Frontline of On-site DX: Latest Trends and Implementation Points for AR As-built Inspection

Table of Contents

• What is AR as-built inspection?

• Challenges of traditional as-built management

• On-site use of AR technology: immediate checks through visualization

• Benefits of introducing AR as-built inspection

• Points to consider when introducing it

• Simple surveying achieved with LRTK

• FAQ

What is AR as-built inspection?

As-built inspection is a quality control process in civil engineering and construction that verifies and records whether completed structures and developed land conform to the design shapes and dimensions. In public works, the results of as-built inspection are often conditions for acceptance and handover of the work, so this is a very important step. Traditionally, direct measurements using surveying instruments and tape measures and photography were used to measure post-construction heights, thicknesses, widths, etc., point by point, and the errors from design values were summarized in charts or photo albums for reporting. However, this manual-centered method inevitably lacked completeness because measured points were limited, which carried the risk of oversights. It also often took time from measurement to reporting, delaying discovery of issues and causing rework. In recent years, labor shortages and workstyle reforms have further increased demand for efficient and reliable inspection methods.

Against this backdrop, a new on-site inspection method called “AR as-built inspection” has attracted attention. It combines AR (Augmented Reality) technology and positioning technology to allow real-time on-site confirmation of as-built conditions. Digital information such as design drawings or 3D models is superimposed on the actual construction site through the camera of a smartphone or tablet, enabling intuitive on-the-spot recognition of discrepancies between the completed work and the design. For example, after paving work, if a virtual horizontal plane representing the design completion elevation is displayed in AR above the ground, you can immediately tell whether the actual ground is higher or lower than that reference plane. The aim of AR as-built inspection is to transform work that used to compare numbers on paper drawings into something that can be directly seen and confirmed on site.

Background and latest trends that make AR as-built inspection notable

DX (digital transformation) is sweeping through the construction industry and accelerating digitalization of construction management. As part of the Ministry of Land, Infrastructure, Transport and Tourism’s *i-Construction* initiatives, as-built management using ICT has been officially encouraged. In particular, the introduction of 3D measurement technologies has progressed in recent years: laser scanners and drone photogrammetry can densely scan structures and terrain to obtain point cloud data (3D measurement data), enabling planar evaluation of as-built conditions. Point cloud measurement, which can cover wide areas that previously could only be sampled at a few points almost without missing anything in a single scan, is becoming the new norm in as-built management.

However, high-performance 3D laser scanners and the like are expensive and require specialized skills, so adoption at small and medium sites lagged. In response, a new simple surveying solution using smartphones + RTK-GNSS has emerged. Recently, small high-precision GNSS receivers that attach to smartphones have been developed, and by using RTK (Real Time Kinematic) satellite positioning correction technology, centimeter-level positioning (half-inch-level positioning) has become easily achievable by anyone. Combined with a smartphone’s built-in camera or LiDAR sensor, terrain and structures can be scanned and converted to point cloud data on the spot. The advent of such “phone surveying” is creating an environment where high-precision as-built data acquisition and AR display can be done on site without relying on veteran surveyors.

A current trend is the practical use of color-coded heat maps created by comparing acquired point cloud data with the design 3D model and projecting the error distribution in AR on-site. For example, point clouds measured for as-built inspection can be analyzed in the cloud against the design model to generate a heat map indicating elevation differences. If you download that to a smartphone and overlay it on site, you can instantly see which areas are several centimeters higher or lower than the design. There have been trials in Ministry of Land, Infrastructure, Transport and Tourism–directed projects using heat maps projected on site with XR technology (AR) for inspection attendance, and this promises to let stakeholders share overall as-built assessments at a glance that were hard to understand from paper drawings. AR as-built inspection is truly the frontline of on-site DX. The era when AR is used as an “everyday tool” in daily construction management is just around the corner.

Benefits of AR as-built inspection

AR as-built inspection offers many advantages not found in conventional methods. The main benefits are summarized below.

• Precise inspection that does not miss even millimeter-level errors: By overlaying design data on camera images, height differences of less than a few centimeters and deficiencies in thickness that are hard to see with the naked eye can be visualized instantly. For example, if you scan the ground surface with a smartphone and compare it with the design model, slight bumps or slope defects can be detected on the spot and corrected. Displaying a color-coded heat map showing “design ±○ cm” will reliably reveal fine discrepancies that even experienced personnel might miss. Objects that become invisible after completion, such as buried pipes, can also be checked after backfilling by AR-transparently displaying previously acquired 3D data, reducing the risk of damage in later processes.

