Towards i-Construction Promotion: How AR As-Built Inspection Is Changing Construction Sites

Table of Contents

• What is AR as-built inspection

• Challenges of traditional as-built verification

• Benefit 1: Precise checks that catch deviations down to millimeters

• Benefit 2: Improved inspection efficiency and smooth consensus building

• Benefit 3: Digitalized as-built records that reliably prove quality

• Benefit 4: Labor savings through simple surveying anyone can do

• Benefit 5: Promoting site DX with remote supervision and cloud sharing

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

• FAQ

What is AR as-built inspection

As-built management (as-built inspection) is a quality-control process in civil engineering and construction that measures and verifies whether the shapes and dimensions of completed structures and developed land have been constructed according to the design drawings. Traditionally, surveyors used total stations (TS), levels, tape measures, and the like to carefully measure heights and thicknesses at each point, recorded the results by hand, and then returned to the office to compare them with the design drawings to decide pass/fail. However, this method often creates a time lag between measurement on site and discovery of problems, which can lead to rework. Measurement and inspection work also rely heavily on the experience and intuition of skilled personnel, and with chronic labor shortages and an aging workforce, improving efficiency has become a major challenge.

Against this background, a new approach called AR as-built inspection has attracted attention in recent years. By utilizing AR (Augmented Reality) technology to overlay 3D design models and construction specification data onto smartphone or tablet camera images, you can directly verify as-built conditions on site. Because as-built checks that used to be done on paper drawings or numerical data can now be compared in real time between the actual object and digital information, even less-experienced technicians can intuitively judge whether the finish is acceptable. In particular, when combined with high-precision GNSS RTK positioning (real-time kinematic), the models and lines displayed in AR can be accurately aligned with actual structures within a few centimeters. Smartphone plus a small RTK-GNSS receiver enables centimeter-level (inch-level) positioning, allowing inspections where the AR display aligns perfectly with the real object without shifting. Additionally, with LiDAR sensors built into recent smart devices, it has become possible to obtain point-cloud data (3D scans) of the site and compare it with design data to visualize differences—an advanced usage that is beginning to be realized.

The Ministry of Land, Infrastructure, Transport and Tourism’s “i-Construction” initiative promotes the use of ICT and 3D data along with the introduction of AR for as-built and progress confirmation. In fact, in some pilot projects, efforts have been published showing as-built inspections performed by overlaying design models and existing conditions on a tablet’s AR screen, and this is expected to streamline and speed up stage confirmations and supervisory inspections. AR as-built inspection improves both on-site productivity and quality control and is attracting attention as a key solution to advance i-Construction.

Challenges of traditional as-built verification

To understand the benefits of AR as-built inspection, first let’s summarize the main issues of traditional as-built verification (as-built inspection) methods. The conventional approach had the following problems:

• Time-consuming and labor-intensive: Survey staff used surveying instruments and tape measures to take measurements point by point and recorded results by hand. When the construction area is wide and there are many measurement points, it can take days to complete all measurements and drawing comparisons.

• Dependence on experienced personnel: Accurate measurement and inspection require experienced survey technicians and often needed two-person teams. With severe labor shortages and an aging technician population, it has become difficult to secure sufficient personnel at each site.

• Expensive equipment required: Measuring deviations from design values to millimeter accuracy requires specialized high-precision equipment such as TS or GNSS receivers. These entail very high initial investment, making adoption difficult for small and medium-sized companies. Maintenance costs and theft risk of such equipment are also non-negligible.

• Risk of human error: Manual measurements are prone to human mistakes such as incorrect notes or transcription errors later. Missed measurements discovered later can require revisiting the site for re-measurement, causing rework.

• Delayed discovery of problems: Because measured values are taken back to the office to be compared with drawings, construction defects may not be noticed on the spot, leading to cases that are too late to fix easily. For example, if concrete thickness or basecourse height is insufficient, discovering this only in subsequent inspections after curing may require major repairs.

• Burden of document creation: As-built management requires creating drawings and reports based on measurements to submit to the client. Traditionally, document preparation also took time and effort and was a major burden for those responsible.

As described above, traditional as-built verification is inherently inefficient and carries the risk of overlooking quality issues. To check as-built conditions in real time and with precision, it was essential to adopt new technologies with site DX in mind.

Benefit 1: Precise checks that catch deviations down to millimeters

One of the greatest advantages of AR as-built inspection is that it can detect construction errors and slight deviations down to the millimeter level. By overlaying design data on camera images, subtle differences in elevation or insufficient thickness that are hard to notice with the naked eye are immediately visualized. For example, in road embankment work, scanning the finished surface with a smartphone to obtain point-cloud data and comparing it on the spot in AR with the design reference model makes small defects in unevenness or slope immediately obvious. If you display a color-coded difference heatmap, you can intuitively see “which points are how many centimeters higher/lower than the design.” As a result, even minute defects that might have been overlooked by experienced personnel can be reliably detected, leading to early correction of quality issues.

