3D CAD設計データを現場で活用：LRTKでつなぐ設計と施工

In recent years, the construction industry has been shifting design documents from flat 2D drawings to 3D CAD (BIM/CIM) models. By leveraging three-dimensional digital design data, all stakeholders can intuitively share the final form of structures, which is expected to optimize construction planning and prevent errors. However, 3D design models become wasted assets if they are not effectively used on site. This article organizes the role of 3D CAD design data in the architecture and civil engineering industries and the common issues that arise when handing designs over to construction sites. It then focuses on a new technology that directly connects design and construction—LRTK—and introduces concrete procedures and use cases for utilizing 3D CAD data on site. Finally, it explains the benefits for both designers and constructors, applications to as-built management, and key points for introduction, proposing that LRTK can be considered as one option for on-site DX.

建築・土木業界における3D CAD設計データの位置づけ

In construction, the use of 3D models is being promoted as a core element of digital transformation (DX). Under the banner of *i-Construction*, the Ministry of Land, Infrastructure, Transport and Tourism has been strongly recommending three-dimensional design using BIM/CIM (Building/Construction Information Modeling), and from April 2023 onward the introduction of BIM/CIM models has begun in principle for nationally commissioned projects. This has accelerated the trend of consistently using 3D CAD design data across entire projects instead of traditional paper drawings.

The greatest advantage of using 3D design data is the ability to grasp the shape and arrangement of structures three-dimensionally. If contractors and clients share the model from the design stage, it becomes possible to visualize design intent that is hard to convey with plan views alone, reducing misunderstandings and communication omissions between designers and builders. For example, complex rebar arrangements or equipment routes are obvious at a glance in 3D, enabling accurate clash checks and quantity takeoffs. Moreover, 3D models can be linked with attribute information such as dimensions and materials, so they can be used across a wide range of tasks including quantity surveying, cost estimation, and simulation of construction sequences. By performing “virtual construction” digitally, alignment between design and construction planning becomes smoother, improving quality and reducing rework.

3D models also play an important role in the maintenance and management phase after completion. If the as-built condition is reflected in the model during construction, it becomes possible to confirm as a digital twin exactly what is buried where during future renovations. In this way, 3D CAD design data is key data that contributes to efficiency across the construction process from planning through construction and maintenance. As the use of BIM/CIM software progresses across companies, working methods based on three-dimensional data are spreading from general contractors to small and medium-sized contractors and clients.

現場への引き継ぎ時に起きやすい課題

On the other hand, various issues have been pointed out when handing over 3D CAD data created at the design stage to the construction site. Utilization of digital models is still in a transitional phase, and gaps tend to arise between design and construction sites as follows.

• 2D図面との乖離: Even if designers iterate on the latest 3D model, information is often still delivered to the site as traditional 2D drawings. As a result, the subtle intentions and three-dimensional relationships embedded in the model may not be fully conveyed on drawings, causing image discrepancies between designers and builders. For example, a clearance between piping and a beam that was cleared in the model might be overlooked on a sectional drawing and only discovered as an interference on site.

• データ活用の難しさ: Even if the site wants to use 3D data, a high barrier can impede adoption. A construction manager opening a laptop on site to display a large BIM model may find that high-performance machines and specialized software are required, which is impractical. Preparing lightweight models for tablet viewing also creates additional work. As a result, valuable 3D data often becomes a “wasted treasure,” and sites end up referring to 2D drawings for construction—a counterproductive situation.

• 座標・精度面の問題: Aligning 3D design models with actual site coordinate systems is another challenge. When trying to use 3D data for positions previously managed by gridlines or string lines on drawings, calibration with site control points is necessary. Traditional AR systems have used methods such as placing QR code markers on the ground as references for model display. However, accurately aligning positions across a wide site is not easy, and small errors can accumulate and shift the model’s position. Typical GPS accuracy (errors of several meters (several ft)) cannot project columns or walls to their exact positions. Because there was no easy on-site mechanism for high-precision alignment, AR uses of 3D data on site remained limited.

