What is RTK That Works Outside Coverage? Centimeter-level Positioning Without Communication Realized by LRTK

Table of Contents

• Introduction

• Conventional RTK positioning and communication challenges

• RTK usable outside coverage: How the CLAS method works

• Differences between conventional RTK and LRTK (CLAS)

• Scenes where it shines outside 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 can obtain centimeter-level positioning accuracy in real time (cm level accuracy (half-inch accuracy)), has become an indispensable technology on surveying and construction sites. However, conventional RTK positioning has depended on correction information from base stations via communication lines or radio, and it has faced the challenge of being ineffective where radio or Internet do not reach. If RTK that works outside coverage can be realized, high-accuracy positioning would become possible even in remote mountains, isolated islands, and disaster sites without communication infrastructure, dramatically improving on-site productivity and peace of mind. This article explains the technology of “centimeter-level positioning without communication,” which is key to that capability, and clarifies the differences and mechanisms compared to conventional methods. Focusing on the new solution LRTK, we delve into the practical benefits and use cases of RTK usable outside coverage, iPhone-linked AR applications, and contributions to on-site DX (digital transformation) from an operational perspective.

Conventional RTK positioning and communication challenges

First, let us organize the basics of RTK positioning and the challenges of conventional methods. RTK is a technique in which a known-position-installed reference station (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 they cancel out errors and obtain high-precision positions. In conventional RTK, the exchange of this correction information has been done using the following methods.

• Local base station method (standalone RTK): The user installs a GNSS receiver as a base station near the survey site and sends correction data to the rover sequentially via radio (such as low-power radio). It is a simple one-to-one configuration, but setting up the base station and preparing radio equipment is laborious, and the usable range is limited to where the radio reaches (a range of a few km to about 10 km (32,808.4 ft)), making it unsuitable for wide-area surveys. Also, as the rover moves away from the base station, correction accuracy degrades, and maintaining centimeter-level accuracy becomes difficult if it is more than 10 km (32,808.4 ft) away.

• Network RTK method (VRS/Ntrip): By using a network of continuously operating reference stations provided by the Geospatial Information Authority of Japan or private operators, the rover obtains correction information over the Internet. The rover is equipped with a communication modem and connects to a correction data distribution service using the Ntrip protocol, enabling high-precision positioning over a wide area. Distance-related degradation is also resolved using Virtual Reference Station (VRS) technology. However, this method assumes a connection to a communication line, so services cannot be used in areas outside mobile phone coverage. In many cases, service usage incurs monthly or annual fees, so running costs are another barrier.

As described above, conventional RTK positioning required either “radio from a base station” or “Internet communication.” Therefore, in areas where mobile signals do not reach, such as mountainous or forested regions, or where base station equipment and communication networks do not function after a large-scale disaster, real-time centimeter-level positioning was often impossible. In such environments, teams had to give up immediate on-site positioning and take data back for post-processing (e.g., PPK), making rapid response difficult. The cost of preparing dedicated base station equipment and paying for subscription services also hindered RTK adoption and spread.

RTK usable outside coverage: How the CLAS method works

A promising new technology to solve the above challenges is the Centimeter Level Augmentation Service (CLAS) provided by Japan’s Quasi-Zenith Satellite System (QZSS, “Michibiki”). By using CLAS, real-time centimeter-level high-precision positioning becomes possible 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 reference station network (satellite orbit errors, clock errors, ionospheric and tropospheric delay errors, etc.) and distributes that information directly to users from the quasi-zenith satellites. Specifically, correction data are loaded onto Michibiki’s L6-band signal, and CLAS-compatible GNSS receivers receive and parse that data to apply corrections to their positioning. It can be considered a “satellite-communication-type RTK” and is technically classified as PPP-RTK (Precise Point Positioning RTK).

With CLAS, users can obtain centimeter-level accuracy with a single receiver without preparing their own base station or obtaining corrections via the Internet. The Michibiki augmentation signal covers all of Japan, and as long as there is a clear view of the sky, it can be received in mountainous areas, islands, and offshore. For this reason, CLAS is attracting strong expectations as a technology that realizes RTK usable outside coverage. CLAS is provided by the government and is free to use; anyone with a compatible receiver can benefit at no cost. The ease of simply powering on the receiver at the site and receiving corrections from the satellite greatly 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 and the new LRTK utilizing the CLAS method. The main differences are summarized below.

