New LRTK Technology Enabling High-Precision Positioning Even Indoors and Outside Communication Coverage

Table of Contents

• How RTK positioning works and limitations of conventional technologies

• Positioning challenges that arise

• Solutions offered by the new LRTK technology

• Benefits in accuracy, operability, and cost

• Expected use cases across diverse sites

• Procedure for simple surveying using LRTK

• On-site benefits from introducing centimeter-level positioning

• Conclusion: A new era of surveying opened by LRTK

Accurate positioning technology is indispensable for maintaining social infrastructure and for operations at construction sites. However, in environments where mobile phone coverage is unavailable—such as tunnels, underground spaces, and mountainous areas—it has been extremely difficult until now to perform high-precision positioning at centimeter-level accuracy. Conventional RTK positioning relies on communication with base stations, and in locations where communication cannot be established or satellite signals cannot reach (indoors), it could not deliver sufficient performance. The new technology called LRTK was developed to solve these problems. This article explains the principles and limits of RTK positioning, the difficulties faced at sites without communication infrastructure or in indoor spaces, and how LRTK overcomes them. It also introduces benefits in terms of accuracy, operability, and cost, concrete use cases, and the procedure for simple surveying using LRTK. We hope this provides valuable insights for civil engineering, construction industry professionals, and municipal survey staff, and helps transform positioning operations in challenging environments.

How RTK positioning works and limitations of conventional technologies

First, we summarize the principles and issues of RTK positioning (Real Time Kinematic), a representative technology for high-precision positioning. RTK is a positioning method that performs real-time error correction using two GNSS receivers (a base station and a rover). The base station is installed at a known, accurate coordinate position and estimates satellite signal errors from systems such as GPS and GLONASS in real time. This correction information is sent to the rover via radio or the Internet, and the rover applies the corrections to the satellite signals it receives, reducing standalone positioning errors of several meters down to about a few centimeters. In other words, RTK is the technology that enables “ultra-high-precision GPS positioning” usable in the field.

RTK positioning has long been used in civil surveying and machine-control guidance, playing a key role in aligning design coordinates on maps with actual positions. However, this excellent technology has several constraints. The biggest hurdle is dependency on communication environments. To transfer correction data from the base station to the rover, dedicated radio or mobile networks are required; in out-of-coverage regions, this communication link cannot be secured and RTK cannot realize its intended accuracy. Also, RTK requires the base and rover to simultaneously track multiple of the same satellites. In environments with limited satellite visibility—such as between tall buildings or in forests—the number of usable satellites can be insufficient, causing unstable positioning or degraded accuracy. Furthermore, base station equipment itself is expensive, and traditionally expert surveyors were required to prepare and operate the equipment. In short, conventional RTK positioning was “highly accurate but labor-intensive.”

Positioning challenges that occur outside coverage and indoors

Because of the above constraints, achieving high-precision positioning in places without communication infrastructure or in indoor environments has traditionally been very difficult. Let us look at specific cases and their challenges.

• Mountainous and remote island sites outside mobile coverage: At remote mountain construction sites or on isolated islands where mobile signals do not reach, correction information cannot be received from network RTK services (such as Ntrip). As a result, GNSS receivers can only operate in standalone mode, and achievable position accuracy remains at best on the order of several meters. Such accuracy is unusable for surveying that requires high precision, and in the worst cases surveying itself had to be abandoned in favor of analog measurements using tapes or compasses. Naturally, this method is inefficient, increases human error, and raises the risk of rework (re-measurement) later.

• Tunnels and underground spaces: Inside underground tunnels or equipment floors, satellite signals are largely blocked and GNSS reception is near impossible. Not only RTK but even ordinary GPS positioning cannot be performed, forcing reliance on optical surveying instruments such as total stations (TS). However, tunnels do not easily allow linear lines of sight, and setting up TS and establishing survey points requires significant effort. Long tunnels require multiple survey stations to be established and connected, demanding meticulous work by specialized technicians and making it very difficult to complete within limited working hours.

