Table of Contents

• What is CLAS (Centimeter Level Augmentation Service)?

• Differences Between RTK Positioning and CLAS

• How Centimeter-level Positioning Is Possible Even Outside Mobile Coverage

• What is LRTK Phone?

• “Solo Surveying” Enabled by LRTK Phone

• Use Cases for LRTK Phone

• The Future of Simple Surveying with LRTK

• FAQ

In sites that require high-precision location information, a new possibility is attracting attention: “centimeter-level positioning even outside mobile coverage.” By utilizing Japan’s Quasi-Zenith Satellite System “Michibiki” and its CLAS (Centimeter Level Augmentation Service), it is possible to obtain real-time positioning with an accuracy of a few centimeters even in mountainous or remote areas where mobile phone signals cannot reach. The groundbreaking device that makes CLAS easy to use is the LRTK Phone. This article explains in detail how CLAS works, how it differs from conventional RTK, and the revolution in solo surveying brought about by the LRTK Phone.

What is CLAS (Centimeter Level Augmentation Service)?

First, let’s explain what CLAS is. CLAS (pronounced “see-las”) stands for Centimeter Level Augmentation Service and is a high-precision positioning service provided by the Quasi-Zenith Satellite System “Michibiki,” often called Japan’s GPS. In simple terms, it is a technology that dramatically improves GNSS (Global Navigation Satellite System) positioning accuracy by using correction information broadcast from satellites. While the built-in GPS in a typical smartphone has errors on the order of several meters, using CLAS can achieve centimeter-level positioning with errors of a few centimeters (a few inches).

The CLAS mechanism distributes positioning error information, calculated from data gathered by electronic reference points (GNSS reference stations) installed nationwide by the Geospatial Information Authority of Japan, to the ground via the Michibiki satellites. Concretely, the error measured at ground reference points is sent to the quasi-zenith satellites as correction signals (broadcast on the L6 band), which the satellites then broadcast widely. If you have a CLAS-capable receiver (a dedicated GNSS terminal), you can receive these correction signals directly and apply them to your positioning data to obtain high-precision position information in real time.

The service area is mainly within Japan (and surrounding regions) and can be used as long as you have a view of the sky. In other words, whether in the mountains or on a remote island, or in places without base stations, you can achieve high-precision positioning as long as you can catch the CLAS signals from the satellites. CLAS is a government-provided service and is free to use. However, as described later, a dedicated high-precision GNSS receiver is required to use CLAS.

Differences Between RTK Positioning and CLAS

When it comes to high-precision positioning, the RTK (Real-Time Kinematic) method has long been well known. RTK uses a base station at a known point and a rover receiver, operating them simultaneously to correct relative errors with respect to the base station to achieve centimeter-level positioning. Recently, network-type RTK that utilizes the Geospatial Information Authority’s network of reference stations (for example, via the Ntrip protocol) has become common, enabling easy high-precision positioning by receiving correction information via a smartphone and a data connection. However, RTK has a weakness: dependence on communication networks. In mountain areas or underground where mobile signals cannot reach, network-delivered correction information cannot be obtained and RTK positioning cannot be established. Conventional RTK with a private base station also incurs costs and effort for equipment setup and personnel deployment.

By contrast, as mentioned above, CLAS allows correction data to be received directly from satellites, so the major difference is that no base station or communication line is required. In extreme terms, as long as you have a receiver, you can achieve centimeter-level positioning via satellites anywhere—from deserts to deep mountains. While RTK is relative positioning to a local base station, CLAS is a “wide-area augmentation” system that uses a nationally maintained network of reference stations combined with satellite communication. For this reason, CLAS is a PPP-RTK approach that balances RTK-level accuracy with the wide-area coverage of PPP (Precise Point Positioning).

There are caveats with CLAS. CLAS itself does not magically improve positioning accuracy without proper receiver-side processing: a dedicated receiver capable of multi-frequency GNSS reception and high-performance processing is required. Initial convergence to high accuracy may take time, making real-time application to fast-moving vehicles (such as autonomous driving at high speed) challenging. However, for handheld measurements or stationary surveying, CLAS’s advantages are fully realized. In particular, the ability to obtain high-precision positioning in places that were previously impossible without internet connectivity is highly significant.

How Centimeter-level Positioning Is Possible Even Outside Mobile Coverage

So why is “centimeter-level positioning even outside mobile coverage” possible? It comes from the combination of CLAS and modern receiver devices. Being outside mobile coverage means you cannot rely on cellular networks, but CLAS delivers correction information via satellite communication. As long as the sky is visible, you can receive position augmentation signals from satellites even if your smartphone shows “no service.”

To summarize the mechanism:

• Previously: Outside coverage, RTK correction data could not be obtained → high-precision positioning was impossible

• Now: Even outside coverage, CLAS signals can be received directly from satellites → high-precision positioning is possible

The key to this difference is a CLAS-capable high-precision GNSS receiver. Standard smartphone GPS cannot receive CLAS signals, so a dedicated device like the LRTK Phone must be combined with the smartphone. CLAS signals are transmitted on the L6 band, a special frequency that consumer GPS chips do not support. However, by using dedicated GNSS chips and receivers designed for high-precision positioning, L6-band signals can be captured and used as correction information.