• 人的リテラシーの差: Younger workers may be familiar with 3D models, but some veterans may only trust 2D drawings. Spreading new technology on site requires training and changes in mindset. If it is not a tool that all site staff can use intuitively, data utilization will not progress. Systems that require complex operations or specialist knowledge are likely to be avoided on busy sites.

For these reasons, a divide has formed where “design is 3D and construction is 2D,” preventing the full benefits of digitization. Solving this requires creating an environment where 3D design data can be referenced and used on site without stress. One approach to achieve this is the use of LRTK, which combines high-precision GNSS and AR technology.

設計と施工をつなぐLRTKの役割（高精度GNSS×AR）

LRTK (Light RTK) is a next-generation high-precision positioning and AR solution that uses smartphones. Specifically, a small RTK-GNSS receiver is attached to a smartphone or tablet to determine the device’s position with centimeter-level (half-inch accuracy) positioning precision while overlaying a 3D model through the device’s camera. While consumer GPS used to have errors of several meters (several ft), the RTK method (Real Time Kinematic) can achieve absolute positioning errors on the order of about 1-2 cm (0.4-0.8 in). LRTK realizes RTK positioning at palm-sized form factors and integrates it with AR display functions, which is a major feature.

By combining high-precision GNSS and AR, design and construction site data can be directly connected. Since 3D models created in the design stage include latitude/longitude or coordinates within a coordinate system, synchronizing those with the world geodetic coordinates obtained by LRTK allows 3D design data to be placed in the real world with pinpoint accuracy. For example, the positions of building columns or curb lines of a road can be overlaid exactly on the real scene using LRTK. This enables users to visualize on site—simply by pointing a smartphone—where elements are to be built, without having to consult drawings and use a tape measure.

LRTK also greatly reduces the need for site calibration. Typical AR displays require marker placement or initial alignment at each site, but because LRTK is based on GNSS absolute coordinates, the model can be displayed in the correct location as soon as the device is switched on. This convenience allows site personnel to compare the design model and the current situation simply by viewing, without special setup. Additionally, smartphone AR apps use Visual-Inertial Odometry (VIO) technologies such as Apple’s ARKit to ensure apparent stability of virtual objects relative to the camera image. In other words, a dual mechanism—GNSS for global positional accuracy and built-in device sensors to suppress visual drift—enables stable overlay of 3D models over wide outdoor areas.

Thanks to these technologies, it has become practically possible for builders to share and use digital models created by designers directly on site. LRTK functions as a bridge connecting design and construction, linking the previously segregated parties in real time and intuitively. The next section looks concretely at how to bring 3D CAD data to the field using LRTK.

LRTKで3D CADデータを現場に展開する手順

With LRTK, cloud data can be linked to on-site smartphones so that 3D models can be handled directly in the field. The basic steps for utilizing design data on site are as follows.

• 3D設計データの準備: First, prepare the 3D CAD model created during design. Formats such as BIM models for architecture or CIM models for civil engineering are acceptable, but it is important that the coordinate system (survey coordinates or latitude/longitude) is set to match the site in advance. If the model’s structures are aligned with geographic coordinates or site control points, they will display without positional shifts in later steps.

• クラウドへのアップロード: Next, upload the model data to the LRTK cloud system. Create a project on the dedicated web platform and register design data (3D models and drawing files). Placing the model in the cloud allows on-site devices to access and download it over the network. Heavy models can be rendered or lightweight versions generated in the cloud, making them smooth to handle on mobile devices.

• 現場でLRTKデバイスをセット: Prepare LRTK on site. Specifically, attach the LRTK receiver to a smartphone or tablet and launch the dedicated LRTK app. The LRTK receiver contains a high-performance GNSS antenna and battery and automatically acquires correction data from reference stations or Japan’s satellite “Michibiki” (CLAS signal) via the internet. This enables centimeter-level (half-inch accuracy) positioning even in mountainous areas or where reference stations are not nearby. No special equipment setup or complex configuration is necessary—simply connect the device to the smartphone and power it on to start positioning.

