Background of the Academia-Industry Bridge-Inspection Initiative

Across Japan, many bridges erected during the rapid-growth era of the 1960s and ’70s are now surpassing 50 years in service, and the swelling number of aging structures has become a major social issue. Ensuring their safety requires regular inspections and appropriate maintenance.

After several serious accidents—most notably the ceiling-panel collapse in an expressway tunnel—road bridges must now undergo a close-up visual inspection every five years. With hundreds of thousands of bridges nationwide, conducting inspections at that frequency imposes a heavy financial and manpower burden on local governments. Skilled engineers perform the work manually, so both time and cost are high and chronic labor shortages are severe. Additional challenges include the safety risks of working at height, traffic restrictions caused by inspection vehicles, and the fact that conventional methods leave inspection results on paper forms or 2-D drawings, making data sharing and archiving inadequate. These realities have created an urgent need for technological innovation that can make bridge inspections more efficient and sophisticated.

Against this backdrop, joint R&D projects between academia and industry are attracting attention. Universities and research institutes are partnering with construction firms and infrastructure operators to apply cutting-edge technology in the field. Student project teams tackle inspection challenges in university labs, while companies provide job sites and share expertise—an arrangement that advances practical technology development and cultivates talent simultaneously. National policy also supports the adoption of new techniques: in 2019 the Guidelines for Periodic Road-Bridge Inspections were revised, allowing certified engineers to substitute drones and other sensor-based “inspection-support technologies” for close-up visual checks. In short, an environment is emerging in which the innovative technologies born of academia-industry collaboration can be moved into full-scale, real-world use.

 

Bridge Inspection Leveraging RTK Positioning and AR Technology
The combination of RTK positioning and augmented-reality (AR) technology is the key to making bridge inspections faster and more sophisticated. First, what is RTK positioning? RTK—short for Real-Time Kinematic—is a high-precision technique that uses Global Navigation Satellite Systems (GNSS). Whereas stand-alone GPS measurements normally have errors of several metres, RTK applies real-time correction data from a reference (base) station and can shrink those errors to just a few centimetres.

Put simply, RTK delivers a dramatic leap in survey accuracy compared with conventional GPS. In situations where standard GPS would show noticeable position drift, RTK can determine the current location almost perfectly, with virtually no offset. The method works by having both a base station—installed at a point of known coordinates—and a rover unit receive satellite signals simultaneously. The base station computes the positioning errors and transmits these corrections to the rover in real time, allowing the rover’s coordinates to be refined to centimetre-level accuracy.

The base station uses its precisely known coordinates together with the satellite data it receives to calculate the positioning error, then transmits that correction—shown here by the yellow dashed line—to the rover. Once the rover applies the correction, a stand-alone GPS error of several metres is reduced to just a few centimetres or less. Thanks to RTK, bridge-inspection crews can therefore pinpoint locations with millimetre- to centimetre-level accuracy and log their inspection findings with exact coordinates.

So why is RTK indispensable for bridge inspections? A key reason is the need to pinpoint inspection data with high precision. Traditional, visually based records capture only rough locations—e.g., “a crack located X metres from section Y of the bridge.” By using RTK, inspectors can log cracks, spalls and other damage at exact map coordinates, making it easy to relocate the same spot during the next inspection or to plan targeted repair work. RTK’s centimetre-level accuracy is also valuable for measuring structural displacements—such as settlement or tilt—allowing gradual changes to be quantified over time.

Moreover, RTK shows its full potential when paired with augmented-reality (AR) technology. AR lets a tablet or smart-glasses overlay digital information directly onto the live view of a structure, but ordinary GPS lacks the accuracy to keep those overlays aligned with the real object—they drift and become unusable. RTK’s centimetre-level positioning solves this problem. By combining RTK with AR during bridge inspections, data that once had to be checked on paper drawings or logbooks can now be projected precisely onto the structure itself on site.

