What next-generation positioning does LRTK pioneer? Expanding uses with smartphones

Table of contents

• How RTK surveying works and its background

• The advent of smartphone RTK surveying and LRTK’s technical features

• The basis for centimeter-level accuracy achieved with smartphone RTK

• Applications to point cloud measurement, as-built management, CAD integration, AR guidance, and cloud sharing

• Field deployment case studies and their effects (labor saving, time reduction, improved safety)

• Barriers to introduction and practical tips for field use

• Introducing simple surveying with LRTK

• FAQ

How RTK surveying works and its background

One indispensable technology for conducting high-precision surveying is RTK surveying. RTK stands for Real Time Kinematic, a real-time high-precision positioning method that uses satellite positioning (GNSS). With ordinary GPS/GNSS positioning, consumer receivers such as those in smartphones typically exhibit errors on the order of several meters. This is due to various error sources—ionospheric and tropospheric signal delays, satellite orbit errors, and receiver clock errors inside the device. RTK surveying corrects these errors in real time by calculating the difference between GNSS data received at a reference station (base station) installed at a known accurate coordinate position and the mobile receiver at the measurement site. As a result, users in the field can determine their position with centimeter-level accuracy.

In Japan, a network RTK service using the Geographical Survey Institute’s nation-wide continuous GNSS network (GEONET) is available. By receiving correction information (differential data) over the internet via a system called Ntrip, a “fixed solution”—the high-precision solution—can typically be obtained about one minute after starting positioning, and thereafter position updates continue at an astonishing accuracy of about 1–2 cm. More recently, the Cabinet Office has introduced a centimeter-level positioning augmentation service (CLAS) via the Quasi-Zenith Satellite System (QZSS, nicknamed Michibiki). Receivers that support CLAS can obtain correction information directly from satellites even in mountainous areas where mobile phone signals do not reach, maintaining high-precision positioning. Even in disaster zones or areas with unstable communications infrastructure, CLAS-capable equipment enables stable centimeter-level positioning, further increasing the utility of RTK technology.

Through RTK, GNSS satellite-based positioning can cancel out error sources thoroughly and determine absolute position to the centimeter level. Historically, achieving such precision required optical instruments like total stations or expensive GNSS surveying equipment operated by skilled surveyors. However, recent technological advances have produced new, more accessible solutions. A prime example is RTK surveying using smartphones, and among these innovations, LRTK is receiving attention as a groundbreaking product.

The advent of smartphone RTK surveying and LRTK’s technical features

Smartphone RTK surveying, as the name suggests, is a method of performing RTK positioning using a smartphone. When one hears “high-precision positioning,” specialized surveying equipment might come to mind, but recently it has become possible to achieve centimeter-level positioning simply by attaching an external device to a smartphone. The pioneer in this area is Lrefixia, a startup spun out of Tokyo Institute of Technology, which developed the LRTK Phone. It is an ultra-compact RTK-GNSS receiver that fits in a pocket and is designed to attach to an iPhone or iPad with a single touch via a dedicated case. Despite its thin, lightweight design—approximately 125 g in weight and about 13 mm (0.51 in) thick—it houses a high-performance antenna and a battery and does not add bulk when mounted on the back of a phone. It communicates with the smartphone via Bluetooth or a Lightning cable and supports both the network RTK (Ntrip) and CLAS signals from the Quasi-Zenith Satellite System, enabling real-time high-precision positioning anywhere in Japan. The internal battery runs continuously for about 6 hours and can be extended via USB power. It is also dustproof and waterproof, so it can be used with confidence in harsh outdoor field conditions.

LRTK provides more than just the hardware receiver. The LRTK system consists of three major components that comprehensively support surveying work in the field. The first is the GNSS terminal described above, the “LRTK Phone.” The second is the LRTK app for iPhone/iPad. With this dedicated app, users can complete all necessary tasks on their smartphone—from starting positioning and data recording to AR display and navigation. For example, you can switch with one tap between single-point measurements and continuous positioning at up to 10 points per second, and the app includes averaging over multiple points to improve accuracy. Collected points are plotted on a map in real time; conversion to Japan’s plane rectangular coordinate system and automatic geoid height calculation are performed in the background. Photos taken with the smartphone camera are automatically tagged with high-precision coordinates and camera orientation and saved. Each photo can also be uploaded to the cloud with a single tap. The app also lets you set recorded points as targets and provides navigation guidance on the map or via AR. Using the camera view to display virtual stakes or markings supports stake-driving and batter board positioning, and allows non-contact positioning of distant targets. In short, measuring, indicating, and recording tasks on site can be completed with a single smartphone.

