First Public Case Example! An As-Built Inspection Project That Succeeded by Introducing AR Inspection

Table of Contents

• Introduction

• What is AR inspection?

• Issues with conventional as-built inspections

• Overview of the AR inspection introduction project

• How AR inspection was conducted

• Effects of introducing AR inspection

• Ministry of Land, Infrastructure, Transport and Tourism trends and the future of AR inspection

• Conclusion

• FAQ

Introduction

In recent years, the construction industry has been swept by waves of ICT and DX (digital transformation), and methods for construction management and inspection are also undergoing significant changes. However, on-site reality is that as-built inspections (inspections to confirm whether completed structures match the design) still require a lot of time and effort. Chronic labor shortages, aging veteran engineers, and the overtime work regulations for the construction industry that came into full effect in 2024 (the so-called “2024 problem”) together increase the need to carry out inspection work efficiently with limited personnel.

One trump card attracting attention to solve these issues is AR (Augmented Reality) technology–based AR inspection. By combining smartphones or tablets with high-precision GNSS (Global Navigation Satellite System) receivers, this method allows on-site overlaying of design data and the real object for verification. It is a cutting-edge approach that aligns with the Ministry of Land, Infrastructure, Transport and Tourism’s *i-Construction* initiative and the broader trend of on-site DX. In this article, we introduce, as a first-public case example, a project that successfully improved as-built inspection efficiency by introducing AR inspection. We explain the background, the implementation process, and the concrete effects obtained, clarifying the benefits AR inspection brings to sites. Finally, we touch on the new possibility of “simple surveying” opened up by AR×RTK technology and offer hints for future on-site applications.

What is AR inspection?

First, “as-built inspection” is an important process in civil engineering and construction that confirms and records whether completed structures or developed land have the shape and dimensions finished according to the design drawings. Especially in public works, results of as-built inspections often determine whether the client accepts the inspection and the conditions for handing over the work, making it an unavoidable process for quality control. Conventionally, these inspections were typically carried out manually using tape measures, leveling staffs, and levels, measuring by hand, comparing measured values with drawings, and compiling photo logs and reports. However, manual measurement work requires considerable time and effort, and the number of points that can be measured is limited, creating an inherent risk of omissions or oversights.

AR inspection is a new method that emerged to solve these on-site inspection issues. By combining AR (augmented reality) technology with high-precision GNSS positioning, it enables real-time overlaying of construction objects and design data on site. Specifically, when viewing the site through a smartphone or tablet camera, the video is overlaid precisely with design drawings or 3D models showing the finished shape, reference lines, and so on. For example, for land development after earthworks, projecting a virtual horizontal plane that shows the design finished elevation in AR makes it immediately obvious whether the actual ground surface is higher or lower than that reference plane. In roadworks, displaying the design vertical alignment and cross-sectional shape overlaid allows instant judgment whether pavement thickness or slope falls within specified values.

The key that makes AR inspection possible is GNSS technology capable of measuring self-position with centimeter-level accuracy (half-inch accuracy) and smartphone attitude sensors and other technologies. By attaching an RTK GNSS receiver to a smartphone and using correction information from a reference station, precision positioning that previously required expensive equipment can be achieved on handheld devices. Using the high-precision position information obtained, design data are aligned to site coordinates and displayed in AR on a smartphone app so the virtual model is superimposed on reality without offset. Even when the operator walks around the site, the 3D model stays in the correct position, allowing a one-to-one comparison between the actual object and the digital design information. AR inspection is transforming the traditional process of “measure and then compare with drawings back at the office” into “measure and confirm immediately on site.”

Issues with conventional as-built inspections

The reason AR inspection is gaining attention is the variety of problems with conventional methods. In conventional as-built inspections, it was common to measure representative parts of completed structures manually and confirm differences from design values. The following problems have been pointed out with this method:

• Significant burden of time and labor: Dimension measurement typically requires work teams of multiple people, and for large sites or many measurement points, inspections alone can take more than a full day. Securing experienced surveying technicians is not easy, and it is a heavy burden to operate with limited human resources.

• Limited coverage and risk of overlooking issues: The number of points measurable manually is limited, making it difficult to completely check widely spread works. Relying only on a limited sample of measurement points runs the risk of missing areas that differ from the design. For large structures, subtle unevenness or finish variability may not be fully grasped, leading to situations where nonconformities are only discovered at the inspection stage and hurried corrective work is required.

• Risk of human error: In busy sites, human errors such as forgotten photos or misrecorded measurements frequently occur. For example, in inspections of buried items, forgetting to photograph before backfilling can make it impossible to prove construction conditions later. There have been cases where transcription errors in measurement results led to quality problems, and conventional methods placed significant psychological burdens on on-site personnel.