For instance, deterioration areas identified in past design drawings or inspection logs can be projected onto the actual bridge via AR, allowing inspectors to pinpoint sections that need repair intuitively. By simply holding up a tablet, the inspector sees real-time video of the bridge with crack history and internal-structure diagrams overlaid, making it far easier to track aging trends and avoid overlooking damaged spots. The high-precision inspection data gathered on site can also be uploaded to the cloud immediately, enabling remote experts to provide guidance and feedback through the same AR view—streamlining the inspection process and raising its technical level.

In this way, integrating RTK positioning with AR technology has the potential to dramatically boost both the accuracy and efficiency of bridge inspections. University-industry student projects are already working on inspection methods that leverage this cutting-edge combination. In the next section, we will look at concrete case studies of how it is being put into practice.

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[Case Study] Successful Bridge Inspection through University-Industry Collaboration
Here are three projects in which university student teams partnered with private-sector companies to apply RTK and AR technologies to bridge inspections. In each case, the collaborators conducted on-site pilot tests to verify the approach in the field.

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Case 1: Inspecting an Aging Bridge with RTK + AR

At the request of a local municipality, a university student project team teamed up with a construction firm to inspect a 50-year-old bridge. Equipped with an RTK-GNSS receiver and a tablet, the students walked the structure and carried out the inspection. Through the tablet’s camera, live images of the bridge were overlaid with past inspection records and design drawings in AR. Thanks to centimeter-level positioning from RTK, crack maps and other defect layers lined up precisely with the actual bridge, letting the team spot new or worsening damage at a glance. For example, a crack that had been 10 cm long at the previous inspection was now 30 cm—a difference they could confirm instantly and use to judge whether emergency repairs were necessary. As a result, the inspection was completed in 30 percent less time than the conventional method, with zero missed anomalies. The students gained hands-on experience with cutting-edge technology, while the company demonstrated the effectiveness of a more efficient inspection workflow.

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Case 2: Digitalizing Bridge Asset Management through Student–Industry Collaboration

At another university, a team of civil-engineering students joined an internship project to develop a bridge-maintenance management system. Working with a small construction company that oversees several bridges, the goal was to digitize inspection data and consolidate it in a single platform. The students built detailed 3-D models (digital twins) of the structures, combining centimeter-level RTK-GNSS coordinates with drone imagery and LiDAR scans to create a comprehensive digital record of each bridge.

They also built a system that overlays inspection results on the 3-D model in augmented reality, allowing inspectors to compare the digital twin with the physical bridge side-by-side on a tablet. During the field trial, student interns and company engineers formed mixed teams, inspected the bridge, and plotted each defect directly onto a digital map in real time. Information that had previously been handwritten on paper checklists was now captured automatically as electronic data and pushed straight to a cloud-based bridge-management platform. This slashed the time needed to compile reports and let supervisors in remote offices monitor inspection progress instantly. The students’ fresh ideas and IT skills sparked a true digital-transformation wave in the company’s bridge-inspection workflow.

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Case ③: Building Data-Driven Infrastructure Management

The third case shows how a project turned accumulated inspection data into a preventive-maintenance program. A university research lab partnered with an expressway company and spent several years collecting and analyzing bridge-inspection data at RTK accuracy. Each year students surveyed and inspected the same bridge with RTK-enabled devices, recording minute changes in crack length and component displacement. They then fed this big data into AI and statistical models to predict deterioration trends and assess risk levels.
For example, the system detected a slight but steady increase in the tilt of one pier and projected how many years remained before reinforcement would be required. Thanks to these forecasts, maintenance teams shifted from reactive repairs to data-driven preventive action, advancing rehabilitation schedules and addressing problems before serious damage occurred. Objective, data-backed insights also helped managers rank repair priorities within limited budgets. The students published papers and presented their findings at conferences, delivering results that benefited both academia and industry.

