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

The Construction and Surveying Productivity Improvement Expo (commonly: CSPI-EXPO) is an annual gathering of cutting-edge construction DX technologies. At the recently held CSPI-EXPO, a smartphone-integrated RTK positioning device drew significant attention. This innovative technology—capable of centimeter-level positioning simply by attaching it to a smartphone—delivers a dramatic efficiency improvement over conventional surveying methods and is transforming how on-site as-built surveying is performed. This article provides a detailed introduction to the smartphone-integrated RTK technology featured at CSPI, covering differences from conventional technologies, the convenience of enabling solo surveying, applications in as-built management, usefulness in disaster response, and multifunctionality such as cloud integration, 3D scanning, AR, and photogrammetry.

The demand for such innovative technology arises from labor shortages and skill transfer challenges in the construction industry, as well as needs for improved safety and quality. Initiatives promoted by the Ministry of Land, Infrastructure, Transport and Tourism, such as “i-Construction,” are also providing tailwinds, accelerating the introduction of digital technologies on sites. High-precision surveying solutions that utilize smartphones can be seen as a hallmark of construction DX that dramatically enhances on-site productivity and efficiency.

For example, the 6th CSPI-EXPO held at Makuhari Messe in May 2024 featured “The Future of Construction” as its theme and showcased a wide range of solutions addressing industry issues such as decarbonization and energy saving, labor reduction and digital construction, and quality control. Attendance has increased year by year, and the 7th edition in 2025 (held as an international event) drew about 57,000 visitors. Among the many exhibits, the easy-to-use, high-precision positioning solutions leveraging smartphones received particularly strong attention.

Differences from Traditional Surveying – What Changes with Smartphone RTK?

In conventional surveying, specialized equipment such as total stations and GPS receivers are used, and tasks are typically performed by multiple people over extended periods. For example, using a total station generally requires one person to set up the instrument while another carries the prism to the survey points; measuring many points can take an entire day. After surveying, it was also necessary to bring the obtained data back to the office for comparison with design drawings, creating inefficiencies from repeated trips between the field and the office.

However, recent miniaturization of high-precision GNSS positioning technology and advances in communication infrastructure have made centimeter-level positioning with smartphones a reality. RTK (Real Time Kinematic) GNSS surveying achieves horizontal accuracy on the order of about 2–3 cm by applying real-time corrections of satellite positioning error information between a known base station and a mobile rover. By attaching an RTK receiver to a smartphone, the several-meter errors typical of standalone smartphone GPS are reduced to a few centimeters, enabling palm-sized equipment to provide positioning accuracy comparable to traditional fixed instruments. Combined with AR (augmented reality) technology, this precise position information enables a revolutionary method for intuitive single-person surveying and layout marking.

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

• Large reductions in personnel and time required: Total station surveys typically required two or more people, but with a smartphone + RTK device, on-site surveying can be completed by 1 person. GNSS positioning allows direct measurement even in locations with obstructed lines of sight (such as inside forests or in the shadow of structures), making it possible to quickly and efficiently measure multiple points. As a result, the days spent on surveying and as-built checks can be drastically reduced.

• Reduced dependence on skilled technicians: Traditionally, experienced technicians operated instruments and read measurements, and accuracy depended on their skills. Smartphone surveying uses dedicated apps that guide measurement procedures and automate data recording, making operation intuitive for anyone. There is no need to follow paper drawings while taking measurements; simply follow on-screen prompts and press a button at the desired point to capture accurate coordinates. This reduces human misreads and recording errors, easing the burden on veterans, aiding skill transfer to younger workers, and helping alleviate labor shortages.

• Real-time on-site verification and sharing: Acquired survey data can be immediately shown as AR display on the smartphone screen and overlaid with design plans or past data for verification. On-site as-built conformance (differences from the design) can be checked instantly, and any detected deviations can be corrected immediately. This dramatically reduces the need for returning later to reconcile data with drawings and remeasure—cutting down on rework. Via the cloud, measurement results can be shared instantly with office staff, allowing remote supervisors or clients to see site conditions in real time and significantly speeding decision-making.

• Improved safety: The need to carry heavy surveying equipment or climb to heights is reduced, minimizing risk on hazardous sites. Visualization through AR reduces measurement and construction errors caused by misperception of site conditions, contributing to accident prevention and fewer near-miss incidents. With everyone sharing the same data, misunderstandings are reduced, supporting safer construction management.

In this way, the new surveying style using smartphones × RTK achieves overwhelming efficiency and labor savings, lowering the barrier to surveying work. The conventional view that “surveying and as-built checks are for specialists only” is being overturned, and a new era is beginning in which anyone on site can measure and verify based on data. Making on-site surveying and as-built checks this straightforward will also significantly change approaches to construction management and quality assurance.

