Table of Contents

• Introduction

• Conventional RTK positioning and communication challenges

• RTK usable out of coverage: How the CLAS method works

• Differences between conventional RTK and LRTK (CLAS)

• Scenes where it shines out of coverage (mountains, forestry, disasters, ports, etc.)

• LRTK structure and advantages

• iPhone integration and AR applications

• Contribution to on-site DX

• Conclusion

• Toward simple surveying with LRTK

• FAQ

Introduction

RTK (Real Time Kinematic), which provides centimeter-level positioning accuracy in real time, has become an indispensable technology for surveying and construction sites. However, conventional RTK positioning has relied on correction information from base stations via communication lines or radios, and this has posed a problem: in places where radio waves or the Internet do not reach, its capabilities cannot be demonstrated. If an RTK that works out of coverage can be realized, high-precision positioning would become possible even in remote mountains, isolated islands, and disaster sites lacking communication infrastructure, greatly improving on-site productivity and peace of mind. This article explains the technology for "centimeter-level positioning without communications" that holds the key, clarifying differences and mechanisms compared with conventional methods. Focusing on the new solution called LRTK, we will also delve into the benefits and use cases of RTK usable out of coverage, iPhone-linked AR applications, and contributions to on-site DX (digital transformation) from a practical perspective.

Conventional RTK positioning and communication challenges

First, let us organize the basics of RTK positioning and the issues with conventional methods. RTK is a technique in which a known-position base station and a rover at the point to be positioned simultaneously receive GNSS satellite signals, and by exchanging their observation data in real time, cancel out errors to obtain highly accurate positions. In conventional RTK, the exchange of this correction information has been performed by the following methods.

• Local base station method (standalone RTK): The user installs a GNSS receiver for the base station near the survey site and sends correction data to the rover sequentially by radio (such as low-power radio). This is a simple one-to-one configuration, but setting up the base station and preparing radio equipment is laborious, and the radio range (several km to about 10 km) limits it, making it unsuitable for wide-area surveys. In addition, as the rover moves away from the base station, correction accuracy degrades, and maintaining centimeter-level precision beyond about 10 km becomes difficult.

• Network RTK method (VRS/Ntrip method): This method uses electronic reference station networks (reference station networks) maintained by the Geospatial Information Authority of Japan or private operators, allowing the rover to obtain correction information via the Internet. By equipping the rover with a communication modem and connecting to a correction data distribution service using the Ntrip protocol, high-accuracy positioning over a wide area becomes possible. Virtual Reference Station (VRS) technology can eliminate accuracy degradation due to distance from reference stations. However, this method assumes a connection to a communication line, so services cannot be used in areas out of cellular coverage. Also, many services charge monthly or annual fees, posing a hurdle in terms of running costs.

As described above, conventional RTK positioning has required either "radio from a base station" or "Internet communication." Therefore, in mountainous or forested areas where cellular signals do not reach, or in large-scale disasters where base station facilities and communication networks are nonfunctional, real-time centimeter-level positioning is often impossible. In such environments, teams have had to give up on immediate on-site positioning and instead return with data for post-processing (such as PPK), which hinders rapid response. The need to prepare dedicated base station equipment and the costs of paid services were also factors that impeded RTK adoption and spread.

RTK usable out of coverage: How the CLAS method works

A new technology attracting attention as a solution to the above challenges is the Centimeter Level Augmentation Service (CLAS) provided by Japan's Quasi-Zenith Satellite System (QZSS, "Michibiki"). With CLAS, it becomes possible to achieve centimeter-level high-precision positioning in real time without the previously essential base stations or communication lines. The mechanism aggregates various error information observed by networks such as the Geospatial Information Authority’s electronic reference stations (satellite orbital errors, clock errors, ionospheric and tropospheric delay errors, etc.) and then distributes that information directly to users from the quasi-zenith satellites. Specifically, error correction data is carried on Michibiki’s L6 band signal, and CLAS-capable GNSS receivers receive and parse that data to apply corrections to their positioning. Technically, it can be described as a "satellite-communication-type RTK" and is categorized as PPP-RTK (Precise Point Positioning RTK).

With the CLAS method, users can obtain centimeter-level accuracy with a single receiver without preparing their own base station or acquiring corrections via the Internet. Michibiki’s augmentation signal covers the entirety of Japan broadly, and as long as there is line-of-sight to the sky, it can be received even in mountainous areas, remote islands, or offshore. For this reason, CLAS is highly anticipated as a technology that enables RTK usable out of coverage. Moreover, CLAS is a government-provided service and is free of charge. Anyone with a compatible receiver can benefit from it at no cost, eliminating concerns about correction service fees that existed previously. The simplicity of just powering on the receiver at the site and having the satellite send correction information also significantly reduces the time and effort required to prepare for positioning in remote locations.

