RTK Overview
Real-Time Kinematic (RTK) is a satellite-based navigation technique that enhances the precision of positioning data. By using the signals from satellites, RTK can achieve centimeter-level accuracy, making it ideal for applications that require precise location tracking, such as autonomous driving, drones, and robotics. In the application of smart lawn mowers, RTK allows for efficient navigation without the need for boundary wires, enabling them to operate seamlessly in a designated area.
What’s the Difference Between RTK, GPS, and GNSS?
GNSS (Global Navigation Satellite System) is a global system that provides positioning, speed, and time data anywhere on Earth. It includes systems like GPS, Galileo, GLONASS, and Beidou.RTK is a specialized technology built on GNSS. It uses satellite signals from GNSS to deliver real-time, centimeter-level accuracy, making it ideal for precision-based applications like robotic lawn mowers.
How RTK Works
RTK achieves real-time, centimeter-level accuracy using GNSS. It relies on a reference station that continuously observes satellite data and sends it to a mobile station. The mobile station receives both the satellite signals and reference station data, then calculates its exact 3D coordinates in real time based on the relative positioning principle.Hardware Components
Reference station: an important component of the RTK system. It is usually set at a point with known coordinates, continuously observes satellites, and sends observation data to the mobile station. The stability and accuracy of the reference station directly affect the measurement accuracy of the entire RTK system.
Mobile station: a device for on-site measurement. It receives satellite signals and data sent by the reference station, and calculates its own position coordinates. Mobile stations are portable and flexible, and can perform measurement operations at different locations.
Data communication link: used to connect the reference station and the mobile station to achieve real-time data transmission. The communication link can use radio, mobile network and other methods to ensure stable and reliable data transmission.
Introduction to RTK Reference Station
In RTK technology, the reference station provides reference data to the mobile station, enabling it to achieve high-precision positioning. Currently, there are mainly two types: local physical base station and virtual base stations based on Ntrip (Networked Transport of RTCM via Internet Protocol).
1. Local Physical Base Station
Local physical base stations are usually composed of GNSS receivers, antennas, communication equipment, and power supplies. They are generally located at fixed positions with known coordinates, such as surveying and mapping control points, rooftops, and other open and stable places. Installation should ensure the stability of the base station and avoid interference from external factors such as vibration.
Pros:
- Strong independence: Without relying on external networks, as long as the base station equipment is working properly, it can provide services to nearby mobile stations. In some remote areas or places with poor network signals, local physical base stations can still play a role.
- High stability: Due to the fixed position of the base station, its observation environment is relatively stable and can provide reliable differential data. In addition, the local physical base station can be customized and optimized according to actual needs to meet specific measurement tasks.
Cons:
- Limited coverage: The signal coverage range of local physical base stations is usually small, generally within a few kilometers. For large-scale measurement tasks, multiple base stations may need to be set up, which increases costs and workload.
- High maintenance costs: Regular maintenance is required to ensure its accuracy and stability. At the same time, the purchase, installation, and maintenance of base station equipment also require certain costs.
2. Virtual Base Station Based on Ntrip
Ntrip is a technology that transmits RTCM (Radio Technical Commission for Maritime Services) differential data over the Internet Protocol. Virtual base stations based on Ntrip do not require actual physical equipment, but are connected to one or more Ntrip servers through the Internet. Users only need to set the corresponding parameters on the mobile station device to connect to the Ntrip server and obtain differential data.
Pros:
- Wide coverage: Due to the fact that Ntrip servers can connect to multiple reference stations and transmit data through the Internet, they can provide services to users worldwide. Users can use RTK technology anywhere with network connections without worrying about the coverage of base stations.
- Low cost: For users, there is no need to purchase and maintain physical base station equipment. They only need to pay a certain service fee to use Ntrip services. This greatly reduces the cost of using RTK technology.
Cons:
- Network dependence: Ntrip-based virtual base stations rely entirely on the Internet. If the network fails or the signal is poor, differential data cannot be obtained, which affects measurement work.
- Accuracy stability: Due to the characteristics of the virtual base station technology solution, it is impossible to guarantee the stability of differential data accuracy at any position in all weather conditions, especially when mobile station zenith meteorological activities are active, such as active ionosphere and solar motion.
- Data Security: Due to the fact that data is transmitted through the Internet, there are certain security risks. It may be threatened by hacker attacks, data tampering, etc. Therefore, corresponding security measures need to be taken to ensure the security of the data.
In summary, local physical base stations and Ntrip-based virtual base stations each have their own advantages and disadvantages. In practical applications, users can choose the appropriate type of reference station according to their own needs and actual situations to achieve efficient and accurate RTK measurement.
Introduction to Data Communication Links
Data communication links play a crucial role in RTK technology, responsible for transmitting real-time observation data from the reference station to the mobile station for high-precision positioning. Currently, common data communication link methods include mobile networks and LoRa. The following are introductions and analysis of their advantages and disadvantages.
1. Mobile Networks
Mobile network utilizes the communication networks of telecommunications operators, such as 4G and 5G, to achieve data transmission between reference stations and mobile stations. In the RTK system, both mobile stations and reference stations need to be equipped with modules that support mobile network communication, and can access the operator's network by inserting SIM cards and other methods. During the data transmission process, the reference station packages the differential data and sends it to the server through the mobile network. The server then forwards the data to the mobile station, and the mobile station calculates and obtains high-precision positioning results after receiving the data.
