High-precision positioning without a reference station! Exploring the capabilities of LRTK compatible with Michibiki

Table of contents

• Basics of GNSS positioning: standalone positioning, RTK, and network RTK

• Problems caused by dependence on reference stations: communication environment, cost, and installation constraints

• How Michibiki’s CLAS provides satellite-based augmentation and its benefits

• How LRTK achieves high-precision positioning without a reference station

• Accuracy, stability, and ease of deployment: field evaluation points

• Main applications in civil engineering and surveying

• LRTK system operation procedures (devices, apps, cloud)

• Summary: a new era of simple surveying enabled by LRTK

In surveying and construction management, highly accurate position measurement that does not allow even errors of a few centimeters is required. However, achieving that usually requires the RTK (real-time kinematic) method, which installs a GNSS reference station (base station) and receives correction information via communication, making it heavily dependent on communication infrastructure such as cellular networks or Internet connections. In environments where a base station cannot be set up—mountain construction sites, surveys on remote islands, or disaster-affected areas immediately after an event—high-precision positioning often has to be abandoned.

Attention is therefore focused on CLAS, the centimeter-level augmentation service provided by Japan’s Quasi-Zenith Satellite System “Michibiki,” and on high-precision GNSS receiver systems that support it, called LRTK. This new technology, which enables centimeter-level real-time positioning without a reference station, is powerful even at sites lacking communication networks. This article clearly explains—from GNSS positioning basics and the shortcomings of conventional technologies to how Michibiki CLAS works and how LRTK achieves high-precision positioning—along with field evaluation points, use cases, and operation procedures.

Basics of GNSS positioning: standalone positioning, RTK, and network RTK

First, let’s organize the basics of positioning using GNSS (Global Navigation Satellite Systems). With a typical single GNSS receiver used alone for standalone positioning, the receiver calculates its position from signals from GPS satellites, etc., but errors of several meters to more than ten meters typically occur due to satellite orbit errors, atmospheric effects, and so on. While this is sufficient for car navigation or smartphone maps, it falls far short of the centimeter-level accuracy required in civil engineering surveying and design.

RTK (real-time kinematic) positioning was developed to correct these errors and obtain centimeter-level accuracy. In RTK, a reference station (base station) with known coordinates and a rover (mobile station) measure satellites simultaneously; the base station computes error information and transmits it to the rover in real time. The rover applies the received corrections to its own solution, reducing standalone errors of several meters to a few centimeters. Communication with the base station uses radio modems or the Internet (Ntrip, etc.), and in any case, continuous communication must be ensured.

Network RTK, which eliminates the need for users to own their own base station, has also become widespread. This service calculates corrections based on networks of continuously operating reference stations maintained nationwide by organizations such as the Geospatial Information Authority of Japan (for example, GEONET with about 1,300 stations) and provides them to subscribed users via the cellular network (VRS methods, etc.). Network RTK removes the need to install a dedicated base station in the field, but it still depends on the local cellular environment. In addition, many network RTK services require subscription fees.

Problems caused by dependence on reference stations: communication environment, cost, and installation constraints

Although RTK enables very useful high-precision positioning, conventional methods have several problems that stem from their dependence on reference stations.

• Dependence on communication infrastructure: As mentioned, RTK and network RTK require communication lines to transmit correction data. Therefore, in mountainous, forested, or remote island areas where cellular signals do not reach, real-time RTK positioning cannot be established; even bringing expensive GNSS surveying equipment to the site will only yield the accuracy of standalone positioning (on the order of several meters). In fact, in major disasters such as heavy rains or earthquakes, communication networks may be severed, making RTK positioning impossible.

• Equipment cost and operational burden: For stand-alone RTK, users must provide their own high-precision GNSS receiver for the base station and associated communication devices. A full base station setup can cost several million yen, which is a barrier for small operators. The time and effort required to set up a base station on site are also significant. Local RTK used in communication blackout areas limits the positioning area to the range where correction radio signals reach (generally a radius of several km to about 10 km (32,808 ft)), and accuracy degrades the farther one moves from the base station. When surveying while moving between multiple sites, repeatedly installing and removing base stations is inefficient.

• Constraints on installation locations: A reference station antenna must be placed in a stable location with good visibility, but in mountainous or island areas, finding a suitable site and securing a safe power supply can be difficult. Especially in disaster response, placing a base station in an unsafe affected area carries risks. Under such conditions, teams have sometimes been forced to rely on PPK (post-processed kinematic), bringing raw observation data back to the office for later processing because real-time positioning was not feasible. However, PPK cannot produce immediate results, delaying on-site decision-making and responses.

