Short answer
A differential GNSS technique using carrier-phase measurements from a known base station to give a moving rover centimetre-level (typically 1–3 cm) horizontal accuracy in real time. The dominant high-precision GNSS technique for cadastral surveying, machine control, and precision agriculture.
Detailed explanation
RTK transmits the raw carrier-phase measurements from a stationary base station (whose position is known) to a moving rover over a radio link (UHF radio, cellular IP, NTRIP). The rover differences its own carrier-phase measurements against the base's and resolves the integer ambiguities to deliver centimetre-level positions in real time — typically 1–3 cm horizontal, 2–5 cm vertical, within seconds of fixing.
RTK accuracy degrades at roughly 1 ppm per kilometre of baseline length under good ionospheric conditions, faster during high solar activity or near the equator. A 10 km baseline is comfortably fixable; a 30 km baseline is sometimes fixable; beyond 50 km usually requires multi-frequency RTK or network RTK (VRS / FKP / MAC) that interpolates corrections from a CORS network.
Modern RTK uses GPS L1/L2 + GLONASS L1/L2 + Galileo E1/E5 + BeiDou B1/B2 — the more constellations and frequencies tracked, the faster the ambiguity fix and the higher the reliability under sky obstructions. Single-frequency RTK is still used in low-cost surveying but limited to roughly 5 km baselines.
RTK requires phase-stable antennas at both ends. Any millimetre-scale phase-centre wander on the antenna translates directly into rover position error, which is why GNSource sells dedicated 3D choke-ring antennas for reference / base stations and multi-frequency survey helices for rovers.
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High-Precision GNSS Measurement
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Open the toolRelated terms
CORS
A permanently-installed GNSS receiver streaming raw measurements 24/7. CORS networks are the backbone of RTK and network-RTK services, geodetic monitoring, and post-processed precise positioning. Typical inter-station spacing is 50–100 km for regional RTK, 200–300 km for national geodetic networks.
PPP
A precise GNSS positioning technique using globally-broadcast precise orbit, clock, and atmospheric corrections to deliver decimetre-to-centimetre accuracy with a single receiver — no local base station required. Convergence times of 10–60 minutes for cm-level; instant for decimetre via PPP-RTK.
Phase center
The apparent electrical centre of an antenna — the point from which signal range is effectively measured by a GNSS receiver. Phase-centre stability (the variation in this point as the signal arrival angle changes) is the single most important parameter for survey-grade and geodetic antennas.
Multipath
Distortion of a GNSS signal caused by reflections off nearby surfaces (buildings, ground, vehicles) arriving at the antenna nanoseconds after the direct path. Adds pseudorange noise of several metres in unmitigated urban environments — the dominant error source for many high-precision applications.