Consider a construction site in the mountains where mobile coverage is unavailable. Traditionally, conducting high-precision surveying there would require setting up your own base station and wirelessly sending corrections to the rover. With a CLAS-capable receiver, however, you can use the correction data coming from the sky and complete positioning by yourself. For example, a municipality in Japan (Fukui City) has introduced a CLAS-capable device that attaches to an iPhone and used it to survey disaster sites after heavy rain. Even without communications infrastructure on site, they were able to quickly perform 3D measurements and surveys of the damage, speeding up recovery planning and reducing costs.

In short, by establishing “surveying infrastructure that falls from the sky,” it has become possible to perform precise surveying alone anywhere.

What is LRTK Phone?

So what is the crucial device that leverages CLAS? The LRTK Phone is a small RTK-GNSS receiver device developed by Reflexia Inc. (a startup originating from Tokyo Institute of Technology). It is an external positioning unit that attaches to a smartphone (currently iPhone and iPad) and turns the phone into a high-precision GNSS surveying instrument. Despite its pocketable compact size, it houses a high-performance antenna, a GNSS receiver engine, and a battery, enabling centimeter-level positioning in real time with just this single device.

Main features of the LRTK Phone:

• Lightweight and thin: Weighs about 165 g, thickness about 1 cm (0.4 in), comparable to a smartphone case. It is highly portable and not burdensome to carry on site.

• Supports high-precision GNSS positioning: Compatible with multiple satellite systems beyond GPS and receives on multiple frequencies such as L1/L2. It also supports the CLAS L6 signal, enabling horizontal accuracy of about ±1–2 cm (±0.4–0.8 in) and vertical accuracy of about ±3 cm (±1.2 in) (typical smartphone GPS accuracy is about 5–10 m (16.4–32.8 ft)).

• Built-in battery: Rechargeable battery enables roughly 6 hours of continuous operation. It can be charged via USB Type-C and operated while powered from a mobile battery.

• Easy smartphone integration: Attaches with a dedicated smartphone case or mount with one touch and communicates with the phone via Bluetooth or Lightning. No complicated setup is required—just launch the dedicated app and positioning begins automatically.

• CLAS-capable and network RTK-capable: LRTK Phone can receive Michibiki’s CLAS signals, enabling correction reception even in areas without mobile coverage. In places with mobile connectivity, it can also connect to network RTK via the Ntrip protocol. It can seamlessly switch between CLAS and network RTK depending on conditions.

• Extensibility: By using the smartphone as a host, position data can be uploaded to the cloud as-is or combined with photos and AR features. For example, you can take geotagged photos, perform distance and area calculations from captured coordinates, or even do 3D point cloud scanning with a single device.

The latest LRTK Phone, released at the end of 2023, offers an optional “Off-coverage Starter Kit” including a CLAS-capable antenna and a dedicated pole (monopod). This makes it even easier to perform positioning at sites without mobile signals and to set up an antenna to achieve stable accuracy.

“Solo Surveying” Enabled by LRTK Phone

The most impactful aspect of LRTK Phone is that it makes “solo surveying” a reality. Traditionally, surveying has been conducted by teams of two or more. For example, total station surveying required an operator and a prism-holder, and RTK surveying often involved several people for base station setup and equipment transport. With LRTK Phone, a single person can complete surveying tasks.

Tasks that previously required experienced surveyors and assistants can now be done by one technician holding a smartphone with an LRTK device, helping to alleviate labor shortages and improve efficiency. On arriving at a site, the user takes out the phone with the LRTK device, presses a button at the point to be measured, and instantly records latitude, longitude, and elevation with centimeter accuracy. Data are automatically saved and organized. Little specialized skill is required—the dedicated app is designed with a simple interface so anyone can operate it.

Supporting solo surveying is the dedicated monopod. While LRTK Phone can be used handheld, attaching it to the included pole enables more accurate single-point measurements. Place the pole tip on the ground or structure point to be measured and press the measurement button on the phone to obtain the 3D coordinates of that tip. The app automatically corrects for the pole’s height offset, so no complicated calculations are necessary. Combined with the monopod, the LRTK Phone replaces the traditional staff-and-instrument workflow: one person simply walks with the pole to collect precise survey points.

Thus, LRTK Phone is a powerful solution for sites where reducing personnel is required. For example, in quality control across large sites or recording disaster damage, surveying that formerly took many people and long hours can be completed quickly by one person, and the data are digitally shared immediately. Achieving solo surveying has the potential to fundamentally change how fieldwork is conducted.

Use Cases for LRTK Phone

Here are several concrete examples of how LRTK Phone and CLAS are being used.

• Disaster recovery site surveying: As mentioned earlier, Fukui City used iPhones with CLAS-capable devices to survey sites after heavy rainfall and landslides. Where previously multiple people were needed over long periods, introducing LRTK allowed immediate terrain measurement and collapsed-soil volume calculations even in mobile-dead mountain areas. This sped up damage assessment and recovery planning while reducing labor costs. It also shortened the time workers spent on dangerous slopes, improving safety.

