Conventional Methods vs AR As-built Inspection: How Do Efficiency and Accuracy Improve?

Table of contents

• What is as-built inspection? Conventional workflow and challenges

• What is AR-based as-built inspection

• Key points where AR as-built inspection improves efficiency

• Key points where AR as-built inspection improves accuracy

• Other benefits of introducing AR technology

• How to deploy AR as-built inspection on site

• Start AR as-built inspection with simple surveying using LRTK

• FAQ

What is as-built inspection? Conventional workflow and challenges

As-built inspection is a quality control process in civil engineering and construction that verifies whether completed structures or developed land have been constructed according to the design drawings. For example, in road works, after construction is completed, measurements are taken at various locations to confirm that the subgrade or pavement thickness, width, and elevation fall within specified tolerance values. As-built inspection is an important part of the client’s construction inspection, and completion of the work is recognized only after the inspection is passed. Therefore, for contractors, producing good results in as-built inspection is indispensable for quality assurance and maintaining trust.

Conventional as-built inspections have mainly relied on manual surveying and photographic records. Surveyors and site technicians use tools such as total stations (TS), levels, and tape measures to physically measure elevations, distances, thicknesses, and other parameters at key points on site. Measurement results are noted on paper drawings or record sheets and, after returning to the office, compared with design drawings to judge pass or fail. At the same time, large numbers of photos during construction and after completion are taken, organized, and compiled into submission documents as evidence.

However, these conventional as-built inspection methods have many issues. Representative problems include the following:

• High labor and time burden: Because measurements and records must be taken carefully point by point, larger sites require enormous effort and many days. Surveying is often done by two-person teams, so securing personnel is a burden. Completing these tasks amid labor shortages and tight schedules places a heavy strain on sites.

• Limited measurement coverage leading to oversights: The number of points that can be measured manually is limited, making it difficult to comprehensively check wide-area terrain or entire structures. Measuring only some points risks missing subtle dimensional deviations, which can lead to last-minute surprises at inspection when discrepancies with the design are pointed out.

• High-precision equipment is expensive: Achieving millimeter-level measurements requires dedicated equipment such as high-precision total stations or GNSS receivers, which are very costly and present a high barrier to adoption for small and medium-sized enterprises. Maintenance costs and theft risk of such equipment are also concerns.

• Risk of human error: On-site measurement and recording are done manually, so recording mistakes and forgotten photos are common. Especially for buried elements that become invisible after completion, missing records can later cause disputes that cannot be proven.

• Delayed problem detection: Because measurement data cannot be analyzed or verified in real time on site, defect detection inevitably lags. Returning to the office to compare with drawings can lead to rework, causing extra time and cost to correct quality issues.

• Time-consuming report preparation: As-built management requires assembling recorded data into submission documents. Traditionally this clerical work also takes time, and during busy periods it is not uncommon for site technicians to work late into the night just to prepare inspection documents.

As described above, conventional as-built inspections are inefficient and carry the risk of oversights, imposing a heavy burden on sites. To solve these problems and improve efficiency and accuracy, the industry is exploring the adoption of new technologies.

What is AR-based as-built inspection

Against this backdrop, AR (Augmented Reality)–based as-built inspection has attracted attention in recent years. AR as-built inspection is a new method that overlays 3D models of design data or measurement data on the live site view captured by a tablet or smartphone camera, allowing on-the-spot verification of as-built conditions.

Instead of relying on numbers on drawings or paper documents as in the past, AR lets you compare digital information and the real object in physical space, enabling even inexperienced technicians to intuitively judge construction quality. For example, overlaying the design model on an AR view of a concrete structure makes it obvious where placement thickness is insufficient or where an inclination deviates. Without looking back at photos or drawings, you can imagine the final condition simply by holding up a smartphone and check the finish on the spot.

Furthermore, combined with high-precision GNSS (satellite positioning) technology, it is possible to align models and graphics displayed in AR with actual structures within a few centimeters. Attaching an RTK-GNSS receiver to a smartphone enables centimeter-level positioning, so digital model display positions align precisely with the actual constructed elements, allowing AR to verify as-built conditions with high reliability.

Modern smart devices also include LiDAR (light detection and ranging) sensors, and using point cloud data (3D scans composed of many points) captured by LiDAR to compare with design data and visualize differences is becoming feasible on site. For example, functions now exist that color-code point clouds of the ground surface in real time on a tablet and visualize embankment or cut-and-fill height differences as a heat map. The Ministry of Land, Infrastructure, Transport and Tourism is also promoting ICT use and 3D as-built management as part of the i-Construction initiative, and AR as-built inspection is gaining attention as a groundbreaking solution that simultaneously improves productivity and quality on site.

Key points where AR as-built inspection improves efficiency

So how exactly does using AR improve the operational efficiency of as-built inspection? The main points are explained below.

• Inspect on site immediately: With AR, you can overlay the design model and the actual object on the spot, eliminating the time lag of discovering issues only after returning to the office. You can check immediately after construction and make corrections right away, significantly reducing rework and re-construction losses.

