By David Dunning, Updated March 24, 2022
AndreyPopov/iStock/GettyImages
Real‑Time Kinematic (RTK) is a high‑precision surveying technique that leverages the Global Positioning System (GPS). GPS satellites—24 in total—broadcast signals that RTK systems process to pinpoint positions with remarkable accuracy. Depending on satellite visibility, RTK delivers either a “fixed” or a “float” solution, each offering distinct precision levels.
RTK relies on a stationary base station and one or more mobile receivers, commonly called rovers. The base station maintains a continuous line of sight to each rover and broadcasts real‑time correction data via radio waves. When enough satellites are in view, the system can resolve an exact position—a fixed solution—within a fraction of an inch. If satellite coverage is insufficient, the system falls back to a float solution, delivering accuracy in the range of a few inches.
In a fixed solution, the RTK algorithm resolves the ambiguity of radio wavelengths between the satellites and the base antenna, yielding integer values that pinpoint the rover’s location to a very tight tolerance. A robust satellite constellation, clear geometry, and a reliable radio link are essential for achieving this high level of precision. When one or more of these conditions are compromised, the system may not be able to lock onto a fixed solution.
When a fixed solution is unattainable, RTK resorts to a float solution. The ambiguity remains a fractional value, which still provides a usable position but with lower precision. Tripod Data Systems reports that a float solution typically offers accuracy between 4 and 18 inches over a distance of just over half a mile. While waiting for improved satellite geometry or reinitializing the system can sometimes upgrade a float to a fixed solution, persistent visibility issues may keep the rover in float mode.
RTK accuracy is inversely related to the distance between the base station and the rover. Maintaining this distance below six miles maximizes precision. RTK units are available in single‑frequency and dual‑frequency models; the latter provide faster convergence, higher accuracy, and longer operational ranges at a higher cost.
