Achieve cm level accuracy (half-inch accuracy) positioning without network connection! CLAS-compatible LRTK

There are cases where accurate positioning is required in environments without communications infrastructure, such as construction sites in mountainous areas, surveying on remote islands, and post-disaster field investigations. Typically, centimeter-class high-precision positioning is achieved using a technique called RTK, but RTK positioning has the drawback of depending on communications; it cannot perform well in locations with unstable networks.

This article focuses on the solution “CLAS-compatible LRTK,” which enables centimeter-level (inch-level) positioning without communications. Aimed at civil engineering and construction contractors and municipal staff involved in surveying, we first explain the principles of RTK positioning and the challenges of conventional technologies, then introduce the mechanism and coverage area of Japan’s quasi-zenith satellite “Michibiki” correction service CLAS (Centimeter Level Augmentation Service). We then describe the features and introduction benefits of CLAS-compatible LRTK, report on positioning accuracy, responsiveness, and environmental robustness confirmed in the field, and present various application examples such as civil works in mountainous areas, disaster response, and boundary surveys on remote islands. We also touch on easy operation through smartphone integration and effects such as labor savings, cost reduction, and elimination of dependence on specific personnel. Finally, we outline new prospects for simple surveying made possible by LRTK.

Principles of RTK positioning and the challenge of communications dependence

First, let us review the principles and challenges of RTK (Real Time Kinematic), a representative high-precision positioning technique. RTK is a real-time relative positioning method using two GNSS receivers; by operating a base station and a rover station simultaneously, it enables position determination with centimeter-level accuracy. Specifically, a base station is installed at a point with known accurate coordinates, and a rover is placed at the point to be surveyed to receive satellite signals. Because the base station knows its precise position, it can calculate in real time the difference (error) between the position derived from received GNSS signals and its true position. This correction information is sent to the rover via radio or the Internet, and by applying the correction at the rover, positioning errors that would normally be several meters (several ft) are reduced to a few centimeters (a few in) in an instant.

The advent of RTK made high-precision positioning in civil surveying and construction management possible on site, which was difficult with standalone positioning. However, RTK positioning has a major issue: its dependence on communications. Because correction information must be exchanged continuously between the base and rover stations, a stable communication method is indispensable. Typical methods include short-range direct communication via low-power radio or UHF for nearby operations, and network RTK over the Internet using mobile phone networks (VRS, etc.) for wide-area coverage. In all cases, the presence of a functioning communications environment is a prerequisite. In mountainous areas, underground locations, remote islands, or situations where infrastructure is severed by disasters, radio signals may not reach or mobile networks may be out of range, making it impossible to receive RTK correction data. As a result, the centimeter accuracy that should be obtainable cannot be realized, positioning becomes unstable, and errors may revert to the order of several meters (several ft).

RTK operations that rely on communications also involve cost and effort. Dedicated radio equipment and communication contracts may be required, and some sites need a base station set up each time or entail complex communication configurations. For network RTK, contracts with service providers and monthly fees are often incurred, and checking radio conditions is essential. In short, while RTK offers high precision, “communication is its lifeline,” making it difficult to use in environments with inadequate communications infrastructure. A new approach that enables centimeter-level positioning without network connection has therefore been sought.

How Michibiki CLAS correction signals work and their coverage area

The solution that has emerged is CLAS (Centimeter Level Augmentation Service), provided by Japan’s Quasi-Zenith Satellite System (QZSS) “Michibiki.” Simply put, CLAS delivers correction information calculated from data collected by the Ministry of Land, Infrastructure, Transport and Tourism’s nationwide network of geodetic control points (GNSS reference station network) directly to users via satellite rather than terrestrial communications. Michibiki satellites carry a dedicated signal for broadcasting error correction data to the Japan region (L6 band: L6D signal), and real-time correction information is embedded in and transmitted on this signal. If users have CLAS-compatible receivers, they can receive the correction signal from the satellite overhead even in areas without mobile coverage and apply it to their GNSS positioning, enabling centimeter-level (inch-level) positioning without relying on terrestrial communications.

