Introduction

Non-destructive testing plays a vital role in supporting public safety and quality by detecting internal defects and deterioration without damaging the inspected object. As social infrastructure such as bridges and tunnels age, regular non-destructive inspections and appropriate maintenance are indispensable. In manufacturing, too, non-destructive testing is widely used for product quality assurance and equipment maintenance.

In practice, with vast infrastructure assets nationwide, inspection needs are expected to grow further—for example, close visual inspections of bridges and tunnels have recently become statutory tasks. To inspect and maintain efficiently with limited personnel, improving workflows through the use of digital technologies is indispensable.

However, there have long been several challenges in the recording and management of inspection results from non-destructive testing. Typical examples include:

• Knowledge silos: Recording and interpreting inspection data tends to depend on the experience and intuition of specific personnel, making information sharing and handover within and between departments difficult.

• Difficulty identifying photo locations: Even when inspection photos are taken, it is often hard to determine later which part of the structure was photographed. On site, operators may number photos sequentially and record locations in separate notes, but this is cumbersome and prone to mistakes.

• Difficulty comparing inspection histories: Managing records in paper ledgers or separate files makes it hard to compare past and new inspection results to track deterioration. Because data are dispersed, analyzing long-term trends requires extra effort.

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

What are coordinate-tagged photos, and how do they differ from traditional inspection records?

“Coordinate-tagged photos” are inspection records in which coordinate information for the photograph’s location (latitude/longitude and elevation, or positional coordinates within a structure) is appended to the image data. Each photo is linked with objective positional data indicating “where it was taken,” distinguishing it from the vague location records typical of traditional paper ledgers or photo albums.

Traditionally, inspectors marked inspection points by hand on paper drawings or numbered photos and recorded locations on separate sheets, manually linking spatial information to photos. While GPS-equipped cameras can record latitude and longitude, typical GPS accuracy has errors on the order of meters, which is insufficient to pinpoint small damaged areas. As a result, problems arose such as “the location written in the report doesn’t match the actual site, causing confusion on site” or “the photo alone doesn’t allow identification of the damage location.”

By contrast, coordinate-tagged photos record accurate position coordinates at the time of capture, dramatically improving recording accuracy and usability. For example, a report that states “a crack at the base of pier A2 of XX bridge” remains ambiguous in text alone, but if numerical coordinates are included, anyone can identify the exact location using a common reference. When each inspection photo is accurately tagged with its location, later review of photos makes it immediately clear “which point was photographed.”

The main benefits of coordinate-tagged photos are summarized as follows:

• Objective and stable location identification: With numerical coordinates attached to photos, spatial ambiguity in reports is eliminated. Without relying on text or memory, anyone can correctly point to the same location, preventing communication loss and misunderstandings.

• Improved traceability of inspection history: If damage locations or measurement points are recorded with coordinate “tags,” the exact same spot can be re-examined in subsequent inspections and deterioration quantitatively compared. Overlaying time-series changes on maps or drawings makes it easy to visualize damage distribution and analyze trends.

• Efficiency of recording and prevention of human error: When location information is recorded automatically at the time of photographing, workers need not take handwritten notes or later annotate photos. This prevents transcription errors and misread notes, improving recording accuracy and operational efficiency both on site and in the office.

• Ease of digital integration: Numeric coordinate data can be readily linked to electronic maps, CAD drawings, GIS, and bridge management ledger systems. It becomes simple to plot photo locations on a map or register images into existing asset databases with location information, facilitating interdepartmental information sharing and integrated data management.

Precision inspection examples combining non-destructive testing methods with coordinate-tagged photos

The advantages of coordinate-tagged photos are realized across the field application of various non-destructive testing methods. Adding a precise positional information layer to traditional inspection techniques dramatically raises the resolution and reliability of inspection results. Below are representative examples of combining coordinate-tagged photos with common non-destructive testing methods.

