Exhibiting at CSPI: Smartphone-Integrated RTK Is Changing On-Site As-Built Surveying

The Construction and Surveying Productivity Improvement Expo (commonly known as CSPI-EXPO) is an annual gathering of cutting-edge construction DX technologies. At the recently held CSPI-EXPO, smartphone-integrated RTK positioning devices drew significant attention. This innovative technology, which enables centimeter-level positioning simply by attaching a device to a smartphone, brings dramatic efficiency improvements compared with traditional surveying methods and is transforming how on-site as-built surveying is conducted. This article provides a detailed look at the smartphone-integrated RTK technology that made waves at CSPI: how it differs from conventional techniques, the convenience of enabling one-person surveys, its application to as-built management, its usefulness in disaster response, and its multifunctionality including cloud integration, 3D scanning, AR, and photogrammetry.

The demand for such innovative technologies stems from labor shortages and skills-transfer challenges in the construction industry, as well as needs for improved safety and quality. Policies such as the Ministry of Land, Infrastructure, Transport and Tourism’s “i-Construction” have provided tailwinds, accelerating the adoption of digital technologies on sites. High-precision surveying solutions that leverage smartphones can be seen as a symbol of construction DX that dramatically boosts on-site productivity and efficiency.

For example, at the 6th CSPI-EXPO held at Makuhari Messe in May 2024, themed “The Future of Construction,” a wide range of solutions addressing industry issues such as decarbonization and energy savings, labor reduction and digital construction, and quality control were showcased. Visitor numbers have increased year by year, and the 7th event in 2025 (to be held as an international event) saw about 57,000 visitors. Among the exhibits, smartphone-based, easy-to-use high-precision positioning solutions attracted particular attention.

Differences from Traditional Surveying – What Changes with Smartphone RTK?

In conventional surveying, specialized equipment such as total stations or GPS receivers is typically used, and the work is often carried out by multiple people over extended time. For example, with a total station one person must set up the instrument while another holds a prism at the survey point, and measuring many points can take an entire day. After surveying, it has been common to bring the data back to the office to compare it with design drawings, so the inefficiency of back-and-forth between the field and the office has been an ongoing issue.

However, advancements in miniaturization of high-precision GNSS positioning technology and communication infrastructure have ushered in an era where smartphones can achieve centimeter-level positioning. GNSS surveying using the RTK (Real Time Kinematic) method achieves high precision—about 2-3 cm (0.8-1.2 in) horizontally—by applying real-time correction of satellite positioning error information between a base station at a known point and a mobile receiver (rover). By attaching an RTK receiver to a smartphone, the meter-level errors typical of a smartphone’s standalone GPS can be reduced to a few centimeters (a few inches), enabling palm-sized positioning accuracy comparable to traditional stationary instruments. Moreover, combining this precise positional information with AR (augmented reality) technology enables a revolutionary method whereby one person can intuitively perform surveying and stakeout.

Smartphone-integrated RTK creates the following differences compared with traditional methods:

• Significant reduction in personnel and time: Total station surveys typically require two or more people, but with a smartphone plus an RTK device, a single operator can complete site surveying. GNSS positioning can directly measure in areas where the line of sight is blocked (such as inside forests or in the shadow of structures), allowing many points to be measured efficiently in a short time. As a result, the days spent on surveying and as-built inspections can be dramatically reduced.

• Reduced dependence on skilled technicians: Traditionally, experienced technicians handled instrument operation and reading, and skill was essential for accurate measurement. Smartphone surveying uses dedicated apps that guide the measurement procedure and automate data recording, making it intuitive for anyone to operate. There is no need to follow paper drawings to track dimensions; at the desired point, users simply follow on-screen prompts and press a button to obtain accurate coordinates. This reduces human reading errors and recording mistakes, easing the burden on veterans, facilitating skill transfer to younger staff, and helping alleviate manpower shortages.

• Real-time on-site verification and sharing: Collected survey data can be displayed on the smartphone screen in AR immediately and overlaid with design drawings or past data for verification. On-site, users can instantly check whether the as-built conforms to the design and, if discrepancies are found, correct them immediately. This greatly reduces rework such as taking data back to the office for comparison and re-surveying later. Data can also be shared instantly with the office via the cloud, allowing supervisors or clients in remote locations to view the site in real time. This significantly speeds up decision-making.

• Improved safety: The need to carry heavy surveying equipment or climb to high places is reduced, minimizing risks in hazardous field conditions. Visualization via AR reduces misperceptions that lead to measurement or construction errors, contributing to accident prevention and fewer near-misses. Because everyone shares the same data, discrepancies in understanding are reduced, supporting safer construction management.

In this way, the new surveying style enabled by smartphone × RTK achieves overwhelming efficiency and labor savings, lowering the barrier to surveying work. The long-held notion that “surveying and as-built inspection are work only for specialists” is being overturned, and a new era is emerging in which anyone on site can measure and verify based on data. As on-site surveying and as-built checks become this easy, the approach to construction management and quality assurance will change significantly.

