Real-Time Kinematic (RTK) GPS Positioning for Surveying

A–B

Accuracy (Centimeter-Level)

Centimeter-level accuracy is the hallmark of RTK GNSS positioning, enabling consistent determination of horizontal and vertical coordinates within 1–2 centimeters of the true position in real time. Standalone GNSS receivers, like those in smartphones, typically deliver 2–10 meter accuracy. RTK overcomes these limitations by leveraging real-time correction data from a base station, making it indispensable for land surveying, machine control, construction, precision agriculture, and autonomous navigation.

RTK achieves this precision using carrier-phase measurements. A fixed base station with a surveyed position transmits corrections representing the difference between its calculated and known coordinates. The rover applies these corrections, removing most errors in satellite signals. Achieving this accuracy requires a reliable, low-latency correction link and adequate satellite visibility (typically five or more satellites), with accuracy degrading over longer baselines or in challenging environments.

Antenna (GNSS)

A GNSS antenna captures signals from satellite constellations like GPS, GLONASS, Galileo, and BeiDou. High-quality, multi-frequency antennas—often geodetic-grade—are critical for RTK. Features such as choke rings or ground planes minimize multipath effects and maintain signal integrity, even in challenging environments. Proper placement, clear sky visibility, and regular calibration are essential for optimal performance. Advances in antenna technology, including multi-constellation support and integrated filtering, further enhance RTK reliability.

Autonomous Vehicles

Autonomous vehicles—land, aerial, or marine—navigate and perform tasks without human intervention, relying on sensors like LIDAR, IMUs, and GNSS. RTK GNSS is vital for precise trajectory control, lane-keeping, and complex maneuvers. In agriculture, RTK guides tractors for efficient fieldwork. For urban transport, self-driving cars use RTK for lane-level localization. Drones use RTK for repeatable, accurate flight paths, reducing manual intervention. Robust correction links, redundancy, and error detection are essential for safety-critical autonomous applications, as emphasized by regulatory authorities.

Base Station

The base station is a fixed GNSS receiver at a precisely known location, serving as the reference for RTK corrections. It continuously calculates errors in satellite signals and broadcasts this correction data—usually in RTCM format—to rover receivers via radio, cellular, or internet links. Base station stability, calibration, and location quality directly impact RTK system accuracy. Deployments may use single-base stations (10–20 km range) or Network RTK (NRTK) for wider coverage.

Baseline Length

Baseline length is the distance between the base station and rover receiver. RTK accuracy is highest when the baseline is short (ideally <10 km), as many GNSS errors are spatially correlated over short distances. As the baseline increases, differences in atmospheric and local errors grow, reducing correction effectiveness. Network RTK and Virtual Reference Station (VRS) methods interpolate corrections from multiple bases, effectively reducing the virtual baseline and supporting high-precision positioning over larger areas.

BeiDou

BeiDou is China’s global GNSS, providing worldwide positioning, navigation, and timing services. Modern RTK receivers support multi-constellation operation, including BeiDou, enhancing satellite visibility, geometry, and reliability—especially in challenging environments. BeiDou’s dual-frequency capability improves ionospheric correction and RTK performance, and international standards recommend multi-constellation support for robust field operations.

C–D

Carrier-Phase Measurement

Carrier-phase measurement tracks the phase of a satellite’s carrier wave, enabling millimeter-level sensitivity. Unlike code-phase measurements, carrier-phase observations can resolve position changes at the centimeter or even millimeter scale, essential for RTK. However, the total number of whole cycles (integer ambiguity) must be determined for absolute positioning. Carrier-phase measurement underpins RTK and other high-precision GNSS techniques, enabling rapid convergence to fixed, precise solutions for demanding applications like boundary surveys and structural monitoring.

Centimeter-Level Precision

Centimeter-level precision is the GNSS system’s ability to pinpoint locations within 1–2 centimeters horizontally and vertically. Achieved through carrier-phase measurement, real-time corrections, and multi-frequency/multi-constellation processing, this precision is vital for cadastral surveying, engineering, precision agriculture, and autonomous navigation. High-quality hardware, robust corrections, optimal satellite visibility, and careful environmental management are required for consistent results.

Communication Link

The communication link is how correction data is transmitted from the base station to the rover. Options include:

• UHF/VHF Radio Modems: Dedicated, low-latency, line-of-sight links (10–20 km).
• Cellular Data (3G/4G/5G): Supports NTRIP for wide-area RTK access.
• Wi-Fi: For short-range, high-bandwidth environments.
• Satellite Communication: For remote/offshore use, but may have higher latency.

Selection depends on site conditions, infrastructure, and reliability needs. Redundancy and robust error correction are essential for maintaining correction data integrity.

Correction Data (Base Station)

Correction data, generated by the base station, represents the cumulative GNSS errors at its location—satellite orbit and clock errors, atmospheric delays, and local effects. Broadcast in RTCM format, these corrections are applied by rover units to achieve centimeter-level positioning. Low-latency delivery (1–2 seconds) is critical, with regular base station calibration and adherence to standards ensuring data quality.

Differential GPS (DGPS)

DGPS is an earlier GNSS correction method, improving accuracy to 0.5–3 meters by broadcasting pseudo-range corrections from reference stations. While suitable for navigation and mapping, DGPS lacks the carrier-phase corrections of RTK, limiting its precision. RTK delivers centimeter-level accuracy, making it the standard for high-precision surveying and automation.

Drone Surveying

Drone surveying uses UAVs with high-resolution cameras, LiDAR, and RTK GNSS to collect geospatial data with centimeter-level accuracy. RTK-equipped drones streamline workflows by reducing or eliminating the need for ground control points, enabling rapid, accurate mapping of large or inaccessible areas. Applications include topographic mapping, construction monitoring, volumetric analysis, agriculture, and infrastructure inspection. Maintaining a continuous RTK correction link is essential, with fallback to PPK workflows if needed.

E–G

Emlid

Emlid is a leading manufacturer of affordable, high-precision RTK GNSS receivers, such as the Reach RS2+ and Reach RX. Emlid devices are widely used in surveying, agriculture, and drone mapping due to their reliability, multi-constellation support, and user-friendly software. Emlid’s commitment to open standards and interoperability has expanded access to RTK technology for professionals and enthusiasts worldwide.

References

• International Civil Aviation Organization (ICAO): GNSS Manual (Doc 9849)
• U.S. National Geodetic Survey (NGS): Guidelines for RTK/RTN GNSS Surveying
• United Nations Office for Outer Space Affairs (UNOOSA): GNSS User Manual
• Emlid Documentation: https://docs.emlid.com/
• RTCM Standards: https://rtcm.myshopify.com/

See Also

• Network RTK (NRTK)
• PPK (Post-Processed Kinematic)
• Virtual Reference Station (VRS)
• Precision Agriculture
• GNSS Antenna Types