Let us look a little closer at the CLAS mechanism. In normal GPS positioning, errors of several meters (several ft) arise from satellite orbit and clock errors, ionospheric delay, and the like. CLAS analyzes these error components from observation data collected by geodetic control points nationwide and creates augmentation information about satellite and atmospheric conditions. This information is sent to Michibiki satellites and broadcast as the L6D signal, allowing users’ receivers to correct errors contained in GPS, GLONASS, and other satellite signals they receive. In other words, CLAS can be regarded as a “public RTK correction service delivered via the nation’s reference station network.” CLAS correction information is provided for Japan, and currently the coverage area is nearly all of Japan (some northern regions and remote islands are still under performance verification, but the service broadly covers the country). In mountainous areas and on remote islands, as long as the sky is open, users can receive correction signals from the quasi-zenith satellites overhead, so CLAS demonstrates its true value in regions where terrestrial communications were previously lacking.

A major advantage of CLAS is that no terrestrial communication lines or base station installations are required. Even in remote mountain areas without mobile phone signals, high-precision positioning can be completed with a single receiver. It is also important that receiving CLAS signals does not incur additional communication fees (the CLAS signal itself is provided free of charge). For this reason, CLAS has attracted attention in fields that require high-precision positioning while moving over wide areas, such as construction surveying, agricultural machinery automation, and infrastructure inspection. However, to receive CLAS signals a compatible dedicated GNSS receiver is required. Conventional surveying instruments cannot receive L6 band signals, so introducing new devices is a prerequisite to benefit from CLAS. This is where CLAS-compatible LRTK was developed to make CLAS easy to use.

Technical features and introduction benefits of CLAS-compatible LRTK

CLAS-compatible LRTK is designed to make the most of CLAS’s high-precision correction signals in the field. LRTK refers to the latest-generation RTK-GNSS receivers and positioning solutions that support receiving the CLAS signal. The biggest feature is that RTK positioning using CLAS is possible even outside mobile network coverage. Typical RTK equipment assumes mobile communications, but LRTK can obtain correction information directly from Michibiki thanks to three-frequency GNSS support. Thus, centimeter-level (inch-level) positioning can be sustained even on sites without mobile signals. In areas with network coverage, conventional network RTK (VRS, etc.) can also be used, so a single unit enables flexible operation depending on the presence or absence of communications.

LRTK receivers adopt an all-in-one design that considers on-site usability. They are compact units that integrate the antenna, receiver, battery, and communication module, offering not only portability but also durability such as water- and dust-resistance. There is no need for complex equipment connections in the field; you can start positioning work simply by turning on the unit and pairing it with a smartphone. A dedicated controller is unnecessary; a personal smartphone or tablet becomes the control terminal, making initial setup easy. Some models include tilt compensation, allowing accurate calculation of the pole tip position even when the survey pole is tilted. This enables measurements even when trees or structures prevent the pole from being held vertically, improving work efficiency.

These technical features bring a variety of introduction benefits. First, because the formerly necessary base station installation is not required, site preparation time is reduced. This is particularly beneficial for operations that move across wide areas, eliminating the need to set up a base station each time and resulting in significant labor savings. Second, communication cost reduction: CLAS is a public service that requires no subscription, so once LRTK is introduced there are no additional fees for using correction information. Reducing data transfer via communication modems can save on mobile line charges and dedicated line usage fees. Third, peace of mind from anywhere: concerns that high-precision positioning may become unavailable in mountainous or disaster sites are alleviated. With a consistently stable positioning environment, planning freedom increases and the risk of interruptions due to problems is reduced. Furthermore, as a high-performance receiver supporting multi-GNSS and three frequencies, faster initialization (shorter time for positioning accuracy to converge) and higher reliability can be expected. Overall, CLAS-compatible LRTK realizes “easy centimeter-level (inch-level) accuracy anytime, anywhere” and provides immeasurable benefits in the field.