• Reduce measurement labor: AR measurements using a smartphone or tablet allow one person to record multiple points in succession. Operations that traditionally required two people, such as setting out benchmarks, can be accurately verified by a single person with AR app guidance. Surveying and inspection can be completed with fewer personnel, making it easier to handle labor shortages on site.

• Cover wide areas in short time: Wide-area as-built checks that were previously measured manually point by point can collect large numbers of points at once with AR plus digital surveying. For example, you can record continuous measurement points while walking with a smartphone and GNSS, or scan the entire terrain with a drone or LiDAR to obtain surface data, thereby covering large areas in a short time. This leads to overall time savings for the inspection process.

• Simplify specialized equipment: AR as-built inspection can be performed with general-purpose smart devices and compact positioning terminals, avoiding the need to bring multiple heavy and complex surveying instruments. Reducing expensive TS or large equipment means less time spent preparing and setting up equipment. The convenience of completing tasks with a single mobile device improves site agility.

• Streamline data organization: Data obtained from digital measurements and AR displays is automatically saved and shared in the cloud. As-built diagrams and reports that were manually compiled in the past can in some cases be auto-generated by software from measurement data. Time spent creating photo albums and organizing documents is reduced, leading to lighter clerical workloads.

As described above, AR as-built inspection eliminates waste in surveying and inspection processes and realizes a system that can reliably verify as-built conditions with fewer people and less time. Digitalizing parts that used to rely on experience or intuition also makes it possible for anyone to conduct inspections efficiently.

Key points where AR as-built inspection improves accuracy

Next, let’s see how AR technology contributes to improving the accuracy of as-built inspections.

• Millimeter-level deviation detection: AR as-built inspection allows direct comparison of the design model displayed on the camera image and the actual object. Step differences or inclinations of a few centimeters that are hard to notice with the naked eye can be immediately recognized as discrepancies on the screen. Especially with RTK-GNSS high-precision alignment, it is possible to detect differences from the design down to the millimeter level. Critical structural parts can be further verified by comparing with acquired point cloud data for more detailed accuracy checks.

• Comprehensive quality checks: Unlike manual point measurements, digital scans enable as-built inspections to grasp the entire structure as surfaces. From the massive point cloud data obtained, you can analyze arbitrary cross-sections or display ground irregularities as color maps, making multi-faceted verification easy. As a result, oversights and unmeasured areas are almost eliminated, allowing quality issues to be reliably identified.

• Reduction of measurement errors: With less reliance on the intuition of experienced personnel and manual work, and with measurement centered on satellite positioning and sensors, human measurement errors decrease. For example, reading errors on tape measures or angle mistakes are eliminated, yielding consistently stable accuracy in data acquisition. LiDAR measurement accuracy is particularly high and can accurately capture complex as-built shapes.

• Reliable records: Digitally acquired as-built data are automatically recorded with timestamps and location information, so there is no worry about illegible numbers like with paper notes. Data stored in the cloud is easily duplicated and shared among inspectors, increasing the reliability of inspection records and avoiding redo work due to omissions.

• Standardization of inspection processes: Introducing AR as-built inspection reduces variability in results between people and advances the standardization and leveling of inspection procedures. By unifying measurement methods and judgment criteria digitally, the same results can be obtained regardless of who measures. This is reassuring for clients and supervisors and raises the level of quality assurance in as-built inspection.

In this way, using AR can be expected to produce drastic improvements in accuracy for as-built inspections. It not only speeds up work but achieves “more accurate and less error-prone inspections,” ensuring construction quality.

Other benefits of introducing AR technology

Beyond efficiency gains and higher accuracy, AR as-built inspection brings many additional benefits to the site.

• Improved safety: Using non-contact measurement with laser scanners, drones, or smartphone LiDAR allows safe verification of as-built conditions on steep slopes or at heights. Scanning inaccessible areas remotely and measuring dimensions on the data reduces worker risk while ensuring thorough inspections.

• Remote supervision and inspection: 3D data and heat maps acquired by AR can be shared via the cloud, enabling distant managers or specialists to participate in as-built verification without traveling to the site. Remote presence where live video is overlaid with design models allows remote on-site inspection, reducing travel time and supporting faster decision-making.

• Easier consensus building: When contractors and clients inspect as-built conditions together on site, viewing AR-displayed completion models and highlighted differences makes understanding the situation easier. Visual explanations are more effective than numbers alone, enabling smooth consensus building without mismatched understanding. Corrective locations can also be shared on the spot.

• Reduced burden on site technicians: With DX tools, site staff can proceed with measurements and inspections without relying solely on specialized surveyors. As labor shortages and aging progress, digital devices complement veteran experience, making it easier to maintain a small-staff operational site. Simplifying inspection tasks also relieves technicians’ psychological burden.

• Support for skill transfer: AR visualization aids training of young technicians. By showing veteran “sense” as numbers and colors, inexperienced personnel can more easily grasp quality check points. Even in the absence of veterans, a certain level of inspection can be performed, helping close the skills transfer gap.