Differences between conventional RTK and LRTK (CLAS)

There are several notable differences between conventional RTK positioning and the new LRTK leveraging the CLAS method. The main distinctions are summarized below.

• How correction information is obtained: Conventional RTK receives correction data from ground reference stations via radio or the Internet, whereas LRTK (CLAS-enabled) receives correction data directly from satellites. This removes the need for a communication link with a base station.

• Available area: Conventional RTK is constrained by distance from base stations and the availability of communication coverage (limited to radio range or cellular coverage), but CLAS provides nationwide service in Japan. Uniform high accuracy can be obtained in places that were previously difficult to position, such as mountainous regions, forests, and the open sea.

• Initial and operational costs: Standalone RTK requires purchase and installation costs for base station equipment, and network RTK requires subscription fees for correction services. CLAS-enabled LRTK requires only a dedicated receiver, and the satellite augmentation signal itself is free. Operation at the site is limited to powering the device, which reduces operational costs and hassle.

• Real-time capability and stability: Conventional RTK, which depends on base stations, experiences accuracy degradation as distance from the base station increases and risks becoming unusable if base stations or communications are down during disasters. LRTK only needs to receive a one-way signal from satellites, so it continues to function when communication networks are cut off and maintains stable accuracy across wide areas. Also, since a single satellite signal can serve multiple roving users concurrently, it is efficient for large sites requiring many positioning operations.

In this way, communication-free LRTK complements and solves the weaknesses of conventional methods, dramatically improving the flexibility and reliability of RTK positioning in the field.

Scenes where it shines out of coverage (mountains, forestry, disasters, ports, etc.)

Because LRTK does not depend on communication infrastructure, it demonstrates its strengths in scenes where high-precision positioning was previously difficult, such as the following.

• Surveying and construction in mountainous regions: For dam construction sites or mountain road works where cellular signals do not reach, conventional practice required temporary radio relays, among other measures, to position. With LRTK, as long as the satellite augmentation signal can be received, centimeter-level RTK positioning is constantly possible, maintaining high accuracy even for surveying and installing structures deep in the mountains.

• Forestry and timber industry: Deep within forests where radio conditions are poor and base station communications have been difficult, LRTK can receive correction signals if there is even partial sky visibility. High-precision GNSS is beginning to be used in forestry for boundary measurement and resource surveys, and communication-free RTK enables agile position measurement within woodlands, contributing to forestry DX.

• Damage assessment at disaster sites: During earthquakes or heavy rains, cellular networks can be disrupted and power may be lost in some areas. Even in such affected areas, LRTK-capable equipment can record and share damage assessments with centimeter precision. There have been reports of successful photogrammetry using LRTK devices in out-of-coverage areas during major earthquakes. The ability to perform positioning without relying on communication infrastructure offers great reassurance in disaster response.

• Positioning in ports and at sea: In port construction and coastal/offshore operations, base station signals are often hard to receive; operators sometimes prepared satellite phones or radio relay vessels. CLAS positioning with LRTK allows direct receipt of satellite corrections at sea, making it useful for precise positioning of equipment for pier construction, dredging operations, or installation of navigational aids. It also contributes to improving the accuracy of GNSS navigation aboard vessels, enhancing the safety and efficiency of port logistics and marine surveys.

Beyond these examples, use cases are expanding wherever "RTK positioning anywhere" is needed: inspections of infrastructure on remote islands, precision agriculture across large farmlands where communications are hard to secure, and so on.

LRTK structure and advantages

So, what is the concrete mechanism of the communication-free RTK solution called LRTK? Let us look at its structure and advantages.

LRTK is a combination of an ultra-compact high-precision GNSS receiver device and a smartphone application — effectively a "pocket-sized surveying instrument." The small receiver housing fits in the palm of your hand and integrates a multi-band GNSS antenna, an RTK processing board, and a battery, and is used by attaching to or connecting via Bluetooth with a smartphone. For example, an LRTK device for iPhone (LRTK Phone) can be attached to a dedicated smartphone case with one touch and used as an integrated unit. Because the device itself contains the antenna and power supply, external antennas and cables that were previously necessary are unnecessary, allowing one-handed positioning operations.

A major characteristic of LRTK receivers is that they support both network RTK and the CLAS method. In other words, where communications are available, they can receive Internet-based correction information (Ntrip, etc.) as before, while at sites out of cellular coverage they automatically receive Michibiki’s CLAS signal directly and use it for corrections. This enables centimeter-level positioning consistently whether online or offline, and the fact users do not need to be aware of the positioning method is a practical advantage. In addition, although compact and lightweight, LRTK devices incorporate high-performance GNSS chips and can use multiple satellite positioning systems simultaneously — GPS, GLONASS, Galileo, BeiDou — to maintain stable reception even in challenging environments.