• Method of obtaining correction information: Conventional RTK receives correction data from ground base stations via radio or the Internet, while LRTK (CLAS-compatible) receives correction data directly broadcast from satellites. This eliminates the need for a communication link with a base station.

• Usable area: Conventional RTK is constrained by distance from base stations and presence of communication coverage (limited to the radio range of base stations or mobile network coverage), whereas the CLAS method provides nationwide coverage in Japan. It delivers uniform high accuracy even in places that were previously difficult to position, such as mountainous areas, forests, and at sea.

• Initial and operating costs: Standalone RTK requires purchase and installation of base station equipment, and network RTK requires subscription fees. CLAS-enabled LRTK requires only a compatible receiver, and use of the satellite augmentation signal itself is free. Operation at the site is reduced to powering on the device, lowering operating costs and effort.

• Real-time performance and stability: Conventional RTK, dependent on base stations, may experience accuracy degradation as distance increases or become unusable if base stations or communications fail during disasters. LRTK only needs to receive a one-way signal from satellites, so it functions even when communication networks are severed and maintains stable accuracy over wide areas. Also, the same satellite signal can serve multiple rovers simultaneously, making it efficient for large sites requiring many simultaneous positions.

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

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

LRTK, which does not depend on communication infrastructure, demonstrates its power in scenes where high-precision positioning was previously difficult:

• Surveying and construction in mountainous areas: At dam construction sites or mountain roadworks, where mobile signals do not reach, conventional approaches required temporary radio relays. With LRTK, as long as the satellite augmentation signal can be received, centimeter-level RTK positioning is always available, enabling high accuracy even deep in the mountains for surveying and installation tasks.

• Forestry: Deep forests often have poor radio conditions and difficulty communicating with base stations, but LRTK can receive correction signals if even partial sky visibility is available. High-precision GNSS is beginning to be used in forestry for boundary measurements and resource surveys; communication-free RTK enables agile positioning inside forests and contributes to the DX of forest management.

• Situation assessment at disaster sites: Mobile networks and power can fail during earthquakes or heavy rain. In such disaster zones, LRTK-equipped devices can record and share damage at centimeter precision. There are reported cases of using LRTK devices for photogrammetry in out-of-coverage areas after large earthquakes. The ability to position without relying on communications provides significant reassurance in disaster response.

• Positioning in ports and at sea: For port works and coastal or offshore operations, base station signals are often hard to reach, and satellite phones or relay vessels have sometimes been required. CLAS positioning allows direct reception of satellite corrections at sea, useful for precise alignment of equipment during pier construction or dredging, and for measuring positions of navigational aids. It contributes to higher-precision GNSS navigation on vessels and is expected to improve safety and efficiency in port logistics and marine surveys.

Beyond these, LRTK use cases expand to infrastructure inspections on remote islands and precision agriculture on large farmlands where communications are hard to maintain—the various sites where “RTK anywhere” is demanded.

LRTK structure and advantages

So what exactly is the concrete solution LRTK that realizes communication-free RTK? Let’s look at its structure and advantages.

LRTK is a “pocket-sized surveying instrument” that combines an ultra-compact high-precision GNSS receiver device with a smartphone application. The small receiver houses a multi-band GNSS antenna, an RTK processing board, and a battery in a compact case, and it is used attached to or connected by Bluetooth to a smartphone. For example, an LRTK device for iPhone (LRTK Phone) can snap into a dedicated phone case and be used as an integrated unit. Since the device itself contains the antenna and power, external antennas and cables that were previously necessary are unnecessary, and positioning tasks can be performed while holding the unit in one hand.

A major feature 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 via Ntrip as before; in areas outside mobile coverage, they automatically receive Michibiki’s CLAS signal directly for corrections. This ensures consistent centimeter-level positioning across online and offline environments without the user needing to think about the positioning method, which is a significant operational advantage. Moreover, LRTK devices are compact and lightweight yet equipped with high-performance GNSS chips, simultaneously using multiple satellite systems such as GPS, GLONASS, Galileo, and BeiDou to maintain stable reception even in challenging environments.

