From surveying to inspection—end-to-end digitalization: On-site reform starting with AR as-built inspection

Table of Contents

• What is as-built inspection (challenges of conventional methods)

• Mechanism and features of AR as-built inspection

• Benefits brought by AR as-built inspection

• Key points to digitalize from surveying to inspection

• What you need to introduce AR as-built inspection

• Start AR as-built inspection with LRTK simplified surveying

• FAQ

What is as-built inspection (challenges of conventional methods)

In construction and civil engineering, as-built inspection is a quality-control process that verifies and records whether the geometry and dimensions of completed structures or developed land conform to the design drawings. It is especially important in public works because the results of as-built inspections often determine whether the client will accept the work or allow handover. In conventional as-built inspections, surveying instruments such as tape measures, staffs (leveling rods), levels, and total stations are used to measure dimensions and heights at various points on the finished work and check deviations from design values. It has also been common practice to bring photos and measurement data taken on site back to the office and compare them with drawings to prepare reports.

However, many issues have been pointed out with these conventional methods. The main problems can be summarized as follows.

• Time-consuming and labor-intensive: Measurements typically require a team of several people, and for large sites or projects with many measurement points it can take a full day or more to complete. Manual, point-by-point measurements are inefficient and place a heavy burden on projects with tight schedules.

• Dependence on skilled technicians: Accurate as-built measurement and judgment require experienced surveyors, and sometimes two-person teams are necessary. The construction industry faces aging technicians and a shortage of young staff, making it difficult to secure sufficient personnel at many sites.

• Specialized equipment is expensive: Measuring discrepancies against design to millimeter precision requires high-performance total stations or GNSS receivers, which have very high initial costs. For small companies or sites, the barrier to adoption is high, and ongoing maintenance costs and theft risk cannot be ignored.

• Limited measurement points with risk of oversight: The number of points that can be measured manually is limited, so the entire site cannot be fully covered. Sampling representative points may miss areas that differ from the design. On larger structures, subtle undulations and variations may not be fully captured, leading to cases where discrepancies are discovered during inspection and hurried rework is required.

• Possibility of human error: Busy sites are susceptible to human mistakes such as forgetting to take photos, errors in notes, or transcription mistakes. For example, if photos are not recorded before backfilling buried utilities, it may be impossible to prove the construction condition after completion. There have been cases where miswritten measurement results or omissions when transcribing into reports led to quality problems.

• Delayed problem detection: Because measurements are compared with drawings back at the office after returning from the site, defects may be discovered after construction is already complete. If not noticed on the spot, it can become too late—for example, discovering later that concrete cover or road slope is inadequate may require extensive rework once the concrete has hardened.

• Burden of report preparation: As-built management requires preparing charts and photo albums based on measurement results and submitting them to the client. Conventional methods require time and effort for creating these documents, which is a significant burden on site personnel.

As described above, conventional as-built inspection has various challenges in terms of efficiency and accuracy, and more efficient and reliable inspection methods have long been sought on sites. Recently, due to chronic labor shortages and the need to improve productivity, expectations for new technologies that can solve these problems have increased. One solution attracting attention is AR as-built inspection.

Mechanism and features of AR as-built inspection

AR as-built inspection, as the name implies, is a new method that uses AR (Augmented Reality) technology to verify as-built conditions. Design drawings or 3D model information are overlaid on the camera view of a smartphone or tablet so that differences between the actual construction and the digital design information can be intuitively understood on the spot. Instead of checking as-built conditions using numerical values on drawings, you can compare the real object and digital data on-site, making it easier even for less experienced technicians to visually judge acceptability.

A key to realizing AR as-built inspection is achieving high-precision alignment in the AR display on the smartphone or tablet. Specifically, high-precision GNSS (Global Navigation Satellite System) is combined to obtain centimeter-level positioning accuracy. In recent years, with the advent of small RTK-GNSS receivers that attach to smartphones and dedicated apps, anyone can easily obtain real-time positioning accuracy within a few centimeters (within a few inches). By fusing GNSS-based high-precision self-positioning with built-in smartphone sensors such as gyros and cameras, digital design data can be accurately overlaid on the real world.

