What is Real-Time Kinematics (RTK)?

An Essential Guide to Understanding Real-Time Kinematics (RTK) Technology

Introduction

Real-Time Kinematics (RTK) refers to a satellite navigation technique used to enhance the precision of position data derived from satellite-based positioning systems like GPS, GLONASS, Galileo, etc. RTK uses carrier-phase measurements in addition to the pseudorange measurements made by standard GNSS receivers. This provides centimeter-level positioning accuracy.

RTK has the ability to provide real-time, highly accurate positioning data making it crucial for applications requiring high-precision positioning, such as it is used in land surveying, agriculture, drone navigation, and autonomous vehicles.

Here in this blog, We are exploring the RTK technology in detail covering sections,

• What is RTK?
• Components of RTK
• How does RTK provide excellent accuracy?
• Measures to improve RTK accuracy
• Use cases of RTK Technology

What is Real-Time Kinematic (RTK) Technology?

Real-Time Kinematic (RTK) technology is renowned for its high-precision positioning capabilities. It offers centimeter-level accuracy, a significant improvement over standalone GNSS receivers, which typically provide meter-level accuracy. This enhanced precision is achieved by correcting the errors inherent in the signals received from GNSS satellites, thereby refining the positioning data in real-time.

RTK Base Station Setup

Components of RTK

GNSS Receivers

An RTK system typically involves at least two receivers: one stationary base station and one or more mobile units.
These are sophisticated devices capable of receiving signals from GNSS ( Global Navigation Satellite Systems) satellites. For more information, refer to our blog on GNSS.

Base Station

The base station is a GNSS receiver positioned at a known, fixed location. It continuously monitors satellite signals and calculates differential corrections based on its known position versus the positions it calculates using satellite data. These corrections account for various errors such as satellite orbit errors, ionospheric and tropospheric delays, and timing issues.

Rover (Mobile Receiver)

The rover is a GNSS receiver that moves around collecting position data. It receives the correction information from the base station (via radio, cellular, or satellite communication) and applies it to its own satellite data to achieve high-precision positional accuracy, often down to centimeters.

Communication Link

This is essential for transmitting the correction data from the base station to the rover. The link can be established through various means including UHF/VHF radio, cellular networks (3G/4G/5G), or even satellite communications in more advanced systems.

Correction Protocols

Protocols such as RTCM (Radio Technical Commission for Maritime Services) are used for the transmission of correction data. These standardized protocols ensure compatibility and interoperability between equipment from different manufacturers.

Software

Both the base station and rover use sophisticated software to process signals, calculate corrections, and apply these corrections to improve positional accuracy. This software also often includes tools for data logging, real-time data analysis, and integration with other systems or applications.

Antennas

High-quality GNSS antennas are crucial for both the base station and rover to receive clear satellite signals. The antennas must be capable of receiving signals from multiple satellite systems across various frequencies to maximize coverage and accuracy.

The combination of these components allows RTK systems to achieve positional accuracy down to the centimeter level in real time, which is a significant improvement over the meter-level accuracy possible with uncorrected GNSS signals.

How does RTK Provide Excellent Accuracy?

RTK works by utilizing a fixed base station and a mobile rover. The base station, positioned at a known location, receives signals from satellites and calculates its position based on the time delay of the received signals. Simultaneously, the rover, which is at an unknown location, also receives signals from the same satellites. The base station then calculates the error in the signals by comparing its known location with the calculated position. This error correction data is transmitted in real-time to the rover, which applies these corrections to its own calculations, thereby significantly enhancing the accuracy of its position data.

RTK Surveyor

The distance between the base station and the rover, known as the baseline length, is a crucial factor. As the baseline length increases, the accuracy can decrease due to the difference in atmospheric conditions affecting the signal at the two locations. Multipath effects, where signals bounce off surrounding objects before reaching the receiver, can also introduce errors. Additionally, the number and geometry of the satellites in view, signal obstructions, and the quality of the GNSS receiver can also impact the accuracy.

Techniques to Improve RTK Accuracy

In Real-Time Kinematic (RTK) positioning, several strategies and technologies are employed to address the challenges posed by factors like baseline length, multipath effects, satellite geometry, signal obstructions, and the quality of GNSS receivers. Here’s how RTK systems typically handle these issues:

1. Managing Baseline Length

Network RTK

• To mitigate the effects of increasing baseline length, Network RTK uses a network of base stations rather than a single base station. This approach provides corrections that account for spatially correlated errors (such as atmospheric delays) over large areas, enhancing accuracy even over longer baselines.

Atmospheric Modeling

• Advanced atmospheric models are used to estimate and correct for the ionospheric and tropospheric delays affecting the signals, improving accuracy over long distances.

2. Reducing Multipath Effects

Antenna Design

• High-quality GNSS antennas are designed to minimize the impact of multipath signals by filtering out or reducing signals coming from certain angles or employing techniques to distinguish between direct and reflected signals.

