A Strong Ally on Construction Sites! CLAS-Enabled Receivers for Centimeter-Level (inch-level) Positioning Even Outside Communication Coverage

On construction sites and surveying locations, GNSS equipment capable of high-precision positioning is indispensable. However, in areas outside communication coverage such as mountainous regions, or when communication infrastructure is down due to large-scale disasters, conventional real-time positioning has been difficult. The CLAS-enabled receiver LRTK is a reliable ally on site, enabling centimeter-level (inch-level) positioning even outside communication coverage. By leveraging CLAS, the cutting-edge positioning service provided by the Quasi-Zenith Satellite System Michibiki (QZSS), this technology delivers precise location information anywhere without base stations or communication lines, and it is poised to significantly transform construction and surveying practices.

This article explains in detail the benefits of using CLAS-enabled receivers (especially LRTK), the technical overview of CLAS, and the differences from conventional RTK. It also introduces specific scenarios where this technology is powerful in communication-dark environments (mountainous areas, disaster response, infrastructure maintenance, etc.), the latest use cases linking with smartphones (iPhone), and applications such as AR technology and point-cloud scanning. At the end of the article we summarize the advantages of simple surveying with LRTK and answer common questions in a Q&A format.

Table of Contents

• What is a CLAS-enabled receiver?

• Conventional RTK positioning methods and challenges

• Benefits of introducing CLAS-enabled receivers

• Scenarios where they excel outside communication coverage

• Expanded convenience through smartphone (iPhone) integration

• Applications to AR technology and point-cloud scanning

• Summary

• FAQ (Frequently Asked Questions)

What is a CLAS-enabled receiver?

CLAS (Centimeter Level Augmentation Service) is a high-precision positioning service provided by Japan’s Quasi-Zenith Satellite System Michibiki (QZSS). Standalone GNSS positioning such as conventional GPS inevitably produces errors on the order of meters, but by using CLAS you can measure positions with dramatically higher accuracy—within a few centimeters (inches). A major feature is that high precision can be achieved without relying on base stations or Internet communication. CLAS correction information is broadcast directly nationwide from Michibiki satellites, so as long as the sky is visible, centimeter-level (inch-level) positioning is stable even in mountainous regions, remote islands, or at sea. This service is available to anyone, and by simply equipping a CLAS-enabled GNSS receiver you can start high-precision positioning without additional communication charges.

LRTK is a next-generation GNSS receiver that supports CLAS. Technically, it uses a positioning method called PPP-RTK, which bases its corrections on error information collected from networks such as the Geographical Survey Institute’s GEONET (satellite orbit and clock errors, ionospheric delays, etc.). Correction data are sent to the receiver via CLAS satellite signals, and real-time position corrections are applied. Without needing to understand the complex mechanics, users can simply power on a CLAS-enabled receiver on site and the satellites will automatically deliver correction information, allowing a single receiver to complete centimeter-level (inch-level) positioning.

Conventional RTK positioning methods and challenges

Real-Time Kinematic (RTK) positioning has long been a common method for high-precision GNSS. In RTK, a base station with known accurate coordinates and a rover receive satellite signals simultaneously; by comparing observation data from both, errors are corrected to achieve centimeter-level accuracy. Standalone positioning errors of about 5–10 m can be reduced to a few centimeters; horizontal positioning typically reaches about 2–3 cm (approximately 5 cm in height), which has made RTK widely used in surveying and construction management. Because the time to obtain a fixed solution is typically only a few seconds, RTK became established as a method for obtaining immediate high precision.

However, conventional RTK has several challenges. The biggest issue is that it requires continuously receiving correction information from a base station in real time. RTK cannot function where base station signals or data communication do not reach. Therefore, two main operational approaches have been used:

• Local base station method (standalone RTK): The user sets up their own GNSS receiver as a base station near the survey site and transmits correction data sequentially to the rover via radio (e.g., low-power radio). This method has a simple one-to-one configuration but requires preparing and installing base station equipment, and is limited to the range in which base station radio reaches (usually a few km to about 10 km). Accuracy also degrades with distance from the base station, and beyond 10 km errors become non-negligible.

• Network RTK (VRS/Ntrip): This method uses reference station networks (such as national or private continuously operating reference stations) and receives correction information over the Internet. The user equips the rover with a communication modem and obtains virtual reference station (VRS) corrections via an Ntrip client. This eliminates the need to prepare your own base station and largely removes accuracy degradation due to distance from a reference station. However, service fees are charged monthly or annually, and it cannot be used where cellular communications are out of coverage.

Because both approaches require either base station installation or communication infrastructure, there have been many situations—deep in the mountains, places with no radio reception, or after major disasters when base station equipment or communication networks are down—where real-time centimeter-level (inch-level) positioning had to be abandoned. In such cases, field teams often had to forego on-site positioning and bring data back to the office for post-processing (PPK: Post-Processed Kinematic), which added time and effort. The costs of base station equipment and communication fees have also been economic barriers to RTK adoption.