• Indoor facilities and building interiors: Warehouses and factory buildings are also typical examples where satellite positioning does not reach. For example, when installing equipment or shelving indoors, it has been common to use tapes or laser distance meters to measure and mark dimensions by hand before construction. Achieving centimeter-level accuracy requires experienced judgment and is difficult alone, so teams often call in specialist surveyors. Meanwhile, demands for high-precision positioning have increased—for example, for automated warehouse vehicles and self-driving forklifts—but conventional indoor positioning technologies (Wi‑Fi/Bluetooth beacon positioning or systems using UWB tags) only achieve accuracy on the order of meters to tens of centimeters and incur significant equipment installation costs. Obtaining high-precision absolute coordinates indoors has been a technological and financial hurdle.

As described above, environments where communication is cut off and environments where satellites cannot be observed have long posed challenges to achieving high-precision positioning. Even when trying to substitute optical surveying or existing indoor positioning infrastructure, accuracy shortfalls and operational inefficiencies were common.

Solutions offered by the new LRTK technology

To break through these limitations, a new positioning technology called LRTK has been developed. In short, LRTK is a solution that realizes “RTK positioning usable anywhere without relying on communications.” The features supporting this capability are as follows.

• QZSS “CLAS” support so no network is required: LRTK leverages Japan’s Quasi-Zenith Satellite System “QZSS” (Michibiki) and its centimeter-level positioning augmentation service (CLAS). CLAS distributes correction data generated from the Geospatial Information Authority of Japan’s continuous GNSS observation network (GEONET) via satellite, and compatible receivers can obtain correction information directly from the satellite without relying on mobile communications. LRTK terminals receive these CLAS signals and apply them to GNSS positioning in real time, achieving centimeter-level positioning even without a base station. This is essentially a PPP-RTK approach that completes the RTK principle via satellite communications, providing uniform accuracy across Japan—from mountainous regions to remote islands and offshore areas. The augmentation signals from the satellite are free to use, so there are no Internet connection charges or correction service fees that were previously required.

• Flexible operation with local base station mode: LRTK can achieve high-precision positioning standalone using CLAS, but it can also be operated as a simple local base station when needed. For example, if a known reference point exists on site, one LRTK terminal can be set up at that point as a mini base station and another used as the rover; this two-device relative positioning ensures high accuracy even in communication-outage areas or regions not covered by CLAS. With this local base station mode, it becomes possible to perform surveying inside closed spaces—such as tunnel construction sites where satellite signals do not penetrate—by sequentially calculating relative coordinates from a reference point measured near the entrance. The flexibility to switch between standalone positioning (CLAS use) and relative positioning (using a self-owned base) depending on site conditions is another strength of LRTK.

• Instant startup with compact, all-in-one devices: Conventional RTK surveying required bulky equipment such as antennas mounted on large tripods, fixed receivers, external batteries, and controllers. In contrast, LRTK is provided as a palm-sized, integrated GNSS receiver that can be attached to the top of a smartphone or tablet. It is lightweight—approximately 150 g—and integrates the antenna, receiver, and battery in an all-in-one design. No cable connections are required; it pairs wirelessly with a smartphone, making handling simple. Turn on the power and go to a place with sky view, and initial positioning completes within tens of seconds, allowing surveying to begin immediately. The ease of use—no complicated setup or long wait times upon arrival and anyone can start positioning work right away—is a major advantage.

• Multi-GNSS support and stable accuracy: LRTK terminals support multiple satellite positioning systems—GPS, GLONASS, Galileo, QZSS (Michibiki), etc.—and utilize multi-frequency signals such as L1/L2. Therefore, even in forests or shaded urban canyons where satellite visibility tends to decrease, they capture as many signals as possible to maintain stable high accuracy. The built-in battery is designed for low power consumption and can operate for extended periods, enduring around a full day of continuous positioning, so it is reliable for outdoor work where power supply is difficult.

As described above, LRTK can be called a next-generation RTK solution that combines “independence from communications infrastructure,” “immediate field response,” and “portability.” Environments where centimeter-level positioning was previously impossible are now realistically within reach with LRTK, enabling high-precision positioning anytime and anywhere.

Benefits in accuracy, operability, and cost

Next, we summarize the concrete benefits of introducing LRTK from the perspectives of accuracy, operability, and cost.

