GNSS & RTK Glossary: 40+ Survey Terms Explained (2026)

GPS (Global Positioning System) — A satellite-based navigation system owned and operated by the United States government. Consisting of a nominal 24-satellite constellation, GPS provides standard positioning service globally. In surveying, GPS signals are tracked on dual or triple frequencies (L1, L2, L5) to calculate absolute point positions on Earth with metric to sub-metric standalone accuracy.

GNSS (Global Navigation Satellite System) — The umbrella term describing all global satellite positioning constellations, including American GPS, Russian GLONASS, Chinese BeiDou, and European Galileo. While GPS is often used colloquially, modern surveying instruments operate as multi-constellation GNSS receivers, tracking 30+ simultaneous satellites to maintain continuous line-of-sight geometry and robust positioning redundancy.

RTK (Real-Time Kinematic) — A high-precision satellite positioning technique that uses carrier-phase differential corrections transmitted instantaneously from a base station or network to a rover receiver. RTK resolves satellite signal ambiguities in real time, delivering ±8mm horizontal and ±15mm vertical accuracy in seconds for live stakeout, boundary demarcation, and earthwork grading.

DGPS (Differential GPS) — An earlier differential positioning method that relies on pseudorange code corrections rather than carrier-phase measurements. Typically broadcast via ground beacons or SBAS geostationary satellites, DGPS compensates for atmospheric delays and satellite clock errors to deliver sub-meter accuracy (0.5m–2m), making it common in marine navigation and general GIS mapping.

RTK vs PPK — Real-Time Kinematic (RTK) calculates centimeter coordinates on-the-fly via a continuous live radio or cellular data link. Post-Processed Kinematic (PPK) logs raw satellite observation data at both base and rover without real-time communication, resolving carrier-phase vectors afterwards in desktop software. (Explore our complete RTK vs PPK difference guide).

Static Surveying — A high-precision GNSS positioning method where two or more stationary receivers log raw satellite carrier-phase data simultaneously over extended observation sessions (typically 1 to 4 hours or more). After baseline post-processing, static surveying achieves sub-millimeter to millimeter-level accuracy (e.g., ±3mm), making it the gold standard for geodetic control networks.

PPP (Precise Point Positioning) — An advanced single-receiver positioning method that utilizes precise satellite orbit and clock corrections delivered globally via L-band satellite broadcasts or internet streams (such as Galileo HAS). PPP eliminates the need for a local base station or nearby CORS network, achieving sub-decimeter to centimeter accuracy after a 10–30 minute convergence period.

Fixed Solution — The optimal RTK status indicating that carrier-phase integer ambiguities between the base and rover are fully resolved mathematically. A Fixed solution delivers true centimeter-level positioning accuracy (typically ±8mm horizontal and ±15mm vertical), providing the verified coordinate reliability required for engineering stakeout and legal boundary surveys.

Float Solution — An intermediate RTK status where the receiver calculates carrier-phase measurements but has not fully resolved integer ambiguities into whole numbers. A Float solution provides decimeter-level accuracy (typically 10cm to 50cm), indicating partial signal obstruction, high DOP, or dropped base corrections that must resolve before staking points.

Single (Autonomous) Solution — The baseline positioning mode where a standalone receiver calculates coordinates using uncorrected satellite broadcast ephemeris without differential data. Single mode delivers standard 1.5m to 3.0m accuracy, typical of consumer smartphones and hand navigation units when no base radio, NTRIP service, or SBAS signal is available.

NTRIP (Networked Transport of RTCM via Internet Protocol) — An open, hyper-text transfer protocol standard designed to stream differential GNSS correction data (in standard RTCM formats) over the internet. NTRIP enables field survey rovers equipped with 4G cellular modems or data collectors to connect directly to CORS networks or remote base servers.

CORS (Continuously Operating Reference Station) — A permanent, highly stable GNSS tracking station installed over a geodetic monument that logs satellite observations 24/7. When interconnected into regional networks, CORS stations compute network-modeled differential corrections (VRS/MAC) and stream them to mobile rovers, eliminating the need for surveyors to set up physical field base stations.

Base Station — A stationary GNSS receiver set up over a known or autonomous control point that continuously observes satellites and broadcasts real-time differential correction packets (RTCM) to nearby rovers via UHF radio, LoRa, or Wi-Fi. (See our guide on setting up RTK base and rover).

Rover — A mobile GNSS receiver mounted on a survey range pole, vehicle, or machinery that receives incoming satellite signals while simultaneously ingesting base differential corrections. The rover resolves integer ambiguities to calculate real-time centimeter-accurate spatial coordinates ($X, Y, Z$) for point capture and visual stakeout.