Benefits of introducing CLAS-enabled receivers

CLAS-enabled receivers solve these conventional challenges in one stroke. By using an LRTK or similar receiver that leverages CLAS, you no longer need to provide your own base station or receive correction data via cellular networks. Because corrections come directly from the satellites, you can achieve uniform high-precision positioning anywhere in Japan—from mountainous regions to remote islands and out at sea—as long as you can receive CLAS signals from the satellites. There is no need to worry about distance to a base station or to search for radio or communication coverage, and centimeter-level (inch-level) accuracy is maintained consistently even for wide-area surveys and tasks involving movement. The time-consuming tasks of setting up base station equipment and arranging communications in advance are eliminated; simply arriving on site and powering on the device starts real-time positioning immediately, which is a major advantage.

Moreover, because real-time positioning with a CLAS-enabled receiver is completed entirely on site, results can be used immediately after measurement. For example, you can check coordinates on the spot for stakeout or as-built verification, or immediately share collected point data to the cloud to collaborate with stakeholders—enabling a fast workflow. Reducing time spent taking data back to the office for post-processing is especially advantageous in urgent disaster-response situations.

Key benefits expected from introducing CLAS-enabled receivers include:

• No base station or communication lines required: Positioning is completed by bringing a single receiver to the site. In mountainous or cellular-dead areas, centimeter-level (inch-level) positioning is possible as long as the CLAS signal from the satellites can be received.

• Stable accuracy nationwide: Michibiki-provided correction information yields uniform accuracy across the country without being affected by distance from base stations. The same accuracy can be maintained at multiple remote sites simply by moving the device.

• Real-time results: Measurement and result confirmation are completed on site, allowing survey results to be immediately reflected in construction decisions. Getting position information in real time speeds up on-site decision-making.

• Reduced cost and effort: There is no need to buy or set up base station equipment or subscribe to communication services, reducing expenses. The simplicity of starting positioning by just turning on the device makes it easy for non-experts to operate after short training.

Scenarios where they excel outside communication coverage

CLAS-enabled receivers show their true value especially in environments where communication does not reach. In scenes where traditional methods would have required giving up positioning, LRTK and other CLAS-enabled receivers can provide centimeter-level (inch-level) accuracy:

• Remote construction sites in mountainous regions: Road works, dam and tunnel construction in mountain areas often fall outside cellular coverage. Bringing a CLAS-enabled receiver to such sites enables obtaining accurate coordinates on the spot without setting up reference points or radio repeaters. Even when surveyors cannot visit the site, local workers can perform positioning, record data, and share it immediately—improving efficiency in remote construction management.

• Disaster response and recovery: Rapid surveying is vital for understanding damage from earthquakes, heavy rain, landslides, and other disasters. Communications and base station power may be down in such situations. CLAS-enabled receivers can capture satellite signals and perform topographic surveys and coordinate recording of affected areas. There are actual cases where local governments used LRTK and smartphones for immediate post-disaster surveys, aiding rapid recovery and cost reduction. A positioning system that does not depend on communications is a powerful tool for disaster prevention and mitigation.

• Infrastructure maintenance and inspection: High-precision positioning is essential for inspecting roads, bridges, dams, and other infrastructure in mountainous or coastal areas. For example, regularly measuring monitoring points on mountain slopes or checking settlement at port facilities on remote islands is easy with a CLAS-enabled receiver. Sites that previously required dispatching survey teams can now be handled by on-site personnel bringing a CLAS-enabled receiver and importing data into GIS directly. Positioning technology that is not affected by communication networks contributes to more efficient management of extensive infrastructure.

Expanded convenience through smartphone (iPhone) integration

CLAS-enabled receivers such as LRTK become even more user-friendly and versatile when integrated with smartphones and tablets. By connecting the receiver to a smartphone app via Bluetooth or similar, high-precision position data can be displayed on the smartphone in real time. You can view your current position on a map on an iPhone, save and manage recorded point coordinates, and operate more intuitively than conventional surveying instruments.

Combining smartphone sensors and camera functions enables advanced uses beyond simple coordinate measurement. For example, attaching the receiver to an iPhone or iPad with a dedicated adapter allows one-handed operation while positioning. Using a dedicated monopod with automatic pole-length offset correction via the smartphone screen makes accurate single-point measurements easy for one person, similar to a professional surveying pole. Because many devices are lightweight—often under 200 g—they are not burdensome to carry while working on site. Battery-powered operation allows long continuous positioning, and you can also power the receiver from a mobile battery via USB, enabling familiar smartphone-style operation during daily tasks.

Applications to AR technology and point-cloud scanning

Combining CLAS-enabled receivers and smartphones makes it easy to utilize advanced digital technologies on site, such as augmented reality (AR) and point-cloud scanning. High-precision position and attitude information enable precise outdoor AR displays and 3D scanning that were previously difficult.

• Improving work efficiency with AR: AR apps are emerging that overlay design drawings or buried utility positions on the real-world view through an iPhone camera. Previously, accurate outdoor AR required placing ground markers or manual alignment. But by combining centimeter-level (inch-level) position information from a CLAS-enabled receiver with accurate heading from the smartphone’s gyro sensor, markerless AR alignment outdoors becomes possible. For example, 3D models of design lines or buried pipes can be visualized on the ground without offset, drastically reducing excavation mistakes and improving as-built verification efficiency. Applications also include following AR guide lines to perform safe and accurate work at night on construction sites.

