What is RTK?

RTK (Real-Time Kinematic) is a GNSS correction technique that achieves centimetre-level positioning accuracy by resolving the integer ambiguity in satellite carrier-phase measurements. A base station (or correction network) at a known location transmits real-time corrections to a rover, allowing it to cancel out atmospheric and satellite errors and compute its position to within 1–2 cm.

How RTK Works

Standard GNSS receivers measure pseudorange — an approximation of the distance to each satellite computed from signal travel time. RTK goes further by also measuring the carrier phase of the satellite signal, which has a much shorter wavelength (~19 cm for GPS L1) and therefore provides far more precise distance measurements.

The challenge is that carrier phase contains an unknown integer number of complete wavelengths between the satellite and the receiver — called the integer ambiguity. RTK resolves this ambiguity using correction data from a reference station (or network of stations) at a precisely known location. Once the ambiguity is resolved to an integer value, the system achieves a “fixed” solution accurate to 1–2 cm horizontally.

The correction data is delivered in real time — typically via NTRIP over an internet connection — in RTCM format. The entire process from startup to fixed solution (Time to First Fix) is typically seconds to a few minutes depending on the correction method and environment.

Fixed RTK vs. Float RTK

When ambiguities are fully resolved to integers, the system achieves a “fixed” RTK solution with 1–2 cm accuracy. When ambiguities are only partially resolved and expressed as decimal values, the system is in a “float” RTK state — still more accurate than standard GNSS (typically 0.1–0.5 m) but less precise than fixed.

A fixed solution is essential for applications requiring centimetre accuracy, such as robotic mowing, precision agriculture, and surveying. Float is often a transitional state that resolves to fixed once sufficient satellite data is collected.

Single-Base RTK vs. Network RTK

Traditional single-base RTK relies on one physical base station. Accuracy degrades with distance — typically beyond 20–30 km the solution degrades significantly due to spatially decorrelated atmospheric errors.

Network RTK (such as Swift’s Skylark Nx RTK) uses a regional network of continuously operating reference stations (CORS) to model atmospheric errors across a wide area. This eliminates the baseline limitation and delivers consistent centimetre accuracy across large geographic regions without the need for users to deploy their own base station.

Applications of RTK

• Robotics: enables autonomous lawnmowers, warehouse robots, and agricultural machines to navigate with centimetre precision.
• GIS & Surveying: replaces traditional survey equipment for field data collection and mapping.
• Drones: enables precise waypoint flight, photogrammetry, and package delivery.
• Construction: guides grading equipment and validates as-built positioning.
• Automotive ADAS: supports lane-level positioning for advanced driver assistance systems.

RTK and Skylark Nx RTK

Swift Navigation’s Skylark Nx RTK is a cloud-based Network RTK service delivering 1–2 cm accuracy with instant fix times. Built on Virtual Reference Station (VRS) technology and powered by a proprietary atmospheric model, it offers 2x the coverage of single-baseline RTK and works with any standards-compliant GNSS receiver.

No base station installation required. View the global Skylark coverage map to see if your region is supported.

Related reading: Inside Skylark’s Atmospheric Model