Smartphone-Integrated RTK Device “LRTK” and Its Features

A representative example of smartphone RTK surveying that attracted attention at CSPI is the device “LRTK.” LRTK is a smartphone-mountable high-precision GNSS receiver developed by a startup originating from Tokyo Institute of Technology. By attaching it to the back of a smartphone or tablet (iPhone/iPad), centimeter-level positioning becomes possible. It weighs only about 125 g and, despite its pocketable size with a thickness of about 13 mm (0.51 in), contains a battery and a high-performance antenna. It can be attached to the back of a smartphone with a dedicated case in one touch (and, with an optional monopod stand, height correction can be measured with one button), offering a design that excels in portability and convenience.

Operation of the device is simple and does not require special training, and initial introduction costs are significantly lower than those of traditional surveying instruments. It was developed as a next-generation instrument intended to be “a surveying instrument you can carry anywhere” and aimed at one unit per person on site.

When LRTK is attached to a smartphone, the smartphone instantly becomes a surveying instrument with centimeter-level precision (inch-level). It supports the centimeter-level augmentation service (CLAS) provided by Japan’s quasi-zenith satellite system Michibiki, enabling stable high-precision positioning even at sites without mobile reception, such as mountainous areas outside internet coverage. In fact, in the Noto Peninsula earthquake disaster in 2023, LRTK proved useful in areas where communication infrastructure was down, enabling rapid precise surveying, recording, and sharing with a single small device. This offline responsiveness independent of network connectivity is a major strength as a field tool.

LRTK is equipped with a variety of functions and is revolutionary in that surveying, construction layout, and record-keeping can be completed with a single device. Key features include:

• High-precision GNSS positioning (single point and continuous): With simple operations on the smartphone screen, users can measure and save coordinates (latitude, longitude, elevation) of arbitrary points with centimeter-level precision (inch-level). The app automatically converts to required coordinate systems (such as plane rectangular coordinates or geoid height), so complex calculations on site are unnecessary. Additionally, an operator can walk while performing continuous positioning at up to 10 points per second to obtain track data, which is effective for long-section longitudinal surveys and large-area terrain surveys.

• AR-based construction navigation: If design drawings or coordinate data for construction points are registered in LRTK’s cloud, the design model or target positions can be displayed in AR through the smartphone camera during field work. For example, if pile-driving positions are uploaded, virtual piles are projected on the smartphone screen at the site, and the user can mark the correct pile points simply by following arrow guidance on the screen. Because LRTK constantly knows its position with cm level accuracy (half-inch accuracy), AR displays on the screen do not drift as the user walks. This intuitive “just look at the screen” stakeout capability dramatically improves the efficiency and accuracy of pile-driving and layout work.

• 3D point cloud scanning and photogrammetry: Using the LiDAR scanner or camera built into the smartphone for scanning (photogrammetry), high-density 3D point cloud data can be collected simply by walking the site. Thanks to LRTK’s high-precision positional corrections, each point is assigned accurate absolute coordinates, minimizing the distortions that typically occur with ordinary walking scans. On the acquired point cloud, arbitrary distances, areas, and volumes between two points can be measured instantly, allowing soil volume calculations for fills or excavations to be performed on the spot. The acquired data can also be uploaded to a cloud 3D viewer and shared via browser with heavy equipment operators and design staff, facilitating smooth overlays with design models for as-built comparisons.

• Efficient photo documentation and reporting: When site photos are taken from the LRTK app, the photo file is automatically tagged with high-precision coordinates of the shooting location and the camera orientation (bearing). Text notes can be input at the time of shooting, and with one tap the photos can be uploaded to the cloud, where they are plotted on a map as “which point and in which direction the photo was taken.” Previously, photos taken with a digital camera had to be taken back to the office, organized, and pasted onto paper drawings to create reports, but such tasks are greatly reduced, helping prevent recording errors. The cloud also allows side-by-side comparison of past photos at the same location, which is powerful when assessing aging in infrastructure inspections.

• Cloud integration and data sharing: All positioning data, point clouds, and photo information acquired with LRTK can be uploaded to the cloud immediately from the field and managed centrally. Office personnel can always view the latest data via a web browser, and positioning data can be downloaded in CSV or SIMA formats. Results can be shared instantly with clients or subcontractors simply by sharing a URL link without requiring them to log into a dedicated system. This minimizes time spent on report preparation and data conversion, smoothing communication between the field and the office and greatly accelerating decision-making.

With these many features, LRTK comprehensively supports on-site tasks such as “measuring,” “indicating,” and “recording” with a single smartphone. Its ease of use and practicality led construction managers at the CSPI exhibition to eagerly try the demos. Many expressed surprise and expectation—“I didn’t think you could do this much with a smartphone” and “This looks ready to use on our sites”—and it drew high interest as a low-barrier DX tool.

