Global Navigation Satellite System (GNSS) technology has revolutionized positioning and navigation, transforming manual calculations into instantly available data. With the increasing demand for higher accuracy in industries such as Geographic Information Systems (GIS), construction, and agriculture, various correction methods have been developed to improve GNSS accuracy. This article explores the major correction techniques, their characteristics, and applications to help you make an informed choice for your specific requirements.
The Evolution of GNSS RTK Technology
The journey of GNSS Real-Time Kinematic (RTK) technology began in the late 1980s and early 1990s with the exploration of the use of carrier phase measurements for high-precision positioning. The first major milestone was the development of dual-frequency receivers, which allowed for more accurate error correction by mitigating ionospheric delays. In the mid-1990s, the advent of commercial RTK systems marked a breakthrough, providing centimeter-level accuracy and enabling widespread adoption.
In the 2000s, improvements in communication technologies, such as cellular network integration and Internet-based corrections, greatly enhanced the reliability and usability of RTK systems. The establishment of Continuously Operating Reference Stations (CORS) networks provided a robust infrastructure for real-time corrections, further extending the reach and accuracy of RTK technology.
In recent years, developments in GNSS constellations, including the addition of new satellites from systems such as Galileo and BeiDou, have increased the availability and redundancy of satellite signals, improving RTK accuracy and reliability. Most recent RTK systems now incorporate multi-frequency and multi-constellation capabilities, making them more resilient to signal obstructions and atmospheric conditions.
CHCNAV LT800 Android Tablet Series available with Autonomous and GNSS RTK Positioning.
How Does RTK Differ from Standard GNSS Positioning Techniques?
Real-Time Kinematic (RTK) positioning differs from standard GNSS positioning techniques primarily in terms of accuracy and the method used to achieve that accuracy.Standard GNSS positioning typically provides meter-level accuracy, which is sufficient for general navigation and many consumer applications. It relies on code phase measurements.
In contrast, RTK positioning achieves centimeter-level accuracy by using carrier-phase measurements, which are much more accurate. The key difference is the use of a base station and a rover. The base station is positioned at a known fixed location and continuously receives GNSS signals and calculates the errors caused by atmospheric conditions, satellite orbits, and clock discrepancies. These error corrections are transmitted in real time to the rover, the mobile GNSS receiver, which uses the correction data to adjust its own GNSS measurements, effectively canceling out the errors.
RTK also uses dual-frequency or multi-frequency receivers, which can mitigate ionospheric delays more effectively than the single-frequency receivers commonly used in standard GNSS. This dual-frequency capability, combined with real-time error correction from the base station, enables RTK to provide higher accuracy.
Exploring GNSS RTK Methods: From Single Base to Network Solutions
Let's take a closer look at the different GNSS RTK methods and their unique characteristics, applications, and benefits. Understanding these methods will help you choose the best solution for your specific geospatial needs.
Single Base RTK (Real-Time Kinematic)
Single Base Station GNSS RTK is a widely used correction method that involves using an on-site base station to provide real-time corrections. Base stations like the CHCNAV iBase are compact allowing for easy deployment across various locations. Portability is particularly beneficial for surveyors who need to move frequently between different work sites, ensuring high-precision positioning wherever they operate.
CHCNAV iBase, Integrated GNSS Base Station
For users with fixed operating areas, high-performance receivers and antennas like CHCNAV's P5U receiver and C220GR2 antenna can provide enhanced accuracy, stability, and coverage.
Application Scenarios
- Construction site positioning
- Precise land surveying and mapping
- Precision agriculture (for smaller fields)
Advantages
- Centimeter to millimeter-level accuracy
- Flexible deployment based on needs
- One-time investment
- Suitable for almost any area
Disadvantages
- Requires technical expertise.
- Limited by baseline length
- Needs a known reference point
GNSS Network RTK
Network RTK enhances traditional RTK by using multiple permanent base stations to cover extensive areas. Base stations continuously upload GNSS correction data to a central server, which then provides precise correction information to users based on their real-time location. This networked approach offers superior accessibility and reliability, making it ideal for users like farmers employing auto-steering tractors, construction professionals, and surveyors who may not have extensive GNSS expertise.
The wide-area coverage ensures that users can maintain seamless connectivity over long distances without needing to reset and reconnect to new base stations. It eliminates the limitations of single-base RTK, where accuracy diminishes with increasing distance from the base station.
