Background of the Academia–Industry Bridge-Inspection Project

Across Japan, many bridges built during the period of rapid economic growth are now approaching—or have surpassed—their 50-year service life, and the rise in aging structures has become a major social issue. Regular inspections and proper maintenance are essential to keep these bridges safe.

Triggered in part by serious accidents—such as the ceiling-panel collapse in an expressway tunnel—road bridges must now undergo close, hands-on inspections every five years. Yet inspecting the nation’s hundreds of thousands of bridges at that frequency places a heavy financial and staffing burden on local governments. Skilled engineers perform the work manually, so it is time-consuming and costly, and the chronic shortage of qualified personnel is acute. Additional challenges include safety risks associated with work at height and the traffic restrictions required for inspection vehicles. Moreover, conventional methods record results on paper or 2-D drawings, leaving data poorly shared and archived. These factors make technological innovation to streamline and upgrade bridge inspections an urgent priority.

Against this backdrop, academia–industry collaborations have begun to attract attention. Universities and research institutes are partnering with construction firms and infrastructure operators to bring cutting-edge technology to the field. In student-led projects, university labs tackle bridge-inspection problems while companies provide sites and share expertise, achieving both practical R&D and human-resource development. The Japanese government is also encouraging adoption of new techniques: the 2019 revision of the Road Bridge Periodic Inspection Manual allows “inspection-support technologies” such as drones and sensors to substitute for close visual checks under a certified engineer’s supervision. In short, conditions are now in place for innovative technologies born of academia–industry cooperation to move into real-world use.

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Bridge Inspections Powered by RTK Positioning and AR Technology

RTK positioning—short for Real-Time Kinematic—is a high-precision GNSS method that suppresses ordinary GPS errors of several metres to just a few centimetres by streaming real-time corrections from a base station to a rover. In other words, it delivers a quantum leap in survey accuracy: locations that would drift with stand-alone GPS remain virtually error-free with RTK. A fixed base station with known coordinates and a mobile rover both receive satellite signals; the base computes the error and transmits the correction (yellow dashed line) to the rover, tightening its position to centimetre level.

Why is RTK essential for bridge inspections? One major reason is the need to pinpoint inspection data precisely. Traditional visual surveys recorded defects only approximately—“a crack X metres from member Y.” With RTK, cracks, spalls, or other damage can be logged with exact map coordinates, making it easy to relocate them in the next inspection or plan repairs. RTK’s centimetre-class accuracy is also invaluable for measuring displacements such as settlement or tilt and tracking them quantitatively over time.

RTK’s full power emerges when it is combined with augmented-reality (AR) technology. AR overlays digital information on a live view from a tablet or smart glasses, but ordinary GPS lacks the accuracy to keep that overlay aligned. RTK’s precise coordinates solve this problem: inspection crews can superimpose past drawings or defect records directly onto the physical bridge. Simply pointing a tablet at the structure shows previous crack histories or internal-member diagrams exactly where they belong, greatly reducing missed defects and clarifying long-term changes. High-precision data captured on site can be uploaded to the cloud in real time, allowing remote experts to advise through the same AR view—streamlining and upgrading the entire inspection workflow.

In short, fusing RTK positioning with AR offers tremendous potential to boost both accuracy and efficiency in bridge inspections. University–industry teams are now developing these advanced methods in student projects. The next section looks at concrete implementation cases.

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[Case Studies] Successful Bridge-Inspection Projects through University–Construction-Company Collaboration
Below are three examples of projects that applied RTK and AR to bridge inspections via academia–industry cooperation. In every case, a student team from a university partnered with a company to carry out on-site pilot trials.

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Case 1: Inspecting an Aging Bridge with RTK and AR

In one municipality, a university student project team partnered with a construction firm to inspect a 50-year-old bridge. The students carried an RTK-GNSS receiver and a tablet as they moved from member to member. Through the tablet’s camera they viewed the bridge while past inspection records and design drawings were over-laid in augmented reality. Because RTK pinpointed each position to the centimetre, crack maps and other data snapped exactly onto the real structure, letting the team see at a glance which defects had appeared or grown since the previous survey. For example, if a crack had stretched from 10 cm to 30 cm, the difference was visible immediately and the need for emergency repair could be judged on the spot. The project finished the inspection in 30 percent less time than the conventional method and reported zero missed anomalies. The students gained hands-on experience with cutting-edge tools, while the company demonstrated the efficiency of this advanced inspection workflow.

