GNSS RTK Positioning - An Overview
Real-time kinematic (RTK) is a powerful technology used to enhance the precision and accuracy of positioning and navigation systems. Whether you're a professional seeking to optimize precision or a tech enthusiast wanting to understand the science behind cutting-edge GNSS technology, this guide breaks down the core concepts of RTK, its applications, and its impact on various industries.
This article will help you understand how RTK works and what makes it different from other positioning techniques. You'll also learn how we at onocoy are contributing and why it's becoming the go-to solution for high-precision tasks.
Understanding the Principle of GNSS RTK Positioning Technology
GNSS has totally transformed the field of positioning, navigation and timing. They provide accurate location information for all kinds of applications, all the time and in all places. As precise location information is already part of our daily life and business, there's been a growing demand for positioning technology that delivers accurate location information. That's why standard pseudorange-based positioning techniques like Single Point Positioning (SPP) and pseudorange Differential GNSS (DGNSS) aren't suitable because of their precision limitations. Instead, carrier phase-based positioning methods like Precise Point Positioning (PPP), Real-Time Kinematic (RTK) and PPP-RTK are becoming more and more important because they're much more precise. You can see a summary of the different positioning methods in terms of accuracy, convergence time, coverage area and positioning type in the following Table.
How can we get an instantaneous, centimeter-level accurate position using RTK technology?
Well, RTK is a differential positioning technique. DGNSS positioning is all about working out where a rover is in relation to a base station. Pseudorange DGNSS can get you pretty close to your actual position, but if you need to be precise to the centimeter, you'll want to use RTK carrier phase DGNSS.
The RTK positioning method combines GNSS measurements from one (or more) reference stations with the user data, to get rid of various GNSS error sources. These include errors in the satellite and receiver clocks, errors in the satellite orbits and delays caused by the atmosphere.
We've found that having access to GNSS correction data from reference stations is essential for achieving the desired accuracy. In practice, there are two main types of reference station configurations.
Single Base RTK is pretty straightforward: one fixed reference station, usually within a range of tens of kilometers, provides its raw measurements along with its highly accurate three-dimensional coordinates. The rover receiver is processing all this information together with its collected raw measurements and computes a position relative to the reference station.
The other option is that the rover receives data from a so-called Virtual Reference Station (VRS). The GNSS reference station network architecture allows a precise modeling of distance-dependent systematic errors principally caused by ionospheric and tropospheric refractions, and satellite orbit errors. This is realized by interpolating the errors obtained from the reference station network into the location of the VRS, which is at or near the initial user location.
Is it possible to get centimeter-level accuracy at any time and at any location?
How accurate RTK positioning can be depends mainly on the quality of the measurement collected by the rover. Assuming a rover located in a high-rise building district of a metropolitan city, we can’t achieve the desired accuracy using only GNSS as a positioning sensor. Having a good visibility condition, meaning nothing is blocking the signal on its path to the antenna, there's a good chance you'll get centimeter-level accuracy.
If the rover has good measurement quality, the accuracy also depends on how far away it is from the base station and whether the real-valued carrier phase ambiguities are resolved to their integer values. For baselines under about 10km, we can resolve the integer ambiguities instantly, which means we can get centimeter-level positioning accuracy after just one epoch. If you're using just one GNSS, or just one frequency, or a long baseline, it'll take longer to fix the ambiguities to their integer values and therefore to obtain the desired positioning accuracy.
How is the real-time feature ensured?
Real-time corrections are the core feature of RTK positioning technology. Real-time capability is guaranteed through continuous communication between the rover receiver and the base station. The base station usually sends out GNSS corrections in a standard format proposed by the Radio Technical Commission for Maritime Services (RTCM). The ranging corrections, which are observed in a nearby (real or virtual) base station, can be transmitted either via the internet using Network Transportation of RTCM Internet Protocol (NTRIP), or using radio signals over short to medium distances, e.g. when a stable internet connectivity isn’t available.
RTK - Advantages and Drawbacks
Advantages
High Precision
RTK provides centimeter-level accuracy, making it ideal for applications requiring precise location data, such as surveying, precision agriculture, and construction.
Real-Time Data
Unlike post-processed data, RTK offers immediate precise location information, enabling real-time decision-making, which is crucial for dynamic environments and applications like, e.g., autonomous driving and unmanned aerial vehicle (UAV) navigation.
Versatility
RTK technology can be employed across various industries, including agriculture, construction, marine navigation, and more, demonstrating its adaptability to different environmental and operational demands.
Drawbacks
Dependency on Base Stations
RTK requires access to a network of base stations that transmit correction signals. In areas with limited infrastructure, this can be a significant limitation.
Limited Coverage
RTK accuracy can degrade over long distances from the base station (typically beyond 10-20 km), which could be an issue in remote or expansive areas.
High Cost
The setup and maintenance of RTK systems, including hardware, software, and subscription to correction data services, can be relatively expensive.
