Table of Contents

• What is LRTK Phone?

• What is pile-driving guidance? Conventional challenges

• What is as-built management? Conventional challenges

• Pile-driving guidance made possible by LRTK Phone

• As-built management made possible by LRTK Phone

• How LRTK Phone achieves high-precision positioning

• Benefits of introducing LRTK Phone

• Use cases of LRTK Phone

• Conclusion

• Simple surveying with LRTK

• FAQ

As digital transformation (DX) at construction sites accelerates, by leveraging the precision of LRTK Phone, tasks that previously required dedicated surveying instruments and specialist technicians—such as “pile-driving guidance” and “as-built management”—can now be accomplished with just a smartphone. High-precision positioning, which used to be costly and labor-intensive, is now achievable with a familiar smartphone combined with a compact GNSS receiver. This article explains the overview of LRTK Phone, its high-precision technology, and concrete ways it can be used for pile-driving guidance and as-built management, along with their advantages.

What is LRTK Phone?

LRTK Phone is a small high-precision GNSS device that attaches to a smartphone. Just by mounting it on your phone, the smartphone instantly becomes a high-precision surveying instrument. LRTK Phone uses satellite positioning technology RTK (real-time kinematic) to achieve centimeter-class positioning accuracy, allowing position determination with very high precision—about 1 cm horizontally and about 2 cm vertically of error (horizontal about 1 cm (0.4 in), vertical about 2 cm (0.8 in)). By combining this “cm level accuracy (half-inch accuracy)” positioning information with the smartphone’s built-in camera and LiDAR sensor, it is a major feature that not only enables point positioning but also allows acquisition of high-precision 3D point cloud data.

LRTK Phone was developed by a startup spun out of the Tokyo Institute of Technology. By uniquely combining smartphone photogrammetry and LiDAR measurements, it can cover narrow spaces and the backsides of structures that are difficult for drones or terrestrial laser scanners to capture, and generate precise point clouds with absolute coordinates (global geodetic system) without placing ground control points (known points). In other words, even without specialized knowledge or large preparatory work, anyone can easily obtain high-precision 3D survey results directly on site.

What is pile-driving guidance? Conventional challenges

Pile-driving guidance refers to the guidance work performed to install piles in civil engineering works at the correct position, depth, and inclination. It involves marking pile installation positions on site and directing equipment operators to match the coordinates and elevations specified in the design drawings. Traditionally, to perform accurate pile-driving guidance, surveyors needed to use total stations or GNSS surveying devices to measure pile locations precisely from reference points and perform layout (pile center setting). For tasks such as aligning multiple piles in a straight line, careful confirmation using lasers and other methods was required, which was time-consuming and labor-intensive.

Conventional challenges include, first, the need for specialized technicians and expensive equipment. Ensuring pile-driving accuracy requires advanced surveying skills, which increases labor costs. Also, surveying is difficult in bad weather or poor visibility, which can affect construction schedules. Moreover, if reference markings become hard to see due to vegetation or snow, guidance mistakes can occur, imposing a heavy burden on site operations.

What is as-built management? Conventional challenges

As-built management involves measuring and verifying whether constructed structures and prepared land match the shapes and dimensions specified in the design drawings. It ensures construction quality by measuring the final shape of roads, dams, and prepared land to check embankment and excavation heights and slopes, and by checking the finished dimensions of structures. The Ministry of Land, Infrastructure, Transport and Tourism has established “as-built management guidelines,” and for public works, implementation and reporting of as-built management after construction are mandatory.

Traditionally, as-built management required a great deal of effort. For example, in earthwork, it is necessary to survey the post-construction terrain and examine the elevation differences with the design surface in detail, but measuring a large number of points manually is extremely demanding. Drone photogrammetry or terrestrial laser scanners can be used for 3D measurement in some cases, but these require expensive equipment and specialized data processing. Also, conventional methods have limits on point density, making it possible to overlook minor surface irregularities. For these reasons, there has been demand for methods that can quickly and precisely capture the current three-dimensional shape and compare it with design data.