GPS (United States) — The original operational global navigation satellite system, managed by the US Space Force. Broadcasting on L1, L2, and L5 carrier frequencies, modern GPS III satellites provide robust signal power, civilian interoperability, and primary positioning baselines across global civil engineering and surveying workflows.

BeiDou / BDS (China) — China's global navigation satellite system, consisting of Geostationary (GEO), Inclined Geosynchronous (IGSO), and Medium Earth Orbit (MEO) satellites. Broadcasting B1, B2, and B3 frequencies, BeiDou provides comprehensive global coverage with exceptionally dense satellite visibility and strong signal geometry across Asia, Africa, and Latin America.

GLONASS (Russia) — Russia's fully operational global satellite constellation, utilizing Frequency Division Multiple Access (FDMA) alongside modern CDMA signals on G1, G2, and G3 bands. GLONASS offers high orbital inclination (64.8°), providing superior satellite visibility and geometric tracking reliability across high-latitude northern and southern geographic regions.

Galileo (European Union) — The European civilian GNSS constellation, recognized for exceptional clock stability and signal precision on E1, E5a, E5b, and E6 bands. Galileo features the free High Accuracy Service (HAS), broadcasting precise orbit and clock corrections directly through the E6B signal to enable global PPP positioning.

QZSS (Quasi-Zenith Satellite System) — Japan's regional satellite positioning system operating in highly inclined, elliptical geosynchronous orbits over the Asia-Oceania region. QZSS broadcasts GPS-interoperable signals alongside specialized sub-meter and centimeter augmentation services (CLAS), significantly improving urban canyon satellite visibility beneath tall skyscrapers and steep mountain slopes.

Multi-Constellation Receiver — A GNSS receiver capable of simultaneously tracking all operational satellite systems (GPS, BeiDou, GLONASS, Galileo, QZSS). By processing 30 to 45+ visible satellites across multiple orbital planes, multi-constellation units optimize Dilution of Precision (DOP) and maintain stable RTK Fixed status in partially obstructed field environments.

IMU (Inertial Measurement Unit) — An onboard electronic sensor combining 3-axis gyroscopes and 3-axis accelerometers that measures receiver orientation, angular velocity, and dynamic tilt angles. In modern GNSS rovers, an integrated IMU computes range pole tip coordinates in real time without being affected by local magnetic interference.

Tilt Compensation — A sensor fusion technology combining GNSS positioning data with IMU orientation tracking to calculate exact point coordinates when the range pole is tilted. Advanced 120° calibration-free IMU tilt compensation allows operators to measure building corners, tree bases, and deep trenches without manually leveling the bubble.

Antenna Phase Center (APC) — The electrical point in a GNSS antenna where incoming satellite radio signals are measured. Because the physical center differs slightly from the electrical phase center and varies by elevation angle, precise APC calibration offsets (such as NOAA NGS antenna calibration) are applied to achieve true sub-centimeter geodetic accuracy.

Channels — Independent hardware tracking circuits inside a GNSS processing board that track specific satellite frequency signals (e.g., GPS L1C/A, BDS B1I). A 1408-channel receiver, such as in APEKS hardware, tracks every frequency across all global constellations simultaneously with spare capacity for regional augmentations and future signal bands.

WGS84 (World Geodetic System 1984) — The standard global geocentric reference coordinate system used natively by GNSS satellite constellations. Defined by an Earth-centered, Earth-fixed Cartesian frame, WGS84 provides the fundamental mathematical foundation for global latitude, longitude, and ellipsoidal height before local map projection transformation.

Datum (Geodetic Datum) — A reference coordinate framework defining the size, shape, origin, and orientation of the coordinate system relative to the Earth. Local datums (like Arc 1950 or SIRGAS) account for regional crustal variations, requiring mathematical Helmert transformation parameters to align with global WGS84 measurements (see our Uganda UGRF geodetic datum guide).

Geoid — The equipotential surface of the Earth's gravity field that closely approximates mean sea level undisturbed by tides or currents. Because GNSS receivers measure purely geometric ellipsoidal heights, a geoid model (such as EGM2008) is required to convert raw satellite heights into physical, gravity-referenced orthometric elevations for civil drainage.

Ellipsoid (Reference Ellipsoid) — A mathematically defined smooth, flattened sphere (such as WGS84 or GRS80) that approximates the geometric shape of the Earth. Ellipsoidal height ($h$) represents the vertical distance from the ellipsoid surface to the receiver antenna, which differs from physical mean sea level elevations.

UTM (Universal Transverse Mercator) — A conformal map projection system that divides the globe into 60 longitudinal zones, each 6 degrees wide. UTM projects curved Earth coordinates onto a flat grid measured in metric Northing and Easting, minimizing scale distortion for regional surveying and civil construction mapping.