• Construction site quality control: In construction and civil engineering, surveying tasks such as setting out foundations and checking earthwork shapes occur frequently. On one site, workers keep an LRTK Phone-equipped smartphone holstered at their waist and measure and record as needed. Its small, lightweight form means it is not intrusive to carry, and it functions as a “one-person, one-device surveyor,” enabling rapid measurement of dozens of height points that previously took half a day—data then shared to the cloud for quality control.

• Civil engineering in agriculture and forestry: For tasks like land parceling or thinning planning in forests—situations where calling in a surveying specialist isn’t warranted but accurate location data are needed—LRTK proves useful. Farmers use LRTK Phone to check field elevation differences and irrigation channel gradients, collecting their own field data. In forestry, it is used for route planning of logging roads and measuring felling areas. Because CLAS enables stable positioning even in remote mountain forests, it is powerful for deep-woods operations.

• Infrastructure inspection and maintenance: Accurate location records are necessary for maintaining roads, bridges, and sewer pipes. LRTK Phone can automatically append high-precision coordinates to inspection photos. In one local government, road patrol staff photograph pavement damage with an LRTK-capable smartphone, recording the coordinates and timestamps on the photos so that locations can be precisely identified later on GIS. Tasks that previously suffered from GPS errors have been dramatically streamlined.

In these ways, LRTK Phone is making it easy to “measure accurately on the spot” across construction, civil engineering, agriculture, forestry, public infrastructure management, and disaster response. Allowing in-house staff to obtain required survey data without calling specialized surveyors accelerates field DX (digital transformation).

The Future of Simple Surveying with LRTK

The wave of solo surveying driven by LRTK Phone is revolutionizing the concept of “simple surveying.” Until now, even when you just wanted a quick measurement, you had to accept meter-level accuracy unless you had specialist equipment and personnel. With LRTK, anyone can get centimeter-level measurements whenever needed, drastically improving the accuracy of everyday simple surveys.

For example, during preliminary site reconnaissance before construction or when preparing rapid disaster reports, LRTK is powerful where speed matters. You can quickly capture geotagged photos or point clouds with your phone and share them, making information flow between the field and the office seamless and shortening decision-making time. In short, by creating an environment where “you can measure when you want,” LRTK changes processes that were previously bottlenecked by surveying.

In the future, mobile high-precision positioning devices like LRTK Phone may become widespread, with each construction worker carrying a personal surveying tool. This would reduce work stoppages waiting for surveys and allow more autonomous and efficient site management—a true era of “one person, one surveying device.”

Simple surveying with LRTK has great value because anyone on site can collect data in spare moments, not just specialists. As this precise-yet-easy approach is further refined, the way we measure in many everyday contexts will surely be transformed.

FAQ

Q1. What is CLAS? How is it different from ordinary GPS? A. CLAS stands for Centimeter Level Augmentation Service and is a correction information service for high-precision positioning broadcast from Japan’s Michibiki satellites. Ordinary GPS typically has errors of about 5–10 m (16.4–32.8 ft), but by using a CLAS-capable receiver and the satellite correction signals, errors can be reduced to a few centimeters. In short, with dedicated equipment, CLAS enables position measurements far more precise than conventional GPS.

Q2. Do I need the internet or a mobile phone connection to use LRTK Phone? A. Basically, no. LRTK Phone can receive CLAS satellite signals directly, so centimeter-level positioning is possible even in areas outside mobile coverage. If a communication network is available, you can also use network RTK correction services, but this is not required. In mountain areas or other locations without signal, LRTK Phone and the satellites alone enable high-precision positioning.

Q3. Can I really survey alone? Is it usable by beginners? A. Yes. LRTK Phone is designed for solo surveying. The dedicated app offers intuitive operation: press the button at the point you want to measure and the app automatically acquires high-precision coordinates. The app handles specialist tasks such as height correction, so those with limited surveying experience can operate it without issue. Basic safety precautions—such as situational awareness during fieldwork—are still necessary.

Q4. What positioning accuracy can I expect? A. In practice, horizontal accuracy of about ±1–2 cm (±0.4–0.8 in) and vertical accuracy of about ±3 cm (±1.2 in) can be obtained. Accuracy depends on satellite reception conditions and the surrounding environment. With a clear sky and stationary measurement, centimeter-level stability is achievable, but accuracy may degrade under tree canopies or in urban canyons due to multipath and signal attenuation.

Q5. What do I need to use LRTK Phone? A. You need the LRTK Phone device itself, a compatible smartphone (currently mainly iPhone/iPad), and the dedicated app. Attach the LRTK Phone to your phone and connect via Bluetooth or wired connection, then launch the app to begin positioning. Positioning data can be displayed on a map in the app and uploaded to the cloud for sharing. No special settings or contracts are required to receive CLAS corrections; as long as you are within the coverage area, corrections are applied automatically.

Going forward, easy-to-use high-precision positioning technologies like LRTK Phone will continue to evolve and be applied across many fields. Experience an era where anyone, anywhere can obtain centimeter-level position information—by yourself, and wherever you are.