• Visual inspection: Close-range and remote visual inspections, which form the basis of infrastructure inspection for bridges, tunnels, and the like, generate numerous photos. Attaching coordinates to these photos allows precise identification of shooting locations on maps and drawings, smoothing later reporting and repair planning. For example, if a crack on a bridge pier is photographed and recorded with coordinates, the same spot can be found easily at the next inspection and rechecked efficiently after repairs. The strength of coordinate-tagged photos is that they raise the fundamental accuracy of inspections by ensuring that abnormal locations are reliably identified and shared.

• Ultrasonic testing (UT): Ultrasonic testing, used to detect voids in concrete, cracks in steel, or thickness reduction in plant piping, also benefits from the addition of coordinates. Traditionally, inspectors marked the tested location or recorded approximate positions on drawings. Managing ultrasonic test photos and measurements with high-precision coordinate tags allows long-term, accurate tracking of “which location had which measured value.” For example, when conducting annual ultrasonic thickness measurements at multiple points on a storage tank or bridge girder, registering coordinates for each measurement point makes year-to-year quantitative evaluation of corrosion progression straightforward. Visualizing locations where thickness reduction exceeds thresholds aids integrity assessment and repair planning.

• Infrared thermography: Surface temperature distribution measurements using infrared cameras are widely used for investigating concrete delamination or moisture ingress and detecting abnormal heating in electrical equipment. Associating thermographic images with coordinates allows precise mapping of observed temperature anomalies onto the actual structure. For instance, when extracting deteriorated areas of tunnel lining concrete via infrared imaging, recording positional coordinates for detected anomalies enables reliable and efficient identification of repair areas and condition mapping. Conducting thermographic surveys at different times and comparing temperature distribution changes at the same coordinates makes time-series monitoring straightforward.

• Other non-destructive testing: Inspection data obtained by X-ray imaging of welds, rebar detection radar for investigating concrete interiors, magnetic particle testing, eddy current testing for surface crack detection, and other methods all gain value when managed together with coordinates of the corresponding measurement locations. Linking inspection results to geographic positions makes it possible to cross-reference them later with other test results (for example, results from other methods or past data) for comprehensive evaluation. Integrating multiple NDT datasets on a map to overview the structure’s overall condition opens the way to building digital inspection ledgers. In such integrated ledgers, results from multiple methods can be cross-referenced along spatial axes, significantly 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 obtain position information with the highest possible accuracy. Built-in GPS cameras and smartphones have positioning errors on the order of meters, which is inadequate for detailed records. Enter LRTK (network-enabled RTK positioning). LRTK brings the RTK (Real Time Kinematic) method—which applies corrections to GNSS satellite positioning—to smartphones in a convenient way, enabling centimeter-level positioning in the field by technical staff themselves, a capability that previously required specialized equipment.

Using LRTK devices, position can be measured with centimeter accuracy at each photograph and automatically attached to the photo data. In addition, by linking with the device’s electronic compass and attitude sensors, the shooting azimuth and angle can also be recorded. This enables inspection records with far more precise, multidimensional information than before. For example, shooting conditions such as “photographed the lower part of the pier from the northeast” can be digitized, so that when reviewing the photo later it is clear “from which direction it was viewed.”

LRTK-based workflows also assume that field-acquired data will be uploaded to the cloud immediately and shared among stakeholders. Via mobile networks, photos and coordinate data accumulate in a cloud-based project database at the moment of capture, eliminating the need to organize photos or manually transcribe ledgers back at the office. This enables real-time information sharing and reduces effort in report preparation. Especially after disasters, rapid sharing of coordinate-tagged photos from the field to headquarters to create damage maps enables swift response.

The accumulated precise positional data also powerfully support time-series change analysis. If historical inspection records are stored in the cloud with coordinates, you can check a site’s “previous comparison” with one click or visualize long-term changes on a map. For example, plotting and graphing crack lengths or corrosion progression annually becomes easy, aiding trend analysis for predictive maintenance.