• High accuracy approaching millimeter-level: LRTK demonstrates positioning accuracy comparable to or, under certain conditions, better than conventional RTK. It acquires true positions with planar accuracy of a few centimeters and vertical accuracy within a few centimeters to a few tens of centimeters, minimizing discrepancies between design drawings and the field, helping prevent construction errors and improving as-built management. Stable accuracy also yields high reliability of measurements, and repeated surveys are less prone to cumulative errors. (Note: when the original text uses "cm 精度", render as "cm level accuracy (half-inch accuracy)".)

• Operability that “anyone can use anytime”: LRTK enables site workers to perform necessary surveys themselves when needed, without relying on specialized survey teams or expensive equipment. The smartphone-mounted ease makes “one device per person” surveying realistic. For example, where machine operators previously had to wait for baseline markings, they can now use a smartphone with an LRTK attachment to measure and verify on the spot. The dedicated app displays current and target coordinates, with an intuitive UI that untrained staff can operate; measurement results can be shared to the cloud in real time, eliminating the need to transcribe data back at the office. This on-the-spot data utilization improves field agility, speeds decision-making, and reduces rework.

• Reduced introduction and operational costs: Traditionally, achieving centimeter-level positioning required not only the receiver but also base station equipment, communication modems, and paid correction service subscriptions, resulting in high initial and running costs. LRTK is an affordable all-in-one device compared to conventional equipment. Moreover, CLAS signals are free to use, so no extra communication fees or monthly service charges are incurred; even if multiple units are introduced, there is no additional maintenance fee burden. Costs associated with halting heavy equipment and calling external survey crews are reduced, and overall LRTK enables a low-cost high-precision positioning environment. Indirect cost savings from reduced transportation of equipment and more efficient personnel deployment are also expected.

Expected use cases across diverse sites

The transformations LRTK brings to the field are expected across many domains. Below are some particularly useful application scenarios.

Collecting positional data for disaster response

Rapid on-site surveying is essential for assessing damage and planning recovery after major disasters. However, when communications infrastructure is disrupted by earthquakes or typhoons, high-precision real-time positioning had to be abandoned. LRTK is powerful in such emergencies. Even in disaster areas where communication networks are paralyzed, a single smartphone equipped with an LRTK device can record accurate position coordinates on the spot. For example, one can walk through areas buried by landslides to measure the location of buried roads or the extent of collapsed structures. Because heavy tripods and generators are not required, teams can work lightly even under the risk of aftershocks. Acquired data can be uploaded from the field to the cloud and shared with relevant agencies immediately, greatly shortening the time to produce damage maps and initial response. LRTK, supporting both speed and accuracy, becomes a reliable tool in disaster response.

Infrastructure inspection and maintenance management

LRTK can be applied to inspection and maintenance work for roads, bridges, tunnels, dams, and other social infrastructure. Previously, high-precision optical surveying or specialized instruments were necessary for tasks such as tunnel displacement measurement or pier tilt measurement, but LRTK makes it possible to obtain position data easily even in narrow spaces or at heights. For instance, when recording crack locations on tunnel walls, measure a reference coordinate near the entrance and then move inside to measure wall points in indoor mode; later you can precisely identify positions on drawings. For bridges, points under girders can be measured from the ground with an LRTK-equipped smartphone, and coordinates of damaged areas can be shared to the cloud with photos. Some inspections that once required night closures and heavy equipment might be performed during daytime with minimal personnel. LRTK is also expected to advance DX (digital transformation) in infrastructure maintenance.

Construction layout and positioning of indoor structures

LRTK is useful for “marking out” (layout) tasks that require precise placement of machinery and fixtures inside buildings. For example, when installing new sorting racks in a warehouse, traditionally a survey team would mark the floor according to drawings. With LRTK, the site installer can call up target coordinates on a smartphone and follow guidance to mark installation positions within a few centimeters. Real-time guidance such as “x cm remaining” on the screen and AR visual cues enable even inexperienced staff to place equipment accurately. After installation, using LRTK and a smartphone’s 3D scanning features to measure as-built geometry allows immediate verification of installation accuracy. With the ability to detect deviations down to the millimeter level, LRTK supports high-quality construction management without rework. In large factories or commercial facilities undergoing renovation, individual workers can perform positioning tasks autonomously across locations, improving both productivity and accuracy.

