiver documentation. When in doubt, look it up.
3
Keep the height consistent between daily setups
- If using AutoBase and returning to the same post/pole daily, the receiver assumes the antenna height is identical to the previous setup.
- If there is ANY chance the height changed (base was moved, different tripod used, different adapter), use SiteWorks to restart the base and re-enter the height rather than relying on AutoBase.
- Never assume the height is the same — always verify physically before starting work.
SiteWorks
Entering Antenna Height in SiteWorks
1
Set the rover antenna height at connection time
- After connecting the rover in SiteWorks, the software prompts for the antenna height immediately.
- Enter the pole height in the correct units — verify meters vs feet matches your project settings.
- Check the quick-release toggle if a QR adapter is in use.
2
Update the height whenever the pole height changes
- In SiteWorks, tap the antenna height indicator in the info bar at any time to update it.
- Every pole height change must be updated in SiteWorks before collecting the next point.
- Missed updates are logged — SiteWorks records every height change with a timestamp in the work order log.
3
Correct a wrong height after the fact
- If you discover the antenna height was wrong after collecting points: go to Data Management → Point Manager in SiteWorks.
- You can correct the rod height for individual points in the Point Manager — SiteWorks will recompute the elevation.
- This only works for a consistent height error — if the height changed inconsistently during collection, each point must be corrected individually.
Troubleshooting
Common Antenna Height Errors and Fixes
| Error symptom | Likely cause | Fix |
|---|---|---|
| All elevations off by exactly the same amount across the whole site | Wrong antenna height entered — rover or base | Identify the exact error amount from a known benchmark. Correct the height in Point Manager or re-collect with correct height. |
| Elevations off by ~32 mm (about 1.25 inches) | Quick-release adapter height not accounted for | Enable the QR toggle in SiteWorks antenna height settings. The QR adds ~32 mm that SiteWorks adds automatically when the toggle is on. |
| Elevations match benchmarks horizontally but are high or low by a consistent offset | Vertical vs slope height confusion | Verify you entered vertical height, not slope height. Re-measure with pole as vertical as possible. |
| Some points correct, others wrong — no consistent offset | Pole height changed during collection without updating SiteWorks | Check the work order log for height change timestamps. Correct individual points in Point Manager. |
| Check shot on known point shows elevation error after calibration | Wrong base antenna height entered when setting up base | Re-measure the base antenna height carefully. Restart the base in SiteWorks with the corrected height. Re-verify on the known point. |
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