Real-Time Kinematic (RTK) is a GNSS positioning technique that achieves centimeter-level accuracy in real-time by processing carrier phase measurements differentially between a base station at a known location and a mobile rover. RTK has become the standard for precision positioning in surveying, construction, agriculture, and increasingly in autonomous vehicles and robotics, where its combination of high accuracy and immediate results enables real-time precision guidance and control.
RTK achieves its accuracy through carrier phase processing, using the phase of the satellite’s carrier wave rather than just the modulated code to determine ranges. Carrier wavelengths are roughly 19 centimeters (L1) to 25 centimeters (L5), enabling millimeter-level measurement precision compared to meter-level precision from code measurements alone. However, carrier phase measurements contain an unknown integer number of complete wavelengths, the ‘ambiguity’, that must be resolved to achieve centimeter accuracy.
Ambiguity resolution is the critical process that distinguishes fixed RTK (centimeter accuracy) from float RTK (decimeter accuracy). Using observations from multiple satellites over time, sophisticated algorithms determine the correct integer ambiguity values for each satellite. When successful, the solution is ‘fixed’ and accuracy improves dramatically. Various conditions affect resolution success: satellite visibility and geometry, signal quality, correction latency, baseline length (distance from base to rover), and atmospheric conditions. Under favorable conditions, modern receivers achieve fixed solutions within seconds.
RTK implementation can take multiple forms. Single-base RTK uses a dedicated base station with radio or cellular link to nearby rovers, simple but limited in coverage. Network RTK services combine data from regional reference station networks to provide corrections over wide areas via internet (NTRIP). Both approaches deliver the same fundamental capability: real-time centimeter positioning that enables precision machine guidance, stake-out to planned coordinates, and accurate survey data collection without post-processing delays.
