What is RTK? The Basics of Real-Time Kinematic Positioning
Published February 28, 2025
Updated on March 26, 2025
"Satellite positioning system" used in car navigation systems and map applications.
Among them, "RTK positioning", which can measure position information with higher accuracy, is attracting attention.
So, in this article, what is RTK-GNSS? And I would like to explain the actual RTK positioning.
Table of Contents
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Definition and Basic Principles of RTK
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Differences from Standard GPS – Causes of Errors and Correction with RTK
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Advantages and Use Cases of RTK
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RTK Utilization in Surveying
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RTK Utilization in Civil Construction and Construction Machinery
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Benefits of RTK on Construction Sites
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Frequently Asked Questions (FAQ)
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Introduction to LRTK and Information on Requesting Materials
Definition and Basic Principles of RTK
RTK (Real-Time Kinematic) is a type of positioning method known as "relative positioning," where at least two GNSS receivers (a rover and a base station) are used simultaneously to determine the position. Unlike the conventional method, which uses only a single receiver, RTK works by performing relative positioning between two points to cancel out common errors.
Main Flow of RTK Positioning:
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Base Station – The base station is set up at a known, accurate coordinate location and receives signals from multiple GNSS satellites. It calculates the difference (error) between the position it calculates and the actual known coordinates in real time.
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Correction Data Transmission – The base station sends the calculated error information (correction data) to the rover via radio or communication channels.
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Rover – The rover (the receiver on the moving object) uses the received correction data to apply adjustments to its own positioning results and calculates high-precision coordinates.
As the name "Real-Time Kinematic" suggests, these corrections are made simultaneously with positioning. The positioning results are immediately available on-site, so there is no need to wait for post-processing, and the position coordinates can be checked or surveying work can proceed on the spot. RTK can be considered an advanced form of traditional Differential GPS (DGPS), particularly utilizing the phase shift of the GNSS signal’s carrier wave, which enables even more precise distance measurements.
Since the wavelength of the carrier wave is just a few tens of centimeters, analyzing this phase difference allows for positioning accuracy down to a few centimeters.
For high-precision corrections, it is important that the distance between the mobile station and the base station is not too far apart. Typically, a baseline length (the distance between the base station and mobile station) of around 10 km is recommended for operation. If the distance is too long, the shared errors between the two stations (as explained later) will change, diminishing the effectiveness of the correction.
In recent years, systems using electronic reference point data from the Geospatial Information Authority of Japan or network-based RTK services (such as Ntrip communication) have been developed to enable corrections over long distances. However, here, let's focus on the basic principle of RTK using a single base station.
Difference from Standard GPS – Causes of Errors and Corrections by RTK
In standalone GPS positioning (using a single receiver), errors typically range from a few meters to several meters. On the other hand, RTK positioning reduces errors to within a few centimeters. The reason RTK is so accurate is because it cancels out the various error factors that affect standard GPS positioning through relative positioning with a base station.
Main Error Factors in GPS Positioning:
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Satellite Orbit Error: Errors caused by slight deviations in the satellite's orbital position.
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Satellite Clock Error: Errors between the atomic clocks on the satellite and the receiver's clock.
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Ionospheric and Tropospheric Delays: Errors caused by delays in signal propagation through the ionosphere and troposphere.
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Multipath Error: Errors caused by signal reflections and interference from buildings or terrain.
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Receiver Noise: Errors caused by internal electronic noise in the receiver or electromagnetic interference from the environment.
In standalone positioning, all of these error factors accumulate, leading to limitations in positioning accuracy. For example, when a smartphone’s GPS displays your current position several meters off on a map, it’s due to the impact of these errors.
With RTK, both the base station and rover receive signals from the same satellites, allowing common error components such as satellite orbit error, clock error, and ionospheric and tropospheric delays to be nearly canceled out. By applying the error information from the base station, the rover can achieve positioning that is much closer to the "true position" by subtracting those errors. However, local errors such as multipath errors caused by signal reflections or receiver-specific noise cannot be fully eliminated.
