GPS technology has become an essential part of our daily lives. We rely on it for everything from navigation to timing synchronisation in telecommunications networks. While basic GPS can provide meter-level accuracy, specific applications require even higher precision. This is where RTK (Real-Time Kinematic) GPS comes in. RTK systems can achieve centimetre-level accuracy, making them ideal for surveying, construction, precision agriculture and other applications where pinpoint positioning is critical. This article will demystify RTK GPS and explain how it achieves such high accuracy.
How RTK GPS Works
RTK GPS builds on traditional GPS using a fixed base station receiver and mobile rover receivers. The base station sits on a surveyed location and tracks all satellites in view. It then relays correction data to rover units in real-time over radio, cellular or satellite links. The rovers apply these corrections to their position calculations to eliminate errors and achieve much higher accuracy.
There are a few key elements that enable the centimetre-level precision of RTK GPS:
Carrier Phase Measurements
While traditional GPS relies solely on analysing the satellite signals’ encoded data, RTK also utilises the carrier wave. The phase of this carrier wave can be measured down to a fraction of its wavelength, enabling precise calculation of change in position over time. This allows RTK units to detect movements as small as a couple of centimetres.
Correcting Signal Errors
RTK eliminates common GPS errors like atmospheric interference, timing offsets and orbital uncertainties. The base station provides correction data to the rovers to account for these errors. This allows the rovers to precisely calculate their coordinates relative to the known base station location.
Relative Positioning
Using a fixed base station as a reference point, the RTK rover can determine its position relative to the base rather than calculating its absolute position. This relative positioning is much more accurate than absolute positioning with a single receiver.
Frequent Updates
The base station transmits correction data to the rovers multiple times per second. This frequent updating allows the RTK system to detect tiny displacements in real-time. Sudden changes in position are immediately accounted for.
With these enhancements, RTK GPS can pinpoint location down to just a couple of centimetres horizontally and vertically. Next, we’ll look at the components of a complete RTK system.
RTK System Components
A complete RTK setup requires both hardware and software elements to work together:
GPS Receivers
Survey-grade dual-frequency receivers are used for both the base and rover. They track all visible satellites on two radio frequencies to get accurate measurements. The rover receiver is paired with an integrated controller or external handheld unit for operation.
Data Links
A radio, cellular modem or satellite transmitter allows real-time correction data to be relayed from the base to the rover at 1-20 Hz. Radio links can communicate up to 15 km, while cellular and satellite links provide longer ranges.
Software
Specialised software handles data processing, coordinate calculations and graphical representation. RTK correction algorithms and features like customisable data formats and quality indicators are built in.
Mounting Equipment
The rover receiver mounts to a range pole via a bracket for surveying applications. The pole allows the rover to be carried to various points for data collection. Tripods, masts and mounts secure the base receiver in its fixed location.
External Devices
For some applications, the rover connects wirelessly to devices like antennas and radios for data transmission back to the office. External displays or data collectors may also link to the receiver to view coordinates, maps and other navigation info.
The system can deliver precise real-time positioning with the right components in place. External augmentation from regional networks or satellite-based systems like SBAS can also be integrated to enhance accuracy and uptime further.
RTK GPS Applications
The centimeter-level accuracy of RTK GPS makes it suitable for a wide range of professional applications:
Surveying and Mapping
RTK is the standard for high-precision surveying boundaries, topography, infrastructure and construction sites. Surveyors can accurately map features within a couple of centimetres horizontally and vertically.
Precision Agriculture
RTK guidance systems steer agricultural equipment like tractors and sprayers precisely through fields. This prevents gaps and overlaps in coverage for planting, fertilising, spraying and other operations.
Construction
RTK is used for precise grading and machine control when constructing roads, buildings, bridges and other structures. Operator-controlled or fully automated equipment can be kept on grade to within a fraction of an inch.
Geophysical Research
RTK helps scientists accurately document and analyse subtle geographic and artificial features, changes and shifts over time for research. It facilitates the precise collection of invaluable reference data.
Autonomous Vehicles
Self-driving vehicles rely on RTK systems to supplement onboard sensors and enable centimetre-level autonomous navigation and positioning. This ensures safe, precise driving and maneuvers.
Infrastructure Monitoring
Bridges, dams, railways, pipelines and other critical infrastructure are regularly checked for structural movements and deflection with RTK systems. Even tiny changes can be detected over time.
With these and other applications, RTK GPS technology enables precise positioning for innovative, safer and more efficient operations across many industries. The future will bring further adoption as costs come down and cellular networks improve.
The Future of RTK GPS
A few key trends will likely shape the advancement of RTK technology in the future:
- Improved cellular networks – As 5G and future cellular systems grow in coverage and bandwidth, they will replace or augment radio links to provide more reliable, longer-range corrections. This expands the range of RTK while lowering hardware costs.
- Affordable receivers – Mainstream high-precision receivers are dropping in price, putting centimetre-level positioning within reach of many new applications and users. This democratisation will fuel wider RTK adoption.
- Multi-constellation support – RTK receivers adding more global navigation satellite systems like Galileo and BeiDou will improve availability and robustness, especially in challenging conditions.
- New signals – The modernised GPS L2C and L5 signals offer benefits like faster acquisition times, while future GPS III satellites will strengthen signals. This bolsters performance.
- Advanced algorithms – Emerging processing techniques like PPP-RTK will enhance ambiguity resolution and position fixing. This can extend RTK to longer baselines of up to 50 km or more.
- Autonomous base stations – “All-in-one” units with built-in communications remove the need for a permanent installed base. This increases flexibility.
As RTK GPS evolves, it will become the premier GNSS-based precision positioning technology for years.
Conclusion
RTK GPS technology takes global navigation satellite systems to the next level, enabling centimetre-level real-time accuracy for a wide range of professional applications. By utilising carrier phase measurements, real-time correction of errors, relative positioning and high update rates, RTK systems achieve a precision far beyond basic GPS. With advancements in cellular networks, algorithms, signals and receivers, this revolutionary technology is becoming accessible to more users than ever. As costs drop and cellular networks expand, innovative high-accuracy positioning applications will continue to increase. For positioning, you can count down to the centimetre; RTK GPS delivers the precision you need.