LRTK positioning photos streamline infrastructure inspections: Preventing record errors with cm-level accuracy (inch-level accuracy)

Contents

• The current state and challenges of infrastructure inspections

• What positioning photos are

• Centimeter accuracy achieved with LRTK

• How positioning photos improve inspection efficiency

• Expansion to simple surveying with LRTK

• Conclusion

• FAQ

As infrastructure facilities age, regular inspections and accurate records are indispensable for safe maintenance. For bridges and tunnels, the law generally mandates close visual inspections roughly once every 5 years, and there are about 700,000 bridges and more than 10,000 tunnels nationwide. To inspect all of these efficiently with limited personnel, digital technologies are key. One emerging approach gaining attention is the new method called "positioning photos". Positioning photos are photos tagged with high-precision location coordinates, enabling you to record “where and what was photographed” with centimeter-level accuracy. This article provides a detailed explanation of how positioning photos improve infrastructure inspection efficiency, addressing the challenges and solutions as well as the technical background. At the end of the article, we also introduce how this technology can be applied to simple surveying.

The current state and challenges of infrastructure inspections

There are several common challenges in infrastructure inspection work. Traditional methods rely heavily on manual recording, which inevitably leads to mistakes, omissions, and inefficiencies. The main issues can be summarized as follows.

• Ambiguous location records: At inspection sites, it is often difficult later on to determine which part of a structure a photo shows. The common practice is to number photos and write handwritten notes on separate drawings indicating “photo number X was taken at location Y,” but this method relies on human judgment to link spatial location information and photos, which can lead to ambiguity and differences in interpretation.

• Recording and communication errors: Inspection results are often managed in paper ledgers or Excel sheets, relying on handwritten notes and later data整理. This can lead to typos in numbers or misreading of notes, causing incorrect records. In addition, because records often depend heavily on the experience and memory of individual personnel, there is also the problem that handover of information within a department or to the next person in charge is difficult.

• Difficulty comparing and utilizing inspection histories: To track deterioration by comparing past inspection results with the latest results, high-precision data accumulation is required. But in the past, photos and location information were managed separately, so matching “which photo from which year and which location should be compared to now” was time-consuming. Trend analysis of long-term changes or understanding the distribution of damage also tended to become inefficient manual tasks of searching and collecting data.

• Labor shortages and work efficiency: Inspection of infrastructure relies heavily on skilled technicians, while the volume of work is vast. Tasks such as two-person high-altitude work or wide-area visual inspections are time- and labor-intensive and burden the field. To carry out inspections and maintenance efficiently with limited personnel, on-site DX (digital transformation) for labor saving is unavoidable.

In response to these challenges, various digital technologies have begun to be adopted in recent years. Approaches under exploration include drone aerial photography, three-dimensional measurement with laser scanners, use of inspection robots, and automated diagnostics by AI image analysis. Among these, one particularly noteworthy solution is precise inspection recording using “positioning photos.”

What are positioning photos

Positioning photos are photos whose image data are recorded together with high-precision coordinate information for the shooting location (latitude, longitude, and elevation) and camera orientation information (direction and angle). Simply put, this is a method of recording numeric data for “where this photo was taken and which way the camera was pointing” for each photo. Traditional inspection photos could only be supplemented by human memory or written notes regarding the shooting location, but with positioning photos each photo is given an objective “coordinate tag,” dramatically improving the accuracy and reproducibility of records.

With traditional methods, for example, when photographing a crack on a bridge pier you might only write in a report “a crack at the base of pier A2 of XX Bridge.” But text alone often leaves ambiguity in identifying the exact location. Commercial GPS-equipped cameras or smartphones can add location information (geotags) to photos, but typical GPS has errors on the order of several meters (several ft), which is insufficient for pinpointing small damage areas. As a result, problems arose such as “the location written in the report does not match the actual site” or “looking at the photo, it is impossible to identify which part is deteriorated.”

By contrast, with positioning photos the accurate location coordinates are automatically recorded at the time of shooting, eliminating such gaps in spatial information. If numeric coordinates are attached to the photo data, it becomes immediately clear later on “at which point the photo was taken.” For example, if a crack at the base of a bridge pier is recorded with a positioning photo, the photo will retain tag information such as “latitude/longitude: XX, elevation: XX m (XX ft), orientation: northeast.” This removes spatial ambiguity in the report and ensures that anyone can identify the exact same point.

Centimeter accuracy achieved with LRTK

To fully leverage the power of positioning photos, the precision of the location information attached to photos is critically important. Ordinary smartphone GPS typically has errors of about 5–10 m (16.4–32.8 ft), making it unable to provide the centimeter-level location identification required for infrastructure inspections. Enter LRTK, a solution that combines smartphones with RTK technology. LRTK consists of a small GNSS receiver device that attaches to a smartphone and a dedicated app, developed as a revolutionary approach to turn a smartphone into a pocket-sized high-precision surveying instrument.

