Introduction

Nondestructive testing plays a crucial role in supporting societal safety and quality by detecting internal defects and deterioration without damaging the target object. As infrastructure such as bridges and tunnels ages, regular nondestructive inspections and appropriate maintenance are indispensable. Nondestructive testing is also widely used in manufacturing for product quality assurance and equipment maintenance.

In fact, with a vast stock of infrastructure assets nationwide, inspection needs are expected to grow further—recently, close visual inspections of bridges and tunnels have even become statutory duties. To carry out inspections and maintenance efficiently with limited personnel, business improvements through the use of digital technologies are essential.

However, there have long been several challenges in the recording and management of inspection results from nondestructive testing. Major examples include the following:

• Information dependence on individuals: Recording and interpreting inspection data tend to rely on the experience and intuition of specific personnel, making information sharing and handover within and across departments difficult.

• Difficulty in locating photos: Even when reviewing inspection photos later, it is often hard to determine which part of the structure was photographed. In the field, operators may number photos sequentially and record the shooting locations in separate notes, but this process is cumbersome and error-prone.

• Difficulty comparing inspection histories: When managed in paper ledgers or separate files, it is hard to match past inspection results with new ones to track the progression of deterioration. Because data are dispersed, analyzing trends over time also requires extra effort.

To address these issues, the recent adoption of various digital technologies at inspection sites has accelerated. Drone photography, 3D measurement with laser scanners, inspection robots, AI image analysis, and AR (augmented reality) for field support are among the approaches being explored as part of the DX (digital transformation) of infrastructure inspection. One particularly notable initiative is precise inspection recording using “coordinate-tagged photos.” This article explains what coordinate-tagged photos are, their advantages, practical examples combining them with nondestructive testing, the latest implementation methods, and future prospects.

What coordinate-tagged photos are, and how they differ from conventional inspection records

“Coordinate-tagged photos” are inspection records in which photographed image data are augmented with coordinate information of the shooting location (such as latitude/longitude and elevation, or position coordinates within a structure). The distinguishing feature is that each photo is linked to objective positional data indicating “where it was taken,” which stands in clear contrast to the vague positional records of traditional paper ledgers or photo albums.

Traditionally, inspectors would hand-mark inspection points on paper drawings or number photos and note shooting locations on separate sheets to manually link spatial information to images. Although cameras with GPS functions can record latitude and longitude in photos, typical GPS accuracy has errors on the order of several meters (several ft), which is not sufficient to pinpoint small damage locations. As a result, problems have arisen such as “the location described in the report differs from the actual site, causing confusion in the field,” or “even looking at a photo, the damaged location cannot be identified.”

By contrast, coordinate-tagged photos allow precise positional coordinates to be stored as data at the time of shooting, greatly improving both recording accuracy and practical utility. For example, a report that merely states “a crack at the base of pier A2 of XX bridge” remains ambiguous, but if numerical coordinates are appended, anyone can identify the exact location using a common reference. If each inspection photo is tagged with an accurate position, it becomes immediately obvious “which point was photographed” when reviewing photos later.

The main benefits provided by coordinate-tagged photos can be summarized as follows:

• Objective, unambiguous location identification: Attaching numerical coordinates to photos eliminates spatial ambiguity in reports. Without relying on written descriptions or memory, anyone can point to the same location accurately, preventing communication loss and misunderstandings.

• Improved traceability of inspection history: If damaged spots or measurement points are recorded with coordinates as “tags,” the exact same location can be re-examined in subsequent inspections, enabling quantitative comparison of deterioration. Visualizing chronological changes on maps or drawings makes it easy to analyze damage distribution and trends.

• Efficiency in recording and prevention of human error: When location information is recorded automatically at the time of photography, workers are spared the trouble of taking handwritten notes or writing locations on photos later. Misrecording due to number transcription errors or illegible notes is avoided, improving recording accuracy and work efficiency both in the field and the office.

• Ease of digital integration: Numerical coordinate data can be linked directly to digital maps, CAD drawings, GIS (geographic information systems), or bridge management ledger systems. Plotting photo locations on maps or registering photos with position information in existing structural databases becomes simple, facilitating interdepartmental information sharing and integrated data management.

Precision inspection cases combining nondestructive testing methods and coordinate-tagged photos

The advantages of coordinate-tagged photos are evident across field applications of all nondestructive testing methods. Adding precise positional information as a layer to conventional inspection techniques dramatically increases the resolution and reliability of inspection results. Here are representative examples of combining coordinate-tagged photos with nondestructive testing methods.

