Voices from Field Staff: Impressions after Introducing AR As-Built Inspections

Contents

• What is AR as-built inspection?

• Challenges of traditional as-built inspections

• Benefits of AR as-built inspection

• Use cases of AR as-built inspection (paving, earthworks, retaining walls)

• Conclusion

• FAQ

(Introduction) In recent years, the construction industry has rapidly focused on construction DX through the use of ICT technologies and AR (augmented reality). Even in small- and medium-scale civil works (paving, earthworks, retaining walls, etc.), there is a growing trend to adopt digital technologies to improve site efficiency and quality. Among these, "AR as-built inspection" is expected as a new method that allows on-site verification of whether completed structures and terrain match the design drawings. This article introduces the effects and changes on site, incorporating the voices of staff who actually introduced AR as-built inspections.

What is AR as-built inspection?

As-built inspection is an inspection to check whether the shapes and dimensions of structures or road surfaces completed in construction conform to the design. Traditionally, measurements were taken using tape measures, levels, total stations, etc., and compared with drawings. In contrast, AR as-built inspection uses Augmented Reality technology to visualize the as-built condition on site. By overlaying design data and reference lines onto the real site view through a smartphone or tablet camera, you can intuitively grasp the "discrepancy between design and actual conditions."

For example, using an AR app that combines a smartphone equipped with a LiDAR scanner and a high-precision GNSS (RTK) receiver, you can 3D-scan the as-built simply by pointing the phone. If you overlay the design model on the acquired point cloud data of the terrain or structure, differences in height and position become immediately apparent. What used to be imagined on drawings can now be confirmed by overlaying the design onto the real thing, enabling real-time inspections where construction results can be checked and judged on the spot.

Another feature of AR is that even non-experts can intuitively evaluate finishes. When you look at the smartphone screen on site, design lines and target heights appear in the real space, making it easier for anyone to visualize the completed form. In short, AR as-built inspection is a revolutionary method that allows you to "compare the as-built with the completed drawings while staying on site."

Challenges of traditional as-built inspections

Before AR was introduced, as-built inspections were analog work relying on manpower and experience. Typical procedures involved site supervisors or survey personnel measuring key dimensions and heights after construction using tape measures or staffs. In paving work, for example, roadbed thickness was measured by digging at several points; in earthworks, heights were checked point by point—everything had to be measured manually and fragmentarily. As a result, many issues have been pointed out.

• Time-consuming and labor-intensive: Setting up equipment at each measurement point, recording measurements, and later comparing them with drawings took a great deal of time. Sometimes more than two people were needed, and the number of points that could be measured in a day was limited. One site supervisor recalled, "Checking the as-built was half a day's work each time, and we had to interrupt other tasks."

• Concerns about missed measurements and errors: It is practically difficult to measure every location in detail, so inspections tend to be sampling-based. Therefore, there was a risk of not noticing errors or defects in unmeasured areas. Also, inspections that involve reading drawings relied heavily on the intuition of experienced staff, leaving room for human error. In practice, differences in measurement methods and judgment between veterans and newcomers sometimes occurred, and some said, "I worried whether inspectors would point things out later."

• Rework occurrence: Traditionally, there was a time lag between measuring the as-built and getting results. For instance, after leveling the roadbed for paving, the survey team might come several days later and point out insufficient height → additional fill or rework would follow. When problems surfaced later and rework was required, it led to schedule delays and extra costs. For site staff, "having to tear up and redo a part you finally finished is mentally taxing."

• Labor shortage and succession of skills: Recently, shortages of survey and construction management personnel have become serious. In particular, the aging of veteran survey technicians has reduced the number of people with seasoned know-how. Small civil engineering firms often cannot employ a dedicated surveyor, and site supervisors sometimes must handle inspections themselves. As a result, voices have risen saying, "The burden is too large and quality control can't be adequately performed."

As described above, traditional as-built inspections had issues such as "time-consuming," "concerns about accuracy and coverage," "risk of rework," and "labor shortages." AR as-built inspection has emerged as a trump card to solve these problems.

Benefits of AR as-built inspection

Field staff who actually introduced AR as-built inspection have reported many benefits. Here are the main effects with voices from the field.

• Significant improvement in work efficiency: With just a smartphone and a small GNSS receiver, you can measure the as-built immediately on site. Surveying that used to require two people can be completed by one person, and some have said "the time required for measurement has been reduced to less than half of what it used to be." There is no need to set up or put away heavy equipment, so freed personnel can be reallocated to other tasks, improving overall site productivity.

• Visualizing discrepancies in real time: AR display allows immediate verification of discrepancies between the design model and actual conditions using color coding and numerical values. At one earthwork site, after grading, they pointed a smartphone and low areas were highlighted in red, enabling corrective fill to be applied the same day. Staff felt, "Because we can respond immediately without waiting for later measurement, rework has drastically decreased." Real-time verification helps catch mistakes early, contributing greatly to preventing rework and ensuring quality.