Smartphone-Integrated RTK Device "LRTK" and Its Features

A representative example of such smartphone RTK surveying, which attracted attention at CSPI, is the device called “LRTK.” Developed by a startup spun out of Tokyo Institute of Technology, LRTK is a smartphone-attached high-precision GNSS receiver that enables centimeter-class positioning simply by attaching it to the back of a smartphone or tablet (iPhone/iPad). Weighing only about 125 g and about 13 mm thick in pocket-size form, it houses a battery and a high-performance antenna. It can be attached to the phone’s back with a dedicated case for one-touch use (and, with an optional monopod stand, height correction can be measured with a single button), offering excellent portability and convenience.

Operation of the device is simple and does not require special training, and initial implementation costs are far lower than those of traditional surveying equipment. It was developed as a next-generation device aiming to be a “surveying instrument you can carry anywhere” and target the concept of one device per person as a field tool.

Attaching LRTK to a smartphone instantly transforms the phone into a surveying instrument with centimeter-level accuracy. It supports the Centimeter-Level Augmentation Service (CLAS) provided by Japan’s Quasi-Zenith Satellite System “Michibiki,” allowing stable high-precision positioning even in internet-unreachable mountain areas where mobile signals are unavailable. In fact, after the 2023 Noto Peninsula earthquake, LRTK proved useful in disaster-affected areas where communications infrastructure was down, enabling precise surveying, recording, and sharing of damage information rapidly with a single small device. This offline responsiveness—the ability to operate without relying on network connectivity—is a major strength as a field tool.

LRTK is equipped with a variety of functions that make it revolutionary in allowing surveying, construction layout, and record-keeping to be completed with a single device. Its main features include:

• High-precision GNSS positioning (single-point and continuous): With simple smartphone screen operations, you can measure and save coordinates (latitude, longitude, altitude) of arbitrary points at centimeter accuracy. The app automatically converts to required coordinate systems (such as plane rectangular coordinates or geoid height), so complex calculations in the field are unnecessary. Also, an operator can perform continuous positioning while walking—up to 10 points per second—to acquire track data, which is effective for long-section longitudinal surveys or wide-area terrain mapping.

• AR construction navigation: If design drawings and construction coordinate data are registered in LRTK’s cloud, you can perform tasks on-site while viewing design models and target positions as AR displays through the smartphone camera. For example, by uploading pile-driving positions, virtual piles will be projected on the phone screen at the site, and the user can mark accurate pile-driving points simply by following arrow guidance on the screen. Because LRTK continuously knows its position with centimeter accuracy, AR displays do not shift even while the user is walking. This intuitive “just look at the screen” approach greatly improves the efficiency and accuracy of stakeout and layout tasks.

• 3D point cloud scanning and photogrammetry: Using the smartphone’s built-in LiDAR scanner or camera-based scanning (photogrammetry), you can obtain high-density 3D point cloud data just by walking through the site. Thanks to LRTK’s high-precision position correction, each point is tagged with accurate absolute coordinates, minimizing distortions that normally occur in walk-through scans. You can instantly measure distances, areas, and volumes between arbitrary points on the acquired point cloud, enabling on-site earthwork volume calculations for fills and excavations. Acquired data can be uploaded to a cloud 3D viewer and shared with heavy equipment operators and design staff via a browser, facilitating overlay comparisons with pre-construction design models and smooth as-built evaluation.

• Streamlined photo records and reporting: When taking site photos from the LRTK app, each photo file is automatically tagged with high-precision coordinates and the camera’s orientation (bearing). You can also enter text notes at the time of shooting, and with one tap upload to the cloud so that the location and direction of each photo are plotted on a map. Traditionally, photos taken with a digital camera had to be brought back, organized, and pasted onto paper drawings to create reports—work that this system greatly reduces, helping prevent recording mistakes. In the cloud, photos from the same point can be displayed side-by-side for comparison, which is powerful when monitoring long-term changes in infrastructure inspections.

• Cloud integration and data sharing: All positioning data, point clouds, and photo information captured with LRTK can be uploaded to the cloud immediately 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. You can also share results immediately with clients or subcontractors simply by sharing a URL link, with no login to a dedicated system required. This minimizes time spent on report creation and data conversion, smoothing information flow between the field and the office and dramatically accelerating decision-making.

With these numerous functions, LRTK comprehensively supports on-site tasks such as “measuring,” “indicating,” and “recording” with a single smartphone. Its ease of use and practicality drew many construction management personnel at the CSPI exhibit to try the demos enthusiastically. Common reactions included surprise and expectation—“I didn’t think a smartphone could do this,” and “This could be used on our sites right away”—making LRTK a highly interesting low-barrier DX tool for many visitors.