Pile-driving guidance made possible by LRTK Phone

So how does pile-driving guidance change when using LRTK Phone? First, the centimeter-precision positioning information provided by LRTK Phone enables accurate navigation to pile positions for pile-driving operations. On the smartphone screen, you can check your current position in real time against the target coordinates of the pile you have set; as you approach the target, arrow and guide displays will notify you with an image like “This is the pile center!”. This allows anyone—not just surveying experts—to quickly locate pile positions.

Furthermore, by utilizing LRTK Phone’s AR (augmented reality) features, you can visualize the design pile positions and reference lines overlaid on the site through your phone’s screen. For example, you can display the alignment of pile rows in AR and confirm on the spot whether piles are placed in a straight line. The linear layout work that used to be done with lasers or strings can instead be easily replaced with virtual guides on your smartphone, dramatically improving both the efficiency and accuracy of pile-driving operations.

Also, LRTK Phone is highly portable and battery-powered, so operators can bring it into the cabin of heavy machinery and check positions themselves. Even reference points hidden by vegetation or snow can be detected with high-precision coordinates once you get close, so being able to identify pile positions reliably under adverse conditions is a major reassurance. Introducing LRTK Phone for pile-driving guidance standardizes tasks that once depended on the intuition and experience of skilled workers, reducing quality variability and labor requirements.

As-built management made possible by LRTK Phone

Next, use for as-built management. With LRTK Phone, you can perform fast and comprehensive 3D scans of the as-built condition and quickly acquire the data necessary for as-built verification. Simply walking around the site with a smartphone in hand allows the camera and LiDAR to capture surrounding terrain and structures, generating point cloud data in real time. That range reaches up to about 50–60 m (164.0–196.9 ft), so a single road or a large slope can be covered in a short time. Acquired point clouds are tagged with absolute coordinates such as latitude/longitude or plane rectangular coordinate systems, making comparison with design drawings or reference surfaces straightforward.

Point cloud data obtained with LRTK Phone can be imported directly into a dedicated cloud viewer or CAD software and overlaid with 3D models of design data for verification. The Ministry of Land, Infrastructure, Transport and Tourism recommends point-cloud measurement using ICT as a method for as-built management, and point clouds acquired with LRTK Phone meet those quality standards. In practice, by analyzing differences from the design surface on the point cloud, you can instantly determine whether constructed areas have the correct height and slope. Areas with no deviation can be shown in blue or green, while areas that are overfilled or over-excavated compared to the plan are shown in red, allowing visual judgment with a heatmap display that prevents oversights.

Thus, as-built management using LRTK Phone greatly streamlines surveying and drawing work that used to take days. There is no need to measure a huge number of points manually; you can obtain high-density data in a short time and, if corrections are needed, respond immediately on site after construction. Also, since data can be shared on the cloud with stakeholders, creating reports for clients is smoother. As a result, LRTK Phone contributes not only to improved as-built management quality but also to shorter construction schedules and cost reductions.

How LRTK Phone achieves high-precision positioning

Behind LRTK Phone’s high precision is advanced satellite positioning technology. The key is the RTK (Real Time Kinematic) method. RTK is a technique that determines high-precision positions by exchanging satellite signal error information observed between a fixed GNSS receiver acting as a base station and a mobile receiver (rover) in real time. For LRTK Phone, cm-level positioning on the smartphone is possible by connecting to network RTK services provided by the Geospatial Information Authority of Japan or private providers, or by receiving the centimeter-class augmentation service (CLAS) broadcast by Japan’s quasi-zenith satellite “Michibiki.” Being a multi-band receiver that can use GNSS signals on multiple frequency bands simultaneously, it is far more stable and has much faster initial convergence than legacy single-frequency GPS.