The third component is the web-based LRTK Cloud. Survey data collected in the field—point coordinates, point clouds, photos, etc.—can be synced to the cloud with one button, enabling immediate sharing and storage without returning to the office to import data to a PC. No dedicated software installation is required; if you have internet access you can view data on maps and in a 3D viewer in your browser. By sharing a link with stakeholders, external contractors or clients without licenses can view the data without needing high-performance PCs or specialized point-cloud viewers. You can track survey points and photos organized in time series, download CSV coordinate lists or point cloud data, and import them into in-house CAD software.

Thus, LRTK is offered as an integrated platform—device + app + cloud—that not only measures high-precision coordinates with GNSS but also completes the subsequent workflow of data processing, utilization, and sharing in the field. Transforming a handheld smartphone into a surveying instrument, this approach delivers accuracy and functionality comparable to conventional high-cost surveying instruments in a much more accessible form, which is revolutionary.

The basis for centimeter-level accuracy achieved with smartphone RTK

When people hear about using a smartphone for surveying, some may question whether such high precision is truly attainable. The basis for achieving centimeter-level accuracy lies in RTK technology. Typical smartphone-integrated GPS chips are not designed for high-precision positioning and therefore yield meter-level errors. However, by connecting a dedicated RTK-capable receiver like LRTK, users can leverage a professional-grade GNSS antenna and positioning engine, which dramatically improves positioning accuracy. Receiving correction information from GEONET via the internet or directly from Michibiki’s CLAS satellite signals removes most of the error sources, enabling smartphone-based positioning to achieve, in principle, comparable accuracy to traditional surveying GNSS equipment.

In practice, the positioning accuracy attainable with LRTK has been confirmed to be comparable to conventional fixed GNSS receivers. For example, in a static positioning test with a fixed LRTK terminal, averaging multiple observations reduced the horizontal standard deviation from about 12 mm (0.47 in) for single observations to about 8 mm (0.31 in) after averaging 60 observations. This indicates that positional accuracy fell below 1 cm (0.4 in), yielding results on par with professional surveying instruments. Of course, accuracy depends on the positioning environment (how open the sky is above and nearby obstructions), but under typical clear outdoor conditions, one can generally expect horizontal accuracy of about 1–2 cm (0.4–0.8 in) and vertical accuracy of about 3–5 cm (1.2–2.0 in). Achieving such accuracy with a smartphone represents a technological leap that was hard to imagine not long ago.

Moreover, various features of the LRTK app help sustain this accuracy. For example, automatic averaging by sampling point data multiple times, and tilt compensation using the smartphone’s attitude sensors (applying vertical correction if the device mounted on a pole is tilted), address common field conditions that might otherwise degrade accuracy. Additionally, CLAS support enables continuous positioning even outside mobile network coverage, so centimeter-level positioning can be maintained regardless of distance from base stations in mountainous areas or under viaducts. These combined elements make smartphone RTK a system that consistently ensures centimeter-level reliability.

Applications to point cloud measurement, as-built management, CAD integration, AR guidance, and cloud sharing

• Point cloud measurement: Using the LiDAR scanner or cameras built into iPhone or iPad, you can acquire surrounding 3D point cloud data. When combined with LRTK, high-precision geographic coordinates (absolute coordinates) can be assigned to every scanned point, greatly reducing distortion and scale errors common with smartphone-only scans. For example, walking while scanning a construction site or structure with a smartphone enables rapid acquisition of accurate 3D point cloud models without positional shifts. Smartphone LiDAR has an effective range of about 5 m (16.4 ft), but when combined with photogrammetry techniques it can cover targets up to about 50–60 m (164.0–196.9 ft) away. This allows efficient collection of point cloud data with absolute coordinates over large areas.

• As-built management: Smartphone RTK is also useful for checking as-built conditions in civil engineering works. Traditionally, volumes of earthworks or shapes of structures would be checked by measuring many points on site and then calculating volumes and comparing drawings back at the office. With LRTK, you can obtain numerous survey points or point clouds immediately after construction and compare them on site with design data to detect discrepancies. As-built inspections that once took a full day can be completed in a few hours, enabling corrective instructions such as additional fill on the same day. This prevents later discovery of errors that require rework and allows daily progress to be quantified for prompt reporting to clients.

• CAD integration: Survey data acquired with LRTK can be smoothly linked to design drawings and CAD software. Coordinates are automatically converted to Japan’s plane rectangular coordinate system on site, so data align with design coordinate systems. You can export CSV coordinate lists or point cloud data from LRTK Cloud and import them into in-house CAD or BIM models. This enables rapid reflection of field measurements in design and construction workflows, greatly speeding up feedback loops.

