Improved Safety: Reducing Entry into Hazardous Areas with AR As-Built Inspections

Table of Contents

• What is AR as-built inspection

• Conventional as-built inspections and safety issues

• Safety improvements achieved by AR as-built inspection

• Other benefits of using AR

• How to introduce AR as-built inspection

• Simple surveying and AR as-built inspection enabled by LRTK

• Frequently Asked Questions

What is AR as-built inspection

As-built inspection is an important process in civil engineering and construction for confirming and recording that completed structures and developed land meet the designed shapes and dimensions. In public works in particular, the results of as-built inspections often determine whether an inspection is passed or whether handover can occur, making them a key element of quality assurance. Traditionally, as-built confirmation has relied on direct measurements using tape measures, staffs (measuring rods), levels, and photography. However, measuring points manually is very time- and labor-intensive, and because the number of measurement points is limited, there is an unavoidable risk of overlooking discrepancies.

Against this background, a next-generation field verification method that has attracted attention in recent years is AR as-built inspection (AR as-built check). This combines AR (Augmented Reality) technology with high-precision GNSS positioning to confirm as-built conditions on site in real time. By overlaying design drawings or 3D model data onto the actual construction site through a smartphone or tablet camera, you can intuitively grasp discrepancies between the constructed work and the design on the spot. For example, if design lines and elevation information are displayed in AR over a paved road or developed land after paving, you can immediately tell whether the finish is within tolerance. Enabling this are RTK-GNSS (satellite positioning) integrated with smartphone sensors to achieve centimeter-level positioning accuracy. In recent years, smartphones and tablets themselves have been equipped with high-performance cameras and LiDAR scanners, creating an environment where such digital construction technologies can be used in daily operations. The Ministry of Land, Infrastructure, Transport and Tourism–led *i-Construction* initiative has also provided momentum, and AR as-built inspection is increasingly expected as a powerful solution to simultaneously improve site efficiency and safety. For sites where constant attention to safety measures to prevent major accidents is necessary, there is growing expectation for technologies that can reduce worker risk.

Conventional as-built inspections and safety issues

In conventional as-built inspections, it is common to measure key points of completed structures and terrain manually and to record and verify the differences from the design values on drawings. For example, in road works, the thickness, width, and elevation of the subgrade and pavement are measured by section, and in slope works the gradient and length of slopes are measured to create as-built management charts (measurement result summary tables). Many long-standing issues have been pointed out with these methods.

First, these tasks require significant time and manpower. Confirming numerous measurement points across a large site often takes a team of two or more people a full day. With a shortage of experienced survey technicians, progressing accurate as-built inspections with limited personnel is a heavy burden. Insufficient coverage is also a problem. With point measurements taken manually, there is a physical limit to how many locations can be measured, and the entire construction area cannot be covered. Only representative points can be checked, which means there is always a risk of overlooking areas that differ from the design. On large structures, slight unevenness or variation can go unnoticed, and later inspections may find discrepancies with drawings that require hurried rework.

Furthermore, safety risks cannot be ignored. Traditional surveying and as-built confirmation tasks often require workers to enter hazardous areas to take measurements. For example, on steep slopes, it is necessary to climb the slope and set a staff, which always carries the risk of falls from height. On road sites, measurements may be taken in areas where vehicles or heavy machinery operate, creating a risk of contact between workers and machinery. When measuring thicknesses on large structures, workers may have to adopt unstable postures, increasing the risk of slips or falls. Thus, conventional as-built inspections had room for improvement not only in work efficiency but also in ensuring worker safety.

Safety improvements achieved by AR as-built inspection

Introducing AR as-built inspection can dramatically improve site safety. The greatest factor is reducing entry into hazardous areas. With AR technology, you can check the shape of the constructed works remotely, so there is no need to force access to dangerous locations that were previously measured up close. For example, measurements at the top of a slope or at height can be completed by placing and guiding AR markers from a safe distance. This reduces opportunities for workers to climb slopes or assume unstable positions at heights, lowering the risk of falls. Even when confirming as-built conditions around operating machinery, measurement points can be guided via AR displays so that workers do not enter machinery operation zones, preventing contact accidents and maintaining safe distances. As a result, AR as-built inspection greatly reduces human risk in site work and strongly supports “safety-first” construction management.

AR visualization of hazardous areas also contributes to improved safety. By displaying 3D-scanned terrain models and construction data in AR, hazardous areas can be recognized at a glance on site. For example, in slope works, post-construction point cloud data can be overlaid on the real scenery in AR so that the entire crew can intuitively share information such as areas at risk of collapse and anchor positions that require reinforcement. Previously, managing as-built conditions over wide areas and at height or detecting defects was difficult, but the combination of AR and digital data enables safer and more reliable inspections. Thus, AR as-built inspection is not only for efficiency and labor saving, but also a powerful solution to the serious issue of ensuring worker safety.