• Visual inspection: Close visual and remote visual inspections, which are the basis of infrastructure inspections for bridges and tunnels, generate many photographic records. If these photos are tagged with coordinates, the shooting locations can be accurately identified on maps or drawings, making subsequent reporting and repair planning smoother. For example, if a crack on a bridge pier is photographed and recorded with coordinates, the same location can be easily found at the next inspection and post-repair re-inspection for re-deterioration checks can be conducted efficiently. The core accuracy of inspections—reliably identifying and sharing abnormal locations—can be elevated by coordinate-tagged photos.

• Ultrasonic testing (UT): Ultrasonic testing, used to detect voids inside concrete, cracks in metal, or wall-thinning in plant piping, also benefits from combination with coordinates. Traditionally, inspectors would mark tested locations or record approximate positions on drawings. By managing ultrasonic test photos and measurements with high-precision coordinate tags, “which location was measured with which value” can be tracked accurately over the long term. For example, when performing annual ultrasonic thickness measurements at multiple points on storage tanks or bridge girders, registering the coordinates of each measurement point makes it easy to quantitatively evaluate corrosion progression year by year. Locations where thickness decreases exceed thresholds can be visualized spatially, aiding health assessments and repair planning.

• Infrared thermography: Surface temperature distribution measurement with infrared cameras is widely used for investigating delamination or moisture ingress in concrete structures and detecting abnormal heating in electrical equipment. Associating thermography images with coordinates allows temperature anomalies to be accurately indicated on the actual structure. For instance, when detecting deteriorated areas by infrared imaging of tunnel lining concrete, recording the coordinates of detected anomalies ensures reliable and efficient identification of repair sites and health mapping. Performing thermographic surveys again after a time interval and comparing temperature distributions at the same coordinates enables straightforward time-series monitoring.

• Other nondestructive testing methods: Inspection data obtained by various methods—X-ray imaging for internal defects in welds, rebar detection radar for investigating concrete interiors, magnetic particle inspection or eddy current testing for surface crack detection, and so on—gain increased value when managed together with coordinates of the respective measurement sites. Linking inspection results to geographic positions makes it possible to cross-reference them with other results (e.g., results from different methods or past results) for comprehensive evaluation. Integrating multiple nondestructive testing datasets on a map-based platform and building a digital inspection ledger that provides an overview of structural health becomes feasible. Such integrated ledgers enable spatial cross-checking of results from multiple methods, further improving inspection coverage and accuracy.

High-precision coordinate and orientation recording with LRTK, plus cloud sharing, time-series analysis, and AR display

To fully realize the value of coordinate-tagged photos, it is important to acquire positional information with the highest possible accuracy. GPS-equipped cameras and smartphones have historically had positioning errors on the order of meters, which is insufficient for detailed records. Enter LRTK (networked RTK positioning). LRTK is a modern technology that makes the RTK (Real Time Kinematic) method—which applies corrections to GNSS satellite positioning data—conveniently usable on smartphones, allowing field technicians themselves to perform centimeter-class positioning that formerly required specialized equipment.

Using an LRTK device, the position at each photo capture can be measured with centimeter-level accuracy (cm level accuracy (half-inch accuracy)) and automatically attached to the photo data. In addition, by linking with the device’s electronic compass and attitude sensors, orientation and camera angle at the time of shooting can be recorded. This enables inspection records with more precise and multidimensional information than before. For example, because shooting conditions such as “photographed the underside of the pier from the northeast” are datafied, it becomes clear when viewing the photo later “from which direction it was seen.”

Moreover, LRTK-based workflows assume that data obtained in the field are uploaded to the cloud immediately and shared among stakeholders. Through mobile networks, photos and coordinate data are accumulated in a cloud project database at the time of shooting, eliminating the need to organize photos back at the office or manually transcribe them into ledgers. This enables real-time information sharing and reduced effort in report preparation. Especially in post-disaster damage surveys, it becomes possible to instantly share coordinate-tagged photos from the field with headquarters and quickly create damage maps.

The precise positional data accumulated in this way also excel for time-series change analysis. If historical inspection records are stored in the cloud with coordinates, one can check a location’s “change since the last inspection” with a click or visualize deterioration over time on a map. For example, plotting annual crack lengths or degrees of corrosion and graphing them becomes easy, aiding predictive maintenance trend analysis.