RTK (Real-Time Kinematic) is a technique that dramatically improves GNSS positioning accuracy by correcting error sources in real time. By exchanging correction information between a fixed base receiver and the mobile smartphone-side device, minute satellite signal errors are canceled out, enabling one’s position to be computed with horizontal accuracy on the order of a few centimeters (a few inches). LRTK makes this RTK method easy to use on smartphones, allowing field technicians themselves to achieve centimeter-class positioning with a phone in hand—something that previously required specialized equipment.

When an LRTK device (a GNSS receiver called an “LRTK Phone”) is attached to a smartphone and the dedicated app is launched, high-precision positioning begins in real time. Position accuracy improves to about ±2–3 cm (±0.8–1.2 in) horizontally (and vertical accuracy of ± several cm (± several in)), matching the accuracy of conventional bench-top surveying instruments while being palm-sized. LRTK also supports multi-frequency satellite signals and network-based correction data, and in Japan can utilize the quasi-zenith satellite “Michibiki” centimeter-level augmentation service (CLAS) for further enhancement. This enables high-precision positioning even in mountainous areas or places with limited communications, and in environments common to infrastructure inspections—such as tunnels or underground pits—relative positioning based on preset reference points can provide usable accuracy.

A notable feature of LRTK is the ability to seamlessly link the precise position data with photo capture. With an LRTK system, the moment you take a photo, the shooting location is measured to centimeter-level accuracy and automatically tagged to the photo file. Moreover, by integrating with the smartphone’s built-in electronic compass and gyro sensors, the orientation and camera angle at the time of shooting can also be recorded. In other words, simply pressing the shutter with LRTK records detailed information about “what was photographed from which direction at which location.” This means information that inspectors previously had to supplement with notes or memory can now be mechanically captured accurately and instantly.

How positioning photos improve inspection efficiency

High-precision positioning photos provided by LRTK bring various benefits to infrastructure inspection sites. Beyond improved recording accuracy, they deliver operational efficiency and prevention of human error, effects that are readily felt in the field. Below we look at how positioning photos concretely transform inspection tasks.

• Objective, unambiguous location identification: With numeric coordinates attached to photos, discrepancies in spatial information in inspection records disappear. You no longer have to rely on textual descriptions or the inspector’s intuition; anyone can identify the same location, preventing communication losses and misunderstandings between departments. For large structures where descriptions like “behind the nth member” are hard to convey, coordinate-tagged photos enable instant sharing of the exact spot.

• Improved traceability of inspection history: If damage locations and measurement points are stored with coordinates as “tags,” it becomes much easier to revisit exactly the same point at the next inspection. LRTK apps often include a “coordinate navigation” function to guide users to previously recorded positions and AR-based orientation guides to reproduce the same framing, so anyone can easily recreate comparative photos over time. This allows quantitative year-by-year tracking of crack width increases or member settlement, enabling early detection and countermeasures.

• Streamlined recording and error prevention: Because location information is recorded automatically at the time of photography, inspectors don’t need to write locations in notebooks or later compile photo ledgers, saving time. The idea is that an electronic ledger is completed with a single-button operation. This prevents number entry errors and omissions, improving efficiency both in the field and during office data整理. For example, before LRTK adoption the typical workflow might have been “take notes on site → organize photos after returning to the office,” but now simply pressing a button on site can organize and save shooting data to the cloud, eliminating unnecessary rework.

• Immediate sharing via cloud integration: LRTK integrates with cloud services, allowing all positioning photos and inspection data captured on site to be uploaded online immediately. Shooting points are plotted on a cloud map, and clicking a photo shows its orientation and details. Not only the on-site staff but also remote managers and partner companies can share information in real time, enabling on-the-spot decisions like “prioritize repair of this location.” Cloud data can also be exported to PDF reports with one click, greatly reducing report preparation time. Data loss risk is reduced, and multiple people can view and collaborate simultaneously, improving the efficiency and reliability of the entire inspection process.

LRTK positioning photos are therefore expected to be a tool that dramatically raises the accuracy and productivity of infrastructure inspections. In practice, in periodic inspections of bridges and tunnels, the ability to accurately locate cracks and abnormalities facilitates smooth formulation of repair plans and progress management. Municipalities managing many assets like road signs and slopes report that cloud sharing of photo data improves coordination among staff, contributing to zero oversight of inspection results and faster response. The data accumulated through positioning photos can become an asset for future AI analysis or digital twin construction, forming a foundation that supports the DX of infrastructure maintenance and management.

Expansion to simple surveying with LRTK

The use of LRTK positioning photos naturally extends beyond infrastructure inspection into the field of simple surveying. A smartphone platform capable of centimeter-level positioning opens up the possibility that on-site staff can perform minor surveying tasks themselves without calling in specialist survey teams.

For example, in construction quality control, measuring distances between important points or checking elevation differences can be done by anyone obtaining accurate coordinates on site and performing calculations with LRTK. Tasks that previously required a total station or level and two operators can in some cases be completed by one person with a smartphone in a short time. LRTK can calculate distances between two surveyed coordinates and compute areas and volumes from position data, making it powerful for simple as-built surveys and quality checks.