Despite this, most of the significant error factors can be corrected, resulting in RTK achieving significantly higher positioning accuracy.
As shown, using RTK dramatically reduces GPS positioning errors. Traditionally, high-precision positioning required static surveys or long-term averaging, but with the advent of RTK, real-time centimeter-level accuracy can be achieved even while moving. This technological innovation has made it possible to replace and streamline tasks that were previously difficult with GPS accuracy through automated GNSS positioning.
Benefits and Use Cases of RTK
The benefits of RTK can be broadly categorized into two main points: "Improved Positioning Accuracy" and "Increased Work Efficiency." With improved accuracy, tasks that previously relied on manual labor for precise positioning can now be replaced by machine-based positioning. As efficiency increases, large-scale surveying and construction management can be carried out in a shorter time with fewer workers. Here, we will introduce specific use cases, primarily in the surveying and construction industries.
Utilization of RTK in Surveying
RTK is highly effective in land and terrain surveying. Traditionally, surveyors would use optical instruments like total stations (TS) to perform detailed observations, but with an RTK-GNSS receiver, the same tasks can be completed in a much shorter time. For example, when surveying the terrain of a large development site, using a base station and rover station allows workers to walk around and instantly obtain the elevation and position of each point, significantly reducing personnel and labor.
The coordinates obtained through RTK positioning are recorded in a global coordinate system based on known points (such as the World Geodetic System in Japan), making it easy to later create drawings and compare with design coordinates.
RTK is also used in reference point surveying. By utilizing network-based RTK (GNSS) surveying that receives real-time correction data from the Geospatial Information Authority of Japan's electronic reference points, new reference points can be established with centimeter-level accuracy, even on remote sites. This streamlines the process of building a survey network on construction sites and reduces the need for long-distance traverse surveying, which was traditionally required.
Recently, RTK-GNSS has also been integrated into drone (UAV) photogrammetry, allowing accurate terrain models to be created from aerial photos without the need to install numerous reference points on the ground.
There have been examples where RTK-equipped UAVs were introduced to survey large construction sites in a short period of time. By providing real-time, high-precision position corrections from the air, the need for ground-based reference point work was reduced.
Utilization of RTK in Civil Construction and Construction Machinery
RTK plays a crucial role in construction management for civil engineering projects. In ICT construction (smart construction), promoted by the Ministry of Land, Infrastructure, Transport, and Tourism, machine guidance and machine control, which use GNSS receivers mounted on construction machinery such as bulldozers and excavators, are becoming widespread for automatic or semi-automatic operation.
For example, by installing an RTK-GNSS receiver on a bulldozer’s blade (the dozer blade), it can be automatically controlled to match the design elevation, or GNSS can be mounted on a backhoe (excavator) to dig along the pre-designated line without the need for traditional markers (stakes or string lines).
There are also applications where an RTK-GNSS receiver is mounted on a road roller (compactor) to manage the number of compaction passes for embankment work. By utilizing high-precision positioning data, construction can be done accurately and safely, without relying on the skill level of the equipment operator.
RTK-GNSS surveying equipment is also used for as-built management (measuring the final earthwork shape), enabling what was once a manual process of measuring many points to be done efficiently by simply walking with a rover receiver, capturing data over a large area.
As a result, RTK technology is essential for improving overall productivity and ensuring quality on construction sites, making it a must-have technology for the next generation of construction projects.
Additionally, RTK is being used in infrastructure maintenance, such as for railways and roads. For example, railway companies require high-precision position tracking for rail inspections and equipment management, so they use GNSS and laser scanners combined with measuring carts for RTK positioning to precisely measure rail and tie distortions. Although there are limitations in environments where satellite signals cannot be received, such as tunnels or areas under elevated structures, RTK and high-precision positioning are expected to become more widely used in the future with the enhancement signals from Japan’s Quasi-Zenith Satellite "Michibiki" and integration with IMU (Inertial Measurement Units).
Benefits of Utilizing RTK in Civil Construction Sites
Improved Surveying Accuracy and Real-Time Data
With the introduction of RTK high-precision GPS devices in civil engineering and construction sites, significant benefits can be realized compared to traditional surveying and construction management practices.