Application to As-Built Surveying and As-Built Management

Smartphone-integrated RTK is also highly useful for terrain surveying after earthwork completion and for verifying the as-built of structures. By scanning wide areas with 3D point cloud data and recording as-built conditions, then overlaying them with the pre-construction design model, excesses or deficits in fills and cuts and the as-built status of structures can be checked immediately. Partial measurements such as measuring elevation at key points with single-point surveying are also easy, drastically shortening as-built inspection tasks that previously took half a day. Speeding up as-built management directly contributes to quality assurance and schedule reduction, so the benefits of this technology are significant. LRTK’s as-built measurement data also conforms to the Ministry of Land, Infrastructure, Transport and Tourism’s 3D as-built management guidelines (draft), making it applicable to public works as-is.

Rapid Field Measurement for Disaster Response

In large-scale disasters, smartphone-integrated RTK devices contribute to rapid initial surveys. As mentioned earlier, LRTK can perform high-precision positioning without internet connection, so it can be brought into disaster areas to immediately measure and record building damage and terrain changes. Its small, lightweight design makes it easy to carry and does not burden emergency transport such as helicopter dispatch. Some local governments have begun equipping LRTK as a disaster-response field measurement tool, and expectations are rising for its use as a means to efficiently assess damage with limited personnel.

Convenience of Cloud Integration for Data Sharing

Using a smartphone-integrated RTK makes it possible to aggregate data collected in the field to the cloud instantly and share it in real time with the entire team. Coordinates, point clouds, and photo information measured on site are automatically uploaded to the cloud and can be checked immediately from office PCs. The convenience of viewing data in a browser without dedicated software is also appealing, and necessary information can be shared with clients and subcontractors simply by sharing a URL link. This greatly reduces the effort of report creation and data handover, smoothing collaboration between the field and the office and dramatically improving decision-making speed.

Other Diverse Use Cases

• Confirming locations of buried or existing structures: By projecting buried pipe routes from drawings onto the field in AR during excavation, the risk of accidentally damaging existing pipes or cables is reduced. Even in locations where GPS signals do not reach, such as under bridges or overpasses, LRTK’s indoor positioning mode can measure the space below from pre-acquired reference points. Non-contact coordinate measurement for unreachable heights or dangerous areas enables safe and efficient preparation for inspections and repairs.

• Infrastructure inspection and maintenance management: LRTK’s photo-based surveying function is useful for routine inspections of road signs, slopes, bridges, and more. Photos tagged with latitude/longitude and orientation are stored in the cloud linked to a map, so when re-surveying the same spot in subsequent years, the app’s coordinate navigation helps you revisit the exact coordinates recorded previously. AR-based directional guidance makes it easy to shoot photos with the same composition as before, making it simple to compare aging over time and bringing innovation to infrastructure asset maintenance.

Field Feedback and Adoption Status

From sites that have actually introduced LRTK, feedback includes “the time required for surveying and as-built checks has been dramatically reduced” and “tasks that previously required two or more people can now be done by one person, so operations can continue even with labor shortages.” A veteran technician commented, “I can trust the younger staff with this. The app guides them, so even newcomers can measure accurately, which is a big help,” showing that ways of working on site are indeed beginning to change. The low initial cost and the fact that it is easy to deploy were also highly rated, with comments such as “I want everyone on site to have one.” Adoption of LRTK has already begun at some construction companies and local governments, and the technology is registered in the Ministry of Land, Infrastructure, Transport and Tourism’s New Technology Information System (NETIS). Its use in public works is being encouraged, and it is quietly gaining attention as a trump card for promoting field DX.

Conclusion: The Future of Sites Opened Up by Smartphone-Integrated RTK

The latest technologies introduced at CSPI reflect visions of future construction sites. Smartphone-integrated RTK devices are among the most innovative solutions symbolizing field DX. Surveying and as-built management, which used to rely on the experience and intuition of skilled workers, are being replaced by digital data, making it realistic for anyone to perform accurate and efficient on-site tasks.

LRTK is expected to be active in a wide range of scenes—from everyday quick surveys to management of large-scale construction and disaster response. As a smartphone × DX solution, it represents a powerful card to address the construction industry’s challenges of productivity improvement and safety assurance. By permeating the digital revolution to every corner of the site and dramatically improving productivity and quality, smartphone-integrated RTK is set to play a leading role on the front lines of field DX, and attention will continue to focus on its diffusion and evolution. In the future, smartphone RTK technology is also expected to link with drone-based automated surveying and automated control of construction machinery, contributing to the full digitalization of construction. In particular, even simple on-site surveying tasks that have relied on the intuition and experience of veterans will soon be within reach for anyone to obtain accurate data easily with LRTK. A new era in which accurate surveying and as-built management can be performed with a single smartphone—the technology heralding that dawn is now spreading from CSPI’s field.