LRTK Phone enables stake-driving guidance and as-built management with a single smartphone at cm precision (cm level accuracy (half-inch accuracy))!

Table of Contents

• What is LRTK Phone?

• What is stake-driving guidance? Traditional challenges

• What is as-built management? Traditional challenges

• Stake-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

• Summary

• Simple surveying with LRTK

• FAQ

As digital transformation (DX) on construction sites accelerates, by leveraging the accuracy of LRTK Phone, what previously required dedicated surveying instruments and specialized technicians—stake-driving guidance and as-built management—can now be accomplished with just a single 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 specific ways to apply it to stake-driving guidance and as-built management, along with the benefits.

What is LRTK Phone?

LRTK Phone is a compact high-precision GNSS device designed to be attached to a smartphone. Simply attaching it to your phone instantly turns the smartphone into a high-precision surveying instrument. LRTK Phone realizes centimeter-level (half-inch accuracy) positioning via satellite positioning technology RTK (Real Time Kinematic), enabling position determination with very high accuracy on the order of approximately 1 cm (0.4 in) horizontally and approximately 2 cm (0.8 in) vertically. By combining this “cm precision (cm level accuracy (half-inch accuracy))” position information with the smartphone’s built-in camera and LiDAR sensor, it is possible not only to locate points but also to acquire high-precision 3D point cloud data—a major feature.

LRTK Phone was developed by a startup originating from Tokyo Institute of Technology. By uniquely combining smartphone photogrammetry and LiDAR measurement, 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 (World Geodetic System) without having to place ground control points (known points). In other words, anyone can easily obtain high-precision 3D survey results on-site without specialized knowledge or extensive preparation.

What is stake-driving guidance? Traditional challenges

Stake-driving guidance refers to the guidance work performed to install piles accurately in position, depth, and inclination in civil engineering works. It involves marking pile installation locations on-site and directing equipment operators to match the coordinates and elevations specified in the design drawings. Traditionally, to perform precise stake-driving guidance, a surveyor needed to use a total station or GNSS surveying instrument to measure pile positions in detail from reference points and perform layout (pile center marking). For tasks such as establishing a straight line of multiple piles (“line setting”), careful checking using lasers and the like was also required, which consumed time and labor.

Traditional challenges include, first, the need for specialized technicians and expensive equipment. Ensuring pile-driving accuracy requires advanced surveying skills, increasing labor costs. Also, surveying work is difficult in bad weather or low-visibility conditions, which can affect construction schedules. Moreover, when reference markings become obscured by vegetation or snow, guidance errors can occur, placing a heavy burden on-site.

What is as-built management? Traditional challenges

As-built management is the inspection and verification work to determine whether completed structures or prepared land conform to the shapes and dimensions specified in the design drawings. It ensures construction quality by measuring the as-built shape of roads, dams, or prepared land to check heights and slopes of fills and cuts, or by checking finished dimensions of structures. The Ministry of Land, Infrastructure, Transport and Tourism has established “as-built management guidelines,” and in public works, implementation and reporting of as-built management after construction are mandatory.

Traditionally, as-built management required considerable effort. For example, earthworks require surveying the post-construction terrain and closely investigating height differences from the design surface, but measuring numerous points manually is extremely demanding. Drone photogrammetry or terrestrial laser scanning can be used for 3D measurement in some cases, but these require expensive equipment and specialized data processing. Also, conventional methods are limited in point density, which may miss subtle unevenness in the as-built shape. For these reasons, methods that can quickly and precisely acquire the current 3D shape and compare it with design data have been sought.

Stake-driving guidance made possible by LRTK Phone

How does stake-driving guidance change when using LRTK Phone? First, the centimeter-level (half-inch accuracy) position information provided by LRTK Phone enables accurate navigation to pile positions. On the smartphone screen, you can check your current position in real time relative to the target coordinates for a pile, and as you approach the target, arrow or guide displays will indicate “This is the pile center!” This allows anyone—not just surveying experts—to quickly find pile locations.

Furthermore, by utilizing LRTK Phone’s AR (augmented reality) function, you can visualize and overlay designed pile positions and reference lines on the site through the smartphone screen. For example, you can display the line of piles in AR and confirm on-site whether piles are being placed in a straight line. Tasks that traditionally required lasers or strings to set straight lines can be easily replaced by virtual guides on a smartphone, dramatically improving the efficiency and accuracy of pile-driving operations.

LRTK Phone is also highly portable and battery-powered, so it can be taken into heavy equipment cabins for operators to check themselves. Even reference points hidden by vegetation or snow can be detected with high-precision coordinates when you approach them, so it provides great assurance that you can accurately identify pile positions under adverse conditions. Introducing LRTK Phone for stake-driving guidance digitalizes work that relied on the instincts and experience of skilled workers, reducing quality variability and labor requirements.