Other benefits of using AR

Introducing AR as-built inspection offers benefits on site beyond safety improvements. Here are some representative effects.

• Real-time problem detection: Construction defects and deviations from design can be discovered immediately on site, allowing corrective measures to be taken at once. If pavement thickness or slope deficiencies are color-coded in AR immediately after construction, you can prevent situations where problems are noticed only after completion. Because PDCA can be run on site, this leads to reduced rework.

• Reduced work time and labor saving: Because a wide area’s as-built conditions can be visualized at once, inspections that used to take days can be sped up significantly. Tasks that once measured point by point with paper drawings and surveying instruments are replaced by intuitive confirmations that simply overlay data in AR, making it possible for one person to perform measurements and inspections. This reduces personnel arrangements and allows limited staff to manage construction efficiently.

• Improved measurement accuracy and coverage: By combining point cloud scanning and high-precision GNSS, large areas can be measured at high density, so millimeter-level errors and subtle unevenness are not overlooked. Checks close to full-coverage inspection, including areas that used to be uncovered, become possible, greatly reducing the risk of overlooking quality defects. Human errors in recordkeeping can also be eliminated through digitalization.

• Streamlined record keeping and reporting: As-built conditions checked in AR can be saved as screenshots or heat map images and attached directly to inspection reports, making materials easier to understand. The time and effort to compile photo albums and charts manually is reduced, easing reporting burdens. Digital data can be shared instantly via the cloud, enabling immediate information sharing and decision-making with stakeholders on site.

• Improved communication and consensus building: Visualizing as-built conditions in AR is highly effective for information sharing among site staff and with clients. If everyone sees the AR visualization of the completed shape on a tablet, it becomes immediately clear which areas need what degree of correction. Discussions can rely on objective visual information rather than the intuition or experience of veterans, reducing misalignment in understanding and facilitating smoother consensus building.

• Cost reduction: Another major advantage is that you may not need to purchase dedicated surveying equipment. A high-precision measurement environment can be built by combining a smartphone with a relatively inexpensive GNSS receiver, reducing initial investment. In addition, reductions in rework and labor costs can be expected to lower total costs.

As described above, AR as-built inspection solves the problems of conventional methods and is a revolutionary solution that simultaneously improves safety, productivity, and quality.

How to introduce AR as-built inspection

Given the many benefits of AR as-built inspection, what preparation and equipment are actually needed to use it on site? Basically, you can get started with an AR-capable smartphone or tablet, an RTK-compatible GNSS receiver to improve positioning accuracy, and an AR surveying app that combines them. If you prepare design data (3D models or digital drawings) in advance and load it into the app, the data can be overlaid on site coordinates in AR while receiving GNSS correction information. Modern iOS/Android devices have improved camera performance and sensor accuracy, making them ideal for AR use, and by pairing a compact GNSS receiver via Bluetooth you can build a positioning environment with centimeter-level accuracy (half-inch accuracy) without dedicated expensive surveying equipment. In outdoor areas with good radio conditions, public GNSS correction services can be used over the internet, allowing high-precision positioning without installing your own base station. Recently, many companies have begun offering easy AR as-built inspection solutions based on mobile devices + GNSS + dedicated apps that are designed to be usable by anyone without special skills.

Simple surveying and AR as-built inspection enabled by LRTK

For example, LRTK, developed by a startup from Tokyo Institute of Technology, is a system composed of a pocket-sized RTK-GNSS receiver that can be attached to an iPhone and a dedicated app. With this, surveying, inspection, recording, and as-built inspection can all be completed with just a smartphone, transforming the site into an environment where high-precision digital construction management can be performed with one device per person. LRTK is designed for intuitive operation so that technicians without specialized training can use it easily and immediately take advantage of centimeter-level accuracy (half-inch accuracy) positioning, point cloud scanning, and AR as-built checks through its simple surveying functions. In practice, many construction companies have introduced this system and begun to achieve significant labor savings and quality improvements compared to conventional methods.

By using such modern tools, AR as-built inspection, which used to have high barriers, can become a routine part of daily work for anyone. You may be surprised how easily inspection tasks done with paper drawings and tape measures can be digitized. The important thing is to try it on site first. LRTK, which enables seamless “measure, record, compare, and share” workflows with just a smartphone, is a solution that strongly supports DX (digital transformation) in construction sites. Why not introduce AR as-built inspection to your own sites using these easy-to-use tools to improve both safety and productivity?