LRTK’s simple surveying is also useful in emergency damage assessments where speed and mobility are essential. Without transporting heavy tripods or equipment, surveying can be completed with a pocket-sized device, allowing rapid collection of point data across disaster sites. Results can be shared to the cloud immediately, enabling a remote headquarters to plot data on a map and analyze the extent of damage in real time.

Thus, LRTK’s combination of ease of use and high precision embodies the concept of “simple surveying.” Compared to conventional surveying equipment, initial investment and maintenance costs are reduced, making it easier for small-to-medium sites and municipalities to adopt; it can become a one-person, one-device pocket surveying tool, a first step in on-site DX. Sites suffering from labor shortages or cost constraints stand to benefit greatly from such simple surveying systems. LRTK is already being adopted by construction companies and local governments across regions, and its reliability and effectiveness are being proven.

From infrastructure inspection to surveying and construction management, the transformation of field operations brought by LRTK has begun. By preventing recording errors and improving efficiency through high-precision positioning photos, and by enabling simple surveying that anyone can perform, previously personalized and analog tasks are steadily becoming digital and smart.

Conclusion

The use of LRTK positioning photos in infrastructure inspections is revolutionizing traditional recording methods. By attaching centimeter-level position information to each photo, it has become possible to accurately and objectively convey “where and what is happening.” This reduces missed records and misinterpretation in reporting, dramatically improving the reliability of inspection data.

Because high-precision data can be easily obtained, the efficiency of inspection work itself is also improved. Using coordinate-tagged photos makes it easier to compare past and present states and accurately grasp deterioration trends. Real-time sharing via the cloud allows all stakeholders to share the latest information and rapidly consider countermeasures.

Moreover, LRTK significantly lowers the barrier to “measuring.” The environment in which anyone can perform precise positioning with a smartphone supports everyday simple surveying and on-site verification, addressing challenges such as shortages of specialists and reducing work time.

Improvements in recording accuracy, increased work efficiency, and reduced human error—the effects of LRTK positioning photos are steadily taking infrastructure maintenance and management to the next stage. It is expected that this technology will be adopted in more sites going forward, realizing safer and smarter infrastructure management.

FAQ

Q: What are positioning photos? A: Positioning photos are photos to which high-precision position coordinate data (latitude, longitude, elevation) and camera orientation information are added. By recording not only when but also where and in which direction a photo was taken, you can accurately identify the location indicated by a photo when reviewing it later. In infrastructure inspections, using positioning photos allows inspection points to be managed by objective coordinates, dramatically improving the reliability of records.

Q: Smartphones can add location information to photos—why is LRTK necessary? A: Typical smartphone GPS accuracy is on the order of several meters (several ft), which is convenient for broad location awareness but insufficient to pinpoint precise components. For example, with several meters of error on a bridge deck, you cannot narrow down which bolt is abnormal. LRTK achieves centimeter-level positioning accuracy on a smartphone using RTK technology, allowing precise coordinates to be attached to each photo. This eliminates risks of misidentifying locations due to meter-scale errors and makes inspection photos much more precise records. LRTK also automatically acquires shooting orientation, so you can know “which direction the scene in the photo was facing,” leaving richer information than before.

Q: Is LRTK difficult to operate? Are special skills or qualifications required? A: Operation is very simple, and no special qualifications or advanced knowledge are required. LRTK’s dedicated app has an intuitive interface, and following on-screen instructions is sufficient to perform accurate positioning and photo recording. The app handles complex settings and calculations automatically, so those accustomed to using smartphones can start using it after a short training period. In practice, young technicians and municipal staff can handle it without issue, and even non-experts can record inspection data with consistent accuracy.

Q: What do I need to use LRTK? A: Three main items are required. The first is the LRTK device itself (a high-precision GNSS receiver), which attaches to a smartphone. The second is a compatible smartphone and the dedicated app. Currently, support is mainly for iOS devices such as iPhone and iPad, with Android support planned in the future. The third is access to positioning correction data. RTK positioning requires correction data from a base station, which you can obtain via an Ntrip service over the Internet or, in Japan, by receiving Michibiki’s CLAS signal. But there is no need to overthink it—basically you only need to attach the LRTK device to your smartphone and launch the app to begin recording positioning photos.

Q: Can LRTK positioning photos be used in places where radio or satellite signals are hard to reach, such as inside tunnels or mountainous areas? A: Yes, they can be supported. Real-time positioning is difficult in completely indoor locations where GPS satellite signals cannot reach directly, but LRTK can be used with appropriate measures even in tunnels or underground areas. For example, you can measure a reference point near the tunnel entrance with LRTK before entering, then use a smartphone’s AR-based relative positioning mode to estimate positions while photographing inside the tunnel. Also, because LRTK supports Japan’s Michibiki CLAS, high-precision positioning is possible from satellite augmentation in mountainous areas without mobile network coverage. By switching positioning modes according to site conditions, you can maintain as much accuracy as possible even in poor radio environments.