No More Doubt! Why AR Inspection Makes As-Built Management Easier

Table of Contents

• What is AR inspection

• Challenges of traditional as-built management

• Why AR inspection makes as-built management easier

• Use cases of AR inspection

• Simple surveying with LRTK

• Frequently Asked Questions

What is AR inspection

"As-built management" is the important process in civil engineering and construction for verifying and recording whether completed structures or terrain match the shapes and dimensions specified in the design drawings. It is essential for quality assurance, and for public works the results of as-built management are conditions for inspection approval and handover. Traditionally, this as-built verification was performed by manual measurements using tape measures, leveling staffs, and levels, along with photography; the resulting measurements were organized into charts and photo logs for reporting.

In recent years, a new method called AR (Augmented Reality) inspection has attracted attention. AR inspection is a technique that overlays design drawings or 3D model information onto the real construction site through the camera of a smartphone or tablet, allowing real-time verification of the as-built condition on site. By combining high-precision GNSS (satellite positioning) location information with device sensors, digital design data can be displayed over actual structures without offset, enabling intuitive recognition of discrepancies from the design. For example, if the designed final shape or reference lines are AR-projected over the completed terrain or structure, you can instantly determine whether the finish is within tolerance. AR × GNSS digitally advances as-built management, which traditionally relied on manual work and visual checks, so that anyone can perform accurate on-site verification without confusion.

Although AR technology has been researched for some time, recent improvements in smartphone and tablet performance have made it practical to use on site without special equipment. The latest mobile devices include high-performance cameras and LiDAR sensors, and with dedicated AR apps that leverage these capabilities, an environment is emerging where anyone can easily perform as-built checks. The industry as a whole, supported by initiatives such as the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction policy, is increasingly looking to AR inspection as a powerful solution to realize DX (digital transformation) on construction sites.

Challenges of traditional as-built management

However, traditional as-built management methods have various issues. Summarizing major points often raised by site engineers, the primary concerns are:

• Time lag from measurement to judgment: There is a delay between on-site measurement and office-based comparison to drawings to determine pass/fail, which often leads to late discovery of problems and rework.

• Huge manpower and time burden: Dimensional measurements typically require teams of two or more and the cooperation of skilled surveyors. In large sites, the number of measurement points increases and can take a full day, imposing a heavy burden amid personnel shortages and an aging workforce.

• Lack of coverage leading to oversights: The number of points that can be measured manually is limited and cannot cover the entire施工範囲. Only representative locations are measured, so there is always a risk of missing parts that differ from the design. For large structures it is difficult to grasp subtle unevenness, and there have been cases where discrepancies are only pointed out at inspection time and hurried corrections are required.

• Risk of human error: In busy sites, human mistakes such as forgetting to take photos or recording measurement values incorrectly tend to occur. Particularly critical are failures like forgetting to photograph buried works whose status cannot be rechecked later, or transcription errors from handwritten notes that lead to quality problems. A paper- and people-dependent approach always carried the anxiety of errors.

Against this backdrop, the use of new technologies has been strongly anticipated from the perspectives of labor saving and productivity improvement. The trump card that has emerged to solve these issues is the AR inspection described next.

Why AR inspection makes as-built management easier

Introducing AR technology can dramatically streamline as-built management while resolving the traditional issues above. Here are the main reasons.

• Real-time problem detection: Construction defects and deviations from the design can be discovered on the spot and corrective actions taken immediately. For example, if insufficient pavement thickness or slope is color-coded on AR right after construction, additional work or trimming can be done the same day. Unlike the traditional workflow where issues are discovered only after returning to the office, running the PDCA cycle on site minimizes rework and prevents quality defects from being left unaddressed.

• Shorter working time and labor saving: AR lets you visualize a wide area of as-built conditions at once by overlaying drawing data, greatly reducing the hassle of measuring individual points. One person can hold a tablet and confirm, simplifying the arrangement of measurement personnel. Inspections that used to take several days can be dramatically sped up, leading to labor savings through reduced staffing.

• Addressing labor shortages: Site personnel themselves can evaluate as-built conditions without relying on specialist surveyors or veteran technicians. Modern AR apps are intuitive; by following on-screen prompts, measurement and inspection can be completed. Because special skills are not required, work does not become person-dependent, and even inexperienced staff can carry out quality checks. Even on sites suffering chronic labor shortages, universal inspection capability allows operations to continue.