Frequently Asked Questions

Q: What do I need to start AR as-built inspection? A: You need an AR-capable smartphone or tablet and a high-precision GNSS receiver, plus a compatible AR surveying app. Specifically, use a modern smartphone together with a Bluetooth-connected compact RTK-GNSS rover (for example, devices such as LRTK that can be attached to a smartphone). Also prepare design 3D model data or drawing data for comparison. With these set up, you can try AR as-built inspection on site immediately.

Q: Can the accuracy of as-built confirmations made with AR be trusted? A: If operated properly, high accuracy and reliability can be achieved. Systems that combine RTK GNSS corrections can realize positioning accuracy on the order of several centimeters in both horizontal and vertical directions, which is within the tolerance required for typical as-built inspections. Using AR heat maps that color-code deviations, you can obtain quantitative information such as “which point is how many cm higher/lower than the design,” enabling more reliable judgments than simple visual inspection. It is important to perform accurate site control point and data alignment (calibration) beforehand and, when necessary, to supplement with conventional verification at key locations. If these points are observed, AR as-built inspection results can be trusted as sufficiently well-founded.

Q: Can AR as-built inspection be used on projects that do not have 3D design data? A: Even without a 3D model, AR can be used with some ingenuity. For example, there are apps that can load 2D drawing data (CAD data, etc.) into the AR space to visualize major lines and positions on site. If the final form is not very complex, a simple method is to mark major dimensions on the ground before construction and compare them by overlaying AR-captured images. That said, the greatest benefit is realized when 3D models are available. Opportunities to receive 3D data such as CIM models from clients are increasing, so it is recommended to prepare 3D data from the design stage if possible. For use cases that compare point cloud measurement data with design drawings, non-AR dedicated software for difference detection may be more suitable in some cases. The key is to enable intuitive on-site confirmation, so choose the method best suited to the availability of model data.

Q: Can AR as-built inspection results be used for official as-built inspection? A: At present, operations that rely solely on AR as the basis for official inspections are just beginning, but they are expected to be accepted increasingly in the future. The Ministry of Land, Infrastructure, Transport and Tourism conducted field demonstrations in fiscal 2023 and confirmed that using AR technology can simplify submission documents. Currently, it is often necessary to supplement records with conventional methods (charts and photo albums), but submitting AR-verified visual materials as supplementary documents can make it easier for inspectors to understand. While there is a growing possibility that AR-generated as-built data itself will be accepted as official deliverables in the future, for the time being it is prudent to use AR as supporting documentation and perform conventional measurements in parallel where necessary.

Q: I’m worried that not all site staff will be able to master these new technologies. A: AR construction support tools are becoming more user-friendly year by year, and basic operations are by no means difficult. In fact, many adopters find both young and experienced staff become proficient after short training. If still concerned, have an experienced operator demonstrate on site first while others observe. If staff experience the benefits firsthand, they are likely to adopt the tools positively. “It’s certainly faster” and “it’s easy to understand” are common reactions once tried on site, which helps reduce resistance. Recent AR apps also offer Japanese-language interfaces and robust support systems, so there is help available when needed. ICT use on construction sites will become increasingly essential, so build an environment where everyone can use the tools gradually without rushing.

Q: Can AR as-built inspection be performed in tunnels or indoors where GNSS cannot be received? A: Unfortunately, pure GNSS positioning cannot be used where there is no sky view. In such cases, one method is to use pre-measured control points as AR markers to perform relative alignment. For example, in tunnel works, coordinates obtained by GNSS near the portal can be used as a reference to correct positions of known interior points and then perform AR displays. Indoors, QR codes or feature markers can be installed and used for AR alignment. Although it requires some extra work, AR as-built inspection can be used even in sites where GNSS is unavailable with appropriate ingenuity.

Q: Do we need special devices such as dedicated AR glasses? A: Currently, smartphones and tablets are sufficient for practical use. See-through AR glasses (goggles) are emerging, but they are very expensive and have challenges such as difficulty combining with safety helmets. Smartphones and tablets, on the other hand, can be used casually on site in dustproof/waterproof cases, and operation via touch panel is simple. Screen resolution and processing power are improving year by year, so handheld devices offer adequate visibility and performance for business use. If glasses-type devices become lightweight and inexpensive in the future, their use may expand, but at present using existing handheld devices for AR is the most realistic and cost-effective approach. It is recommended to start with familiar smartphone AR and consider future device expansion as needed.