These issues drove demand for a “high-precision positioning method that can be used easily on site without relying on communication infrastructure.” A groundbreaking solution to that demand is the satellite-delivered RTK service “CLAS” provided by the Michibiki QZSS.

How Michibiki’s CLAS provides satellite-based augmentation and its benefits

CLAS (Centimeter Level Augmentation Service), provided by Japan’s QZSS “Michibiki,” is attracting attention as a new form of high-precision positioning that does not rely on ground reference stations. As the name implies, CLAS is a service that augments positioning to the centimeter level, and its distinguishing feature is that it distributes correction information from satellites rather than from the ground.

Operationally, CLAS generates correction information based on data such as satellite orbit and clock errors and ionospheric/tropospheric delays observed by the Geospatial Information Authority of Japan’s network of reference stations, and broadcasts that information nationwide via Michibiki’s L6-band signals. User receivers pick up the correction data contained in the L6 signal—such as grid-based error information subdivided by region—and apply it in real time to the positioning solutions computed from GPS, GLONASS, and other GNSS satellites. It is as if an “invisible reference station placed in space” constantly provides corrective information: without preparing a dedicated ground base station or communication lines, a standalone receiver can achieve RTK-level accuracy.

Using CLAS, the typical standalone GNSS error of about 5-10 m can be reduced at once to the order of a few centimeters. The correction service is provided free of charge as a public service, and as long as Michibiki satellites are visible overhead anywhere in Japan, you can receive the same service in mountainous areas and over the sea—another major advantage is its wide coverage. Because communication infrastructure is unnecessary, high-precision positioning is possible in areas without cellular coverage as long as satellites are visible.

Technically, CLAS uses a PPP-RTK approach (a fusion of precise point positioning and RTK). Conventional static PPP could require roughly 30 minutes for initial convergence to high accuracy, but CLAS combines dynamic RTK-like augmentation so it is designed to reach centimeter-level accuracy within about one minute. Compared with reference-station RTK, CLAS may take slightly longer from startup to obtaining a Fix solution (high-precision solution), but about one minute is generally not a practical impediment. Once a high-precision position is fixed, continuous corrections maintain stable positioning within a few centimeters.

The greatest advantage of CLAS is that real-time positioning is completed without any reliance on ground communications or base station installation. For example, for RTK surveying deep in the mountains, conventional practice required preparing a base station or finding a location with radio coverage. With a CLAS-capable receiver, simply powering up on site allows automatic reception of correction data from satellites, enabling immediate positioning. Because coverage is nearly uniform nationwide even where cellular service is absent, and the correction service is free, once the appropriate equipment is procured, running costs are extremely low.

How LRTK achieves high-precision positioning without a reference station

To benefit from CLAS, a GNSS receiver that can receive L6-band augmentation signals and perform high-precision phase measurements is required. Standard GPS chips built into smartphones or commercial car navigation devices cannot directly receive CLAS signals, so to perform centimeter-level positioning you need hardware with a dedicated antenna and receiver circuitry (a CLAS-compatible receiver). LRTK, which has emerged recently, packages such CLAS-compatible GNSS capabilities into a compact terminal and pairs it with a smartphone for easy operation. By linking an LRTK terminal (the receiver unit), a smartphone app, and cloud services, centimeter-level surveying can be carried out on site even by non-experts.

How exactly does an LRTK device enable “base-station-less” high-precision positioning? The main points are as follows.

• Nationwide positioning without communication infrastructure: An LRTK terminal receives correction information directly from Michibiki satellites, so no data communication via a mobile router or radio is required. Even at sites with no cellular coverage—mountainous areas or remote islands—if the sky is open, a single unit can achieve centimeter accuracy. For example, in disaster areas where the communication network is severed by a major earthquake, an LRTK unit can immediately begin surveying and record the locations of damage. Because the correction data are free, LRTK enables “RTK positioning anywhere without a base station,” regardless of urban or rural location.

• Low power consumption and long operating time: Because LRTK devices do not use radio links to a base station or 4G modules, their power consumption is reduced and battery life is long. Depending on the model, some can handle a full day (more than 10 hours) of continuous surveying, reducing concerns about battery depletion in remote mountain work where external power is hard to arrange. Because there is no need to search for cellular signals, the smartphone’s battery drain is also reduced. The result is stable operation during extended fieldwork.