For example, if the design finished shape or reference lines are projected in AR over the ground or structures after construction, you can immediately see whether the actual finish is within tolerances. Areas where the virtual reference surface appears to float above the ground indicate insufficient fill, while areas where it appears sunk indicate excess fill. Because GNSS positioning is accurately corrected, the virtual model does not drift away from the real object even if the operator walks around the site—this is a major feature. Rather than measuring and then verifying back at the office as before, the innovative aspect of AR as-built inspection is that you can compare the real object and design data 1:1 on the spot.

Moreover, some of the latest iPhones and iPads are equipped with LiDAR scanners, making on-site 3D scanning simple. If you scan terrain or structures by waving a smartphone, you can obtain high-density point cloud data, which can be compared with the design 3D model to generate a color-coded deviation heatmap. If the heatmap showing as-built error distribution is projected in AR on site, you can immediately see which areas are overfilled or overexcavated compared to design and proceed directly to corrective work such as additional filling or trimming. By combining advanced verification using point cloud measurement data, millimeter-level precision inspections are increasingly achievable on site.

Thus, by combining AR technology with high-precision positioning, inspections that were previously done with paper drawings and numerical data are becoming digital. Surveying, as-built verification, and photo documentation can be completed almost in real time on site, and necessary data can be shared immediately via the cloud. An end-to-end digital workflow—from surveying to inspection—is starting to be realized on site.

Benefits brought by AR as-built inspection

AR as-built inspection addresses the challenges mentioned above and is notable for the significant benefits it brings to the field. Here are some concrete advantages.

• Precise inspections that do not miss even millimeter-level deviations: Because design data can be overlaid on camera images for as-built checks, minute errors that were difficult to find with conventional methods can be intuitively discovered. You can visually inspect the entire construction area and detect height differences or steps of a few centimeters (a few inches) that the naked eye or a tape measure might miss. Buried items that become invisible after completion can also be confirmed by displaying pre-scanned point cloud models in AR even after backfilling. This capability captures even small deviations and greatly contributes to preventing quality defects.

• Streamlined inspection work and on-the-spot pass/fail decisions: Because digital verification can be performed directly on site, the conventional process of measuring, returning to the office, and comparing with drawings becomes unnecessary. You can confirm the finish immediately where it was measured and make a pass/fail decision on the spot. For example, if pavement thickness is insufficient, you can instruct additional work right away, minimizing rework. AR visual checks also facilitate communication; supervisors and craftsmen can easily share the finish status, making on-site consensus building smooth.

• Digitalization of as-built records and reliable evidence: AR as-built inspection allows inspection results to be recorded directly as data. For example, photos of the AR display taken by a smartphone automatically include position coordinates and orientation information, serving as reliable inspection evidence. Point cloud data can be used to automatically generate heatmaps and cross-sections for reports. Records based on digital data become objective evidence and increase the reliability of documentation supporting inspection acceptance.

• Labor savings: easy surveying that anyone can use to reduce workload. Surveying and as-built verification that previously required professional surveyors can now be performed by site personnel using AR and smartphone positioning technology. Modern AR-enabled apps have intuitive UIs and are easy to operate, so they can be used without veterans. A single person can walk around holding the device and perform measurement and recording, making it easier to cope with labor shortages and reducing the effort required for surveying. It also enables uniform quality control that does not rely on the experience of skilled workers.

• Remote supervision and cloud sharing for site DX: Because data can be shared via the cloud, you can check inspection status from the office or immediately share information with remote supervisors or clients. Sharing as-built data and photos obtained on site with stakeholders on the same day and obtaining necessary decisions—remote supervision—has become realistic. This can improve the efficiency of inspection attendance and reduce travel time, and it aligns with the remote, contactless inspections sought during the COVID-19 pandemic. As data accumulation and analysis progress in the cloud, digital transformation (DX) of overall site operations is accelerated.

As described above, AR as-built inspection is expected to be a solution that dramatically improves both efficiency and quality on construction sites. It resolves many of the issues associated with conventional methods and can be a major step toward on-site reform and operational improvement.

