In the previous support tip, we explored how receivers calculate position using GNSS signals. Today, we’re focusing on high-precision or survey-grade RTK GNSS receivers like Reach that convert satellite signals into centimeter-accurate location data.
What is an RTK GNSS receiver?
Reach RTK GNSS receivers are designed for accuracy-critical tasks in fields like surveying, construction, agriculture, etc. They not only determine position by triangulating signals from multiple satellites across all the available constellations but also correct for various errors, such as those described in the previous tip, to achieve centimeter-precise positioning.
After determining their position, Reach receivers take advantage of correction techniques such as RTK (Real-Time Kinematic), PPK (Post-Processed Kinematic ), and PPP/PPP-RTK (precise point positioning) to achieve centimeter-level precision. These techniques enhance positioning accuracy by minimizing errors from satellite signals and/or atmospheric errors. Additionally, there are other techniques, such as SBAS, providing regional corrections for improved precision in aviation, navigation, and GIS mapping.
Understanding GNSS correction techniques
All GNSS correction techniques share a core principle: they improve positioning accuracy by accounting for errors in satellite data. This is typically achieved by supplying the rover receiver with additional information, either from a physical base receiver, a virtual reference station, or global services.
There are two primary approaches to delivering these corrections:
- OSR corrections (Observation Space Representation, like RTK and PPK): These rely on the assumption that both the base and rover observe the same satellite errors. By comparing their observations, the system effectively cancels out shared errors like satellite clock drift or atmospheric delays—without explicitly modeling them. In RTK or PPK, the position is refined based on the difference between what both receivers “see.”
- SSR corrections (Space State Representation, like PPP): These rely on complex atmospheric and orbital models to calculate and apply corrections on the rover. The satellites and reference stations broadcast not just navigation data but also estimates of the remaining errors. The rover then uses this global data to compute its position independently—no nearby base needed.
In short, RTK assumes shared errors and subtracts them, while PPP receives modeled corrections and applies them. Both improve accuracy, but through fundamentally different strategies.
GNSS correction techniques comparison
The table below compares the most common GNSS correction techniques to help you choose the one that best fits your workflow:
| Technique | Description | Accuracy | Used In |
|---|---|---|---|
| RTK (Real-Time Kinematic) | Uses two GNSS receivers—a stationary base and a moving rover. The base continuously receives satellite signals and transmits correction data and its known position to the rover. The rover uses this data to eliminate common errors and calculate its own position in real time. | Centimeter | Ideal for land surveying, construction layout, precision farming, utility mapping, and drone inspections. |
| NRTK (Network RTK) | Uses a network of permanent GNSS reference stations. These send data to a central server, which models errors and delivers location-specific corrections via the internet. | Centimeter | Great for mobile fieldwork and multi-site projects where you don’t need to set up a local base station. |
| PPK (Post-Processed Kinematic) | Both base and rover log raw satellite data independently. After the survey, software compares the rover’s data to the known base position to apply corrections. | Centimeter | Widely used in drone mapping and areas without reliable real-time correction. |
| Online Post-Processing Services (e.g., OPUS, NRCAN, AUSPOS, IBGЕ-PPP, CSRS-PPP) | Use precise satellite orbit and clock data for correction, often through PPP. No nearby base is needed. Requires internet or satellite access and longer convergence times. | Centimeter | Ideal for offshore surveying, geophysical research, and remote/global projects without local base stations. |
| SBAS (Satellite-Based Augmentation System) | Improves GNSS accuracy by broadcasting corrections from geostationary satellites, based on data from ground reference stations. | ~1 m | Suitable for aviation, tractor guidance. |
| Galileo HAS (High Accuracy Service) | HAS focuses on providing decimeter-level accuracy through PPP. It achieves this by broadcasting PPP corrections generated by ground reference stations directly from Galileo satellites. | Decimeter | Mainly used in such applications as surveying, precision agriculture, civil engineering, and geodesy. |
| PPP-RTK | A hybrid GNSS correction technique, PPP-RTK combines precise satellite orbit and clock data—like in PPP—with real-time, centimeter-level accuracy similar to RTK. Unlike traditional RTK, it doesn’t require a nearby base station. Instead, it relies on corrections streamed from a network of reference stations via a provider. | Centimeter | This technique is especially useful where RTK networks are unavailable but high accuracy and real-time feedback are still needed. It suits for large-scale or mobile operations with no base station and good internet access. |
Of all available GNSS correction methods, RTK remains the most widely adopted. It offers the best balance of accuracy, speed, infrastructure availability, and cost-effectiveness, making it the go-to choice for many professional applications. In our next support tip, we’ll examine how RTK works and why it’s so effective.