• Cost reduction: AR inspection using smartphones or tablets eliminates the need to purchase expensive total stations (TS) or GNSS surveying instruments. Typical surveying equipment can require initial investments of several million yen, but a measurement environment with centimeter precision can be built at low cost by combining commercial mobile devices with relatively inexpensive GNSS receivers. Maintenance and transport costs of dedicated equipment are also reduced, yielding substantial overall cost savings.

• Improved measurement accuracy and reliability: Using AR reduces the risk of human measurement errors and recording mistakes. Digital comparison of data eliminates memo errors and transcription mistakes, enabling consistently accurate judgments. Further, when combined with high-precision positioning technologies such as RTK-GNSS, measurement results can achieve centimeter-level precision (half-inch accuracy) aligned to public coordinate systems, enabling more reliable as-built verification than before.

• Streamlined recording and reporting: AR-verified inspection results can be recorded and shared as intuitive visuals. For example, attaching AR screen screenshots or heatmap images that color-code differences between current point cloud and design data to a report makes deliverables far easier to understand than conventional numerical and textual materials. Ministry of Land, Infrastructure, Transport and Tourism field trials have confirmed that using AR can simplify submitted as-built drawings and documents. Because histories are retained as digital data, later traceability is easy, greatly reducing the burden of inspection reporting tasks.

• Improved consensus-building and communication: AR visualization also aids information sharing among stakeholders on and off site. Showing the completed image overlaid on the real object via tablet during construction makes explanations during client inspections much smoother. Displaying as-built conditions in AR reduces misunderstandings and enables on-the-spot agreement on corrective locations. According to MLIT reports, AR is being used not only for construction management but also for pre-construction resident briefings and meetings with subcontractors, and is expected to facilitate communication.

Use cases of AR inspection

In actual sites, AR-based as-built checks are beginning to be used in various applications. Here are some representative cases.

• Position confirmation of rebar and structures: AR is effective for checking rebar layout before concrete placement or the installation position of structures during construction. For example, when inspecting whether a column’s rebar position is off, displaying the rebar layout in AR on site and checking counts and spacing makes what used to require scale measurements instantly visible. By overlaying the design 3D model on the real object you can detect subtle errors and proceed quickly while ensuring accuracy. There are reported cases where AR on-site verification enabled early correction of defects, reducing rework and material waste.

• Visualization and inspection of buried works: AR can "see through" to verify pipes, cables, and other items buried underground that become invisible after completion. For example, in sewer pipe work, pipes can be 3D-scanned before burial and the accurate position and depth point cloud data saved to the cloud; after backfilling, anyone can understand the route and depth of underground pipes simply by holding up a smartphone. This can eliminate the marking work traditionally required just after burial, and during future maintenance AR display makes excavation that avoids buried objects easy. The ability to visualize normally invisible items is another major advantage of AR inspection.

Simple surveying with LRTK

A solution attracting attention for making AR as-built inspection easier and more accurate is LRTK. LRTK is a modern tool that attaches a compact high-precision GNSS receiver to a smartphone to perform RTK positioning, allowing anyone to obtain centimeter-class positioning accuracy (half-inch accuracy). Tasks that previously required specialized equipment and skilled operators can be completed by one person, greatly lowering the barrier to surveying and inspection on site.

LRTK seamlessly links AR functions with a dedicated app, allowing 2D/3D design data to be overlaid perfectly on site based on high-precision GNSS position information. Complex alignment work is unnecessary and there is no worry about model drift. For example, just walking the site with a tablet can accurately show the virtual stake-out positions on the actual ground, enabling target points to be identified at a glance even from a distance. It also includes a function that automatically compares acquired point cloud data of the current condition with the design model on the LRTK cloud and generates a difference heatmap, enabling instant checks of whether construction matches the plan.

LRTK provides a cloud platform so that measured and scanned data on site are automatically synchronized to the cloud. From office PCs you can view the site point clouds and measurement point information in real time, and collaborate with remote supervisors and colleagues while conducting verification. Distance, area, and volume measurements, as well as lists of geotagged photos, are available with a single click on the cloud. This enables collaboration across the boundaries of site and office and significantly transforms the as-built inspection workflow.

Additionally, LRTK offers various features beyond as-built management, such as a "coordinate navigation" function that guides stake-out positions for a single operator, a function to calculate earthwork volumes from point clouds acquired by LiDAR scanners, and high-precision geotagged photo cloud sharing. In other words, it is designed to complete processes that used to require multiple devices—from surveying to inspection and record keeping—using just a smartphone. Data obtained on site can also be used or delivered in formats compliant with the MLIT as-built management procedures, and many construction companies have begun adopting LRTK to achieve both labor savings and quality improvement.