• Intuitive and easy to understand: Because 3D design data is overlaid on the camera view, even those not accustomed to drawings can understand the situation at a glance. Young site engineers said, "Differences in slope and height that didn't make sense from numbers or drawings are obvious at a glance." Being able to show the screen to clients and workers from other trades makes communication smoother and speeds up consensus building.

• High accuracy and reliability: Some may be concerned about accuracy when they hear "AR," but centimeter-level positioning using RTK-GNSS achieves accuracy comparable to traditional surveying instruments. At sites where it was introduced, verification showed "errors on the order of several millimeters to about 1 centimeter (several mm to about 1 cm (several 0.04 in to about 0.4 in)), which is comparable to handheld total stations." This created a sense of security that "digital is trustworthy enough." Even seasoned surveyors endorsed it, saying, "I was surprised there was no large difference from the values I measured myself."

• Labor saving and burden reduction: Because it is smartphone-based simple surveying, there is no need to carry heavy equipment. Inspections can be done simply by "one person carrying a smartphone each," reducing situations where people had to measure in awkward or hazardous postures. As-built on steep slopes can be checked from a safe location via AR display, reducing dangerous measurement tasks. It also reduced the burden on surveyors, and some said, "We felt we could manage sites even with labor shortages." Veteran staff also noted that following always-accurate guidance eased mental stress.

• Data utilization and DX promotion: Point cloud data and measurement results obtained by AR as-built inspections can be stored and shared in the cloud as digital data. This eliminates the need to record on paper drawings and later digitize them in the office. Site-collected data can be shared immediately with headquarters and clients, enabling real-time decision-making. Accumulated as-built data can be analyzed for quality control or linked with BIM/CIM models to enhance construction management, leading to next-generation construction management. Site supervisors appreciated that "data remains for later review," and it has proven effective as a first step toward DX starting from small sites.

With the introduction of AR as-built inspection, work time has been shortened, errors reduced, quality improved, and business efficiency increased through digitalization. Many site staff said positively, "I wish we had used it earlier" and "Once you use it you can't go back to the old way."

※ Of course, introducing new technology initially had some hurdles. Some experienced staff were hesitant about tablet operation at first, but after repeated hands-on training they accepted it as "easier than expected" and "convenient." High-precision positioning requires a GNSS environment (establishing a base station or using correction information), but network RTK services are now common, and environments that enable smooth on-site use are being established. These initial issues can be overcome with operational adjustments and support, and site concerns have been alleviated in light of the large benefits.

Use cases of AR as-built inspection (paving, earthworks, retaining walls)

AR as-built inspection can be used in various civil works. Here are concrete ways to use it in typical sites such as paving, earthworks, and retaining walls.

• Use in paving work: When constructing roadbeds or subbases, you can confirm on site whether heights match the design. For example, after shaping the roadbed, pointing a smartphone shows the height difference color-coded on the screen. Because height differences are obvious at a glance, you can immediately decide to add fill to low areas. Also, as-built pavement thickness can be calculated by comparing point clouds of the ground before and after paving, enabling a full-surface thickness check without relying solely on future core sampling. This helps ensure uniform pavement quality and reduces future risks of rutting or subsidence.

• Use in earthworks: For residential land development or site grading, it is important that the finished ground heights and slopes match the design. AR as-built inspection allows planar checking of ground surface heights even on large sites. By overlaying the design finished-ground model on the point cloud of the entire scanned site, you can instantly find leftover cut or insufficient fill areas. For example, if a corner of the site is short in height, the screen will display "XX cm low," allowing immediate instruction to the heavy equipment operator. After completion, the as-built 3D data can be used directly in inspection documents, making reporting to authorities smoother. Responsible personnel praised that "inspection drawing creation has been almost automated, significantly reducing labor." (Note: when expressing "cm precision" in documentation, this is referred to as cm level accuracy (half-inch accuracy).)

• Use in retaining wall work: AR as-built inspection is also effective for retaining walls and earth-retaining structures. For foundation layout, the design retaining wall line can be projected onto the ground with AR during excavation or formwork installation, allowing accurate line confirmation on site without following paper dimensions. Some said, "We no longer worry about excavation positions being off." After pouring a retaining wall, scan the finished wall surface with a smartphone and compare it with the design model to check vertical deviations or tilt. Verticality checks that previously relied on craftsmen's visual inspection or plumb lines can now be confirmed numerically with AR. Additionally, for slope works, slope gradients can be measured from a distance without personnel climbing dangerous slopes by using AR display. Backfill thickness behind retaining walls can also be compared on the spot with cross-sectional fill models, helping to prevent overlooking insufficient backfill.