As-built management made possible by LRTK Phone

Next, applications for as-built management. With LRTK Phone, you can rapidly and comprehensively 3D scan post-construction conditions and quickly obtain the data needed for as-built verification. Simply walking the site with a smartphone in hand, the camera and LiDAR capture surrounding terrain and structures while point cloud data is generated in real time. The range reaches about 50–60 m (164.0–196.9 ft), so you can cover a road or a large slope in a short time. The acquired point cloud is tagged with absolute coordinates such as latitude/longitude or plane rectangular coordinate systems, making comparison with design drawings or reference surfaces straightforward.

Point clouds obtained with LRTK Phone can be uploaded to a cloud viewer or imported into CAD software to overlay and verify against the 3D design model. The Ministry of Land, Infrastructure, Transport and Tourism recommends point cloud measurement using ICT as a method for as-built management, and point clouds from LRTK Phone meet those quality standards. By analyzing differences between the point cloud and the design surface, you can immediately see whether construction locations meet the design heights and slopes. Areas without deviation can be shown in blue or green, while areas that are overfilled or over-excavated compared to the plan can be shown in red, enabling heatmap visualization for easy visual assessment and ensuring no defects are overlooked.

Thus, as-built management with LRTK Phone significantly streamlines surveying and drawing tasks that formerly took days. Because there is no need to measure an enormous number of points manually and high-density data can be obtained in a short time, you can check the as-built condition immediately after construction and take corrective action on the spot if needed. Acquired data can be shared in the cloud with stakeholders, smoothing report preparation for clients. As a result, LRTK Phone contributes not only to improved as-built management quality but also to shorter 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 exchanges satellite signal error information observed between a base GNSS receiver and a rover in real time to compute highly accurate positions. For LRTK Phone, connecting to network RTK services provided by the Geospatial Information Authority of Japan or private providers, or receiving the centimeter-level augmentation service (CLAS) broadcast by Japan’s quasi-zenith satellite system “Michibiki,” enables centimeter-level positioning on a smartphone. Because it is a multi-band receiver that can use GNSS signals on multiple frequency bands simultaneously, it offers much better positioning stability and faster initial convergence compared to single-frequency GPS.

In addition, the smartphone’s sensors contribute to improved accuracy. Modern smart devices like iPhones and iPads are equipped with high-performance IMUs (inertial measurement units) and cameras, which help “interpolate” position when GNSS signals are temporarily unavailable. The LRTK Phone app fuses smartphone sensor data with GNSS positioning (sensor fusion), allowing it to maintain positioning and generate stable location data even in locations where satellite reception is temporarily difficult, such as under bridges or in forests. Furthermore, by overlaying captured position data with smartphone camera images and LiDAR measurements, you can obtain rich deliverables 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 one person: Because everything is completed with just a smartphone and a small device, on-site personnel can perform necessary measurements without assembling a dedicated surveying team, enabling labor reduction and streamlining.

• Significant cost savings: Compared to purchasing high-precision GNSS receivers, laser scanners, or drone surveying systems separately, the initial investment can be suppressed. LRTK Phone’s multi-purpose capability is advantageous in terms of equipment purchase and maintenance costs.

• Speedy data acquisition and decision-making: Real-time high-precision data enables immediate on-site judgments. By confirming pile positions and as-built conformity without waiting, construction time losses are prevented.

• Precise quality control: Point cloud data visualizes and detects details of errors that were often overlooked before, helping reduce human error and ensure quality, thereby increasing the reliability of as-built documentation.

• Improved safety: Remote or high-up objects can be measured non-contact via zoom or LiDAR, reducing the number of times people need to enter hazardous areas. Shorter measurement times also lower the risk of accidents caused by prolonged heavy labor.

• Data linkage and sharing: Integrated with cloud services, measured data can be shared immediately within and outside the company. This reduces the time spent processing and reporting after returning to the office, 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 various domestic sites. As part of initiatives like i-Construction and ICT civil engineering promoted by the Ministry of Land, Infrastructure, Transport and Tourism and local governments, it is being adopted as a new technology replacing traditional surveying. For example, one local government introduced LRTK Phone for as-built management of roadworks and began performing point cloud measurement in-house in a short time instead of outsourcing to specialists. As a result, lead times for report preparation were greatly shortened and client inspections passed smoothly.