Furthermore, LRTK is designed with field usability in mind. Wireless connection to a smartphone eliminates cumbersome cables, and the device can send data via Bluetooth even when detached from the phone, enabling measurements from long poles or tripods for high or fixed-point positioning. The dedicated app has a simple UI and includes a one-tap single-point positioning mode and a logging mode to record points continuously while moving. Observation times and satellite status are automatically recorded alongside positioning, making post-checks and data sharing easy as an electronic field notebook. Acquired positioning data, photos, and point clouds can be uploaded to the cloud for management, allowing instant confirmation of field results from the office. This hardware-software integrated setup makes LRTK an all-in-one RTK solution that field staff without specialized knowledge can intuitively operate.

iPhone integration and AR applications

Attention is also focused on the new uses that emerge when LRTK integrates with smartphones. Combining LRTK with high-performance cameras, LiDAR sensors, and displays available on devices like the iPhone makes on-site AR (augmented reality) applications practical.

For example, combining centimeter-level positioning from LRTK with a smartphone’s GPS compass enables AR-assisted stakeout. If construction drawings or a list of coordinates for points to be staked out are preloaded into the smartphone app, the app can guide the user on-screen with arrows indicating direction and distance to each point. When approaching the target location, switching to the camera view overlays a virtual marker (target) on the screen at the intended point. The worker can place a stake or mark at that marker, allowing a single person to accurately perform stakeout and layout tasks that previously required several people. Because work is performed while visually confirming through the phone’s screen, human errors from measuring tapes or manual marking are also reduced.

Also, overlaying 3D design data in AR is a powerful application of LRTK and smartphones. For example, if a full-scale 3D model of the intended structure is prepared in advance and displayed on a smartphone while LRTK tracks precise position and orientation, the life-size 3D model can be superimposed on the real site view. This enables clients and construction teams to intuitively share the expected completed appearance at the site, instead of relying solely on drawings or scale models. Moreover, by scanning the current state with the smartphone’s LiDAR while using LRTK, and overlaying the resulting point cloud onto the design model, onsite checks of as-built deviations can be performed instantly. Because the point cloud has absolute coordinates (public coordinate system), scanned results can be immediately uploaded to the cloud for quantity calculations and difference analysis. Tasks that previously required specialized equipment and advanced measurement skills, such as 3D measurement and as-built management, can now be easily performed by anyone with a smartphone and LRTK.

In addition, LRTK offers advantages for photogrammetry and site documentation. Photos taken with the LRTK app are automatically tagged with high-precision positioning, allowing them to be accurately plotted on a map. The shooting direction of the photo is also recorded, so when revisiting in the office you can reproduce "which direction the photo was taken" precisely. This is very useful when taking many facility photos for infrastructure inspection or recording disaster damage, enabling efficient report creation by cross-referencing photos and location data. Processes that previously involved inaccurate GPS info per photo or handwritten location notes are now automated and accurate thanks to LRTK and smartphones.

Thus, through smartphone integration, LRTK is evolving from a mere positioning device into a next-generation field tool that handles measurement, guidance, recording, and visualization in an integrated manner. AR-driven "visualized site management" is an innovative initiative that strongly supports on-site DX.

Contribution to on-site DX

The RTK technology that works out of coverage delivered by LRTK and its smartphone integration greatly contributes to on-site digital transformation (DX). In terms of productivity gains, it can transform tasks that previously required two people into single-person operations, and automatically digitize data collection that used to be recorded by hand in paper field notebooks. Because highly accurate data can be obtained in real time and shared and analyzed in the cloud, communication between the field and the office becomes smoother, accelerating decision-making. Survey checks and incorporation into drawings can be done the same day, reducing rework and iterations.

Also, by making high-precision positioning easy, LRTK enables tasks that once relied on specialist contractors and expensive equipment to be insourced by in-house staff. For example, minor earthworks as-built checks or structural settlement monitoring can be performed on demand. If each site worker can carry a "survey instrument in their pocket" and measure as needed, the accuracy and efficiency of site management will improve dramatically.

There are also safety benefits that support DX. Shorter survey times reduce exposure in hazardous areas, fewer personnel are required which optimizes staffing, and AR-based visualization can prevent mistakes and oversights. For instance, displaying the positions of underground utilities in AR for excavation crews reduces the risk of damaging pipes. In these ways, smartphone surveying centered on LRTK not only increases positioning accuracy but also transforms on-site work practices.

