What is RTK GPS? Real-time kinematic surveying explained
Key takeaways
- RTK GPS combines carrier-phase measurements with corrections from a nearby reference to give centimetre-level positions in real time.
- Corrections come from your own base station by radio, or from a CORS network over the internet using NTRIP.
- A fixed solution means the rover has resolved the carrier-phase ambiguities; only fixed solutions should be used for survey-grade work.
- Accuracy degrades with distance from the reference, typically quoted as a few millimetres plus 1 ppm of baseline length.
- RTK is the workhorse for topographic surveys, stakeout, GIS, machine guidance and precision agriculture.
What is RTK GPS?
RTK GPS is a method of satellite positioning that corrects errors in real time to reach centimetre accuracy. RTK stands for real-time kinematic: "real-time" because the corrected position is available immediately, and "kinematic" because the receiver can move while it measures.
A standard GNSS receiver is typically accurate to a few metres. RTK closes that gap by pairing two receivers. A base sits on a point with known coordinates, and a rover moves around the site. Because both see nearly the same atmospheric and orbit errors, the base can tell the rover how to remove them.
Although people still say "RTK GPS", modern RTK receivers track all major constellations, including GPS, GLONASS, Galileo and BeiDou. The term RTK GNSS is more precise, but both mean the same technology.
How does RTK work?
RTK works by measuring the carrier phase of satellite signals instead of relying only on the coded timing signal. The carrier is a radio wave with a wavelength of roughly 19 cm on the GPS L1 frequency, so measuring its phase gives millimetre-level precision.
The catch is ambiguity: the receiver knows the fraction of a wavelength precisely but not the whole number of wavelengths between it and the satellite. RTK solves this in a few steps:
- The base station records carrier-phase and code measurements from every satellite it tracks.
- It sends these observations or corrections to the rover, usually as RTCM messages, once per second or faster.
- The rover differences its own measurements against the base data, cancelling most satellite clock, orbit and atmospheric errors.
- Its software searches for the integer number of wavelengths to each satellite. This is called ambiguity resolution.
- Once the integers are found, the rover reports a fixed solution with centimetre accuracy and keeps it as long as it holds lock.
Before ambiguities are resolved, the rover shows a float solution, typically decimetre-level. Survey crews should only store points when the receiver shows fixed status.
RTK rover and base vs network RTK
There are two main ways to get RTK corrections: your own base station, or a network of permanent reference stations. Both produce the same kind of fixed solution; the difference is logistics.
| Factor | Base and rover (radio) | Network RTK (NTRIP/CORS) |
|---|---|---|
| Equipment | Two receivers, radio link | One rover with internet access |
| Correction link | UHF radio, typically a few km to about 15 km | Mobile data over 4G |
| Coverage | Anywhere, including remote areas | Where a network and mobile signal exist |
| Running costs | None beyond equipment | Usually a subscription |
| Coordinate datum | Set by your base point | Set by the network |
Many public RTK networks are run by national mapping agencies and regional governments; some are free, others charge. A network rover connects with an NTRIP client, logs into a caster and receives corrections for its location. Our guide to RTK base-rover vs network RTK compares both in depth, and NTRIP and CORS explained covers the network side.
How accurate is RTK GPS surveying?
RTK GPS surveying typically achieves about 8 mm to 1 cm horizontally and 1.5 to 2 cm vertically, plus 1 ppm of the distance to the reference station. One ppm (part per million) adds 1 mm per kilometre of baseline.
That means a rover 10 km from its base adds about 1 cm to the stated accuracy. For single-base RTK, many users keep baselines within roughly 10 to 20 km, because ambiguity resolution becomes slower and less reliable as atmospheric differences grow. Network RTK models these errors across stations to reduce the effect.
Other factors matter as much as distance: sky view, multipath from walls and vehicles, the number of satellites and frequencies tracked, and the quality of the antenna and pole setup. Use our RTK accuracy calculator to estimate expected accuracy for a given baseline.