There are also reported uses in emergency disaster response. At a recovery site after an earthquake in the Hokuriku region, LRTK Phone was used to quickly scan collapsed slopes, aiding calculation of collapse volumes and consideration of restoration methods. Where people would traditionally have had to survey dangerous slopes by hand, detailed terrain data could be obtained in a short time from a safe distance—an appreciated advantage.

Moreover, construction and surveying companies are increasingly adopting LRTK Phone. Small- and medium-sized operators that do not own expensive laser scanners or drones can relatively inexpensively adopt modern 3D surveying with LRTK Phone. At exhibitions and technical seminars, many construction management technicians have expressed surprise at its ease of use and accuracy. As such on-site evaluations and achievements accumulate, the use of LRTK Phone is expected to expand further.

Summary

LRTK Phone is an innovative tool that realizes centimeter-level accuracy with a single smartphone and dramatically transforms important civil construction processes like stake-driving guidance and as-built management. By fusing high-precision GNSS with smartphone technology, surveying work that previously required specialists has become accessible to anyone. As a result, on-site efficiency and labor reduction have progressed, and the level of quality control has improved.

Because high-precision positioning and 3D measurement were traditionally costly and complex, they were limited to some large-scale sites. However, with the advent of LRTK Phone, even small-scale projects and regional sites can easily utilize advanced technologies. Now that the smartphone has evolved into an all-purpose surveying instrument, DX at construction sites is set to accelerate further.

Simple surveying with LRTK

So far we have looked at applications for stake-driving guidance and as-built management, but LRTK technology is also useful in many other situations. One such use is everyday simple surveying. Tasks like measuring small plot dimensions, recording locations of buried items, or checking heights of existing structures used to be done with tape measures or handheld surveying tools, taking time. With LRTK Phone, these simple surveys can be quickly done with a smartphone.

For example, if you want to record the location of an obstacle not shown on the design drawings at a building site, you can obtain the point’s coordinates with LRTK Phone and record it along with a photo to preserve accurate location information. If you want to quickly measure existing height differences before land development, walking around to acquire a point cloud will immediately reveal cross-sections, areas, and elevation differences. Surveying tasks that used to require a specialist can now be performed by anyone, immediately, and at low cost with LRTK.

Using LRTK for simple surveys speeds up daily site management and meetings. Because you can measure and share data as needed, you won’t spend time collecting information for decisions. LRTK Phone is therefore a reliable tool not only for large tasks like stake-driving and as-built management but also for everyday “just measure this” needs.

FAQ

Q1. Is LRTK Phone’s positioning accuracy really at the centimeter level?

A1. Yes. LRTK Phone uses the RTK method to achieve horizontal accuracy of about ±1 cm (±0.4 in) and vertical accuracy of about ±2 cm (±0.8 in) (RMS values). Internal comparative experiments have confirmed that coordinates measured with LRTK Phone are nearly equivalent in accuracy to a Class-1 GNSS surveying instrument. When operated appropriately on-site, it provides sufficient high accuracy for pile center marking and as-built verification.

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

A2. LRTK Phone operates with a small GNSS receiver attached to a smartphone and a dedicated app. By combining the smartphone’s high-performance camera and IMU with accurate position information from GNSS, surveying comparable to dedicated equipment becomes possible. If you follow the guidance in the dedicated app, you can operate it intuitively without specialized surveying knowledge.

Q3. How does it guide position during stake-driving?

A3. When you specify the coordinates of the planned pile in the app, the smartphone screen displays arrows and distance to the target to guide the operator to the pile position. As you approach the target, the remaining distance (e.g., “X cm to go”) is shown, and when you are directly above the point, a marker indicates the location. In AR mode, the design position of the pile can be overlaid on the camera view, allowing intuitive, accurate position understanding.

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

A4. Yes. Point clouds and coordinate data obtained 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 used in public works as-built management and have been attached and submitted to as-built documentation without issues. However, depending on the format required by the contracting organization (e.g., electronic delivery formats), you may need to convert data from the cloud to DXF or LAS formats before submission.

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

A5. Exact prices cannot be stated here, but the barrier to introduction is lower compared to typical high-precision GNSS instruments or 3D scanners. It is less expensive than purchasing a full set of equipment and can be used for multiple purposes with a single device, offering good cost performance. Rental options and subscription services are also being considered, enabling flexible use for only the required period.

Q6. Which smartphone models and OS are supported?

A6. At present, use on iOS devices such as iPhone and iPad is the primary option. Models from iPhone 12 Pro onward and iPad Pro series equipped with LiDAR scanners are recommended because they can make the most of both photogrammetry and LiDAR. Support for Android devices may be considered in the future, but because the latest iPhone/iPad feature high-performance sensors, iOS environments will be the focus for the time being.