Also, because you can compare the numbers on the drawings with the actual object while viewing them, it helps reduce human errors such as misreading figures or recording mistakes. Compared with inspections that relied solely on numerical data, inspection accuracy dramatically improves, enabling more reliable quality control. In addition, items that become invisible after completion, such as buried pipes or underground structures, can be confirmed even after backfilling by visualizing pre-scanned point-cloud models in AR. For example, if a sewer pipe is recorded in 3D before installation, you can still check its alignment and depth on a smartphone screen after paving is completed, reducing the risk of accidental damage in later processes. AR as-built inspection captures even minor on-site deviations, contributing greatly to preventing quality troubles.

Benefit 2: Improved inspection efficiency and smooth consensus building

The use of AR technology greatly speeds up as-built inspection efficiency and consensus building among stakeholders. Because you can measure wide areas in 3D at once, it significantly reduces time compared to point-by-point measurements, and applications automatically process measurement result analysis and pass/fail judgment. For example, using drone photogrammetry or iPhone LiDAR scanning, work that used to take half a day to measure a slope can be completed in tens of minutes in some cases. Acquired point-cloud data are automatically compared with design data in the cloud, and deviations from standards are immediately highlighted. Inspectors can grasp inspection results on a tablet screen on site, saving the effort of punching numbers into a calculator or recording on drawings by hand.

Furthermore, 3D visualization of inspection results via AR facilitates communication with clients and supervisors. Clients who previously only heard numerical reports can be much more satisfied when they can visually confirm discrepancies between the finished form and the current state through a tablet on site. In remote attendance (remote witnessing) situations, sharing the on-site AR images allows the office-side personnel to accurately understand the situation and prevents communication loss due to differing perceptions. This visualization effect deepens the understanding of all stakeholders, enabling reliable consensus building and dramatically streamlining the approval process.

Benefit 3: Digitalized as-built records that reliably prove quality

AR as-built inspection also stands out for its ability to fully digitalize on-site as-built records and contribute to reliable proof of quality. Once you obtain high-precision point-cloud data via 3D scanning, you can record construction results comprehensively without “missed measurements” or “missed photos.” While conventional methods estimated as-built conditions by measuring only a few critical points, 3D data allow you to understand the entire structure down to every corner.

The acquired point-cloud data and geotagged photos become digital inspection evidence as they are. If you prepare automatically generated color-coded difference diagrams and cross-section comparison drawings, you can objectively explain and prove later “was this really built according to design?” even after the fact. Tiny discrepancies that were hard to convey on paper drawings can be shown on a 3D model for immediate understanding, improving explainability during as-built management.

Moreover, these digital records can be securely stored and shared in the cloud, making electronic delivery to clients easy. Document creation for inspections can be largely automated, reducing the reporting burden on site supervisors. When planning similar future works, accumulated as-built data can be used as reference materials, enabling data-driven decision making. The digital quality proof provided by AR as-built inspection is expected to contribute to long-term reliability assurance and know-how accumulation.

Benefit 4: Labor savings through simple surveying anyone can do

Modern AR as-built inspection tools run on smartphones and tablets, enabling simple surveying that even those with limited experience operating specialized equipment can intuitively use. For example, with an RTK-GNSS compatible device attached to a smartphone and a dedicated app, you can achieve centimeter-level positioning and 3D scan measurement just by following on-screen instructions, without complicated settings or difficult calculations. User interfaces and workflows designed for ease of use allow even novice technicians to acquire and verify as-built data with a consistent level of accuracy, even when veteran surveyors are not present.

Digital measurement can record wide areas at once, significantly reducing manual labor. If surveying work that used to require two people can be done by one, this reduces labor costs and the burden of personnel coordination. There is no need to carry heavy equipment around the site repeatedly or spend time setting up and packing equipment. As a result, work can progress even with limited staff, and the physical and mental burden on each worker is reduced.

The time and effort saved can be redirected to other quality control or safety management tasks. AR as-built inspection leads to smart construction that doesn’t rely on people, and can serve as a trump card to mitigate the worsening labor shortage.

Benefit 5: Promoting site DX with remote supervision and cloud sharing

Digitalization of as-built data and AR display enable new workflows for remote supervision and support of sites, strongly promoting site DX (digital transformation). If 3D point clouds and AR images captured on site are shared instantly via the cloud, technicians can monitor and guide multiple sites’ construction status in real time from a distant office.

For example, when on-site staff upload a scanned point-cloud model or live AR footage to the cloud from a smartphone, head office engineers or clients can grasp as-built status from their desks. They can easily add comments to the data or issue additional instructions remotely as needed. If inspections, witnessings, or meetings can be conducted without visiting the site, travel time and costs can be reduced and decision-making accelerated.

Also, as-built data accumulated in the cloud are always accessible as the latest information by all stakeholders. Time lags such as “I can’t decide because I don’t have the latest drawings” are eliminated, and information sharing between site and office, client and contractor becomes seamless. Compared with traditional methods that relied on paper management charts, the workflow of construction management will be greatly transformed. This new system of remote supervision + data sharing is expected to become the standard for smart construction sites in the future.