High-precision position alignment provided by LRTK also opens the door for integration with AR (augmented reality) technology. AR, which overlays digital information onto the real world when viewing the site through a smart device camera, is gaining attention in the inspection field. With centimeter-level positioning from LRTK, markers and annotations based on drawing coordinates can be overlaid on real structures with almost no error. For example, AR visualization of previously recorded damage locations on-site helps inspectors quickly find abnormalities without overlooking them. Other applications include overlaying the routes of underground utilities or design 3D models (BIM/CIM data) on-site to visualize unseen risk areas and perform quality verification. The combination of LRTK and AR is likely to dramatically increase both the amount of information available at inspection sites and intuitive understanding.

Furthermore, single-person surveying using LRTK is becoming realistic. By using a compact, high-precision GNSS receiver and a smartphone app, inspection personnel themselves can perform simple surveying without calling a specialist survey team. For example, by measuring multiple reference points around a structure, photos recorded during inspections can be saved in the same coordinate system as the design drawings. Also, by combining with a smartphone’s built-in LiDAR scanner, inspectors could walk and quickly 3D-scan large areas of structures to acquire detailed point-cloud models of inspection targets. If the acquired point-cloud data include coordinates, they can be used to quantitatively evaluate deformations or verify as-built conditions. In this way, LRTK can serve as a hub for various digital technologies, forming a platform for field DX.

A future inspection workflow leading to centralized data management and predictive maintenance, and spillover effects on education, knowledge transfer, and labor saving

Building a digital inspection record platform that includes coordinate-tagged photos is expected to significantly change how inspection work is carried out in the future. Below are prospects and peripheral effects that could be realized through advanced data utilization.

• Centralized data management and digital twinning: By centrally storing inspection data with coordinates, it becomes possible to build “digital ledgers” or “digital twins” (replicated models in virtual space) for each structure. A database that integrates photos, drawings, and inspection results with spatial information provides a foundation for sharing the latest information across departments. Insights that were overlooked in paper reports or files on personal PCs can be easily searched and retrieved within a database. In the future, AI may analyze such integrated data to automatically extract deterioration patterns or suggest repair priorities.

• Promotion of predictive maintenance: If inspection records are comprehensively stored as time-series data, organizations can move toward predictive maintenance that detects early signs of abnormalities and prevents failures or accidents. By analyzing historical to current data and detecting slight changes or accelerating deterioration, repairs or part replacements can be scheduled at appropriate times between regular inspections. This approach advances beyond conventional periodic maintenance and directly contributes to reducing equipment downtime and accident risks. Because coordinate-tagged photos preserve spatial bias within the data, analyses about “which parts tend to deteriorate and how” become more convincing.

• Contribution to knowledge transfer and human resource development: Digital inspection records provide a foundation for accumulating veteran technicians’ knowledge within the organization and passing it on to the next generation. When past inspection photos and findings are stored with coordinates, even less experienced technicians can quickly locate the same site and check previously discovered anomalies without relying on individual intuition. With everyone able to make judgments based on unified information rather than personal “gut feeling and experience,” the quality of on-the-job training (OJT) and technical education improves. New employees can independently learn from accumulated data about past failure patterns and remediation methods. Field DX therefore brings substantial value in terms of human resource development and skills transfer.

• Labor saving, efficiency improvements, and work-style reform: Introducing digital technologies into inspection work directly boosts field productivity. Coordinate-tagged photos and cloud-based recording greatly reduce double work such as preparing paper reports and manual data entry. Time spent on report creation and ledger organization can be reallocated to other tasks, allowing limited resources to cover more assets and reducing maintenance costs despite labor shortages. The spread of AR-assisted inspections and single-person surveying will also increase opportunities to perform tasks that previously required multiple personnel with fewer people. Together with replacing dangerous site entry by drones or remotely operated robots, these trends enhance inspector safety and support work-style reforms.

Conclusion

Incorporating coordinate-tagged photos into nondestructive testing sites dramatically increases the precision and usability of inspection records. Advanced solutions such as centralized data management, high-level analysis, and AR support depend on a foundation of high-precision location information to be effective. Fortunately, RTK-enabled receivers and positioning services have become more accessible in recent years, making centimeter-level positioning—once left to specialists—practically usable in the field. Rather than shying away from these technologies as “too difficult,” why not start by simply adding coordinates to routine inspection photo records? Combining simple GNSS surveying as needed will allow you to accurately determine shooting locations later and reliably improve the quality of inspection ledgers.

It may be a small first step, but the path to field DX naturally opens from such initiatives. Let us leverage accumulated precise data to advance planned maintenance and realize safe, efficient infrastructure operations. Now is the time to ally with the new tool of coordinate-tagged photos and evolve nondestructive testing practices to the next stage.