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Enhanced Surveying Accuracy and Immediate Results: RTK positioning enables centimeter-level accuracy, reducing the need for setting reference points and leveling. In contrast to traditional methods, where survey teams use total stations or expensive GNSS equipment, RTK allows anyone to instantly perform high-precision surveying and compare as-built data on-site. For instance, by using LRTK, smartphone GPS accuracy is improved from errors of several meters to within ±2cm, providing immediate survey results.
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Improved Efficiency and Productivity: LRTK is compact and portable, allowing each on-site worker to carry their own surveying device. This eliminates waiting time and enables multiple workers to perform surveying tasks simultaneously. For example, instead of waiting for one GNSS device per team, each worker with their own LRTK device can independently carry out measurements, resulting in a significant increase in overall site productivity. Additionally, since the device is small enough to fit in a pocket, it is easy to transport and can be used in high or tight spaces.
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Cost Reduction and Lower Barriers to Adoption: Traditional high-precision GNSS equipment and surveying instruments were costly and required specialized knowledge, but LRTK is offered at a relatively affordable price. Since it integrates with smartphones, there is no need to purchase multiple dedicated devices, and you can utilize the smartphones you already have. The software is user-friendly and can be easily operated with minimal training, making it accessible even for small to medium-sized construction companies. Furthermore, subscription plans that include cloud services are available, allowing you to start with lower initial costs.
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Promoting Digitalization and Information Sharing: LRTK integrates with a dedicated cloud service, allowing point data and photos taken on-site to be immediately plotted on cloud-based maps and shared. Data collected on-site can be uploaded with a single tap on the smartphone, and office staff or partner companies can instantly review or download it via a web browser. This eliminates the need for the cumbersome process of recording data on paper and brings real-time information sharing and backup to the site. For example, in infrastructure inspections, photos of bridge cracks can be stored with accurate coordinates and orientation on the cloud, allowing all stakeholders to access the precise location later. This significantly contributes to efficient maintenance and report creation.
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Strength in Harsh Environments and During Disasters: LRTK is also highly effective in areas where mobile signals are unavailable, such as mountainous dam construction sites or tunnels on highways. As mentioned earlier, LRTK devices are compatible with Michibiki's CLAS, allowing for satellite-based correction data to be obtained even in offline environments, providing centimeter-level positioning. In fact, during the 2023 Noto Peninsula earthquake, LRTK played a crucial role in a disaster area where mobile networks were down, helping to accurately record and share the damage with precise location data. In disaster response situations, where large equipment may not be easily brought in, a single portable LRTK device can greatly enhance the speed and accuracy of on-site data collection and sharing. This capability, which does not rely on communication infrastructure, provides significant peace of mind for those responsible for infrastructure inspections and disaster prevention.
In summary, the introduction of LRTK brings significant benefits in terms of "accuracy," "efficiency," "digitalization," and "reliability." It is a tool that can dramatically streamline data collection on construction sites and is expected to play a key role in advancing construction DX (Digital Transformation) and i-Construction initiatives.
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Frequently Asked Questions (FAQ)
What is the difference between RTK and standard GPS?
A: Standard GPS positioning is done with a single receiver, and errors of several meters typically occur. In contrast, RTK positioning uses two devices: a base station and a rover, with the base station providing error corrections to achieve centimeter-level accuracy. In simple terms, RTK improves accuracy by "correcting each other using another GPS."
What is needed to perform RTK positioning?
A: Generally, three components are required: a GNSS receiver for the base station, a GNSS receiver for the rover (the object to be positioned), and a communication link (such as radio or internet) between the two. Additionally, the accurate coordinates of the base station need to be determined in advance. If a base station is not set up on-site, correction data can be obtained from national or private base station networks (such as electronic reference points or VRS services) over the internet.
How accurate is RTK positioning?