A Reference Station with CHCNAV C220GR2 Antenna (Image credit RG-Solution)
Application Scenarios
- Precision agriculture across large farms
- Autonomous vehicles in urban areas
- Large-scale construction projects
Advantages
- High accessibility
- Wide-area coverage
- Consistent accuracy over large regions
Disadvantages
- Performance affected by base station density
- Requires good cellular network coverage
- Ongoing subscription costs
PPP (Precise Point Positioning) and PPP-RTK
Precise Point Positioning (PPP) is a highly accurate correction technique that uses satellites and a single receiver to achieve precise positioning. It relies on a global network of base stations that calculates local corrections that are transmitted via satellite to cover large areas without the need for cellular networks. Free PPP services such as Galileo's HAS and BeiDou's B2b PPP provide decimeter-level accuracy, while commercial services offer even higher accuracy, often reaching sub-decimeter accuracy.
PPP-RTK combines PPP and Real-Time Kinematic (RTK) techniques to provide centimeter-level accuracy. PPP-RTK corrections are available via L-band satellite transmission using GNSS signals and additional corrections from geostationary satellites, requiring compatible GNSS receivers and a subscription. In addition, PPP-RTK corrections can be delivered via cellular networks, increasing availability especially in areas with strong cellular coverage.
A John Deere Tractor with CHCNAV NX510SE Auto Steering System
Application Scenarios
- Marine navigation
- Remote area surveying
- Precision agriculture in areas with poor cellular coverage
Advantages
- Coverage in remote areas and oceans
- Adaptable to varying network conditions
- Global availability
Disadvantages
- Expensive subscription fees for high-precision services
- Decimeter-level accuracy may not be sufficient for some applications.
- Longer convergence time compared to RTK
PPK (Post-Processing Kinematic)
Post-Processing Kinematic (PPK) is a non-real-time correction method used to enhance GNSS data accuracy. During field operations, the rover records GNSS signal data while a base station simultaneously logs its own data. After completing the fieldwork, the recorded data is corrected using post-processing software such as CHCNAV's CGO.
PPK is particularly effective for applications like aerial mapping with drones. It offers reliable corrections in challenging terrains, such as mountainous regions and areas over water, where keeping a continuous data transmission of RTK corrections can be difficult.
CHCNAV BB4 Drone and AA15 Airborne LiDAR
Application Scenarios
- Drone-based aerial surveying and mapping
- Mapping in areas with poor radio or cellular connectivity
- High-precision surveying in challenging environments
Advantages
- High accuracy, sometimes exceeding 1 cm
- Allows for longer baselines
- Reliable in complex terrains
Disadvantages
- Requires specialized skills
- No real-time corrections
- Requires post-processing time and software
Selecting the Optimal GNSS Correction Method for Your Needs
Each GNSS correction method has its strengths and limitations. The best choice depends on your specific application, technical expertise, and operational environment. Real-Time Kinematic (RTK) offers real-time corrections, ideal for applications needing immediate accuracy, such as construction and surveying. In contrast, Post-Processing Kinematic (PPK) provides high accuracy in challenging terrains where keeping a continuous data link is difficult, making it suitable for aerial mapping. Precise Point Positioning (PPP and PPP-RTK) delivers wide-area coverage without the need for a local base station, beneficial for global or remote operations.
There is no one-size-fits-all solution. Instead, different options address diverse needs and scenarios. Understanding the unique advantages and limitations of each method will help you select the most proper GNSS correction technique for your project.
CHCNAV stands ready to support you with the latest GNSS technology and the ability to help you navigate the complexities of precise positioning. Whether you're involved in surveying, agriculture, construction, or any other field requiring high-precision GNSS, CHCNAV has the solutions to meet your needs and drive your success.
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About CHC Navigation
CHC Navigation (CHCNAV) develops advanced mapping, navigation and positioning solutions designed to increase productivity and efficiency. Serving industries such as geospatial, agriculture, construction and autonomy, CHCNAV delivers innovative technologies that empower professionals and drive industry advancement. With a global presence spanning over 130 countries and a team of more than 1,900 professionals, CHC Navigation is recognized as a leader in the geospatial industry and beyond.For more information about CHC Navigation [Huace:300627.SZ], please visit: www.chcnav.com