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These case studies show that deploying RTK and AR goes far beyond simple efficiency gains—it can fundamentally change the way we maintain infrastructure. They also highlight how academia-industry collaborations allow the next generation of engineers to hone cutting-edge technologies on real sites while actively contributing to infrastructure preservation.

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How to Introduce RTK-Based Bridge Inspections

What concrete preparations are required to implement an innovative RTK × AR bridge-inspection workflow? Below you’ll find an outline of the essential equipment, systems, and key considerations for a smooth rollout.

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Required Equipment and Costs

To carry out bridge inspections with RTK, you will need the following items:

• RTK-GNSS receiver (rover) – Procure a GNSS receiver capable of centimetre-level positioning. It can be used in tandem with an on-site fixed base station and a rover carried by the inspector, or—by receiving correction data over existing communications infrastructure—via a network-RTK service such as VRS. Compact, lightweight, and affordable receivers have appeared in recent years, so initial costs can start at only a few hundred-thousand yen. If you subscribe to a CORS network (e.g., the Geospatial Information Authority of Japan’s GEONET or a private commercial service), you can operate with just the rover and dispense with your own base station.

• AR display device – You’ll need hardware capable of presenting augmented-reality overlays on-site. In practice this is usually a tablet or large smartphone running a dedicated AR application. A rugged, dust- and water-resistant tablet is preferable for fieldwork. Hands-free options such as HoloLens or other AR glasses may become practical in the future, but for now a tablet-based setup is the most realistic choice.

• Communications (wireless equipment) – A data link is essential for sending and receiving RTK correction information in real time. You can connect the base station and rover directly via radio, or you can rely on a cellular network to reach an internet-based correction-data service. In areas with no cell coverage—mountainous sites, for example—you may need a simple two-way radio system or a locally installed base station. A mobile data connection is also required if inspection data will be saved to, and shared from, the cloud.

 

Equipment costs are now considerably lower than those of the bulky surveying instruments used in the past. A typical RTK-capable GNSS receiver runs from several hundred thousand yen up to about one million yen (roughly a few to ten thousand U.S. dollars), and both rental and lease options are available. Off-the-shelf tablets can substitute for dedicated field controllers. Although you may incur system-development expenses—for the AR application or data-integration modules, for instance—those are one-time costs; once the system is built, it can be deployed on other bridges as well, so the return on investment is expected to be favorable.

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Leveraging Survey Data and Integrating It into Bridge-Management Systems

When you introduce an RTK × AR inspection workflow, it is essential to make full use of the positioning data and inspection results and merge them with your existing bridge-management platform. Damage records and photographs—saved with centimeter-level coordinates—should be imported into the bridge ledger or asset-management database and stored there. This not only makes it easy to compare new findings with previous data during the next inspection, but also lets you examine deterioration trends across multiple bridges from a single, comprehensive viewpoint.

Municipal governments and expressway operators may already be using digital ledger systems for bridge management. In those cases, be sure the data captured with the RTK × AR workflow can be converted or exported into formats compatible with the existing platform—for example, CAD drawings with coordinates, GIS layers, or inspection-history tables. Fortunately, Japan’s Ministry of Land, Infrastructure and Transport is actively promoting inspection-support technologies, and standards and exchange formats for such data are steadily being developed. Ensuring that field-collected information is not isolated but stored in a centralized infrastructure database turns it into an “asset” that supports long-term infrastructure management.

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Cautions When Introducing RTK

Finally, here are some key points and precautions to keep in mind when adopting RTK for bridge inspections.

• Securing a Suitable GNSS Environment
  RTK accuracy is heavily influenced by the satellite-view conditions around a bridge. In locations where a clear sky view is limited—such as beneath viaducts, in mountain valleys, or in urban canyons between tall buildings—high precision may be difficult to achieve even with correction data. If necessary, place a base station closer to the structure or combine the GNSS receiver with an inertial measurement unit (IMU) to assist positioning. Using a receiver that supports Japan’s Quasi-Zenith Satellite System (Michibiki/QZSS) is also advantageous, as it helps maintain accuracy in areas with a restricted sky view.

