RTK
RTK GNSS Surveying: Accuracy and Quality Control
Summary
Real-time kinematic (RTK) GNSS uses carrier-phase measurements and corrections from a base station or network to position a rover to about 1–2 cm horizontally and 2–4 cm vertically within seconds. Results are only trustworthy with a fixed ambiguity solution, good satellite geometry, a correctly defined datum and independent checks on known control.
Definition
RTK: GNSS positioning that resolves carrier-phase integer ambiguities in real time using corrections from a reference receiver.
- Typical: 1–2 cm H, 2–4 cm V
- Needs a fixed solution
- Accuracy degrades with baseline length
- Check known control daily
How RTK works
A base receiver on a known point (or a network of reference stations) streams its observations or corrections to the rover over radio or internet (NTRIP). The rover forms double differences, resolves the integer number of carrier wavelengths, and obtains a precise baseline from the base.
Single base versus network RTK
| Single base | Network RTK (VRS, MAC, FKP) | |
|---|---|---|
| Range | Typically up to 10–20 km | Across the network area |
| Datum | Defined by base coordinates | Defined by network operator |
| Setup | Base and radio needed | NTRIP login only |
| Main risk | Wrong base coordinates | Network datum or epoch mismatch |
Datum and coordinate system
RTK coordinates are in the reference frame of the corrections, for example a national frame such as KSA-GRF17 or an ITRF realization. Projecting to a grid such as UTM and converting ellipsoidal to orthometric heights with a geoid model must use the same frame as the project control.
Quality control on site
- Accept only fixed solutions; reject float.
- Check PDOP (for example ≤ 3–4) and the reported precision.
- Occupy a known control point at the start and end of each session.
- Re-observe a sample of points at a different time of day for independent satellite geometry.
- Avoid multipath near buildings, fences and vehicles.
FAQ
How accurate is RTK?
Typically 8 mm + 1 ppm horizontally and 15 mm + 1 ppm vertically (1σ) under good conditions, which is roughly 1–2 cm and 2–4 cm in practice.
Why are my RTK heights different from benchmarks?
RTK gives ellipsoidal heights. You need the correct geoid model, and the benchmark datum must match the vertical datum you convert to.
Can I use RTK for control surveys?
For many engineering projects yes, with redundant occupations and checks. Primary control is usually established with static GNSS.
Related tools and articles
Tools
- Field Visit SurveyRecord and check field observations.
- Coordinate TransformationConvert between EPSG coordinate systems.
- Field Visit SurveyDocument site visits with mapped points.
Articles
- GPS / GNSS Surveying Methods ComparedGNSS surveying positions points from satellite signals of GPS, GLONASS, Galileo and BeiDou. Methods range from…
- Static SurveyReference topic
- GNSS Quality ControlReference topic
- KSA-GRF17: Saudi Arabia Geodetic Reference FrameKSA-GRF17 is the national geodetic reference frame of Saudi Arabia, defined by GEOSA and aligned to ITRF2014 a…
- UTM Coordinate System ExplainedUTM divides the world between 80°S and 84°N into 60 zones, each 6° of longitude wide and projected with a Tran…
References
- NOAA National Geodetic Survey. Guidelines for Real Time GNSS Networks and NGS-58/59 GNSS height guidelines.
- Hofmann-Wellenhof, B., Lichtenegger, H. & Wasle, E. GNSS – Global Navigation Satellite Systems, Springer, 2008.
Cite this page
GeoCAD Bridge. “RTK GNSS Surveying: Accuracy and Quality Control.” GeoCAD Bridge Knowledge Center, updated 2026-10-05. https://www.geocadbridge.com/knowledge/survey-rtk-survey/