A: Properly operated RTK positioning provides an accuracy of about 2-3 cm in horizontal positioning and several centimeters in elevation. In optimal conditions, it can achieve even higher accuracy, such as 1 cm. However, in areas with tall buildings or where there are fewer satellites, the accuracy may decrease.
How far can RTK be used?
A: When using a single base station, it is recommended that the distance between the base station and rover be within 10 km, as accuracy decreases with distance due to atmospheric differences. For larger areas, network RTK, which uses data from multiple base stations (such as electronic reference points), can provide high-precision corrections even for rovers several tens of kilometers away.
Is RTK used in fields other than surveying and civil engineering?
A: Yes, it is. For example, in agriculture, RTK is used for the autonomous operation (auto-steering) of tractors, enabling precision agriculture for tasks like pesticide spraying and seeding. Additionally, RTK technology is applied in various fields requiring high-precision positioning, such as high-accuracy surveying and mapping via drone photography, as well as in self-driving vehicle localization.
Can RTK be used with a smartphone?
A: Yes, it is now possible to use RTK positioning with smartphones. By using a small RTK-compatible GNSS receiver and a dedicated app that attaches to the smartphone, the location data obtained by the phone can be enhanced to centimeter-level accuracy. For example, by attaching a device like our LRTK Phone to a smartphone, high-precision positioning can be easily performed without the need for traditional surveying equipment.
Are RTK-compatible devices expensive?
A: Traditionally, full RTK-GNSS surveying equipment could cost several million yen. However, in recent years, affordable GNSS modules and small receivers have become available, making them accessible to individuals. There are even receivers that can be purchased for less than a few hundred thousand yen, and products that can be combined with smartphones are beginning to become more widespread. While high-performance RTK equipment tends to be more expensive, there are now more affordable options available depending on the required accuracy and functionality.
Introduction to LRTK and Information on Requesting Materials
To effectively utilize high-precision positioning on-site, the introduction of easy-to-use RTK-compatible equipment is key. That’s where our digital positioning technology, LRTK, comes into focus.
LRTK is a solution that combines an RTK-GNSS receiver with a dedicated app and cloud service, designed so that even those using RTK for the first time can easily start centimeter-level positioning.
For example, by using the small device LRTK Phone, which can be easily attached to a smartphone, the location data obtained through the smartphone can be enhanced to centimeter-level accuracy.
By attaching a handheld-sized receiver with a built-in antenna and battery to the smartphone and simply launching the app, high-precision coordinates can be recorded on-site just like using a map application. It’s also easy to record the coordinates of measurement points while taking photos, which means that anyone can easily use RTK positioning without needing traditional surveying equipment. This is a significant advantage.
For more professional on-site use, we also offer the LRTK Pro series, which is designed to be dustproof, waterproof, and capable of long hours of operation. This rugged device integrates the antenna, GNSS receiver, radio, and battery into a single unit. It can independently perform positioning using Japan's Quasi-Zenith Satellite System (QZSS) augmentation signals (CLAS), even in mountainous areas where internet connectivity is difficult.
The LRTK Pro series also features an inclination correction function that adjusts the position of the antenna even when the pole is tilted, making it highly effective in surveying on sites with many obstacles.
Additionally, a unique product, the LRTK Helmet, is available. This helmet integrates the antenna and receiver, allowing workers to perform surveys simply by wearing the helmet and walking, leaving their hands free. This significantly improves both on-site safety and efficiency.
Significantly Improve Surveying Accuracy and Work Efficiency on Site with LRTK
The LRTK series enables high-precision GNSS positioning in the fields of construction, civil engineering, and surveying, allowing for reduced work time and a significant increase in productivity. It is also compatible with the Ministry of Land, Infrastructure, Transport and Tourism's i-Construction initiative, making it an ideal solution to accelerate the digitalization of the construction industry.
For more details about LRTK, please visit the links below:
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What is LRTK? | LRTK Official Website
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LRTK Series | Device List Page
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Case Studies | Examples of On-Site Applications
For product inquiries, quotes, or consultations regarding implementation, please feel free to contact us via this contact form. Let LRTK help take your site to the next stage of development.