Moreover, the smartphone’s sensors also contribute to improved accuracy. Modern smart devices like iPhones and iPads are equipped with high-performance IMUs (inertial measurement units) and cameras, and when GNSS reception is temporarily unavailable, the IMU can continue to estimate position, playing a role similar to “interpolation.” The LRTK Phone app fuses this sensor information from the smartphone with GNSS positioning (sensor fusion), enabling continued and stable positioning data generation even in situations where satellite capture is temporarily difficult, such as under bridges or in forests. In addition, by overlaying the acquired position data with smartphone camera images and LiDAR measurements, you can obtain rich outputs such as geotagged photos and high-precision point clouds.

Benefits of introducing LRTK Phone

The benefits of deploying LRTK Phone on site are immense. Key points include:

• Surveying can be done easily by a single person: Because it only requires a smartphone and a small device, measurements can be performed by a single site staff member without assembling a dedicated surveying team. This leads to reduced personnel and labor savings.

• Significant cost reduction: Compared to separately acquiring high-precision GNSS receivers, laser scanners, and drone survey equipment, initial investment is lower. LRTK Phone, being multi-purpose with one device, is advantageous in terms of equipment purchase costs and maintenance expenses.

• Speedy data acquisition and decision-making: Because high-precision data is available in real time, situations can be assessed on site immediately. Confirming pile positions or judging the acceptability of as-built conditions without waiting prevents construction time loss.

• Accurate quality control: Point cloud data visualizes even small errors that were previously easy to miss. This helps reduce human error and ensures quality, increasing the reliability of as-built management documentation.

• Improved safety: Remote or high-up targets can be measured non-contact using zoom or LiDAR, reducing the number of times people need to enter hazardous areas. Short measurement times also reduce the risk of accidents caused by long hours of strenuous labor.

• Data integration and sharing: Integrated with cloud services, measured data can be shared within and outside the company immediately. The need to return to the office for data processing and reporting is reduced, speeding up information sharing. Explanations and discussions with clients are smoother when 3D data can be shown.

These benefits make LRTK Phone an attractive solution for simultaneously improving on-site productivity and construction quality.

Use cases of LRTK Phone

In practice, LRTK Phone is being adopted across a variety of domestic sites. As part of initiatives such as i-Construction and ICT civil engineering promoted by the Ministry of Land, Infrastructure, Transport and Tourism and local governments, it is being introduced as a new technology to replace conventional surveying. For example, one local government introduced LRTK Phone for road construction as-built management and was able to perform point-cloud measurement in-house in a short time instead of outsourcing it to specialists. As a result, lead time for report creation was dramatically shortened, and client inspections passed smoothly.

There are also reports of its use in emergency disaster response. At a recovery site following an earthquake in the Hokuriku region, LRTK Phone was used to quickly scan collapsed slopes, aiding in calculating landslide volumes and considering restoration methods. Where people would previously have had to survey dangerous slopes by hand, detailed terrain data could be obtained from a safe distance in a short time, which was highly valued.

Furthermore, construction and surveying companies are increasingly adopting LRTK Phone. Even small- and medium-sized firms that do not own expensive laser scanners or drones can incorporate modern 3D surveying relatively affordably with LRTK Phone. In fact, LRTK Phone has been showcased at various exhibitions and technical seminars, and many construction management engineers have been impressed by its ease of use and accuracy. Accumulating such field evaluations and achievements is expected to further expand LRTK Phone usage going forward.

Conclusion

LRTK Phone is an innovative tool that achieves centimeter-class accuracy with just a smartphone, and it is transforming important civil engineering processes such as pile-driving guidance and as-built management. By fusing high-precision GNSS and smartphone technology, surveying tasks that once required specialists have become accessible to anyone. As a result, efficiency and labor savings are progressing on site, and the level of quality control has also improved.