• Point-cloud scanning with a smartphone: With LRTK and a smartphone, you can obtain point-cloud data on site without specialized 3D laser scanners. Using an iPhone’s built-in LiDAR sensor or camera to scan surrounding structures and terrain, and correcting each point’s coordinates with high-precision data from the LRTK receiver, you can generate point-cloud models aligned to an absolute coordinate system. The captured point cloud can be immediately overlaid on existing topographic maps or CAD drawings, making it effective for comparing as-built conditions to design. For example, for slope displacement measurements, you can walk along a slope up to 100 m (328.1 ft) while scanning with a smartphone to obtain a high-density point cloud, enabling detailed assessment of surface irregularities and erosion. Cross-sections and automated volume calculations can be generated on site from the point cloud, reducing the need to outsource measurement and analysis work. Sharing data via the cloud allows remote experts to review results in real time.

Summary

CLAS-enabled receivers, which provide centimeter-level (inch-level) positioning anywhere without being tied to base stations or communication environments, are truly strong allies on site. Devices like LRTK can dramatically improve efficiency and accuracy across many construction and surveying scenarios. They offer peace of mind by providing reliable real-time positioning even in difficult situations such as mountain construction or disaster response. Integration with smartphones enables one-person surveying, AR-based verification of design data, and point-cloud scanning to record as-built conditions—accelerating digital transformation on site.

Above all, the major advantage of simple surveying with LRTK is that accurate positioning becomes possible after short training, even for non-specialist personnel. If tasks previously outsourced to surveyors can be handled in-house, you gain not only cost savings but also faster turnaround. The era when anyone can carry a receiver and smartphone to instantly obtain and share position information is near, and CLAS-enabled receivers like LRTK hold the key. They are poised to play an increasingly important role as tools supporting on-site DX (digital transformation).

FAQ (Frequently Asked Questions)

Q1. What is a CLAS-enabled receiver (LRTK)? A1. A CLAS-enabled receiver is a high-precision GNSS device that can receive the Centimeter Level Augmentation Service (CLAS) broadcast by Michibiki, Japan’s QZSS (often called the Japanese GPS). LRTK is one variant that can achieve centimeter-level (inch-level) positioning by itself without relying on base stations or communications.

Q2. Can it really position without communication coverage? A2. Yes. CLAS-enabled receivers receive correction signals directly from satellites even outside cellular coverage, so centimeter-level (inch-level) positioning is possible in mountainous areas or on remote islands. However, GNSS satellite signals must be receivable, so it cannot be used indoors or in tunnels where the sky is not visible (positioning resumes once you move to a location with satellite visibility).

Q3. How accurate is the positioning, and does initial convergence take time? A3. CLAS-enabled receivers including LRTK achieve horizontal accuracy on the order of several centimeters (inches), comparable in practice to conventional RTK and sufficient for many surveying and construction tasks. It does take some time after power-up to converge to centimeter-level accuracy (fixed solution). Convergence typically occurs in about 30 seconds to 1 minute, during which time the solution may be a float with errors on the order of several tens of centimeters. Once a fixed solution is obtained, high precision is maintained stably.

Q4. How do you use it with a smartphone? Can it be used with an iPhone? A4. Yes, it can be used with an iPhone. The LRTK receiver connects to a smartphone via Bluetooth or similar, and is operated via a dedicated app. The app allows you to check coordinates, record points with names, and load drawing data. Using the iPhone or iPad screen combined with maps and camera views is more intuitive than traditional survey instruments; real-time display of your position on a map makes point measurement and navigation easy.

Q5. Can anyone operate it? Are specialized skills or qualifications required? A5. Basic operation is done through a smartphone app, so it is much simpler than dedicated survey equipment. Some GIS or surveying knowledge is helpful, but with instruction users such as site workers can handle it. Complex calculations are automatically processed by the receiver and app, so the user follows on-screen prompts to record and verify points. Certain official surveying tasks still require national qualifications, but for routine as-built checks and preliminary surveys, it can be used without qualifications.

Q6. What applications and sites are suitable? A6. In construction, it’s used for as-built measurements of roads and earthworks, stakeout for foundations, and guidance for heavy machinery. For infrastructure inspection, it’s used in displacement measurements of bridges and tunnels, damage mapping at disaster sites, and in agriculture for field surveys or for corrections for autonomous tractors. Its independence from communications makes it particularly suitable for mountain construction, remote island works, and emergency surveys immediately after disasters—anywhere you need reliable accuracy anytime, anywhere.

Q7. Are there running costs or service fees? A7. CLAS itself is free to use. Michibiki’s CLAS signal is provided as a public service, and once you purchase a compatible receiver you do not pay additional fees to receive correction information. However, you do need to cover the initial cost of the receiver and any smartphone app setup. For LRTK, the purchase cost is the main expense and there are no ongoing monthly fees, making it possible to greatly reduce running costs compared with network RTK services.