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Case 2: Digitizing Bridge Maintenance through Student–Industry Collaboration

At another university, a civil-engineering student team joined an internship project to develop a digital bridge-maintenance system together with a mid-sized construction company. Targeting bridges managed by the partner firm, the students set out to digitize inspection data and centralize asset management. They built a detailed digital twin by combining centimeter-level coordinates from RTK GNSS with drone imagery and LiDAR scans.

The team then developed an AR-based tool that visualizes inspection results directly on the 3-D model. Using a tablet, inspectors can compare the virtual model with the actual bridge in real time. During field trials, students and company engineers worked side by side, plotting every defect onto a digital map on site. Information that had previously been written by hand on paper forms was converted automatically to electronic data and uploaded instantly to a cloud-based bridge-management platform. This greatly reduced the time needed to compile reports and allowed staff in remote offices to monitor inspection progress in real time.

The project is a prime example of how students’ fresh ideas and IT skills can drive digital transformation in a company’s bridge-inspection workflow.

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Case 3: Achieving Data-Driven Infrastructure Management

The third project shows how accumulated data can shift bridge maintenance from reactive repairs to predictive, preventive care. A university research lab teamed up with an expressway operator to collect and analyse bridge-inspection data with RTK accuracy over several years. Each year the students surveyed the same bridges with RTK-enabled devices, recording crack growth and member displacements in detail. They then fed this “big data” into AI and statistical models to forecast deterioration and assess risk.

For example, they detected a minute but steady increase in the tilt of a pier and predicted how many years would pass before reinforcement became necessary. Thanks to the system, the infrastructure owner was able to advance its repair schedule and intervene before serious damage appeared. With objective, data-driven evidence, managers could also rank repair priorities and allocate limited budgets more effectively.

The students authored papers and presented their findings at conferences, making the collaboration valuable for both academia and industry.

These case studies show that introducing RTK and AR does more than streamline workflows—it can fundamentally transform the entire approach to maintenance and management. They also highlight how academia-industry projects let the next generation of engineers hone cutting-edge skills in the field while actively contributing to infrastructure preservation.

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How to Implement RTK-Based Bridge Inspections

What preparations are required to put an innovative RTK × AR bridge-inspection workflow into practice? The following section explains the necessary equipment and systems and highlights the key considerations for a successful rollout.

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Required Equipment and Costs
To carry out bridge inspections with RTK, you will need the following gear.

• RTK-GNSS receiver (rover):
  Secure a GNSS unit capable of centimeter-level positioning. You can operate with a paired arrangement—one fixed base station and one rover carried by the inspector—or adopt a network RTK solution (e.g., VRS) that receives correction data via existing telecom infrastructure. Compact, affordable receivers have appeared in recent years, allowing initial outlay from only a few hundred thousand yen. If you use an electronic reference-station network (such as the Geospatial Information Authority of Japan’s system or a private correction-data service), you can operate with the rover alone and dispense with a dedicated base.

• AR display device:
  A field device is required for augmented-reality overlays. The most common choice is a tablet or large smartphone running a dedicated AR application; a rugged, dust- and water-resistant tablet is preferable. In the future, hands-free AR glasses such as HoloLens could be used, but at present the tablet approach is the most practical.

• Communications environment (wireless gear):
  Real-time exchange of RTK corrections is essential. You may link the base and rover directly via radio, or connect through the mobile network to an internet-based correction-data service. In areas with no cellular coverage—such as mountain regions—consider simple radios or setting up a local base station. A mobile data connection is also necessary if inspection data will be stored and shared in the cloud.

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As for equipment costs, prices have dropped considerably compared with the large, specialized instruments of the past. A standard RTK-enabled GNSS receiver now runs from a few hundred thousand yen up to roughly one million yen, and rental or lease options are available. Off-the-shelf tablets can substitute for dedicated field units. While you will incur some system-development expenses—such as creating the AR app and data-integration modules—once the platform is in place it can be reused on additional bridges, making the return on investment highly attractive.