Boundary surveying and agricultural land surveys in mountainous areas

LRTK is also suitable for confirming land boundaries in forests and mountainous areas and for surveying farmland. Previously, measuring boundary stakes required clearing brush to establish lines of sight and operating survey instruments with multiple people. With LRTK, a single surveyor can visit boundary points and press a button at each location to obtain coordinates in the global geodetic system. Measured data can be automatically converted to the prescribed plane rectangular coordinate system and elevations, making it easy to share and confirm results on site. This eliminates later office work to replot points on drawings. A case using LRTK for on-site boundary surveys in forested areas reported that boundary point measurement that previously took half a day was completed in a short time, contributing to more efficient forestry operations and neighborly agreement formation. LRTK also enables rapid measurement of elevation differences and areas for terraced fields or other uneven farmland, aiding the collection of basic data for regional development.

Procedure for simple surveying using LRTK

Finally, imagine the basic flow for performing simple field surveying with LRTK. The operation is intuitive even without specialized knowledge, and the general workflow is as follows.

• Preparation and setup: Before starting surveying, attach the LRTK device to a smartphone or tablet. Turn on the device, launch the dedicated app, and select the positioning mode. Outdoors, satellite augmentation mode (CLAS reception) is enabled automatically without special settings, and centimeter-level positioning becomes possible within tens of seconds. For indoor surveying, first measure and register the current location at a point where satellite signals are available—such as near the building entrance—as a reference (starting point) in the app.

• Measuring and recording points: Move to the target location and execute measurements following the smartphone’s on-screen instructions. For point measurements, simply press the “measure” button in the app at the location and the current coordinates are recorded. You can take photos and associate them with measurement points as needed. In indoor mode, after registering the reference point once, the smartphone’s internal sensors (gyroscope, accelerometer, camera AR kit, etc.) track the travel route and estimate absolute coordinates even inside areas with poor satellite reception. Thus, even when moving to the back of a warehouse or an underground floor, you can select “measure here” on the smartphone and each point’s coordinates are recorded in a global reference coordinate system.

• Positioning and guidance (when needed): To mark a known design coordinate (planned installation point) on site, input the target coordinate into the app and switch to guidance mode. The smartphone displays the direction and distance from your current position to the target. The worker walks in the direction of the arrow until distance reaches zero. As you approach the target, fine guidance such as “x cm remaining” appears, allowing you to pinpoint the location with minimal error. Once at the required spot, mark the ground with spray paint or chalk. With LRTK, even without specialist skills, accurate layout work can be performed solo.

• Data review and sharing: After surveying, review all collected points in the app. Coordinates are converted to the preset coordinate system (for example, public coordinates) and displayed in lists or maps. Data can be uploaded to cloud storage from the smartphone or exported in CSV or DXF formats for import into other CAD/GIS software. Real-time shared survey points on the cloud can be viewed instantly by office-based engineers, facilitating smooth communication between the field and office. Since there is no need to record in paper field books and bring them back, digital data capture on-site and sharing with all stakeholders is a major advantage.

This is the typical flow of simple surveying with LRTK. Because setup, measurement, recording, and sharing are all integrated and seamless, field work efficiency is dramatically improved.

Conclusion: A new era of surveying opened by LRTK

LRTK’s arrival is making the ideal field environment—where anyone can use high-precision positioning whenever needed, regardless of communication coverage or indoor conditions—into a reality. By overcoming RTK’s dependency on communications and combining small devices with smartphone integration, a surveying style of “anytime, anywhere, anyone” is beginning to spread. This change will not only streamline positioning tasks but also accelerate disaster response, enhance infrastructure maintenance, and promote DX in construction sites, generating ripple effects across many fields.

Where surveying was once the domain of specialists, the emergence of easy-to-use high-precision tools like LRTK is rapidly changing conventional practices. Civil construction managers and municipal staff can expect to experience improved operational efficiency and higher quality outcomes by adopting this new technology. If you face challenges with surveying outside communication coverage or with indoor layout tasks, consider a simple surveying solution using LRTK. With advanced technology on your side, you will be able to “measure and mark” smoothly even in places you previously had to give up on, greatly improving productivity and safety on site. We hope LRTK, pioneering a new era of high-precision positioning, will become a trusted partner for your field operations.