Ministry of Land, Infrastructure, Transport and Tourism (MLIT)-Compliant 3D As-Built Management! High-Precision Positioning Is Transforming Construction Management

Introduction: The Importance and Challenges of As-Built Management

On construction sites, as-built management, which verifies whether completed structures have been finished according to the design, is indispensable. As-built management is the process of recording and verifying, based on measurement data, whether the constructed portions (as-builts) meet the client's specification standards. In public works, it is an important management task that serves as a condition for passing inspections and for handover, and it plays a role in ensuring construction quality. Also, for items buried underground that become invisible afterward, if as-built records are not made during construction, it may become impossible to prove them later. Therefore, measurements and photographic records should be taken at the completion of each stage, and rework performed as necessary.

However, conventional as-built management methods had various issues. Until now, they centered on direct measurements using surveying instruments such as tape measures, staffs (leveling rods), and levels, and on photographic documentation. For example, in road construction, the thickness, width, and height of the roadbed and pavement are manually measured at representative locations after completion and each measurement is checked against the design specification values. The measurement results are then typically compiled and submitted as as-built management charts and photo logs.

The following problems have been identified with conventional, manual-centered as-built management.

• Labor- and time-intensive: Measuring dimensions requires multiple people and can take many hours, placing a major burden on site supervisors. It also requires securing experienced surveying technicians, making it difficult to proceed efficiently within the construction schedule amid labor shortages.

• Lack of comprehensiveness and risk of oversights: Manual measurement limits the number of points that can be physically measured, making it difficult to fully grasp the as-built condition over a wide area. With only limited measurement points, differences from the design can be missed, and during inspections there is a risk of being told "this differs from the drawings" and having to rush corrective work. The larger the structure, the more likely manual measurements are to produce variability and to miss small irregularities.

• Possibility of human error: On busy sites, human mistakes such as forgetting to take photos or errors in recording measurements can occur. For example, if photos of buried items are not taken before backfilling, the work may not be provable after completion and could, in the worst case, lead to rework or disputes. In this way, traditional methods that "measure only at points" and rely on manual labor imposed significant burdens and risks on site personnel.

As a result of the above issues, there has been strong demand on construction sites for methods that enable more efficient and reliable as-built management.

The Trend of DX in Construction Management and the Emergence of 3D As-Built Management

In recent years, the wave of digital transformation (DX) has reached the construction industry, and methods of construction management have begun to change significantly. Supported by the Ministry of Land, Infrastructure, Transport and Tourism’s *i-Construction*, construction management using ICT (information and communication technology) is becoming widespread. Specifically, BIM/CIM, which utilizes three-dimensional models from the design stage, and 3D surveying technologies, which perform measurements using drones and terrestrial laser scanners, have been permeating sites. In the field of as-built management as well, 3D technologies capable of non-contact, high-density measurement of structures and terrain are becoming practical.

For example, point cloud data (point cloud) obtained by laser scanners is full-scale 3D information of a site consisting of countless measurement points. Because it can scan a wide area in a short time, using point clouds for as-built management allows you to understand construction works on an areal (entire-area) basis and prevent oversights. The use of such 3D technology is now becoming the "new normal".

On the other hand, high-performance 3D laser scanners and surveying equipment are often very expensive and frequently require specialized knowledge to operate, creating barriers to adoption at small- to medium-sized sites. A new approach attracting attention is the combination of smartphones and RTK-GNSS. By combining a smartphone’s built-in camera and LiDAR sensors with the high-precision positioning technology RTK (Real Time Kinematic), which uses artificial satellites, solutions have emerged that allow anyone to easily achieve centimeter-level positioning (half-inch accuracy). This "smartphone × RTK" technology is expected to significantly streamline surveying and as-built measurement tasks that previously relied on costly equipment and expert technicians, improving productivity. The use of high-precision positioning is changing the very approach to construction management itself.

New as-built management enabled by smartphones + high-precision positioning

Among the solutions that have emerged in this trend, an attention-grabbing one is a compact device called LRTK, developed by Refixia, a venture company spun out from Tokyo Institute of Technology. LRTK (el-arr-tee-kay) is a pocket-sized RTK-GNSS receiver that attaches to smartphones and tablets and works in conjunction with a dedicated smartphone app, "LRTK". By utilizing RTK error correction, it enables real-time centimeter-level high-precision positioning anytime, anywhere (cm level accuracy, half-inch accuracy). The main unit weighs approximately 165 g and has an ultra-compact, lightweight design with a thickness of about 10 mm (0.39 in); it also has a built-in battery, making it portable enough to carry on-site and use immediately when needed.