Field-verified positioning accuracy, responsiveness, and environmental robustness

In real-world applications, CLAS-compatible LRTK has demonstrated the expected performance. In open-sky (good visibility) environments, LRTK positioning accuracy has been reported to be below a few centimeters (below a few in) in horizontal positioning, with similar performance in height. That level of accuracy, which would be impossible with conventional standalone positioning, is remarkable given that no additional base station is required. Once high-precision positioning has converged, centimeter-level (inch-level) accuracy can be maintained even while moving. For dynamic measurements, position updates at several times per second (e.g., about 5–10 Hz) are possible, supporting applications that record trajectories or require continuous positioning.

In terms of responsiveness, LRTK offers practically sufficient performance. Generally, PPP-RTK methods that use satellite correction information (CLAS) can take somewhat longer to initial convergence compared to traditional local RTK. However, LRTK’s multi-frequency capability and high-performance chips shorten this convergence time. From power-up, centimeter-level (inch-level) accuracy is typically reached in on the order of tens of seconds to about 1 minute, after which real-time high-precision positions are continuously provided. If positioning is interrupted and reacquisition occurs, reconvergence is fast and does not substantially disrupt field operations. Therefore, LRTK’s responsiveness is adequate for scenarios such as static point observations, walking surveys, and vehicle-mounted positioning.

Moreover, LRTK meets the field requirement of environmental robustness. The device body is water- and dust-resistant, reducing the risk of failure in outdoor work exposed to soil and rain. The design considers shock and vibration resistance, enabling it to withstand the tough handling typical of construction and surveying sites. The operating temperature range is wide, so LRTK performs stably under direct summer sunlight or in extreme cold. Built-in batteries allow long continuous operation, typically enduring a normal workday without recharging. Field tests have shown stable results for positioning in mountainous areas and under adverse weather conditions, confirming LRTK’s reliability and ruggedness.

Thus, CLAS-compatible LRTK has demonstrated in the field a trio of strengths—high accuracy, rapid positioning start, and adaptability to field environments. In terms of positioning accuracy, responsiveness, and durability, it is comparable to conventional high-precision methods and, in environments with unstable communications, clearly advantageous.

Diverse applications such as civil works, disaster response, and boundary surveys

Because CLAS-compatible LRTK is unaffected by communications environments, it is being used in a variety of field applications. Below are representative use cases.

• Civil works in mountainous areas: For road construction deep in the mountains or dam construction sites where mobile signals are weak, LRTK enables high-precision positioning. Sites that previously required base stations or relied on provisional surveys with reduced accuracy can now obtain accurate coordinates in real time with LRTK. This reduces the need to allocate personnel for surveying or interrupt work, improving efficiency in remote construction. Being able to check survey data sequentially during construction helps detect errors early and prevent rework.

• On-site surveys for disaster response: Immediately after earthquakes or landslides, communications infrastructure may be damaged. Even in such situations, LRTK allows surveying and investigation in disaster areas. For example, it is useful for taking photographs with precisely recorded positions of damaged locations or measuring the spread of debris. There are reports that LRTK was used in areas where mobile networks were down to record collapse sites with centimeter-accurate coordinates. The assurance of “a positioning system that works anywhere” is invaluable in disaster response, expediting recovery planning and the sharing of damage assessments.

• Boundary surveying on remote islands and wide-area sites: LRTK is powerful where a small team must survey wide areas, such as cadastral surveys on remote islands or boundary checks in forested areas. On islands where reference stations may be distant, CLAS enables direct positioning in the national common reference coordinate system, allowing precise surveying to be completed within the island. In forest and agricultural boundary confirmations, visibility is often poor, but because quasi-zenith satellites fly at high elevation angles they can relatively easily provide correction signals even in mountainous areas. This dramatically improves measurement accuracy in remote locations where errors were previously large, contributing to the prevention of boundary disputes and more efficient land management. Municipal infrastructure inspection tasks (e.g., periodic measurement of tunnels and dams) can also obtain stable survey data in remote locations with LRTK, improving maintenance management accuracy.

As described above, LRTK significantly relaxes field constraints in civil works, disaster prevention, and surveying, enabling precise positioning that was previously difficult. Its freedom from communications infrastructure suggests future applications in other fields such as autonomous vehicle guidance and agriculture.