• 3Dモデルデータのダウンロード: In the app, select the project uploaded to the cloud and load the 3D model onto the field device. If network coverage is unavailable, the model can be pre-saved on the device for offline viewing. When the model is opened, 3D objects are displayed over the camera image on the smartphone screen. Because the model is automatically placed based on GNSS position information, users do not need to manually align it. For a bridge model, for example, the nearby piers may appear to rise from the actual ground in the correct locations.

• AR表示で現場確認: Point the smartphone or tablet and confirm the 3D model overlaid on the real scene. Users can zoom and rotate freely on the screen, and toggle displayed elements (rebar, piping, etc.) as needed. Walking around the site and viewing the model from various angles enables discovery of issues or questions that could not be noticed from drawings alone. Because AR displays are intuitive and easy to understand, even non-specialists can conduct discussions while pointing at the model, enabling on-the-spot alignment between designers and constructors.

• 現場での計測・記録: LRTK supports not only model display but also surveying and recording tasks on site. Users can leave photos and notes at locations confirmed in AR. For example, tapping a point on the model can capture and record its design coordinates, or save photos that include the model overlaid in the camera image to the cloud. If the device has LiDAR, the current condition can be scanned into a point cloud and used for comparison with the design model.

• クラウド共有と事後活用: Positioning data, photos, point clouds, and other data acquired on site are automatically uploaded and shared in the cloud. There is no need to copy data by USB after returning to the office; designers and clients away from the site can immediately view results via a browser. Because 3D models and sections can be displayed on the web without installing a dedicated viewer, the site and the office can always synchronize the latest information. This enables real-time responses such as reporting and discussing as-built confirmations on the same day.

These are the steps for deploying and verifying 3D CAD design data on site using LRTK. The required equipment is simple—a smartphone plus a small receiver—and once initial setup is complete anyone can start using it immediately, which is another significant appeal.

現場での具体的活用例：配筋確認や墨出しへの応用

What changes will LRTK bring to actual construction management tasks? Below are several concrete on-site use cases.

• 鉄筋の仮想配筋検査: In reinforced concrete work, rebar quantity, spacing, and diameter are inspected before concrete placement. With LRTK, the 3D rebar model from the design stage can be AR-displayed over the real rebar on site, allowing instant confirmation that the rebar is placed according to the drawings. Compared to traditional manual checks with a tape measure, this prevents oversight and counting errors, dramatically improving inspection accuracy and efficiency. Overlaying the model also helps detect interference with formwork (e.g., rebar protruding from formwork) in advance, preventing rework or problems during placement.

• 構造物のライン・位置出し確認: For bridges, building foundations, and the like, accurate staking of pile centers and structural edge lines is crucial. LRTK includes coordinate navigation functions that allow workers to follow arrow guidance on the smartphone screen to move to a point and mark it. For example, even if a pile must be driven at a position 5 m (16.4 ft) east of a reference point, the app can guide the user in real time with arrows and distance readouts so that precise layout can be achieved without specialized surveying knowledge. Tasks that previously required surveyors to set batter boards or string lines can be completed by one person, reducing labor and human error.

• 埋設配管や設備機器のAR透視: Buried pipes and equipment that become invisible after construction can be managed with 3D data and easily checked later. If the positions of buried items are scanned and recorded with LRTK during construction, the pipe locations and depths under a road can be “seen through” with AR simply by pointing a smartphone even after backfilling. This allows accurate identification of buried utilities before future excavation and prevents accidental damage. When installing new piping routes, projecting the design model onto the ground helps confirm layout and flexibly accommodate on-site route changes.

• 出来形検査・記録: LRTK is powerful for as-built verification after construction. For example, after removing formwork from concrete, scanning the structure with a smartphone LiDAR can instantly generate a point cloud record of as-built dimensions. The acquired point cloud is automatically linked to design coordinates, enabling verification by overlaying it with the design 3D model in the office or extracting necessary dimensions to automatically generate as-built documentation. Compared with traditional point measurements and handwritten records, this allows comprehensive surface checks that raise quality assurance levels. AR images and measurement data are organized in the cloud and can be used directly as evidence in as-built reports, reducing documentation burdens.