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Utilizing Survey Data and Integrating It into Bridge-Management Systems

When an RTK × AR inspection workflow is adopted, it is essential to put the resulting positioning data and inspection findings to full use by integrating them into the existing bridge-management system. Damage locations and photographs—captured with centimeter-level coordinates—should be imported into the bridge inventory or maintenance database. This not only makes it easy to compare conditions with previous inspections, but also allows engineers to analyze deterioration trends across many structures.

Many municipalities and expressway operators already run digital ledger systems for bridge management. In such cases, be sure that data collected with RTK × AR can be exported in formats compatible with those platforms—for example, CAD drawings or GIS layers with coordinates and inspection-history tables. The Ministry of Land, Infrastructure, Transport and Tourism is promoting the use of inspection-support technologies, and standards for data exchange are steadily being established. Ensuring that field data flow into a centralized infrastructure database prevents information silos and turns each record into a long-term asset for infrastructure management.

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Precautions for Introducing RTK
Finally, here is a summary of key points and considerations when deploying RTK in bridge-inspection work.

• Securing a Suitable GNSS Environment
  RTK accuracy depends heavily on GNSS reception conditions around a bridge. In settings such as underpasses, mountain valleys, or urban canyons where the sky view is restricted, centimeter-level precision may be hard to achieve even with corrections. Where necessary, place a base station closer to the structure or supplement satellite positioning with an inertial measurement unit. A receiver that supports Japan’s Quasi-Zenith Satellite System (QZSS “Michibiki”) also helps maintain accuracy in confined sky-view environments.

• Handling and Calibrating the Equipment
  An RTK GNSS receiver is a precision instrument. Any shift or tilt of the antenna introduces error. A fixed unit should sit on a stable tripod; a handheld rover should be kept plumb with the pole’s bubble level. Newer models offer tilt compensation, but regular calibration and accuracy checks remain essential.

• Power and Communications Back-ups
  Lengthy inspection shifts can drain the batteries of receivers, tablets, and radios. Carry spares and set up in-vehicle charging if possible. Survey cellular coverage in advance; if reception is spotty—typical in mountains—be ready to switch to a local RTK link via short-range radio.

• Training and Operating Rules
  Introducing new technology demands proper training. Provide manuals on RTK/AR operation, how to combine them with traditional visual inspection, and how to interpret the data, then share them across the team. Final evaluations still rest with certified inspectors, so establish procedures that blend professional judgment with digital tools. Remember: these technologies support human decision-making—they do not replace it.

By keeping these points in mind, you can launch an RTK × AR bridge-inspection program smoothly. A sensible approach is to start with a small-scale pilot on a single bridge, verify the results and challenges, and then gradually expand the system to additional structures.

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Introducing LRTK

Finally, let us introduce LRTK, an RTK-positioning product already being adopted in the field.
LRTK, provided by Refixia Inc., is a compact, high-precision GNSS device that pairs with a smartphone or tablet to deliver centimeter-level positioning. Designed specifically to support digital transformation (DX) in civil-engineering applications—including bridge inspections—it offers a form factor that is easy to handle on site.

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Key Features of LRTK and On-Site Adoption Examples

• Compact and Lightweight: The LRTK receiver fits in the palm of your hand and weighs only a few hundred grams. It can be mounted on a survey pole, hard hat, or other equipment without adding noticeable weight, making it easy to handle even during bridge inspections or other work at height. Some models measure just over 10 cm in diameter and weigh about 280 g, so all the gear can be carried in a backpack while you move around the site.

• High-Precision Positioning: The device supports multi-band GNSS reception and works with both network RTK services and CLAS corrections broadcast by Japan’s Quasi-Zenith Satellite System (QZSS). This enables centimeter-level accuracy nationwide—from city centers to remote mountain areas. Field tests consistently show stable positioning within 2–3 cm. Thanks to this precision, LRTK is used not only for bridge inspections but also for machine guidance, as-built checks, drone surveys, and many other applications.

• Instant Connectivity and Ease of Use: LRTK pairs with smartphones or tablets via Bluetooth or Wi-Fi. Through a dedicated app, it receives correction data and logs positions, while the screen displays real-time accuracy and satellite status; a single tap starts positioning. No complicated procedures are required, so technicians without specialized surveying knowledge can master the system after a short training session. The receiver integrates smoothly into existing workflows and can be used flexibly alongside other surveying instruments.