These issues have long driven the demand for new approaches to carry out as-built inspections more efficiently and reliably. The recent promotion of ICT and workstyle reforms has further increased expectations for technological innovations that can balance productivity improvements and quality assurance. One promising solution is the aforementioned AR inspection.

Overview of the AR inspection introduction project

Now, let us introduce an example project that actually introduced AR inspection and achieved results. This was a small-scale earthwork project (embankment and excavation) carried out by a construction company in Gifu Prefecture. Conventionally, this site used drone photogrammetry for as-built measurement, but planning the flight, aerial photography, generating point cloud data from photos, and drawing took half a day (over 5 hours). Therefore, as a pilot, the site decided to introduce AR inspection as a new point cloud measurement method using smartphones/tablets.

Specifically, a small RTK GNSS receiver (LRTK device) was attached to a tablet equipped with a LiDAR sensor, and the operator walked around scanning the target area on site (an excavation area of approximately 150 m² (1,614.6 ft²)). This made it possible to acquire high-density 3D point cloud data in about 15 minutes, and the data were immediately uploaded to the cloud from the site where automatic drawing and sharing were completed. With the conventional method, image processing and data preparation took time, but with the introduction of AR inspection, the total time required from measurement to drawing was reduced to approximately 30 minutes.

How AR inspection was conducted

Let us follow the specific procedures of the AR inspection adopted in this project. First, as preparation, design drawing data for the target construction area and reference values used for as-built management (design elevations and slopes, etc.) were prepared as digital data and loaded into a dedicated app on the tablet. On site, the RTK GNSS receiver attached to the tablet was started and high-precision positioning commenced. In Japan, by using correction services such as the quasi-zenith satellite “Michibiki” CLAS (Centimeter Level Augmentation Service) or network RTK via the internet as correction information, it is easy to obtain positioning accuracy within a few centimeters (within a few inches). Once positioning stabilized, the design data were overlaid in AR display mode on the tablet camera image, and alignment between the site and the drawings was confirmed. If necessary, orientation sensor calibration was also performed to correct any offsets between digital data and the real-world space.

With preparations complete, the operator walked through the measurement area while scanning the terrain with the tablet. With a LiDAR-equipped device, surrounding terrain can be densely point-cloud scanned in a short time. In this case, the roughly 150 m² (1,614.6 ft²) area was scanned in a few minutes, and the acquired point cloud data were automatically uploaded to the cloud on the spot. On the cloud side, comparisons with design data and earthwork volume calculations were carried out immediately, and difference heat maps of as-built conditions and computed fill/excavation volumes were available while still on site. These result data could be checked on the tablet and, if necessary, overlaid on the site view in AR. For example, displaying a heat map in AR visually color-codes which points of the terrain are several centimeters higher or lower than the design (several inches), allowing immediate identification of locations that require additional excavation or filling. Inspectors could grasp the situation on site immediately and share information with construction staff such as heavy equipment operators to issue immediate correction instructions.

Effects of introducing AR inspection

At this site, the pilot introduction of AR inspection produced the following notable effects.

• Major reduction in measurement work time: As-built measurements that previously took over 5 hours using drone photogrammetry were completed in about 30 minutes. Tasks that used to require a surveying team half a day to complete were finished in a short time, accelerating overall site progress management.

• Real-time sharing and reduction of rework: Acquired data were immediately shared in the cloud, eliminating the need for post-return data processing and alignment work at the office. Point cloud data could be analyzed on the spot, and fill/excavation calculations and as-built pass/fail judgments could be performed in real time, reducing the risk of discovering nonconformities after the inspection and having to perform rework. “Confirm on site, correct on site” became possible, dramatically speeding up decision-making in construction management.

• Improved personnel efficiency: AR inspection can be operated by a single person, allowing wide-area surveying and inspection coverage even with few personnel. In fact, in this case, some said it felt “as if we had twice the manpower,” as the amount of information and speed one person could handle increased significantly. Because digital tools enable reliable data acquisition and analysis without relying on veteran intuition or skilled techniques, it also reduced operator burden and helped level out workloads.

• Enhanced quality control and safety: Visualization via AR made it harder to miss minor defects. Since errors can be visually grasped and corrected on the spot, the number of issues pointed out in final inspections decreased, helping prevent quality problems. In addition, AR display makes it easier to publicize locations of hazards or buried items, producing secondary effects such as reduced near-miss incidents during work and improved safety awareness.

As shown, AR inspection brought major improvements in both productivity and quality. The effects directly linked to shortening schedules and alleviating labor shortages represent undeniable benefits for future construction sites.