By leveraging these modern tools, anyone can easily perform high-precision as-built checks and break free from traditional constraints. Even sites struggling with labor shortages can shorten work time, reduce human error, and improve information sharing among stakeholders by using a "one-person one-device" smartphone surveying tool combined with AR. Embrace these technological innovations and promote DX in your as-built management on site.

Frequently Asked Questions

Q: What equipment and preparations are needed to start AR inspection? A: Basically, prepare AR-capable devices such as smartphones or tablets and a high-precision GNSS receiver (RTK-capable unit) that achieves centimeter-class accuracy (half-inch accuracy). In addition, you need design data for comparison, such as 3D models or drawing files. Load these data into a dedicated AR app and you can perform AR inspection on site immediately. For AR in indoor or underground spaces where GNSS cannot be used, additional measures such as setting reference points beforehand for alignment or using marker-based AR displays will be required.

Q: Can the accuracy of AR inspection be trusted? A: Yes, if operated properly, AR inspection can provide highly accurate and reliable verification. Systems using RTK-GNSS corrections can achieve horizontal and vertical errors down to several centimeters (several inches). However, for stable positioning you should calibrate with known coordinates of survey control points and operate in environments where satellites can be adequately received. Scanning the current condition with LiDAR-equipped devices enables accuracy verification by automatic comparison between point clouds and the design model. Under appropriate procedures, AR inspection can achieve accuracy comparable to traditional surveying inspection.

Q: Can AR inspection results be used as submission documents to the supervising authority or client? A: Yes. Currently, MLIT is promoting simplification of as-built management using 3D data and AR technology as part of the i-Construction initiative. Heatmap images and point cloud data obtained from AR inspection can replace or supplement conventional as-built documents. There are increasing cases where inspection was conducted using as-built documents created with AR, and systems that support data output compliant with national guidelines have emerged. However, because required submission formats may vary by client or project, it is advisable to use AR outputs in parallel on a trial basis initially and confirm requirements.

Q: How much does it cost to introduce AR inspection? A: It depends on the case, but it is far less expensive than equipping traditional surveying instruments. By utilizing smartphones or tablets you already have and introducing a high-precision GNSS receiver and dedicated software costing on the order of a few hundred thousand yen, you can start. You don’t need to purchase multiple expensive TS units or 3D scanners, so initial investment can be greatly reduced. Considering labor cost reductions from improved efficiency, AR inspection is a technology with high cost-effectiveness.

Q: Is AR inspection possible without 3D design data? A: Yes. Even if BIM/CIM 3D models are not available, you can create simple 3D data from 2D drawings or use on-site point cloud scans of completed structures for comparison with the design. As CIM spreads, more projects are producing 3D models from the design stage, and in the future 3D data will likely become easier to obtain at any site. Familiarizing your company early with handling 3D data will make AR inspection implementation smoother.

Q: Are special devices like AR glasses required? A: No, not necessarily. Currently, AR apps running on tablet-type mobile devices are commonly used and are practically sufficient on site as long as you have a device that is easy to handle. However, in the future head-mounted displays (AR glasses) may enable workers to perform inspections with both hands free, offering further efficiency gains.

Q: What types of construction or sites can AR inspection be applied to? A: AR inspection can be applied widely—from civil works such as roads, land development, and river works to structural works like bridges and tunnels, and even construction management in the building sector. As long as you want to compare design drawings with the site—such as checking embankment height, pavement thickness, dimensions of concrete structures, or rebar placement—AR is generally effective regardless of project size. You can start with small-scale trials on part of a site and expand the scope as you confirm benefits.

Q: Any tips for establishing AR inspection on site? A: To reduce resistance to new technology and achieve smooth adoption, follow several points. First, introduce AR inspection on a small-scale task to verify benefits and issues. Demonstrating actual use so staff can experience that "anyone can easily measure" deepens understanding. Also, incorporate AR inspection procedures into construction plans and checklists in advance so it is clear "when, who, and at what timing" it should be used, which makes on-site operation easier. Provide training and OJT to share operational methods, and show veteran employees the benefits to facilitate internal consensus. By accumulating such practices, you can maximize the advantages of AR inspection and steadily advance DX on site.