With this single device integrated with a smartphone, you can perform all the tasks that previously required separate equipment and multiple personnel. In addition to obtaining high-precision positional coordinates, it supports point cloud scan using the smartphone's camera and LiDAR, layout (positioning) work and photo documentation that compare design data with the site, and even as-built verification using AR (augmented reality). Measured data is synchronized to the cloud on-site, enabling immediate sharing and use from the field. Special dedicated equipment becomes unnecessary, and the price is set very affordably compared with conventional surveying instruments, making it a practical tool that field staff can carry with a "one smartphone per person" approach.

With the advent of LRTK, as-built measurements that previously required expensive equipment and skilled technicians can now be performed easily by anyone. Surveys that were traditionally conducted by two-person teams using total stations or large GNSS units can, with LRTK, be completed with a smartphone in hand and by one person. Low cost, high mobility, and intuitive operation reinvent surveying styles, making it an innovative tool that powerfully advances on-site DX (digitalization).

Complete 3D As-built Management on a Smartphone in Accordance with the Ministry of Land, Infrastructure, Transport and Tourism Standards

With LRTK, you can complete measurement and recording for as-built management on a smartphone alone, in compliance with the Ministry of Land, Infrastructure, Transport and Tourism’s "Guidelines for As-built Management Using 3D Measurement Technologies (draft)". High-precision positioning via RTK-GNSS and point-cloud measurement sufficiently ensure the required measurement accuracy and measurement density, enabling verification of as-built conditions with reliability equal to or greater than traditional methods that relied on control-point surveying and batter boards (height reference). LRTK is a solution that aligns with the intent of these latest guidelines and provides data of quality and format that can withstand official inspection and reporting. There is no longer a need to rely on expensive surveying equipment or cumbersome manual work. The fact that as-built management compliant with the Ministry’s standards can be performed with just a single smartphone represents a revolutionary advance for the field.

In practice, positioning data and point cloud data acquired with the LRTK app are automatically converted to a world geodetic coordinate system (such as JGD2011), and elevations are corrected by geoid height. Even beginners can obtain accurate coordinate values and elevation information without having to perform complicated calculations on site. Also, by organizing measurement data in the cloud, the creation of as-built management charts and 3D models can be carried out smoothly. Document preparation for as-built management, which had previously taken a long time, is also centralized digitally, enabling efficient preparation of deliverables for inspection submission.

Transform construction management with all-in-one features

With LRTK alone, you can handle all on-site surveying, recording, and verification tasks with a single smartphone. The main features and benefits are summarized below.

• High-precision RTK positioning: By using RTK correction information from satellites, high-precision position coordinates (latitude, longitude, height) with horizontal and vertical errors kept to a few centimeters (a few in) can be obtained in real time. Simply point your smartphone at the point you want to measure and press a button to instantly record the coordinates of that location.

• Point cloud scanning: Using the smartphone’s built-in LiDAR scanner or camera, you can continuously scan structures and terrain to acquire 3D data (point clouds). It can measure wide areas in a short time and record detailed shapes composed of a large number of points, allowing you to grasp the as-built surface area and not miss slight height differences or irregularities.

• AR-based as-built verification: You can overlay and compare planned shapes from design drawings or 3D models with actual as-built data on the smartphone screen. With AR functions you can overlay design lines, elevation references, and as-built heat maps (diagrams that show errors in color) onto real-world imagery, making it possible to instantly confirm whether construction locations match the design. A major advantage is that anyone can visually check the as-built condition without relying on a veteran’s intuition.

• Photo and note recording: You can take photos of necessary locations with your smartphone camera and link and save them with the measurement position data. You can also leave comments or voice memos for each measurement point in the app, serving as a substitute for handwritten notes. The photo album essential for as-built management can be completed within the app, reducing the risk of missed shots or lost photos.

• Cloud sync and sharing: Measurement data and photos are uploaded to the cloud in real time and securely backed up. Because the data can be shared instantly with office engineers and clients, communication between the field and the office becomes smoother. There is no need to bring data back on a USB drive or print and mail paper copies. The as-built data centralized in the cloud can be managed company-wide and is useful for later report generation and maintenance management.

An intuitive smartphone app and a compact device like this make LRTK highly appealing: staff without specialized knowledge can use it confidently. Because even new or junior staff can operate it, on-site as-built management can proceed without relying on experienced surveyors, helping to alleviate labor shortages.