• Compact, lightweight, and highly mobile: LRTK receivers are compact with integrated antennas and weigh only a few hundred grams, making them very lightweight. The convenience of obtaining positions by attaching a palm-sized receiver to a smartphone and holding it in one hand—without carrying tripods or long poles—is revolutionary. Rugged dustproof and waterproof designs allow durability in harsh construction site environments, so the device can be easily brought to any site. LRTK is particularly effective for single-person surveys covering multiple points on foot, or in places where traditional equipment installation was difficult, such as under tree canopies or along cliffs.

• Real-time high-precision positioning: Satellite-based correction signals arrive almost in real time, and the LRTK terminal immediately computes high-precision positions. It takes tens of seconds to about one minute to converge to a Fix solution after first powering on, but once centimeter-level accuracy is reached, continuous high-precision positioning is maintained even while moving. Because results are available on site, there is no need to bring data back for post-processing; measurements can be used immediately for verification of as-built conditions and progress management, fully leveraging the benefits of real-time high precision.

As described above, LRTK brings a new positioning style to the field that “operates without base stations or communications.” This makes it possible for anyone to obtain centimeter-level position information easily in mountainous areas and other locations where high-precision positioning was previously difficult.

Accuracy, stability, and ease of deployment: field evaluation points

Field reports indicate favorable evaluations of positioning accuracy and usability. Positioning using CLAS typically achieves horizontal accuracy of a few centimeters and vertical errors on the order of several tens of centimeters. For example, in stationary tests more than 95% of points were reported to lie within horizontal errors of 6 cm (2.4 in) and vertical errors of 12 cm (4.7 in). This is a dramatic improvement over conventional standalone positioning (errors of about 5-10 m) and matches the practical accuracy of network RTK and other reference-station methods. While satellite visibility and the surrounding environment cause some variation, CLAS generally provides stable accuracy sufficient for normal surveying and design tasks.

Once a Fix solution is obtained, positioning remains stable within a few centimeters, allowing continuous surveying while moving. Although it is necessary to wait tens of seconds at startup, an initial convergence of under one minute usually does not significantly disrupt field workflow.

Field technicians report that LRTK dramatically improves ease of positioning. Tasks that formerly required specialized surveying equipment and advanced skills to achieve centimeter accuracy can now be handled with a smartphone and a small receiver. Because there is no need for communication setup or base station installation, teams can begin measuring as soon as they arrive on site—this convenience yields major time savings. The reassurance of being able to survey without worrying about communication conditions also enhances operational reliability (risk hedging). For example, during the 2024 Noto Peninsula earthquake, LRTK receivers were used in areas where communications were cut, enabling immediate on-site measurement of cracks and subsidence. LRTK, which is not dependent on communications or large equipment, is attracting attention as a backup surveying method in emergencies.

LRTK systems also deliver major cost advantages. By avoiding the need for conventional RTK surveying equipment costing several million yen and leveraging the free CLAS augmentation, operating costs for high-precision positioning can be reduced to nearly zero. Eliminating the need for base station equipment and communication subscriptions results in significant savings in acquisition and maintenance expenses. Furthermore, enabling one-person-per-smartphone surveying reduces idle staffing time and improves overall productivity. Intuitive operation by staff without specialized training facilitates smooth adoption on site. For these reasons, simple positioning tools like LRTK are being adopted not only by construction and surveying firms but also by municipalities and disaster management agencies.

Main applications in civil engineering and surveying

Base-station-less high-precision positioning with LRTK opens new possibilities across various field operations in civil engineering and surveying. Representative application examples include:

• Remote earthwork surveying: For roadwork in mountainous areas or dam construction sites with poor communications, LRTK enables onsite as-built surveys and staking checks without relying on communications. Previously, securing communications or transporting large equipment was a bottleneck, but carrying an LRTK device allows immediate acquisition and sharing of position data for progress management. On remote islands, surveys can be conducted without transporting heavy base stations by boat, improving efficiency and safety.

• Boundary surveys and land investigations: LRTK is effective for boundary verification in forests, farmland, and other areas lacking reference marks or communications. Even without known control points, LRTK instantly provides high-precision coordinates, streamlining the placement and verification of boundary markers. Because a single person can carry out surveys without an assistant, it is well-suited to sites with labor shortages. Municipal public land surveys are beginning to use simple LRTK positioning.