• Improved inspection efficiency and on-the-spot consensus building: AR enables inspection of wide-area as-built conditions at once, making it vastly quicker than point-by-point hand measurements. Software can automatically analyze errors and even judge pass/fail, reducing the burden on field staff. Also, by viewing the screen together with the client (inspector) on site, you can share and explain finish quality immediately, making it easier to reach consensus on the spot without relying on later meetings.

• Digitalization of as-built records and reliable quality evidence: AR as-built inspection allows inspection results to be stored as digital data. If you save georeferenced photos, point cloud data, heat map figures, etc., in the cloud, you reduce the paperwork burden and can later use them as objective evidence. Human errors such as incorrect handwritten notes of measurement points are prevented, improving the reliability of inspection materials.

• Labor reduction with simple surveying usable by non-specialists: With just a smartphone, a small GNSS receiver, and a compatible app, a system that anyone can handle is feasible, allowing on-site staff to confirm as-built conditions without being expert surveyors. Tasks that used to require two people, like layout marking and batter board checks, can be handled accurately by one person using AR displays. This allows surveying work to proceed smoothly even at sites with labor shortages, directly leading to reduced manpower and labor savings.

• On-site DX effects through remote attendance and cloud sharing: Digitized as-built data can be shared instantly with stakeholders via the cloud, making it easier to grasp construction management status without being on site. If measurement data or AR screens are shared in an online meeting as needed, remote inspection attendance from a distant office becomes possible. Accumulated 3D data can also be used for future renovation planning, becoming an asset that contributes to DX in maintenance management after construction.

Points to consider when introducing AR as-built inspection

To reap these benefits, here are points to keep in mind when actually introducing AR as-built inspection on site.

• Prepare digital design data: To display design information in AR, digital data such as reference drawings or BIM/CIM models are necessary. If possible, prepare a 3D design model and align it with the site’s surveying coordinate system. From fiscal 2023, the Ministry’s direct projects began principal application of BIM/CIM, and many projects now have 3D models prepared. Using digital design information in your own projects as much as possible is the first step in introducing AR as-built inspection.

• Provide necessary equipment and environment: The basic configuration is “smartphone/tablet + RTK-capable GNSS receiver + dedicated app.” Prepare compatible devices and apps in advance and ensure the GNSS receiver can receive correction information at the site. In Japan, centimeter-level positioning correction services using “Michibiki” (Quasi-Zenith Satellite System) such as CLAS and internet-based network RTK services are available; contracting these allows cm accuracy (half-inch accuracy) positioning without installing your own base station. In mountainous areas with no radio coverage, consider preparing a mobile base station. Once positioning is stable, start the app’s AR display mode and calibrate the device’s orientation sensors (electronic compass) as needed.

• Operate according to site conditions: RTK precision positioning cannot be used directly in tunnels or indoors where GNSS cannot be received. In such cases, there are methods to transfer the reference based on previously surveyed known points. For example, in tunnel work you can set a local reference using coordinates measured at the portal and then perform AR display from that point. For indoor or underground spaces, techniques that install QR code markers or feature-point markers and use smartphone image recognition for alignment are emerging. Choose the optimal positioning and alignment method according to your site conditions.

• Consider introduction costs and benefits: New devices and software come with costs, but starting up is far less expensive than purchasing dedicated large surveying instruments. Many people on site already own smartphones, and the price of small GNSS receivers is much more affordable compared to traditional surveying equipment. Software is often provided as a cloud service, allowing flexible licensing for only the required period. Above all, the time savings and personnel reductions translate to significant cost reductions, so overall you can expect returns that exceed the investment. It is recommended to start with a pilot on a small site to verify effects and then expand internally.

• Operation training and support system: At first you may be unsure about handling equipment or calibration procedures, but basic operations are not difficult as they follow app instructions. Conduct simple pre-training and trial operations so that responsible personnel become accustomed to operations. Also confirm that there is a support desk for inquiries and a way to receive software update information. As site staff use the system daily, they will get a feel for it and operations will gradually become smoother.