How to deploy AR as-built inspection on site

Given the benefits described so far, AR as-built inspection is attracting attention as a strong alternative to conventional methods. So what preparations are needed to actually deploy AR as-built inspection on site?

Basically, you can start with a tablet or smartphone, a high-precision GNSS receiver capable of centimeter-level positioning, and an surveying application that supports AR as-built inspection. Recently, solutions have appeared that attach a compact GNSS antenna to commercially available smartphones to enable high-precision positioning and 3D scanning. For example, using a system like the LRTK series, a smartphone can be transformed into a surveying instrument, with acquired point clouds and design data displayed in AR on the spot for as-built checks. Once you have the digital design data used in construction (BIM/CIM models or electronic drawings) and the site control point coordinates, you can begin AR-based inspection immediately after construction completion.

There are no particularly difficult operations required for deployment; following the app guidance allows intuitive operation for surveying and AR verification. No special programming or advanced surveying knowledge is necessary. The data used on site are preprepared design models and drawings, so you simply select the data as you would with paper drawings and follow on-screen guides to verify. Even if specialists initially support deployment, site personnel can master the app with short training.

Start AR as-built inspection with simple surveying using LRTK

As a supporting technology for the AR as-built inspection described above, simple surveying that fuses smartphones and GNSS is attracting attention. In particular, the LRTK series, developed by a startup originating from Tokyo Institute of Technology, is an all-in-one solution that achieves high-precision positioning simply by attaching a compact GNSS receiver to a smartphone, enabling anyone to easily perform surveying, point cloud scanning, and AR as-built checks.

Using LRTK simple surveying, tasks such as positioning, layout marking, and as-built verification, which previously required separate equipment and personnel, are connected seamlessly on a single platform. For example, scanning terrain on site, uploading it to the cloud, and instantly comparing it with design data in AR can all be completed within a single app. As a result, the speed and accuracy of site inspections improve dramatically, and the as-built inspection quality assurance process is beginning to change significantly. LRTK has already been adopted on many construction sites, contributing to shortened schedules, reduced personnel needs, and faster disaster recovery, among other benefits.

If you want to introduce AR as-built inspection but don’t know where to start, a simple surveying tool like LRTK lets you launch operations in a relatively short period. Combining the advantages of the latest technology with site usability, LRTK can become a reliable partner in future construction management.

FAQ

Q: What do I need to start AR-based as-built inspection on site? A: You can start with a tablet or smartphone, a high-precision GNSS receiver, and an app that supports AR as-built inspection. Specifically, prepare a compact GNSS antenna that attaches to a commercial smartphone and a dedicated app, then load design drawing data and control point information so anyone can perform AR as-built checks on site. For example, using the LRTK series, attaching an antenna to an iPhone or iPad enables centimeter-level positioning, and acquired point clouds and design models can be overlaid for on-site inspection.

Q: Can AR as-built inspection really guarantee high accuracy? A: Yes. Using high-precision GNSS and LiDAR can ensure sufficient inspection accuracy. Standard smartphone GPS has errors of several meters, but with RTK corrections the error is reduced to a few centimeters. LRTK simple surveying has confirmed horizontal accuracy of approximately 1-2 cm (0.4-0.8 in), comparable to conventional first-class surveying instruments. Because AR displays align with the real object, differences or gaps of a few centimeters can be reliably detected. For critical points, checking against point cloud data enables millimeter-level inspections.

Q: Can AR as-built inspection be used in public works inspections? A: The Ministry of Land, Infrastructure, Transport and Tourism promotes the use of 3D data and AR technologies as part of i-Construction, and trial cases of performing as-built inspections by overlaying design models on tablet AR screens have been published. However, at present AR use is not explicitly stated in official construction inspection procedures. That said, combining as-built management using point cloud data with AR is increasingly common in supervision and inspection. If guidelines are developed in the future, AR as-built inspection could well become part of official inspection processes.

Q: Is AR as-built inspection difficult to operate? Can people who are not familiar with digital tools use it? A: The operation is simple and intuitive. You just follow on-screen prompts while looking through the smartphone or tablet camera and tapping, so even those who are not good with machines can learn it in a short training period. Even without specialized surveying skills, anyone can perform accurate as-built verification by following guidance. Visual presentation of results also makes them easy to understand and facilitates smooth information sharing within teams.

Q: Is AR as-built inspection effective on any construction site? A: Yes. AR as-built inspection is effective on any site where you want to verify differences between design and construction results, regardless of civil or building works. It is especially useful for roadworks or land development requiring wide-area elevation control, where heat maps of acquired data make low and high areas immediately apparent. For large structures such as tunnels and dams, comparing concrete thickness and shapes with 3D models helps detect defects that are otherwise hard to see. In the building sector, AR can be used to compare column and wall positions with BIM models or to pre-check piping clashes. In short, AR as-built inspection is effective wherever there is a need to verify a completed object on site. The benefits are particularly large for processes where rework is difficult or correction costs are high.