Pros:
- Wide coverage: Telecom operators have relatively complete network infrastructure buildings, which allows RTK measurement work to be carried out in a larger area without geographical restrictions, which is very advantageous for long-distance measurement tasks or projects that require measurement in different regions.
- Fast transmission speed: Mobile networks such as 4G and 5G have high data transmission speed, which can quickly transmit a large amount of differential data to the mobile station, ensuring the real-time and efficient performance of the RTK system.
- Easy to use: No additional equipment setup or complex settings are required, just insert the SIM card and activate the corresponding data service to use.
Cons:
- Signal stability is greatly affected by the environment: in some densely built urban areas, mountainous areas, or underground areas where signal obstruction is severe, mobile network signals may be weakened or interfered with, resulting in data transmission delays, packet loss, and other problems, affecting the positioning accuracy and stability of the RTK system
- Communication fees: Using mobile networks requires payment of certain communication fees, including monthly fees for SIM cards, data traffic fees, etc.
- Cyber security risk: Since the data is transmitted through the public mobile network, there are certain cyber security risks, such as data theft, tampering, etc.
2. LoRa
LoRa is a low-power wide area network (LPWAN) communication technology, an ultra-long-distance wireless transmission solution based on spread spectrum technology. In RTK systems, LoRa technology achieves wireless data transmission by installing LoRa modules on the reference station and mobile station respectively.
Pros:
- Long transmission distance: It can reach several kilometers in open environments and hundreds of meters under comprehensive working conditions. This makes LoRa an effective data communication link in areas with poor mobile network signal coverage.
- Strong anti-interference ability: It adopts spread spectrum technology and forward error correction coding technology, which has strong anti-interference ability and can stably transmit data in complex electromagnetic environments.
- Low power consumption: The power consumption of LoRa modules is very low, which can extend the service life of devices, reduce usage costs and maintenance workload.
- Flexible Network Setup: Users can independently set up a LoRa network according to their own needs, without being restricted by telecommunications operators, with high autonomy and flexibility.
Cons:
- Low transmission rate: Compared to mobile networks, LoRa has a lower transmission rate, usually between a few hundred bits per second and tens of kilobits per second.
- Signal stability is affected by the environment: In some densely populated urban areas, mountainous areas, or places with severe signal obstruction such as basements, the signal may be weakened or interfered with, leading to problems such as data transmission delay and packet loss.
(CR: https://youtu.be/uFMkjIFyHfU?si=s6kLmUwVlBp2WMEl)
Advantages and Disadvantages of RTK Technology
Advantages
- High-precision positioning: RTK technology can achieve centimeter-level positioning accuracy, far higher than traditional measurement methods. This enables it to provide more accurate data in fields such as engineering surveying and terrain mapping.
- Real-time performance is strong: RTK technology can obtain measurement results in real-time without waiting for post-processing. This greatly improves work efficiency and reduces measurement time.
- High work efficiency: Due to the fact that RTK technology can achieve single-person operation and fast measurement speed, it can greatly improve the efficiency of measurement work. At the same time, it can also reduce the investment of manpower and material resources, and reduce measurement costs.
Disadvantages
- Signal susceptibility to interference: In some complex terrain environments, such as urban high-rise areas, mountainous valleys, etc., satellite signals may be blocked or interfered with, resulting in a decrease in RTK positioning accuracy or even failure to work normally.
- Data communication is limited: RTK technology relies on data communication links to achieve data transmission between the reference station and the mobile station. If the communication signal is unstable or interfered with, it may affect the real-time and accuracy of the measurement. In remote areas, insufficient communication network coverage may also limit the application of RTK technology.
- Initialization time is long: In some cases, RTK mobile stations require a certain amount of time to initialize after booting up in order to obtain stable high-precision positioning results. This may affect work efficiency, especially in situations where rapid measurement is required.
- The cost is relatively high: The equipment cost of RTK system is relatively high, including reference stations, mobile stations, and data communication equipment. In addition, in order to ensure measurement accuracy, regular calibration and maintenance of the equipment are required, which also increases the usage cost.
The Development Prospects of RTK Technology
With the continuous improvement of global navigation satellite systems and the continuous advancement of technology, RTK technology will also continue to develop and innovate. Currently, RTK technology is mainly developing in the following areas:
- Multi-system fusion: fusing different global navigation satellite systems to improve positioning accuracy and reliability.
- Multi-sensor fusion: Fusion and positioning of observation data from different sensors to solve the positioning problem of unreliable RTK conditions.
- Intelligent development: combining artificial intelligence, big data and other technologies to achieve automatic processing and analysis of measurement data, improve work accuracy and stability.
Lymow One on Kickstarter:
https://www.kickstarter.com/projects/lymowone/lymow-one-boundary-free-robot-mower-for-any-terrain-and-size
2 comments
François Klinkenberg
Hi.
I just participated to your kickstarter project and after looking out the videos and reviews I have one question.
Do we need an antenna as shown in one review to accurately locate the robot ?
Thanks
alper
hello. I am in China and I would like to meet you. I want to sell your products in my country. My WeChat ID is alpi5252 Add me and let’s contact here. thank you
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