Future outlook for AR as-built inspection

Although AR as-built inspection is still a new technology, it is expected to become increasingly widespread. The Ministry of Land, Infrastructure, Transport and Tourism is promoting ICT use in construction management and officially recognizes use of 3D data and AR. For example, submitting heat map drawings made from point clouds as as-built management deliverables is becoming more common, and direct inspections using AR may become standard in the future. Currently use is centered on smart devices, but wearable devices such as AR glasses (smart glasses) may allow workers to perform inspections hands-free. There is also anticipation for expansion into smart construction, where acquired as-built data is analyzed by AI to automatically indicate pass/fail and areas needing touch-ups.

On the other hand, some challenges will need to be addressed as the technology advances. These include improving indoor positioning technologies for environments where GNSS is difficult and developing cloud infrastructures that efficiently handle massive point cloud data. From the field there are comments such as “even if things are digitized, it’s meaningless unless people can actually use them,” but intuitive AR interfaces will ease such concerns and enable on-site DX that anyone from young workers to veterans can participate in. AR as-built inspection is expected to continue evolving as a solution that simultaneously enhances productivity and quality at construction sites.

Simple surveying with LRTK

One solution that easily realizes AR as-built inspection is LRTK. LRTK is a system consisting of a pocket-sized RTK-GNSS antenna that attaches to a smartphone and a dedicated app, and it is an all-purpose surveying tool that enables anyone to perform centimeter-level positioning and point cloud measurement. By combining design data with real-time positioning, it enables immediate AR as-built confirmation on site. With high-precision positioning and cloud linkage, surveying, as-built management, and photo recording can be performed end-to-end by a single person, greatly improving efficiency and reducing manpower. It is a cutting-edge technology compatible with the Ministry’s i-Construction initiative and has already been adopted at many sites. If you are considering introducing AR as-built inspection at your company, consider LRTK’s simple surveying to achieve smart and high-precision construction management.

FAQ

Q: If AR is used for as-built inspection, can the accuracy be trusted? A: AR combined with high-precision position correction using RTK-GNSS can reduce errors to on the order of several centimeters. General smartphone GPS has errors of several meters, but RTK allows self-positioning with the same precision as surveying control points, and AR displays can be overlaid with almost no offset. Proper calibration of device gyroscopes and electronic compasses also keeps directional accuracy at a practically acceptable level.

Q: What preparation and equipment are needed to perform AR display on site? A: The basic configuration is smartphone/tablet + RTK-capable GNSS receiver + dedicated app. Prepare design data (drawings or 3D models) in digital form in advance and load them into the app aligned to site coordinates. A GNSS receiver that can receive correction information (CLAS or network RTK) via the internet is convenient. Outdoors with radio connectivity, high-precision positioning is possible without a special base station.

Q: What should be done in environments where GNSS cannot be used, such as inside tunnels or buildings? A: Pure GNSS positioning cannot be used where there is no sky view. In such cases, respond using alignment based on known points. For example, in tunnel work you can set reference coordinates measured near the entrance and set relative positions for known points inside the tunnel, then perform AR display from those reference points. For indoor work, installing markers such as QR codes and using the camera to read them for alignment is another method. In short, if you devise a way to link digital data and the site without GNSS, AR as-built inspection can be applied.

Q: Isn’t introducing AR as-built inspection expensive? A: It is considerably lower cost than equipping large conventional surveying instruments. You can use smartphones or tablets you already have, and small RTK-GNSS receivers are available at accessible price points through purchase, rental, or lease. Apps and cloud services are typically subscription-based, allowing you to contract only the functions you need. Initial investment can be kept relatively low, and the benefits from reduced labor costs and shortened schedules often result in high cost-effectiveness.

Q: Can people who are not good with machines use it? Are special skills required? A: Basic operations are simple and designed to be intuitive even without specialized surveying qualifications. For example, systems like LRTK let you hold the antenna-equipped phone over the point to be measured and record coordinates with a single tap, and AR display simply overlays the model from a menu. However, some practice is necessary until you become familiar with equipment handling. If you learn the operation procedures beforehand through trials, you should be able to handle on-site situations calmly. As you use it, you’ll gradually pick up tips and anyone can eventually use it efficiently.

Q: For what kinds of work or tasks can AR as-built inspection be used? A: It can be used across a wide range from civil engineering to building construction. It is particularly effective in earthworks such as roads and land development for verifying ground elevation and slope, and in paving work for checking thickness and flatness. It is also useful for checking the dimensions of concrete structures and the installation positions of buried pipes. If you have pre-acquired drawing data or BIM/CIM models, AR visualization of as-built conditions can be implemented at virtually any site. In short, AR as-built inspection contributes to quality control in any situation that involves shape or dimensional verification.