Start AR as-built inspection with simple surveying using LRTK

As described, AR as-built inspection can greatly improve on-site productivity and ensure quality. However, many may wonder, “I’m interested, but don’t know where to start.” A suitable solution in such cases is simple surveying using a smartphone-mounted RTK-GNSS system called LRTK.

LRTK is an all-in-one high-precision measurement system that enables surveying and as-built inspection on site with just a smartphone and a small GNSS receiver. RTK-GNSS enables centimeter-level positioning accuracy of horizontal ±1-2 cm (±0.4-0.8 in) and vertical ±3 cm (±1.2 in), allowing you to identify positions with precision comparable to dedicated surveying instruments. Based on the acquired high-precision coordinates, you can project and display design models in AR on the spot and compare them with point-cloud data. Stable AR display without positional drift lets anyone perform intuitive as-built checks that are not possible with paper drawings.

Moreover, LRTK includes a point-cloud measurement function that leverages the smartphone’s built-in LiDAR sensor and camera. Even complex-shaped structures can be scanned simply by holding up the smartphone to generate high-precision 3D point-cloud models. Because acquired point-cloud data are assigned absolute coordinates derived from RTK-GNSS, they can be immediately used for comparisons with design data or volume calculations. Also, by recording coordinates of measured points, LRTK’s coordinate navigation (guidance) function is powerful when performing stakeout or equipment installation at the same positions later. By following guide arrows on the smartphone screen, you can be guided to the specified coordinate point with only a few centimeters of error, making one-person stake positioning possible where it used to be difficult.

By using LRTK simple surveying, which integrates AR display, point-cloud acquisition, coordinate guidance, and as-built inspection on a single platform, tasks that used to be performed with separate devices and software connect seamlessly and site DX accelerates dramatically. In fact, LRTK is being adopted at construction sites nationwide and has contributed significantly to speeding disaster recovery and improving construction management efficiency. LRTK, which combines the advantages of the latest technology with ease of use, allows sites introducing AR as-built inspection for the first time to start operations in a relatively short period. As a tool to lead smart construction in the i-Construction era, simple surveying with LRTK will become a reliable ally for future sites.

FAQ

Q: What is required to introduce AR as-built inspection on site? A: Basically, you need a device such as a tablet or smartphone, a high-precision GNSS receiver (RTK-capable), and an AR application for as-built inspection to get started. For example, using a solution like LRTK allows centimeter-level positioning by simply attaching a small GNSS antenna to a commercially available iPhone or iPad, and 3D design data and point clouds can be handled within a dedicated app. Beyond that, if you can prepare the design data used during construction (BIM/CIM models or electronic drawings) and the site control point coordinates, you can start AR as-built inspection on the spot.

Q: Is the measurement accuracy of AR-based as-built inspection reliable? A: Yes. When properly combined with high-precision GNSS, AR as-built inspection can achieve sufficiently reliable accuracy. Standard smartphone GPS can have errors of several meters, but with RTK correction the error can be reduced to a few centimeters. In fact, LRTK simple surveying has confirmed positioning accuracy of around horizontal 1–2 cm, comparable to conventional first-class surveying instruments. With AR displays aligned to high precision, there is almost no discrepancy with the actual object, so step differences or gaps of several centimeters can be reliably detected. For critical areas, verifying together with acquired point-cloud data allows millimeter-level accuracy checks if required.

Q: Can AR as-built inspection be used for public works as-built inspections? A: At present, AR is not explicitly stated in official inspection procedures, but the Ministry of Land, Infrastructure, Transport and Tourism actively promotes ICT construction and 3D as-built management, and AR utilization is being demonstrated in various places. In some pilot projects, as-built inspections have been reported where design models and actual conditions are overlaid on a tablet’s AR screen. Combining point-cloud-based as-built management diagrams with remote witnessing, cases of incorporating AR for as-built confirmation into supervision and inspection are increasing. If guidelines are developed in the future, AR as-built inspection could become part of official inspection methods.

Q: What kinds of construction and sites see the greatest benefit from AR as-built inspection? A: AR as-built inspection is effective wherever you need to check discrepancies between design models and as-built conditions, regardless of civil or building works. It is particularly beneficial in civil engineering fields such as road construction, land development, tunnels, and dams, where managing wide-area shapes is necessary and on-site visualization has significant advantages. In the building sector, initiatives have started to compare BIM models with actual conditions for rebar inspection and equipment installation position checks. In short, for any use case that involves verifying “is it built according to design,” AR as-built inspection works effectively regardless of scale.

Q: Is operating AR as-built inspection difficult? Can young or inexperienced workers use it? A: The operation itself is intuitive and not difficult. Basic operations, such as overlaying design data on a smartphone or tablet camera image, are done much like taking a photo. Dedicated app UIs are guided and simple, so even those unfamiliar with digital devices can master them with short training. Without special surveying skills, you can perform accurate as-built inspections simply by following on-screen instructions. Results are displayed visually, making them easy to understand and facilitating internal information sharing and reporting. AR as-built inspection is a technology that can be used by everyone from newcomers to veterans.