As described above, AR as-built inspection is a strong ally in various trades such as paving, earthworks, and retaining walls. The common advantage across sites is that "inspections can be done at the moment, and corrections can be made immediately," directly improving quality control. It is fully usable even in small- to medium-scale works, and its effect is especially high on sites with few dedicated technicians.

Conclusion

From the voices of field staff who introduced AR as-built inspection, you can sense its dramatic effects. True to the words "fast, simple, accurate," the greatest attraction is that it can achieve both efficiency and quality assurance that were difficult with traditional methods. Time-consuming as-built inspections have become speedy, and reduction in mistakes and rework has created breathing room across sites. Because confirmation can be done with data rather than relying on veteran experience, younger staff can take on inspection tasks, and "quality management that anyone can do" is becoming a reality even amid labor shortages.

Moreover, the spread of AR as-built inspection is not limited to productivity gains; it is an important step to advance site DX. By accumulating and utilizing data, future AI analysis and integration with other ICT construction tools become possible, connecting to the next stage of construction management. This aligns with the Ministry of Land, Infrastructure, Transport and Tourism's i-Construction initiative, and proactively adopting technologies such as AR and RTK is the posture required of future construction sites.

Recommendation for simple surveying with LRTK: As a solution to easily realize AR as-built inspection, the LRTK series developed by Lefixea, a venture from Tokyo Institute of Technology, is attracting attention. LRTK is an ultra-compact RTK-GNSS receiver that can be attached to a smartphone, turning the phone into a centimeter-precision surveying instrument (cm level accuracy (half-inch accuracy)). Combined with a dedicated app, it handles everything from layout positioning to point cloud measurement and AR as-built checks in a single device. Initial investment is lower than with conventional equipment, and the ease of giving every staff member "a smartphone surveying device" is another attraction. It is being adopted at many construction sites, receiving high praise that "anyone can perform high-precision surveying with LRTK." If you are considering introducing AR as-built inspection at your sites, why not start with simple surveying using LRTK? Embrace the latest technology and evolve your sites to the next stage. For details, please also visit the [LRTK official site](https://www.lrtk.lefixea.com).

FAQ

Q: What is AR as-built inspection? A: AR as-built inspection is a method that uses the AR (augmented reality) functions of smartphones or tablets to verify on site whether completed structures or terrain conform to the design drawings. Design data is overlaid on the site view to intuitively check for discrepancies or deficiencies. It digitalizes and streamlines traditional as-built inspections performed with tape measures and levels.

Q: On what sites or works can it be used? A: It is applicable to a wide range of civil works such as road paving, residential land development, and retaining wall construction. It is useful wherever you need to verify consistency with design, such as ground height checks, thickness checks, and position/dimensional inspections of structures. Its benefits are especially large on small sites where surveying personnel are limited.

Q: Do I need special equipment or skills to introduce it? A: Basically, you need a smartphone or tablet, an RTK-GNSS receiver to connect to it, and an app for AR as-built inspection. Recent smartphones (LiDAR-equipped models are even better) are compatible. Operation is intuitive—just point the device according to the app's instructions—so you can handle it without specialized surveying knowledge. While you may be hesitant at first, many staff can master it in a short period through training and hands-on practice.

Q: Is the measurement accuracy reliable? A: Yes. By combining high-precision RTK-GNSS, you can achieve centimeter-level positioning (cm level accuracy (half-inch accuracy)). There are performance records showing accuracy comparable to conventional total stations and levels. However, obtaining high accuracy requires a good satellite positioning environment (clear sky view and receiving corrections from a base station). RTK correction services are now available across Japan, and typical outdoor construction sites can obtain sufficient accuracy. If in doubt, you can double-check critical points with conventional methods.

Q: How will operations actually change after introducing AR as-built inspection? A: The time required for as-built verification will be dramatically reduced. Since the inspector only needs to point a smartphone on site, setting up measurement points and later drawing checks become unnecessary, and pass/fail decisions can be made immediately. The reduction in rework is significant—issues can be corrected immediately and the schedule shortened. Records remain as digital data, and report creation can be automated and simplified. Overall, site supervisors who used to be overwhelmed by inspections can reduce their burden and allocate more time to core construction management and other tasks.

Q: What is LRTK? A: LRTK is a high-precision positioning solution for smartphones developed by Lefixea. A pocket-sized RTK-GNSS receiver attaches to a smartphone and is used with a dedicated app. This turns the smartphone into a surveying instrument capable of centimeter-level position measurement, point cloud scanning, and AR-based as-built checks. In short, it is a device that "makes a smartphone a versatile surveying instrument," designed so anyone can perform high-precision surveying and as-built management easily. As a powerful tool for practicing AR as-built inspection, it is being adopted at many sites. If interested, please check LRTK details on the official site.