Effects Demonstrated at Various Sites

High-precision 3D as-built management using LRTK demonstrates powerful results across virtually all civil engineering construction sites. Let’s look at some examples of its application and the benefits achieved in several scenarios.

• Road construction: Tasks that measure the thickness and elevation of the subgrade and pavement at specified locations to verify conformity with the design can be dramatically streamlined by introducing LRTK. Where road as-built checks traditionally required many manual measurements at multiple points, they can now be completed in a short time, and there are cases where cloud sharing was finished within the same day. In addition, AR functionality makes tasks that once routinely required two-person teams—such as installing batter boards and staking out reference points—accurately performable by a single person. Even on long stretches of road, many survey points can be recorded instantly while walking, allowing on-site confirmation of as-built data to prevent oversights. As a result, there is more leeway in preparing for inspections.

• Bridge construction: LRTK is also effective in bridge works, which have many as-built items to check, such as the position and elevation of abutments and piers and the thickness of deck slabs. Being able to complete surveys quickly and accurately is important for safety management, even on sites with frequent high-elevation work or night shifts. For example, if the top elevation of a pier can be measured immediately with LRTK to confirm it matches the design, subsequent rework can be avoided and quality ensured. It is also possible to display a model of the structure under construction in AR to check bolt hole alignment or the placement of bearings. LRTK makes as-built management for bridge works rapid and reliable, reducing worker burden and lowering the risk of work stoppages.

• Slopes and development sites: In steep slope works, as-built management to verify final gradients and surface irregularities is important, but there were limits to conventional surveying on hazardous slopes. With LRTK, workers can measure the entire slope from a safe remote location using point-cloud scans without climbing the slope. In just a few minutes you can acquire wide-area 3D shape data, grasp gradients and surface irregularities in detail, and immediately identify locations that need repair. Because measurements are non-contact and remote, nothing is missed, and entry into hazardous areas is minimized. Safety and work efficiency will dramatically improve.

• Disaster sites: LRTK is useful for rapidly assessing disaster sites such as landslides and road collapses caused by earthquakes or heavy rain. Quickly surveying affected areas is essential for recovery planning and damage reporting, but with LRTK, responders can begin surveying on site immediately without waiting for heavy machinery or large survey teams. The extent of collapsed slopes or washed-away sediment can be recorded as point-cloud data, and volumes can be calculated on the spot to estimate the amount of debris. Cloud sharing enables the latest situation to be shared in real time with stakeholders, synchronizing information with officials issuing directives and support teams. It is also useful for reducing time spent working in hazardous disaster areas, enabling rapid and safe situational assessment during disaster response.

Also Noted as a Cost-Effective, Easy-to-Adopt Technology

While the latest ICT tools may evoke an image of high expense, LRTK delivers excellent cost performance that makes it easy for small and medium-sized construction companies to adopt. A major advantage is that the initial investment can be kept low. LRTK devices themselves are less expensive than traditional surveying instruments, and because you can leverage existing smartphones, they are significantly cheaper than buying costly dedicated equipment outright. Compared with purchasing total stations or 3D laser scanners that cost several million yen, LRTK is in a much more accessible price range.

There are also advantages in terms of operating costs. By sharing via the cloud, you can reduce expenses such as printing paper drawings, photo processing, and postage, saving on day-to-day costs. If you have been outsourcing surveying work, those expenses can also be reduced. If you operate LRTK in-house, you will no longer need to hire external surveying companies for each job, which leads to long-term cost reductions. Furthermore, as mentioned above, the surveying can be completed by a single person, enabling optimal personnel allocation and contributing to measures against labor shortages. Because it is a tool that requires no specialized knowledge and can be used by anyone, the burden of training new employees is also small, helping to promote smooth DX within the company.

Conclusion: Transform Construction Management with High-Precision Technology

Thus, the combination of 3D as-built management and high-precision positioning technology is significantly changing the way construction management is conducted. In line with the Ministry of Land, Infrastructure, Transport and Tourism's promotion of i-Construction and BIM/CIM, construction management based on digital data will increasingly become the norm at more and more sites. DX of as-built management (digital transformation) will be the key to dramatically improving on-site productivity while enhancing quality and safety.

In this context, LRTK, a simple surveying solution that anyone can use with a smartphone, is becoming the trump card for on-site DX. By leveraging LRTK, which makes it easy to introduce 3D as-built management through high-precision positioning, why not realize a new form of construction management at your site? With reliable quality compliant with the Ministry of Land, Infrastructure, Transport and Tourism, simple surveying with LRTK is optimal for advancing construction management DX. Take this opportunity to step into innovation at your construction site with the power of LRTK.