Key points to digitalize from surveying to inspection

To make the most of AR as-built inspection, it is important to digitalize not only the as-built verification itself but the surrounding processes as well. Handling the chain of information—from terrain and structure data obtained by surveying, to design documents, construction management, and final inspection—as digital data enables dramatic efficiency gains.

For example, if pre-construction surveying is done by drone photogrammetry or 3D laser scanning to create a point cloud model, and design is done using BIM/CIM or other 3D data, the same data can be used during construction and for as-built inspection. In the past, surveying, design, construction, and inspection each used separate data, with information passed via paper drawings or manual forms. Using unified digital data prevents duplicated work and transcription errors while connecting each phase seamlessly. In particular, for as-built inspection, using the 3D model from the design phase or point cloud data obtained during construction directly for on-site verification greatly improves efficiency and accuracy.

Government support also encourages this site DX. The Ministry of Land, Infrastructure, Transport and Tourism promotes digitalization of construction production processes under the “i-Construction” initiative and is advancing the implementation of 3D measurement technologies and AR utilization in as-built management. The ministry drafted the “Guidelines for As-Built Management Using 3D Measurement Technologies (draft)” and has organized procedures for as-built measurement using drones and ground LiDAR. Furthermore, the 2022 revision of the as-built management guidelines explicitly allows as-built measurement using simple surveying devices such as smartphones, making clear that 3D as-built management is possible without expensive specialized equipment. From 2024, trials of supervision and inspection using digital data in national projects have begun, including a new approach that projects 3D models created during the construction phase onto the site with AR and performs on-the-spot as-built measurement. This aims to simplify the conventional process of creating heatmaps from point clouds for submission and then re-measuring on-site during inspection by enabling direct AR verification.

Thus, public and private sectors are promoting digitalization and efficiency from surveying to inspection, and AR as-built inspection aligns closely with this trend. When introducing it on your own sites, preparing the surrounding environment—such as digitizing surveying data and utilizing BIM/CIM—will help you realize its benefits more smoothly.

What you need to introduce AR as-built inspection

What preparations and equipment are required to actually introduce AR as-built inspection on site? The basic elements are as follows.

• Digital design data: As a prerequisite, design drawings or models to be inspected must be available in digital form. BIM/CIM models or CAD data and other 3D or digitized design information that can be used for as-built inspection are desirable. If only paper drawings exist, converting them to CAD beforehand allows their use in AR displays.

• Reference coordinate information: To perform accurate alignment in AR, you need reference point data in the site’s survey coordinate system. Matching the design data to the site coordinate system allows digital information to be overlaid at the correct location on site. Preparing GNSS positioning reference stations or correction information (e.g., network RTK or satellite correction services) is also important.

• AR-capable smart devices: Prepare smartphones or tablets that support AR display. Recent iOS/Android devices support AR apps, and the latest iPhones and iPads equipped with LiDAR sensors can also perform 3D scanning. Because these devices are used on site, having dustproof/waterproof and shock-resistant cases and other rugged accessories is reassuring.

• High-precision GNSS receiver: Prepare a small RTK-GNSS receiver that can connect to your smartphone or tablet. This improves the device’s position information to centimeter-level accuracy. Bluetooth-connected small antennas are now commercially available and can be introduced more easily than dedicated equipment.

• AR as-built inspection application: Use dedicated software that can load design data and link GNSS position information to AR display and measurement. Software that supports 3D model display, point cloud difference display, photo capture, and cloud storage is desirable for as-built inspection. An app that runs on smart devices enables immediate operation on site.

• Cloud integration environment (optional): Not mandatory, but a cloud environment for data sharing is convenient. Measurement data and photos can be uploaded from the site via mobile communications for immediate office-side confirmation. This facilitates data sharing with remote parties and backup, so it is worth considering when introducing the system.

At first glance these preparations may seem numerous, but all-in-one solutions that provide these capabilities are now emerging. Some products bundle the necessary hardware and software so that carrying only a smartphone and antenna to the site is enough to perform AR as-built inspection. Next, we introduce one example: a smartphone surveying system called LRTK.