Ministry of Land, Infrastructure, Transport and Tourism trends and the future of AR inspection

Even though it is state-of-the-art technology, AR-based as-built inspection is by no means an eccentric practice that violates site-specific rules. The Ministry of Land, Infrastructure, Transport and Tourism is actively promoting ICT utilization in construction management and supporting the digitalization of as-built management across public and private sectors. For example, as part of the i-Construction initiative, the “As-Built Management Guideline Using 3D Measurement Technology (draft)” has been formulated, and procedures for using new technologies such as drone photogrammetry and terrestrial laser scanners have been established. Furthermore, in 2022 the as-built management guidelines were revised to officially allow the use of simple mobile devices such as smartphones and tablets for as-built measurements in public works. This means environments where anyone can easily perform digital measurements without expensive dedicated equipment are increasingly being realized.

Additionally, in 2024, a notice was issued for trials of supervision and inspection that utilize digital data in ministry-managed projects, where a new method was shown: “projecting 3D models created during the construction stage onto the site using AR technology and conducting as-built inspections on the spot.” Conventionally, it was common to create heat map drawings from point cloud data and submit them, with inspectors separately re-measuring on site to confirm. By using AR to complete data confirmation directly on site, inspection workflow efficiency is expected to improve. In this way, on-site DX is progressing across the construction industry, including administration, and AR inspection fits squarely into this trend. As labor shortages and workstyle reform demands grow, AR inspection is expected to spread as a key technology that balances efficiency and quality.

Conclusion

As introduced here, introducing AR inspection brought significant transformation to on-site as-built inspections. By leveraging digital technologies, tasks that previously relied on manpower or artisan intuition have been made more efficient and sophisticated, demonstrating that safe, high-quality construction management can be achieved even with limited personnel. Indeed, the new norm of “simple surveying” opened up by AR×RTK technology is beginning to significantly change how sites operate.

As a solution supporting such AR inspections, our company has developed the LRTK series. LRTK enables centimeter-level positioning accuracy (half-inch accuracy) and AR display with just a smartphone, realizing “simple surveying” that allows anyone to intuitively perform on-site 3D measurements and as-built checks. LRTK is a user-friendly tool compatible with i-Construction and on-site DX and has already contributed to productivity improvements at many construction sites. If you are interested in introducing AR technology to your site, please consider trying this simple surveying with LRTK. We are confident you will experience new possibilities in site management.

FAQ

Q: Can anyone immediately become proficient in AR inspection? Is special skill required? A: Basic operations are not difficult if you follow the guidance in the dedicated app. For example, in the LRTK system, you attach an antenna to the smartphone, point it at the location to be measured, and press a button to record coordinates; AR display is also done simply by selecting the model data from the menu and overlaying it. However, when introducing the system for the first time, it is advisable to provide brief pre-training on device handling and sensor calibration methods for peace of mind. After using it on site a few times, users should pick up the necessary skills.

Q: Can a smartphone really achieve high-precision measurements? A: Yes. By utilizing high-precision RTK GNSS positioning, smartphones and tablets can measure positions with centimeter-level accuracy (half-inch accuracy). It is possible to secure as-built accuracy comparable to conventional instruments such as total stations and levels. In addition, built-in LiDAR enables close-range shape measurement, and combining with photogrammetry techniques allows acquisition of wide-area 3D data when needed. Since official as-built management guidelines now include measurements using smartphones, under certain conditions this method is recognized as sufficient for inspections.

Q: How much does it cost to introduce AR inspection? A: Compared with purchasing expensive dedicated equipment, the costs for necessary elements such as smartphones, small GNSS antennas, and software fees can be kept significantly lower. You can often use smartphones you already own, and small GNSS receivers are more affordable than before. Many software solutions are offered as cloud services, allowing flexible operations such as licensing only for the required period. Above all, the cost benefits from reduced work time and labor costs are very large, so overall you can expect outcomes that exceed the investment.

Q: Is AR inspection possible in places where GNSS cannot be used, such as tunnels or indoors? A: In environments where satellite signals from the sky cannot reach, RTK GNSS positioning cannot be used as is, so ingenuity is required. In tunnels, one approach is to use reference coordinates obtained near the entrance and perform relative alignment to known points inside the tunnel (points whose positions have been determined by surveying). In indoor or underground spaces, cases exist where QR code markers or feature-point markers are installed and recognized by the camera to enable AR display. In short, where GNSS is difficult, using alternative reference markers can expand the applicable range of AR inspection.

Q: Besides as-built inspections, what other construction management tasks can AR technology help with? A: AR×RTK technology is being used across many on-site tasks beyond as-built inspections. For example, marking pile-driving positions can be done by AR-displaying virtual piles based on design coordinates, enabling even one person to efficiently and accurately identify points. Projecting 3D models of buried pipes or cables that are usually invisible helps prevent accidental damage during excavation and raises awareness among stakeholders. Visualizing completed road or development images with BIM/CIM models on site is also being tried to smooth consensus-building with clients and local residents. Thus, AR contributes to productivity and improved communication across a wide range of uses, including plan presentations and safety management, not just inspections.