• Handling and Calibration of Equipment
  Because an RTK-GNSS receiver is a high-precision instrument, it must be handled with care in the field. Any shift or tilt of the antenna introduces error, so a fixed unit should be mounted on a stable tripod, while a portable unit should be kept perfectly vertical using the bubble level when it is attached to the top of a survey pole. Many newer models include tilt-compensation, allowing small lean angles to be auto-corrected, but regular calibration and accuracy checks are still essential.

• Power and Communication Back-ups
  During extended inspection work, keep a close eye on battery life for the GNSS receiver, tablet, and communication devices. Carry spare batteries and arrange ways to recharge equipment from a vehicle or other power source. For communications, survey radio-signal conditions in advance—especially in mountainous areas—and be ready to switch to a local RTK link (short-range radio) if the cellular connection proves unreliable.

• Personnel Training and Operating Protocols
  When introducing new technology, thorough training for field technicians is essential. Develop manuals that cover not only the operation of RTK and AR systems, but also how to combine them with conventional visual inspections and interpret the resulting data, and share these materials within the team. Because the final assessment of inspection results must rest with certified inspectors, it is also important to establish operating rules that blend their professional experience with digital tools. Remember that new technologies are support instruments—they are not intended to replace human judgment.

By keeping the above considerations in mind, you should be able to launch RTK-plus-AR bridge inspections smoothly. Start with a pilot on a small bridge, evaluate the outcomes and challenges, and then broaden the deployment step by step.

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Introducing LRTK
Finally, let us present LRTK, an RTK-based positioning system that is already being adopted on job-sites. LRTK is a compact, high-precision GNSS device from Refixia Inc. that pairs with a smartphone or tablet to deliver centimeter-level positioning accuracy.
Developed to drive digital transformation (DX) in civil-engineering fields—including bridge inspections—it is designed for effortless use right at the worksite.

Key Features of LRTK and On-site Use Cases

• Compact & lightweight – The LRTK receiver fits in the palm of your hand and weighs only a few hundred grams. Because it adds almost no load when mounted on a survey pole, hardhat, or other gear, it is easy to maneuver even during elevated bridge-inspection work. Some models measure just over 10 cm in diameter and about 280 g, so the entire kit can be carried in a backpack while you move freely around the site.

• High-precision positioning – The receiver handles multi-band GNSS signals and is compatible with both network-based RTK services and the CLAS corrections broadcast by Japan’s QZSS (Michibiki). As a result, centimetre-level accuracy can be achieved nationwide—from dense urban “canyons” to remote mountain sites. Field trials consistently report stable errors of just 2–3 cm. This accuracy makes the unit valuable not only for bridge inspections but also for machine guidance, as-built/grade-control surveys, drone mapping, and many other construction and surveying tasks.

• Instant connectivity & ease of use – LRTK pairs with a smartphone or tablet via Bluetooth or Wi-Fi. Through the dedicated app you can stream correction data, log positions, and view real-time metrics such as current accuracy and satellite status—all on the phone’s screen. One-tap start-up replaces complicated workflows, so even technicians with no surveying background can master the device after a short briefing. The user-friendly design drops smoothly into existing field processes and integrates flexibly alongside other surveying instruments.

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One real-world deployment example comes from a highway bridge-pier reinforcement project, where LRTK was put to excellent use.Using LRTK, the site supervisor projected the mounting points for the reinforcement members in augmented reality and verified each one, allowing the installation work to proceed with millimeter-level accuracy. During periodic inspections of a railway viaduct, the inspection team worked with an LRTK-equipped tablet that overlaid a crack map of the bridge piers in real time, achieving zero overlooked defects. These cases highlight how LRTK delivers both greater efficiency and higher precision on site.