• AR guidance: The LRTK app includes augmented reality (AR) features that overlay virtual markers or models on the smartphone screen. This allows quick identification of stake-driving or batter board positions by following virtual stakes or lines displayed on the screen. Positioning tasks that previously required two or more people—stretching lines or operating surveying instruments—can now be performed accurately by a single worker using a smartphone. It also enables non-contact measurement of distant targets by aiming the camera at them instead of approaching them directly. Dangerous areas or difficult footing can be surveyed safely from a distance by indicating positions through AR.

• Cloud sharing: Instant cloud sharing of surveyed data is another major advantage. Points, photos, and point cloud data uploaded from the smartphone are shared with office staff and clients in real time. This eliminates the need to hand over USB drives or annotate paper drawings, dramatically improving the speed and accuracy of information sharing. With all stakeholders able to view the latest survey results immediately, communication losses between the field and office are reduced and decision-making accelerates.

Field deployment case studies and their effects (labor saving, time reduction, improved safety)

In real-world deployments of smartphone RTK, effects such as labor saving, time reduction, and improved safety have been reported compared with conventional methods. Here are three concrete cases.

Case 1: Improving efficiency of stake-driving work at a road construction site – At one paving project, positioning work that used to require a two-person team and more than half a day to set out positions from reference points was streamlined after introducing LRTK. One worker could identify stake locations using the smartphone AR guidance and simply mark the spot on site. The same task was completed in only a few dozen minutes, and headcount was halved, resulting in substantial efficiency gains. The site supervisor remarked that “one person can do it, so other personnel can be reassigned to different tasks and productivity has increased.”

Case 2: Speeding up as-built inspections in earthworks – For as-built management of cut-and-fill volumes, conventional workflows required measuring hundreds of points and returning to the office for volume calculations. On one site, LRTK was used to acquire a point cloud immediately after construction, and volume differences from the design model were calculated on the cloud in real time. As a result, an inspection that used to take a full day was completed in a few hours, and corrective instructions for additional fill were issued on the same day. Not only did this prevent rework discovered later, it also allowed daily progress to be quantified and reported promptly to the client.

Case 3: Safe surveying at disaster sites – A local government used smartphone RTK to support restoration design for a slope that collapsed in heavy rain. Surveying a landslide area carries the risk of secondary disasters, so detailed on-site surveys are usually difficult until restoration works begin. In this case, a staff member wearing an LRTK-equipped smartphone scanned the collapsed area from a safe distance, calculating an approximate volume of displaced soil and the slope angle within minutes. The work was completed by one person in a matter of tens of minutes without entering dangerous areas, greatly speeding initial response and ensuring staff safety. The municipality plans to continue using smartphone surveying for disaster response, noting that “surveying is completed just by carrying the device.”

As shown above, introducing smartphone RTK on site has demonstrated its effectiveness in addressing labor shortages, reducing work time, and ensuring worker safety. In terms of equipment costs, solutions like LRTK are significantly less expensive than conventional surveying instruments, so if widely adopted they could enable an efficient “one person, one device” workflow in many field situations.

Barriers to introduction and practical tips for field use

Although smartphone RTK is innovative, there are several barriers to consider when introducing it on site. First, some field staff may feel uneasy or resistant, asking “Is a smartphone really reliable?” Experienced surveyors and technicians accustomed to traditional equipment may be skeptical of new technologies. This concern is best dispelled by actually using the system and seeing its benefits, so it’s advisable to start with auxiliary use cases and gradually expand. For example, continue to use total stations for critical control points while trying smartphone RTK for simpler surveying tasks and progress checks to build trust step by step.

Next is the cost consideration. Introducing smartphone RTK involves some expense for receiver devices and service fees, but it is far less costly than total stations or 3D laser scanners. Organizations already using iPhones or iPads on site may only need to purchase the dedicated receiver to start. Public subsidies under national or local ICT construction promotion programs may also apply, lowering the cost barrier. From a return-on-investment perspective, compare reduced labor and time costs with equipment expenses to persuade management.

Technical limitations also deserve attention. Because GNSS relies on satellite signals, positioning is unstable or impossible in environments where the sky is not open (urban canyons between tall buildings, dense forests, inside tunnels, etc.). In such environments, avoid forcing GNSS-only workflows and combine with conventional methods or use remote positioning features (measuring distant objects with the smartphone camera) when possible. Also provide adequate training and clear manuals for workers unfamiliar with smartphones. Fortunately, the LRTK app is designed with an intuitive UI, and basic operation can be learned in a short training session, but practice beforehand will prevent confusion on site.