• Initial disaster response surveying: After large earthquakes or landslides, rapid recording of damage is necessary. LRTK can position independently of communication infrastructure, making it suitable for initial on-site surveys in disaster areas. For large-scale slope failures, personnel can use lightweight LRTK terminals to measure the perimeter points of collapse and positions of damaged structures and plot them on digital maps. Tasks that were previously difficult for a single person in disaster response can now be performed safely and rapidly with an LRTK terminal and smartphone. Recorded data can be shared immediately, providing valuable input for initial response decisions.

• Infrastructure inspection and maintenance: High-precision GNSS is becoming a useful tool for inspecting tunnels, bridges, railways, and roads. When an anomaly is found during routine inspections, recording accurate coordinates with LRTK prevents memory errors or documentation mistakes. For example, in track inspections, measuring the coordinates of a detected deformation with LRTK allows accurate relocation for future repairs. In bridge inspections, geotagging photos of damage with LRTK-derived coordinates makes it easier to compare the same location during later inspections. Improving the precision of such digital records is expected to contribute to the DX (digital transformation) of infrastructure maintenance.

• Improving accuracy of drone surveying and photogrammetry: LRTK is useful for aerial photogrammetry using UAVs (drones). If the drone’s position or the onboard camera’s location during flight can be accurately determined with LRTK, the accuracy of 3D models and drawings derived from aerial photos can be improved without placing numerous ground control points (GCPs). Ground-based 360° cameras and smartphone photography can also benefit from LRTK by embedding high-precision coordinate tags with captured images, enabling accurate mapping and management of site photos. LRTK positioning is thus applied to enhanced field records and more efficient photogrammetry.

In these ways, simple surveying with smartphone × LRTK is spreading beyond surveying firms to construction companies, municipalities, and disaster response organizations. Its flexibility to match field conditions is a major advantage, and application areas are likely to expand further.

LRTK system operation procedures (devices, apps, cloud)

Using LRTK is relatively easy to start, even without specialized knowledge. Keep the basic workflow in mind.

• Preparing compatible devices and apps: First, obtain a Michibiki CLAS-compatible GNSS receiver (LRTK terminal) and install the dedicated positioning app on a smartphone. The LRTK terminal can be connected to the smartphone via a wired connection or mounted with a special holder.

• Starting positioning on site: Upon arrival, turn on the LRTK terminal and the smartphone and launch the app. The receiver will begin tracking GPS and Michibiki satellites and start receiving CLAS augmentation. In an open area with satellite visibility, set the device so it has a clear view of the sky.

• Obtaining high-precision data: Positioning accuracy converges to centimeter level in tens of seconds to about one minute after satellite acquisition. Check the current accuracy and satellite count on the app; once a stable Fix solution is obtained, begin measurements. Press the measurement button in the smartphone app at the desired point to record high-precision coordinates for that location. You can also take photos as needed, embedding location tags in the photo files. For multiple points, repeat the same operation to accumulate data.

• Cloud linkage and data sharing: Measurement data are stored on the smartphone and can also be uploaded from the field to the cloud for sharing. If you link with a dedicated cloud service, coordinate data, photos, and notes can be shared with the office in real time. This makes it easy to immediately confirm field results on a map and to consult with remote colleagues. Cloud data can later be imported into CAD drawings or GIS, greatly improving post-survey workflows.

With these steps, LRTK-based surveying is intuitive and simple. Without the time-consuming base station setup or communication configuration of the past, the ideal workflow of “arrive on site and start measuring immediately” becomes a reality.

Summary: a new era of simple surveying enabled by LRTK

Michibiki’s CLAS is revolutionary as a high-precision positioning service available nationwide without a base station or communication infrastructure. The advent of LRTK, which makes CLAS easy to use in the field, is transforming surveying workflows. In mountainous areas, on remote islands, or amid the chaos immediately after a disaster, large-scale equipment and extensive site preparation are no longer necessary to obtain high-precision location information. With a smartphone and a small receiver, anyone can perform accurate on-site surveying.

This technological innovation delivers great value not only to construction management and surveying but also to disaster prevention and infrastructure management. Field measurement efficiency and safety will dramatically improve, and tasks that previously required specialized technicians can increasingly be handled by on-site staff. The burden of transporting heavy surveying and communication equipment is reduced, and real-time access to precise data accelerates decision-making.

Truly, a new era of simple surveying enabled by LRTK is dawning. Such easy-to-use high-precision GNSS tools are being introduced one after another, and a broad range of users—from construction and surveying companies to municipal employees and disaster response personnel—are experiencing their benefits. Why not try LRTK, which can “turn your smartphone into a universal surveying instrument,” at your next site to experience unprecedented productivity gains and peace of mind?