By using LRTK, 3D data utilization becomes possible across a wide range of scenarios—from pre-construction simulation to surveying and inspection during construction, to as-built confirmation after completion. Site staff can complete “viewing, measuring, and recording” tasks with a single device, transforming workflows to be digital-first and achieving both efficiency gains and accuracy improvements.

設計意図の共有・変更対応・出来形検査への展開

Using 3D data with LRTK not only improves on-site operational efficiency but also qualitatively enhances communication between design and construction. When designers and construction managers can discuss using the same model, rework caused by misreading drawings is reduced and design intent is more reliably reflected on site. For example, during pre-construction meetings, displaying the finished image on a tablet AR screen and indicating “this wall will be at this position and height” conveys nuances that are hard to communicate verbally or on drawings, smoothing consensus with the client.

It also supports rapid response to design changes. Traditionally, design changes required time for revising drawings and disseminating them to stakeholders, but if BIM/CIM models are centrally managed in the cloud, everyone can view the latest model immediately. With LRTK, it is easy to bring updated models to the site and compare old and new versions on the spot. For instance, concerns such as “we added rebar—will it fit?” can be checked by AR-displaying the revised model to verify potential clashes and constructability issues in advance. Being able to instantly grasp discrepancies between real and digital conditions enhances on-site flexibility and minimizes schedule delays and errors caused by changes.

Expansion into as-built management is also notable. The Ministry of Land, Infrastructure, Transport and Tourism has been establishing as-built management guidelines using 3D data and officially adopting surface management methods using point cloud data. As-built data acquired with LRTK is saved with absolute coordinates in public coordinate systems, so deliverables compliant with these latest guidelines can be produced. In practice, point clouds and measurement point data output from LRTK have the accuracy and formats usable directly in inspection documents, promising substantial efficiency gains compared to traditional manual inspections. This contributes not only to higher quality control but also to reduced workload for on-site technicians and faster inspections. As a solution aligned with the ministry’s push for ICT-based as-built management, LRTK is likely to attract increasing attention.

Thus, on-site DX driven by LRTK benefits both design and construction, realizing productivity improvements through consistent data utilization. Leveraging 3D CAD design data on site is not merely a technology adoption but a key to transforming team communication and business processes.

現場DXの実現に向けて：LRTKを選択肢の一つに

LRTK, which promotes on-site use of 3D CAD data, is a powerful tool for digital construction. However, it is not a magic wand that everyone can immediately adopt. To realize on-site DX, it is important to plan a phased introduction that fits your company’s workflows and personnel structure. In that context, there is great value in considering an easy-to-use, versatile solution like LRTK as one option.

In actual implementations, there are reports that young employees who had never handled surveying equipment were able to perform as-built measurements and model sharing alone using LRTK, dramatically reducing the burden on site supervisors. Smartphone-based operation is intuitive, and even veteran workers reportedly became proficient after brief instruction, making the technology approachable for those not comfortable with ICT. As an all-in-one system, initial investment can be minimal, allowing small- and medium-sized sites that cannot station a dedicated surveyor to use high-precision surveying and AR technologies at low cost. This can be one solution to industry challenges such as labor shortages and an aging workforce.

Of course, establishing 3D data utilization requires changes in mindset and operational rule setting on site. Maximizing effects requires addressing surrounding elements such as update workflows, cloud management rules, and training on device use. Conversely, introducing a tool like LRTK can serve as a catalyst for organizational DX and help cultivate a culture of “making data useful on site.”

Finally, it is important to emphasize that the goal is not merely to use 3D CAD design data on site, but to achieve productivity gains, quality assurance, and work style reforms through that use. LRTK is one effective means to achieve those objectives. By bridging the information gap between design and construction and enabling everyone to share the same vision to lead projects to success, LRTK is worth considering as a bridging tool. As on-site DX progresses in the coming era, adopting technologies that turn 3D data into a practical advantage will help construction sites evolve into smarter and more creative environments.