LRTK is also engineered for on-site usability. Wireless smartphone linkage removes cable clutter, and because the device can transmit data via Bluetooth even when detached from the phone, it can be mounted on long poles or tripods for high or fixed-point positioning. The dedicated app has a simple UI, offering a one-tap single-point measurement mode and a logging mode for continuous point recording while moving. Observation times and satellite status are recorded automatically with positioning, making it easy to perform post hoc accuracy checks and data sharing as an electronic field notebook. Positioning data, photos, and point clouds can be uploaded to the cloud for management, allowing immediate verification of site results from the office. This hardware-software integration makes LRTK an all-in-one RTK solution that intuitive for field staff without specialized knowledge.

iPhone integration and AR applications

Attention is growing for new uses that arise when LRTK is combined with smartphones. In particular, pairing with high-performance devices like the iPhone—equipped with cameras, LiDAR sensors, and high-resolution displays—makes on-site AR (augmented reality) applications realistic.

For example, combining centimeter-level positioning data from LRTK with a smartphone’s GPS compass enables AR-assisted stakeout. If planned coordinates or a list of points to be marked are loaded into the app in advance, the app can guide the user on-screen with arrows showing direction and distance to each point. When the user approaches the target, switching to the camera view will overlay a virtual marker (target) at the intended location in AR. The worker can place stakes or marks at that virtual marker, allowing stakeout and layout tasks that once required several people to be done accurately by one person. Working while looking at the phone reduces human errors associated with measuring tapes and manual layout.

Also, overlaying 3D design models in AR is a powerful use of LRTK and smartphones. By preloading a model of the planned structure and tracking precise position and orientation with LRTK, a true-to-scale 3D model can be superimposed on the real site scene on the phone. Stakeholders can intuitively share the finished appearance on site rather than relying solely on drawings or physical models. Moreover, scanning the current state with a LiDAR-equipped phone and overlaying the point cloud with the design model allows immediate on-site checks for deviations from the planned shape. Since the point cloud is tied to absolute (public) coordinates, scanned results can be quickly uploaded to the cloud for quantity calculations or difference analysis. Tasks that used to require specialized equipment and skills—3D measurement and as-built management—can now be performed easily with just a smartphone and LRTK.

There are also benefits for photogrammetry and site records. Photos taken with the LRTK app are automatically tagged with high-precision positioning, enabling exact plotting on a map of where each photo was taken. Because shooting direction is recorded, an office reviewer can reproduce the photo’s orientation later. This is extremely useful for infrastructure inspections or disaster damage recording, allowing efficient report preparation by correlating photos and location data. Work that once involved inaccurate GPS tags per photo or manual location notes can now be automated and made accurate with LRTK and smartphones.

Thus, smartphone integration turns LRTK into more than a positioning device: it becomes a next-generation field tool that handles measurement, guidance, recording, and visualization. AR-driven “visualized site management” is an innovative effort that strongly supports on-site DX.

Contribution to on-site DX

LRTK’s communication-free RTK capability and smartphone integration contribute significantly to digital transformation (DX) on site. In terms of productivity, tasks that previously required two people for surveying can be completed by one, and data collection that once was handwritten in field notebooks can be digitized automatically on site. Because high-accuracy data are obtained in real time and shared and analyzed in the cloud, communication between the field and the office becomes smoother and decision-making accelerates. Survey checks and reflection into drawings can be done the same day, reducing rework.

Furthermore, the ease of high-precision positioning through LRTK means tasks that once relied on specialists or expensive equipment can increasingly be handled in-house. Small-scale as-built checks or monitoring structural settlement can be performed on demand by company staff. If each field worker carries a “survey instrument in their pocket,” measurements can be taken immediately when needed, dramatically improving on-site management accuracy and efficiency.

There are also safety benefits for DX. Faster surveys reduce exposure time in hazardous areas; fewer personnel are required, allowing optimized staffing; and AR visualization helps prevent mistakes and oversights. For example, AR-displayed locations of buried utilities can be shared with excavation crews to reduce the risk of accidental damage. In these ways, smartphone surveying centered on LRTK not only improves positioning accuracy but transforms on-site work styles.