Easy operation via smartphone integration

The convenience of CLAS-compatible LRTK is further enhanced by integration with smartphones and tablets. LRTK receivers wirelessly pair with personal devices and are operated and managed via dedicated apps. This eliminates the need to carry expensive dedicated controllers or laptops; on site, anyone can view and save positioning data on a familiar smartphone screen. Intuitive app UIs display satellite reception status, current accuracy, and acquired coordinates in real time, making operation smooth even without specialized equipment handling skills.

Smartphone integration offers many additional benefits. For example, users can plot points on a map on the spot based on the precise positions obtained by the receiver, or immediately create surveying deliverables for electronic submission. Combining the smartphone camera makes it easy to tag photos with positioning coordinates and save them. Photo records of disaster sites or progress photos of construction with accurate coordinates are highly useful for later analysis and reporting. Furthermore, when Internet access is available, positioning data and photos can be uploaded to the cloud and shared with stakeholders. Real-time sharing of high-precision data acquired on site and using it for office instructions is a strength unique to LRTK with smartphone integration.

Additionally, using a smartphone as the control terminal makes the overall system compact and lightweight. The receiver itself is palm-sized, and with only a smartphone needed, individual workers can carry it easily and start positioning immediately when required. In other words, the concept of a “high-precision positioning device per person” becomes feasible. This enables field staff themselves to perform tasks that previously required specialized surveying teams. Because the tool is easy to use even for non-experts, dependence on specific skilled personnel is reduced and organizational work efficiency is expected to improve.

Labor savings, cost reduction, and elimination of dependence on specific personnel through LRTK introduction

Finally, we summarize the effects of introducing CLAS-compatible LRTK. Feedback from the field and case studies from adopting companies have made the following benefits clear.

• Labor savings in surveying work: Time and effort previously spent on base station setup and communication equipment configuration are no longer necessary, allowing teams to concentrate on the surveying itself. One person can measure multiple points rapidly, and tasks that formerly required two-person teams can increasingly be handled by a single person. This leads to more efficient personnel allocation and expected reductions in overtime.

• Reduced operating costs: Investment in communications infrastructure and dedicated equipment can be reduced. Since obtaining correction information does not incur additional fees, long-term operating costs can be kept down. Improved work efficiency reduces days and labor costs, directly lowering expenses. Internalizing tasks that were previously outsourced to surveying companies can yield significant cost savings.

• Elimination of dependence on specific personnel in positioning tasks: Stable accuracy can be achieved without relying on veteran surveyors, reducing quality variation due to skill and experience. The system automatically performs correction calculations and data recording, which lowers the risk of human error. Consistent accuracy regardless of the operator promotes standardization and leveling of work. Because the tool is easy for younger technicians to use, it also aids in human resource development.

• Improved safety and speed: Ancillary effects include reduced risks associated with surveying. For example, there is no need to adopt awkward poses to install base station antennas or climb to high locations to search for signal conditions, improving work safety. Preventing time loss from interrupted communications and rework allows survey operations to proceed confidently even on tight construction schedules.

As described, LRTK introduction transforms field work itself and achieves the triple benefits of labor savings, cost reduction, and high precision. It removes the hassles and anxieties of conventional RTK operations and makes surveying smarter and more reliable.

Conclusion: Expanding possibilities for simple surveying with LRTK

CLAS-compatible LRTK, which enables immediate centimeter-level (inch-level) positioning on site without being hindered by communications, is changing the way surveying is done. The advantage of not requiring network connectivity extends precision positioning to sites that previously had to forgo high accuracy, making LRTK a reliable partner across a wide range of fields from civil works to disaster response. With LRTK, simple surveying tasks that once required significant time and experience can now be performed astonishingly easily and accurately. By drastically shortening the time spent on “preparing for positioning,” workers can focus more on core tasks, yielding benefits in both productivity and quality.

High-precision positioning technology is evolving from something used only by specialists into a common tool available to everyone in the field. CLAS-compatible LRTK symbolizes this shift and is the key to realizing smart surveying that does not rely on individual expertise. We encourage you to adopt this new solution that removes concerns about network connectivity and experience firsthand the assurance of being able to “measure accurately anywhere.” The potential for simple surveying enabled by LRTK is limitless, and it is expected to revolutionize future positioning work.