Start AR as-built inspection with LRTK simplified surveying

LRTK simplified surveying makes it easy to introduce the surveying and data-processing workflow that supports AR as-built inspection. LRTK is a high-precision positioning and measurement system that leverages smartphones; by bringing just an iPhone/iPad and a small GNSS receiver to the site, surveying through as-built verification can be completed. Using RTK GNSS, it achieves positioning accuracy of about ±1–2 cm (±0.4–0.8 in) horizontally and ±3 cm (±1.2 in) vertically, allowing location determination with accuracy comparable to conventional total stations or first-class surveying instruments. Based on that high-precision coordinate information, you can project design models in AR on site and compare them with point cloud data. The 3D model displayed on the smartphone screen overlays the real object without offset, enabling anyone to intuitively perform as-built checks that reveal differences of a few centimeters (a few inches) in level or gaps—information not attainable from paper drawings.

LRTK also enables point cloud measurement using the iPhone’s built-in LiDAR scanner and camera functions. Even for complex-shaped structures, simply scanning with a smartphone can generate high-density 3D point cloud models. The acquired point cloud data carry accurate coordinates derived from RTK-GNSS, making them immediately usable for comparisons with design data and volume calculations. For example, during an as-built inspection you can upload a point cloud scanned on site to the cloud, automatically generate a difference heatmap, download it back to the smartphone, and display it in AR—all as a one-stop workflow. Surveying, point cloud processing, as-built verification, and record keeping that previously required separate devices and software are now connected seamlessly on a single platform, accelerating on-site DX.

LRTK is already being adopted at construction sites across the country, contributing to rapid as-built verification in disaster recovery work and to improving the efficiency of infrastructure inspections. For sites wondering where to start with AR as-built inspection, LRTK enables rapid deployment. As a practical solution that balances cutting-edge technology with site-oriented ease of use, LRTK simplified surveying is poised to play a major role in end-to-end digitalization from surveying to inspection and the on-site reforms that follow.

FAQ

Q: What is AR as-built inspection? A: It is a method that uses AR (augmented reality) technology to directly confirm as-built conditions on site. Design data are overlaid on the screen of a smartphone or tablet so that discrepancies with the actual work can be checked on the spot. Think of it as digitalizing conventional tape-measure and level inspections to improve accuracy and efficiency.

Q: What preparations and data are required to carry it out? A: You need digital design drawings or 3D models of the inspection target. Also prepare reference point coordinates (survey coordinates) for the site and align the design data to the site coordinates. Using a smartphone or tablet paired with a high-precision GNSS receiver for positioning and loading the design data into a dedicated AR app, you can start AR as-built inspection on site immediately.

Q: Do I need specialized AR equipment? A: High-cost items such as dedicated AR glasses are not necessarily required. Attaching a small GNSS antenna to a commercially available smartphone or tablet is sufficient for centimeter-level AR as-built inspection. Many modern smartphones already support AR display, so leveraging that functionality is the typical approach.

Q: Can it be used by non-experts? A: Yes. AR as-built inspection is a visual method that is easy to understand intuitively. Dedicated apps guide the user through operations, so people without advanced surveying knowledge can use it on site. In fact, systems like LRTK can be operated by new technicians after a short training period.

Q: What level of accuracy can be achieved? A: Using GNSS (RTK) corrections, horizontal positioning can be kept to a few centimeters and vertical errors to several centimeters to several tens of centimeters. In the case of LRTK simplified surveying, actual measured accuracy of about ±1–2 cm (±0.4–0.8 in) horizontally and around ±3 cm (±1.2 in) vertically has been confirmed, comparable to conventional optical surveying instruments. For critical parts, combining with point cloud measurement data enables millimeter-level accuracy verification.

Q: What kinds of sites and works can it be used for? A: It is widely applicable wherever design and as-built verification are required, regardless of civil or building works. It is effective for checking heights and slopes in road and land development works, cross-sectional inspections in river and dam works, verifying component placement accuracy in bridge work, and any situation requiring shape or dimension verification. It is also useful for locating buried pipes and underground structures that become invisible after completion.