The Role of onocoy in RTK Technology
GNSS technology has become ubiquitous, an indispensable component of consumer, automotive and industrial applications. However, high-precision GNSS technology has been unable to penetrate mass market applications due to the lack of a global, open and dense GNSS reference station network. To date, the service landscape is regionally fragmented, characterized by poor coverage in emerging markets and high maintenance costs for service providers. All these drawbacks limit the adoption of high-precision GNSS in mass markets.
onocoy is on a mission to make high-precision positioning accessible to all. Using advanced blockchain technology, we have deployed a transparent sharing platform for high quality GNSS reference station data, based on open standards, with a dense global network of community owned reference stations. It overcomes the limitations of RTK technology by providing a platform that integrates existing and newly deployed reference station infrastructure into one common network, resulting in global coverage and high network density. Both sides of the business benefit, it’s a win-win! Operators benefit from higher utilization of their infrastructure and users save on data costs.
onocoy's platform is designed to give you instant access to GNSS data, no matter where you are in the world. Our network is designed for seamless connectivity, providing you with reliable data whenever and wherever you need it. Users benefit from a decentralized system with rigorous quality control to ensure transparency and confidence in the data for all stakeholders.
How to get precise location information using onocoy’s data?
All you need is a receiver that is capable of RTK and an antenna attached to it. Set up the receiver in the way provided in the manual. Connect to onocoy’s server via NTRIP (plain and encrypted communication is available) and the RTK rover will receive correction data in the standardized RTCM format. When everything is set up accordingly, you’ll have access to single base RTK, offering access to the nearest reference station with seamless handover and fallback capabilities. While onocoy is on the way to global coverage, please still make sure you have coverage by checking the explorer (link).
Applications of RTK Technology
Agriculture and Precision Farming
One of the most significant beneficiaries of RTK technology is the agriculture sector. Precision farming, powered by RTK, allows farmers to optimize field-level management regarding crop farming. The accurate positioning data provided by RTK systems enables automated tractors and machinery to plant, fertilize, and harvest crops with unparalleled accuracy.
Construction
In construction, RTK technology is changing how we design and build structures. With RTK, construction teams can lay out buildings, roads, and infrastructure with exacting precision, which means projects stick closely to the design specifications, reducing errors and the need for costly adjustments. RTK also makes it easier to integrate Building Information Modeling (BIM) processes, where precise geospatial data is key for accuracy.
Navigation / Autonomous Vehicles
The rise of autonomous vehicle technology relies strongly on accurate positioning systems, where GNSS plays a crucial role by providing absolute position information. Using RTK technology self-driving cars, drones and UAVs are able to navigate precisely, ensuring safe operation within tight tolerances.
Environmental Monitoring
Environmental scientists and researchers utilize RTK technology to monitor and manage ecosystems with high precision. RTK aids in the surveying of natural landscapes, tracking changes in topography and environmental conditions.
Other Precise GNSS Positioning Technologies
Precise Point Positioning (PPP): PPP combines pseudorange observations with carrier phase observations, as those are much more precise. Usually, observations from two or more frequencies are combined to eliminate ionospheric delays. Broadcast satellite orbit and clock information are replaced by precise estimates, which are downloaded or obtained in real-time from service providers (e.g. IGS products) using internet or satellite links.
As there's no need for measurements from nearby reference stations, PPP is available worldwide using just one GNSS receiver. This makes it flexible to use, especially in areas without a lot of reference stations. This flexibility does mean that we have to be careful when modeling local station and environmental effects, to reach decimeter-level accuracy. The State Space Representation (SSR) method is used to estimate the various error sources separately by a network of Continuously Operating Reference Stations (CORS), before sending them to the receiver.
While PPP can deliver highly precise positioning results worldwide, it often requires longer observation periods to achieve this accuracy. The convergence time is mainly influenced by the existing carrier phase ambiguities and its linear dependency with other parameters to be estimated.
PPP-RTK: PPP-RTK is a combination of the best of both worlds when it comes to PPP and RTK positioning. All the relevant GNSS error sources, such as satellite orbits, clocks, pseudorange and carrier phase biases and ionosphere and troposphere errors, are identified and sent via SSR. The main issue with PPP is that it can take a long time to converge and it's not always super accurate.
But by combining it with RTK, we can get more precise estimates of the errors caused by the satellites, clocks and other factors. This means we can resolve the integer ambiguities more quickly, but still not instantaneously as with RTK.
Conclusion
RTK positioning is transforming how we use precise location data across various fields, from agriculture to autonomous navigation. By enhancing GNSS technology with real-time, centimeter-level accuracy, RTK provides a reliable foundation for tasks where precision is essential. While the setup can be costly and reliant on a network of base stations, the advantages in speed and accuracy make it the go-to choice for high-stakes applications.
onocoy’s platform tackles common challenges with RTK, offering a community-driven, decentralized network that expands accessibility and reduces costs. With onocoy, high-precision positioning becomes more accessible globally, supporting industries that depend on accurate, real-time location data. As the demand for precision grows, RTK and platforms like onocoy are set to play a key role in shaping the future of positioning technology.
Ready to enhance your project with high-precision positioning? Contact onocoy today to see how our network can support your goals.