As a practical tip, appoint a champion within your organization to lead adoption and share know-how. Staff familiar with digital surveying should take the initiative to master the tool and disseminate successful results internally, helping others understand how easily outcomes can be achieved. Starting with small pilot sites or trial deployments to accumulate successful experiences is also effective. This will help the benefits of smartphone RTK spread throughout the organization and support smooth adoption.

Introducing simple surveying with LRTK

As we have seen, combining smartphones with RTK technology is transforming surveying. Solutions like LRTK are turning tasks that used to require specialized surveying teams into simple surveying that anyone can perform. Without complicated equipment or workflows, field personnel can collect needed data on site and use it immediately.

The ability to perform RTK surveying with a smartphone not only increases operational efficiency but also has the potential to change how work is done on site. Processes that previously had to wait for a surveyor’s arrival can now proceed quickly based on the field technician’s judgment. Real-time digital sharing of survey results enables multiple people to collaborate remotely and provide immediate feedback. Under the slogan “one survey device per person,” smartphone RTK is becoming the field standard.

Adopting new technology can be daunting, but LRTK’s ease of getting started with just a smartphone is appealing. If you are interested, consider trying simple, small-scale deployments to experience smartphone-based simple surveying. Once you can handle centimeter-level position information, productivity and creativity on site will improve dramatically. As a first step toward a new surveying style of the future, please consider adopting LRTK.

FAQ

Q: Can smartphone RTK really achieve centimeter-level accuracy? A: Yes—when appropriate equipment and conditions are met. Using an RTK-capable receiver like LRTK and correction services (network base station data via Ntrip or CLAS satellite signals), high-precision positioning with horizontal errors of about 1–2 cm (0.4–0.8 in) is achievable. Some conditions, such as ensuring a clear view of the sky, are required, but in clear outdoor conditions smartphone-based positioning can match the accuracy of conventional high-precision GNSS surveying equipment.

Q: What devices and preparations are needed to start smartphone RTK? A: Essentially, attach a dedicated RTK receiver to your smartphone (currently mainly iPhone and iPad supported) and install the compatible app. For LRTK, the receiver device “LRTK Phone” and a smartphone case are sold as a set and magnetically attach easily. You’ll also need internet access to obtain correction information (for example, a smartphone 4G/5G connection on site), but if you have CLAS support you can receive corrections directly from satellites even where mobile signals are absent. There is no need to set up your own base station, so introduction is relatively straightforward.

Q: Can it be used in mountainous areas or locations outside mobile coverage? A: Yes. The LRTK receiver supports triple-frequency GNSS and can utilize CLAS signals from Michibiki for positioning augmentation. Therefore, in remote mountain areas or islands without mobile coverage, if the sky is open, centimeter-level positioning can be maintained. There are practical examples of use in forest surveys and disaster sites, making it a useful tool that does not depend on communications infrastructure. However, in locations where satellite signals themselves cannot be received—such as inside tunnels or in deep shadows of skyscrapers—use becomes difficult, and combining with conventional methods or other workarounds is necessary.

Q: Is operation difficult? Can people who are not good with machines use it? A: If you are familiar with smartphone apps, operation is not difficult. The LRTK app is designed with an intuitive user interface so that positioning and recording can be performed by tapping on-screen buttons while viewing a map. For example, “record point” is one tap, and “take and save photo” is one tap—complex configuration is unnecessary. Even those who are not good with devices can start surveying quickly after basic instruction. The app also includes in-app help and support services for additional assistance.

Q: Can smartphone RTK replace conventional surveying instruments (total stations or high-precision GNSS receivers)? A: It depends on the application. For general topographic surveys, as-built measurements, and stake setting, smartphone RTK can substitute in many cases. It is particularly advantageous for wide-area surveys, sequential point recording, and point cloud measurement where one-person mobility is beneficial. However, for tasks requiring millimeter-level precision, such as displacement monitoring, or for indoor/underground positioning, conventional total stations or specialized instruments remain indispensable. Smartphone RTK should be considered one tool among many and used in combination with traditional equipment according to site needs. Currently, it is more often used to complement and improve efficiency rather than to completely replace all existing instruments.

Q: Is it available for Android smartphones? A: At present, the LRTK series is provided for iOS (iPhone/iPad). Apple devices have consistent access to high-precision GNSS features and stable sensor performance, so initial product releases target iOS. Demand for Android support is high, and development is likely being considered—please check the latest official information. For now, Android users can use LRTK with iOS devices; tablets such as iPad are also supported and are being used on site in some cases.