Applications in As-Built Surveying and As-Built Management

Smartphone-integrated RTK is also highly useful for post-earthwork terrain surveys and checking the as-built shapes of structures. By scanning broad areas into 3D point clouds and recording as-built conditions, then overlaying them with pre-construction design models, you can instantly check for excesses or shortages in fills and cuts and verify the as-built shapes of structures. Partial measurements, such as measuring heights at key points with single-point surveys, are also easy, drastically shortening as-built inspection tasks that used to take half a day. Accelerating as-built management directly contributes to quality assurance and shorter schedules, making the benefits of this technology considerable. LRTK’s as-built measurement data also conforms to the Ministry of Land, Infrastructure, Transport and Tourism’s 3D As-Built Management Guidelines (draft), so it can be used directly for public works as-built management.

Rapid On-Site Measurement for Disaster Response

In major disaster scenes, smartphone-integrated RTK devices contribute to rapid initial surveys. As noted earlier, LRTK can perform high-precision positioning without an internet connection, so it can be brought into disaster areas to immediately survey and record building damage and terrain changes. Its small size and light weight make it easy to carry, reducing the burden of transporting equipment during emergency deployments by helicopter, for example. Some local governments have begun to deploy LRTK as a disaster response field measurement tool, and expectations are growing for its use as a means for limited personnel to efficiently assess damage.

Convenience of Cloud Integration for Data Sharing

Using smartphone-integrated RTK allows data collected on-site to be aggregated to the cloud immediately and shared in real time across the team. Coordinates, point clouds, and photo information measured on site are automatically uploaded to the cloud and can be checked instantly from an office PC. The ease of viewing in a browser without dedicated software is also attractive, and necessary information can be shared with clients or subcontractors simply by sharing a URL link. This greatly reduces the effort required for report creation and data handover, smoothing coordination between the field and the office and dramatically accelerating decision-making.

Other Diverse Use Cases

• Location confirmation of buried objects and existing structures: By projecting buried pipe routes from drawings as AR overlays during excavation, the risk of damaging existing pipes or cables can be reduced. Even in places where GPS signals do not reach, such as under bridges or elevated structures, LRTK’s indoor positioning mode can measure the space beneath them from pre-acquired control points. Non-contact coordinate measurement of inaccessible heights or hazardous areas enables safe and efficient preparation for inspections and repair planning.

• Infrastructure inspection and maintenance management: LRTK’s photogrammetry features are useful for routine inspections of road signs, slopes, bridges, and the like. Photos tagged with latitude/longitude and bearing are stored in the cloud linked to a map, so when reassessing the same site in subsequent years you can revisit the previously recorded coordinates using a coordinate navigation function. AR-based bearing guidance makes it easy to capture the same framing as before, making comparisons of long-term deterioration straightforward and bringing innovation to infrastructure asset maintenance management.

Field Feedback and Adoption Status

Field reports from sites that have adopted LRTK include comments such as “the time required for surveying and as-built checks was dramatically shortened” and “tasks that used to require two or more people can now be done by one person, allowing work to continue despite labor shortages.” A veteran technician commented, “I feel confident leaving it to younger staff. The app guides them, so even newcomers can measure accurately, which is helpful,” reflecting a tangible change in work styles on site. The relatively low initial cost and low adoption barrier were also highly praised, with some saying, “I want everyone on the site to have one.” Some construction companies and local governments have already started adopting LRTK, 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 attracting attention as a trump card for promoting on-site DX.

Closing: The On-Site Future Opened by Smartphone-Integrated RTK

The technologies showcased at CSPI reflect the future of construction sites. Among them, smartphone-integrated RTK devices stand out as an innovative solution emblematic of on-site DX. Surveying and as-built management, which previously relied on the experience and intuition of skilled personnel, are being replaced by digital data, and an era in which anyone can perform accurate and efficient field tasks is becoming increasingly plausible.

LRTK is expected to play an active role across a wide range of scenarios—from everyday simple surveys to large-scale construction management and disaster response. For the construction industry’s challenges of improving productivity and ensuring safety, smartphone × DX solutions like this will be a powerful trump card. Spreading the digital revolution to every corner of the site to dramatically improve productivity and quality—smartphone-integrated RTK is poised to take the lead in on-site DX, and attention will remain focused on its continued adoption and evolution. Going forward, smartphone RTK technology is also expected to integrate with drone-based automated surveying and automated control of construction machinery, contributing to fully digitalized construction processes. In particular, simpler on-site surveying tasks that have relied on veterans’ intuition are now on the verge of becoming accessible to anyone through LRTK, allowing easy acquisition of accurate data. A new era in which accurate surveying and as-built management can be performed with a single smartphone—the technology heralding that beginning is now spreading from CSPI’s show floors.