Signal Processing

• Advanced signal processing techniques, such as carrier-phase measurements and signal-to-noise ratio (SNR) monitoring, help in identifying and mitigating the effects of multipath errors.

3. Improving Satellite Geometry and Visibility

Multi-constellation Support

• By supporting multiple GNSS constellations (e.g., GPS, GLONASS, Galileo, BeiDou), RTK systems increase the number of satellites in view, improving the geometry and thus the accuracy and reliability of the positioning.

Planning Tools

• GNSS planning tools allow users to predict satellite availability and plan surveying tasks for times when satellite geometry is most favorable.

4. Addressing Signal Obstructions

Adaptive Tracking Algorithms

• GNSS receivers with adaptive tracking algorithms can maintain lock on satellites even in challenging environments, such as urban canyons or near tall trees, by dynamically adjusting to signal fluctuations.

Hybrid Positioning Techniques

• Combining GNSS data with other sensors (e.g., IMUs, LIDAR) allows RTK systems to provide accurate positioning even when GNSS signals are partially obstructed or temporarily unavailable.

5. Ensuring High-Quality GNSS Receivers

Receiver Design

• High-quality GNSS receivers are crucial for RTK systems. These receivers are designed with advanced signal processing capabilities, robust tracking algorithms, and the ability to mitigate noise and interference, ensuring accurate and reliable measurements.

Firmware Updates

• Regular firmware updates can enhance the performance of GNSS receivers by improving their algorithms for signal processing, error correction, and handling of challenging environments.

Regular firmware updates can enhance the performance of GNSS receivers by improving their algorithms for signal processing, error correction, and handling of challenging environments.

Differential RTK

Differential RTK GPS, on the other hand, is a further enhancement of the RTK GPS technique. It involves the use of two or more stationary reference stations, instead of one, to provide corrections. These reference stations are strategically located to cover a specific area and continuously monitor GPS signals. The error corrections calculated by these stations are then used to correct the position data of rovers within that area.

The primary difference between RTK GPS and Differential RTK GPS lies in the number of reference stations used and the coverage area. While RTK GPS uses a single reference station and is suitable for localized applications, Differential RTK GPS uses multiple reference stations, allowing it to cover a larger area and provide more accurate corrections, especially in regions with varying atmospheric conditions.

Critical Applications of RTK Technology

Real-Time Kinematic (RTK) technology has a wide range of applications across various industries due to its ability to provide high-precision, real-time positioning data.

Agriculture

In agriculture, RTK is used in precision farming techniques to enhance efficiency and productivity. For instance, it is used in automated tractor guidance, crop scouting, and yield mapping. By providing centimeter-level accuracy, RTK allows farmers to precisely manage their fields, reducing overlaps and gaps in coverage, optimizing resource usage, and ultimately increasing crop yields.

Drones

RTK adds a new level of precision to drone navigation and data collection. Drones equipped with RTK can follow predetermined flight paths with high accuracy, which is crucial for tasks like aerial surveying, precision agriculture, and delivery services. Furthermore, when capturing aerial imagery, RTK allows drones to record the precise location of each image, resulting in georeferenced images that can be used to create highly accurate maps and 3D models.

Construction and Surveying

In construction and surveying, RTK plays a pivotal role. It is used in land surveying to accurately measure and map the topography of a site before construction begins. During construction, it aids in machine control, allowing heavy equipment like excavators and graders to operate with high precision, reducing errors, and improving efficiency. In surveying, RTK is used to measure and map the topography of a site with centimeter-level accuracy. Surveyors can collect highly accurate data quickly and efficiently. The base station is set up at a known location, and the rover is used to measure various points relative to the base station. This allows for precise measurements that are crucial in planning and executing construction projects, land division, and mapping.

What is the Current Cost Factor of RTK?

Implementing Real-Time Kinematic (RTK) GPS can be a significant investment, as the cost is influenced by several factors. The price of RTK GPS systems can range from a few thousand to tens of thousands of dollars, depending on the complexity and precision of the system. The cost includes the purchase of hardware such as the base station and rovers, and often a subscription fee for correction data services. While the initial setup cost can be high, the investment can be justified by the substantial improvements in accuracy, efficiency, and productivity that RTK GPS brings to operations, particularly in industries like agriculture, surveying, and construction.

Conclusion

Real-Time Kinematic (RTK) technology is a game-changer in the realm of satellite-based positioning systems. With centimeter-level accuracy in real-time, It provides a significant improvement over standalone GNSS receivers. The RTK technology is poised to play a crucial role in shaping the future of industries like autonomous vehicles, and smart farming, and possesses immense potential in shaping an automated connected world.

To learn more about topics related to GNSS-integrated IoT modules, check out
https://www.cavliwireless.com/iot-modules/cellular-modules.html