High-precision positioning and 3D measurement used to be limited to some large-scale sites due to high cost and complexity. However, with the advent of LRTK Phone, even small-scale projects and regional sites can easily utilize advanced technology. Now that smartphones have evolved into versatile surveying instruments, DX at construction sites is set to accelerate even further.

Simple surveying with LRTK

So far we have looked at applications for pile-driving guidance and as-built management, but LRTK technology is also very useful in other situations. One is everyday simple surveying. Tasks such as measuring the dimensions of a small lot, recording the positions of buried objects, or checking the height of existing structures used to take effort with tape measures and handheld surveying tools. With LRTK Phone, these simple surveys can be handled quickly with a smartphone.

For example, on a building site where you need to record the position of an obstacle not shown on the design drawings, simply obtaining the coordinate of that point with LRTK Phone and recording it with a photo will preserve accurate position information. Also, if you want to quickly check elevation differences before site development, walking around to acquire a point cloud will immediately reveal cross sections, areas, and elevation differences. Survey tasks that used to be outsourced to specialists can now be performed by anyone, immediately, and at low cost with LRTK.

Using LRTK for simple surveying speeds up daily site management and meetings. Because you can measure and share data whenever needed, you won’t spend time gathering information for decisions. LRTK Phone is therefore a reliable tool not only for large-scale tasks like pile-driving and as-built management but also for everyday needs when you “just want to measure something.”

FAQ

Q1. Is LRTK Phone’s positioning accuracy really centimeter-class?

A1. Yes. LRTK Phone achieves accuracy of about ±1 cm horizontally and about ±2 cm vertically (RMS values) using the RTK method (about ±1 cm (±0.4 in) horizontal, about ±2 cm (±0.8 in) vertical). Internal comparative experiments have confirmed that coordinates measured with LRTK Phone are nearly equivalent in accuracy to class-1 GNSS surveying instruments. With proper on-site operation, it provides sufficiently high precision for pile-center setting and as-built verification.

Q2. Can surveying really be done with just a smartphone?

A2. LRTK Phone operates with a small GNSS receiver that attaches to a smartphone and a dedicated app. By combining the smartphone’s high-performance camera and IMU with accurate positioning from GNSS, surveying comparable to dedicated equipment is possible. If you follow the guidance in the dedicated app, it is intuitive to operate even without surveying expertise, so you can be confident in using it.

Q3. How does it guide positions for pile-driving?

A3. When you specify the coordinates of planned piles in the app, the smartphone screen displays arrows and distance readouts to guide the operator to the target point. As you approach the target, the app shows the remaining distance like “○ cm to go,” and when you are directly above it a marker indicates the position. In AR mode, you can overlay pile design positions on the camera image, allowing intuitive and accurate position recognition.

Q4. Can the acquired point cloud data and survey results be submitted as official deliverables?

A4. Yes. Point clouds and coordinate data acquired with LRTK Phone meet the quality standards set out in the Ministry of Land, Infrastructure, Transport and Tourism’s as-built management guidelines. They are actually used for as-built management in public works and are attached and submitted without issue. However, you may need to convert outputs from the cloud into the output formats requested by the client (e.g., electronic delivery formats) such as DXF or LAS before submission.

Q5. How much does it cost to introduce LRTK Phone?

A5. Exact prices cannot be stated here, but generally the introduction barrier is lower compared with high-precision GNSS equipment or 3D scanners. It is less expensive than acquiring an entire set of equipment, and because one unit can serve multiple purposes it offers good cost performance. Rental options and subscription-based services are also considered, allowing flexible use for just the period you need.

Q6. Which smartphone models and OS are supported?

A6. Currently, use on iOS devices such as iPhone and iPad is the primary option. In particular, models with LiDAR scanners—such as iPhone 12 Pro and later, and iPad Pro series—are recommended because they allow full utilization of both photogrammetry and LiDAR. Support for Android devices may be considered in the future, but since the latest iPhone/iPad models have high-performance sensors, iOS-based use will remain the focus for the time being.