RTK GPS vs DGPS, PPK and PPP
RTK is one of several high-accuracy GNSS methods. The right choice depends on whether you need results in the field and how much accuracy you need.
| Method | How it works | Typical accuracy | Results |
|---|---|---|---|
| DGPS / DGNSS | Code-based corrections from a reference | Sub-metre | Real time |
| RTK | Carrier phase with real-time corrections | About 1–2 cm | Real time |
| PPK | Carrier phase, corrections applied after the survey | About 1–2 cm | After processing |
| PPP | Precise satellite orbits and clocks, no local base | Centimetre to decimetre, after convergence | Real time or post-processed |
RTK is the standard for stakeout and live surveying because you see the corrected coordinate immediately. PPK is popular on drones, and PPP suits remote areas where no base or network exists.
RTK survey equipment: what you need
A complete RTK survey kit includes receivers, a correction link, a controller and accessories. What you need depends on whether you run your own base.
- RTK receiver (rover): a multi-constellation, multi-frequency GNSS receiver, ideally with IMU tilt compensation.
- Base receiver: a second receiver on a tripod and tribrach, if you are not using a network.
- Correction link: internal or external UHF radio, or 4G for NTRIP.
- Controller: a rugged handheld or tablet running survey software.
- Accessories: range pole, bipod, tripod, tribrach and bracket.
The Mars Geosystems E1 Pro GNSS receiver with screen is a typical example: a 1408-channel full-constellation engine, RTK initialisation in under 5 s typically with over 99.9 % reliability, and 5–15 km internal radio range. For network-only work, the 409 g Mini network RTK rover adds IMU tilt up to 60°. IMU tilt is explained in our article on IMU tilt compensation in GNSS receivers.
What is RTK used for?
RTK positioning is used wherever centimetre accuracy is needed in real time. It is now standard equipment across surveying, construction and agriculture.
- Topographic surveys: recording ground levels and features for design.
- Construction stakeout: setting out roads, buildings and utilities from design coordinates.
- RTK mapping and GIS: capturing assets with survey-grade positions.
- Machine control and guidance: graders, dozers and tractors using RTK for automatic steering.
- Drone mapping: RTK or PPK drones reduce the number of ground control points.
RTK heading is a related technique: two antennas on one vehicle or vessel, both RTK-fixed, give an accurate heading from the vector between them. It is common in machine guidance and marine applications.
Getting started with RTK GPS
Getting started with RTK GPS is straightforward once you decide how you will get corrections. Check network coverage first, then pick receivers to match.
If your region has a reliable CORS network, a single network rover may be all you need. If you work in remote areas, plan for a base and rover pair with radio. Our step-by-step guide to setting up an RTK base station covers the field procedure.
Mars Geosystems supplies RTK receivers from one unit, with OEM and ODM options for distributors from 10 units. Tell us your application and region to request a quote for RTK equipment.
Frequently asked questions
What is RTK in GPS?
RTK in GPS stands for real-time kinematic, a technique that uses the carrier phase of satellite signals and corrections from a nearby reference station to calculate positions with centimetre accuracy in real time. It improves standard GPS accuracy from a few metres to about one or two centimetres.
What is the difference between an RTK base and an RTK rover?
The RTK base is a receiver set up over a point with known coordinates. It stays still and transmits corrections. The rover is the receiver that moves around the site, receives those corrections and calculates its own precise position. In network RTK, a CORS network replaces your own base station.
How far can an RTK rover be from the base?
With a radio link, range is limited by the radio, typically a few kilometres to about 15 km depending on terrain and power. For accuracy, single-base RTK users usually keep baselines within roughly 10 to 20 km, because error grows by about 1 mm per kilometre and fixing becomes slower over longer distances.
What does fixed and float mean in RTK?
A fixed solution means the rover has resolved the integer number of carrier wavelengths to each satellite and is delivering centimetre-level accuracy. A float solution means those integers are not yet resolved, so accuracy is typically decimetre-level. Survey points should only be stored when the receiver reports a fixed solution.
Do I need internet for RTK GPS?
Only for network RTK. If you use NTRIP corrections from a CORS network, the rover needs mobile data. If you run your own base station with a UHF radio, no internet is needed, which makes base-and-rover RTK suitable for remote sites without mobile coverage.
Can RTK GPS work under trees or near buildings?
RTK works best with a clear view of the sky. Under trees or beside tall buildings, signals are blocked or reflected, which can slow fixing or cause errors. Multi-constellation receivers help by tracking more satellites, but for heavy obstruction a total station or offset measurement is often more reliable.
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