In the trends of i-Construction and construction DX promoted by the Ministry of Land, Infrastructure, Transport and Tourism, accessible high-precision positioning tools are a key factor. As solutions like LRTK spread, surveying and positioning work will become more routine and real-time, accelerating digitization across construction production processes. LRTK is expected to become a foundational technology supporting on-site DX from the ground up, and "RTK that is not affected by communication infrastructure" is anticipated to permeate the field.

Conclusion

Historically, real-time centimeter-level positioning always required securing communication environments or installing base stations. However, with the advent of Japan’s CLAS satellite positioning technology and the development of accessible LRTK solutions that leverage it, RTK usable even out of coverage has become a reality. LRTK enables stable, high-precision positioning regardless of location — from remote mountains to disaster response sites — dramatically improving the efficiency and reliability of on-site work. Smartphone integration also creates new value through AR and cloud functionality, greatly expanding the concept of positioning and surveying.

In the coming era of construction and surveying, communication-free RTK technology will become indispensable infrastructure. The easy-to-use and powerful centimeter-level positioning that LRTK realizes is opening an age where not only specialists but any field worker can use it as a matter of course. Embrace RTK technology that works out of coverage, and take the first step toward DX at your site.

Toward simple surveying with LRTK

As high-precision RTK positioning becomes more accessible, daily simple surveying tasks are changing. Tasks such as checking slight elevation differences on a site or quick as-built checks before and after work, which used to be done with tapes or levels, can now yield accurate numerical results on the spot with LRTK and a smartphone. The ease of measuring with a single button in a smartphone app, even for non-specialists, is a major attraction of simple surveying with LRTK. This enables anyone to "just measure it" and supports more frequent PDCA cycles on site. LRTK is truly delivering centimeter-level reassurance even for everyday site management and verification tasks.

FAQ

Q: What is RTK? A: RTK (Real Time Kinematic) is a technique that uses two GNSS receivers (a base station and a rover) to correct positioning errors in real time, dramatically improving satellite positioning accuracy. While ordinary GNSS positioning has errors of several meters, RTK cancels errors through relative positioning with a base station to achieve centimeter-level accuracy. It is widely used in surveying and construction when accurate horizontal and vertical positions are required.

Q: What specifically does LRTK refer to? A: LRTK is the name of a positioning solution composed of a compact high-precision GNSS receiver and a smartphone application. By attaching or pairing it with a smartphone, the phone becomes a surveying instrument capable of centimeter-level positioning. Its distinguishing feature is support for both network RTK and Michibiki’s CLAS signal, allowing high-precision positioning to continue even where communication lines are unavailable — this is its greatest strength.

Q: Why can LRTK perform RTK positioning out of coverage? A: The secret of why LRTK works out of coverage is that it can directly receive CLAS augmentation information broadcast from QZSS (Michibiki) satellites. Correction data that was previously received via the Internet is provided via satellite communications, so correction information can be obtained even in environments where cellular networks are out of range. In other words, the satellite plays the role of a base station, enabling RTK positioning that does not depend on ground infrastructure.

Q: In what situations is LRTK suitable? A: Because LRTK does not depend on communication infrastructure, it is powerful in areas such as mountains, forests, remote islands, and at sea where coverage is limited. Examples include surveying in mountainous sites, boundary checks in forests, infrastructure inspections on remote islands, port construction sites with unstable cellular coverage, and disaster-area surveys immediately after an event — basically, situations where real-time positioning was previously difficult. It is also useful in urban areas for convenient smartphone-based surveys and AR-assisted construction management.

Q: What positioning accuracy does LRTK achieve, and are there additional usage fees? A: With LRTK, horizontal accuracy on the order of ± a few centimeters and vertical accuracy in the range of several centimeters to the low centimeters can be expected (depending on environment and satellite reception, but comparable to conventional RTK). Regarding costs, receiving the CLAS correction signal itself is free and Internet communication is unnecessary when out of coverage. Therefore, aside from the initial LRTK device purchase, there are generally no additional service fees for CLAS use (note that using conventional network RTK normally may incur communication charges or service subscriptions, but these are unnecessary when using CLAS).

Q: Is LRTK difficult to operate? Will site staff be able to use it? A: LRTK is designed to be usable by non-survey professionals at the site. The dedicated app has a simple interface: press a button to record a position, and positioning data management and coordinate transformations are automated. With Japanese on-screen guidance, you can start using it without special expertise. Many field staff can operate LRTK after brief instruction and report that it is far simpler and more intuitive than traditional surveying instruments. It can also integrate with cloud services as needed, so sharing and utilizing measured data is smooth.