Furthermore, LRTK’s high-precision positioning opens the door to integration with AR (augmented reality). AR—displaying digital information over the real world when viewing a site through a smart device’s camera—is gaining attention in inspection work. Centimeter-level positioning from LRTK makes it possible to overlay markers and annotations based on drawing coordinates onto real structures with minimal error. For example, visualizing past recorded damage locations on-site via AR helps inspectors quickly find issues without overlooking them. It is also possible to overlay the routes of buried utilities or 3D design models (BIM/CIM data) onto the field to visualize hidden risk locations or verify construction quality. Combining LRTK and AR will dramatically increase the amount of information available at inspection sites and enhance intuitive understanding.

Additionally, one-person surveying using LRTK is becoming realistic. With a compact high-precision GNSS receiver and a smartphone app, inspection staff can conduct simple surveying without calling in a specialized survey team. For example, by measuring several reference points around a structure, photos recorded during inspections can be saved in the same coordinate system as the design drawings. Combining with a smartphone’s built-in LiDAR (Light Detection and Ranging) scanner, one can also perform a quick 3D scan of a wide area while walking to obtain a detailed point cloud model of the inspection target. If the acquired point cloud data include coordinates, they can be used for quantitative deformation assessment or verification of as-built conditions. In this way, LRTK can serve as a platform hub for various digital technologies in field DX.

Future image of inspection work leading to centralized data management and predictive maintenance, and ripple effects on training, knowledge transfer, and labor-saving

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

• Centralized data management and digital twinning: Centralizing inspection data with coordinates enables the construction of per-structure “digital ledgers” and “digital twins” (virtual replicas). A database that integrates photos, drawings, and test results with spatial information becomes a platform for sharing up-to-date information across departments. Insights that were overlooked in paper reports or personal PC files become searchable and extractable in a database. In the future, AI could analyze integrated data to automatically extract deterioration patterns or suggest repair priorities.

• Promotion of predictive maintenance: If inspection records are comprehensively accumulated in time series, organizations can step into “predictive maintenance” that detects early signs of anomalies to prevent failures and accidents. Analyzing historical to current data to detect subtle changes or acceleration in deterioration allows scheduling repairs or part replacements at appropriate times between regular inspections. This is a step beyond periodic maintenance and directly contributes to reduced equipment downtime and lower accident risk. Coordinate-tagged photos retain spatial bias in data, strengthening trend analysis about “which parts tend to deteriorate and how.”

• Contribution to skills transfer and human resource development: Digital inspection records provide a foundation for capturing veteran technicians’ knowledge within an organization and passing it to the next generation. When past inspection photos and findings are stored with coordinates, even less-experienced technicians can quickly locate the same onsite spots and check for previously found anomalies without missing them. Relying less on personal “intuition and experience” and more on unified information improves the quality of OJT (on-the-job training) and technical education. New staff can also study past failure trends and countermeasures autonomously by reviewing accumulated data. Field DX thus offers significant value for training and skill transfer.

• Labor-saving, efficiency gains, and work-style reform: Introducing digital technologies in inspection work directly raises on-site productivity. Using coordinate-tagged photos and the cloud for recording greatly reduces paper reporting and double data entry. Time spent on report preparation and ledger management can be redirected to other tasks, allowing limited resources to cover more assets amid labor shortages and reducing maintenance costs. AR-assisted inspections and wider use of one-person surveying will increase instances where tasks previously requiring multiple personnel can be handled by fewer people. Together with replacing risky entries by drones or remotely operated robots, these trends will improve inspector safety and support work-style reforms.

Conclusion

Incorporating coordinate-tagged photos into non-destructive testing on site dramatically increases the precision and usability of inspection records. Advanced solutions such as centralized data management, sophisticated analysis, and AR support are effective only when grounded on high-precision location information. Fortunately, RTK-capable receivers and positioning services have become more available in recent years, and centimeter-level positioning—once the domain of specialists—can now be handled easily in the field. Rather than shying away from these technologies as “too difficult,” why not start by adding coordinate information to everyday inspection photos? Combining simple GNSS surveying as needed makes it possible to accurately determine photo 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 efforts. Leverage accumulated precise data to carry out planned maintenance and realize safe, efficient infrastructure operation. Now is the time to adopt coordinate-tagged photos as a new tool and advance non-destructive testing practices to the next stage.