In the context of government-driven initiatives like i-Construction and construction DX promoted by the Ministry of Land, Infrastructure, Transport and Tourism, easy-to-use high-precision positioning tools are a key enabler. Wider adoption of solutions like LRTK will turn surveying into more routine, real-time data acquisition tasks, accelerating digitalization of the entire construction production process. LRTK and similar communication-independent RTK technologies are expected to become foundational technologies that support on-site DX from the ground up.

Conclusion

Historically, real-time centimeter-level positioning always required communication access or base station installation. However, with the advent of CLAS from Japan’s satellite positioning technology and the development of user-friendly LRTK solutions, RTK usable outside coverage is becoming a reality. LRTK enables stable, high-precision positioning regardless of location, from remote mountains to disaster response sites, dramatically improving efficiency and reliability of field operations. Smartphone integration also creates new value—AR and cloud capabilities—that greatly expand the concept of positioning and surveying.

In the future of construction and surveying, communication-free RTK will become indispensable infrastructure. The easy and powerful centimeter-level positioning offered by LRTK is opening an era in which not only specialists but also ordinary field personnel can use high-precision positioning as a matter of course. Embrace RTK technology that works outside coverage, and take the first step toward DX at your site.

Toward simple surveying with LRTK

As high-precision RTK becomes more accessible, even routine simple surveying tasks are changing. For example, quick slope or elevation checks on a lot or simple as-built checks before and after work—tasks that used to be done with measuring 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 press in a smartphone app is a major attraction of simple surveying with LRTK. This enables anyone to “measure on a whim,” allowing finer-grained PDCA cycles on site. LRTK brings centimeter-level assurance even to everyday site management and verification tasks.

FAQ

Q: What is RTK? A: RTK (Real Time Kinematic) is a technology that uses two GNSS receivers (a reference station and a rover) to correct positioning errors in real time, dramatically improving satellite positioning accuracy. Ordinary GNSS positioning may have errors of several meters, but RTK cancels errors through relative positioning with the reference station and can achieve accuracy on the order of centimeters. It is widely used in surveying and construction when accurate horizontal and vertical positions are required.

Q: What exactly does LRTK refer to? A: LRTK refers to a positioning solution composed of a compact high-precision GNSS receiver and a smartphone application. By attaching or linking it to a smartphone, the phone becomes a surveying instrument capable of centimeter-level positioning. Its distinguishing feature is support for both conventional network RTK and CLAS signals from the QZSS Michibiki satellites, allowing high-precision positioning to continue even where there is no communication line—this is its greatest strength.

Q: Why can LRTK perform RTK positioning outside coverage? A: The secret of LRTK’s out-of-coverage capability is that it can directly receive CLAS augmentation information broadcast from QZSS (Michibiki). Instead of receiving correction data via the Internet as before, the corrections are delivered via satellite, so correction information is available even in environments outside mobile networks. In other words, the satellite functions in place of a base station, enabling RTK positioning without dependence on ground infrastructure.

Q: In what situations is LRTK suitable? A: Because LRTK does not depend on communication infrastructure, it is powerful in areas outside coverage such as mountainous regions, forests, islands, and at sea. Examples include mountain site surveying, forest boundary checks, infrastructure inspections on remote islands, port works where mobile networks are unreliable, and post-disaster surveys. It is also useful in urban areas for quick smartphone-based surveying and AR-assisted construction management.

Q: What positioning accuracy can be expected with LRTK, and are there additional usage fees? A: With LRTK, horizontal accuracy of approximately ± several centimeters and vertical accuracy in the range of several centimeters to low double-digit centimeters can be expected (depending on the environment and satellite reception), comparable to conventional RTK. CLAS correction reception itself is free, and Internet communication is unnecessary in out-of-coverage areas. Therefore, aside from the cost of acquiring an LRTK device, no additional usage fees generally apply (※ using conventional network RTK may incur separate communication or service subscription fees, but these are unnecessary when using CLAS).

Q: Is operating LRTK difficult? Will field staff be able to use it? A: LRTK is designed to be usable by field staff without surveying expertise. The dedicated app has a simple interface; you can record positions by pressing a button, and data management and coordinate transformations are automated. With Japanese on-screen guidance, special expertise is not required to start using it. Many field personnel can operate LRTK after only brief instruction and report that it is much easier and more intuitive than traditional surveying instruments. It can also integrate with cloud services for smooth sharing and utilization of measured data.