3D CAD Models Displayed On Site in AR: High-Precision Construction Management Enabled by LRTK

The role of 3D CAD models in building and equipment construction and the demand for their use

In recent years, on construction and equipment installation sites, the 3D conversion of design data—so-called “3D CAD models” and BIM (Building Information Modeling)—has been progressing rapidly. Three-dimensional models that visualize an entire building or equipment such as piping and ducts are useful not only for clash detection and planning construction sequences during the design phase, but they also hold great potential for construction management. Complex spatial relationships that were hard to represent on traditional 2D drawings can be intuitively understood with 3D models, making it easier for stakeholders to share a common image.

In fact, use of 3D data including BIM is accelerating domestically, and the Ministry of Land, Infrastructure, Transport and Tourism is promoting BIM/CIM adoption, particularly for large-scale projects. From fiscal 2023, the use of 3D models has become standard in some public works, and in the future BIM/CIM use is expected to be mandated for almost all public projects. Against this backdrop, general contractors and equipment contractors are adopting BIM software and developing human resources, reexamining workflows that were centered on design drawings, and increasing their need to utilize 3D models during the construction phase. There is a growing movement not only to centralize and enhance design data but to leverage it on site to drive productivity improvements and quality assurance.

Challenges in on-site plan checks and model verification (the limitations of paper drawings and the gap between 2D and the field)

However, even when detailed 3D CAD models or BIM data are created, many construction sites still rely primarily on paper drawings or PDF plans. Site supervisors and craftsmen compare paper drawings with the actual conditions, but paper drawings alone make it difficult to accurately imagine spatial relationships and elevation dimensions. For example, clearances between pipes above a ceiling or the relative positions of penetration holes in a wall must be mentally reconstructed from 2D drawings. This gap can cause miscommunication and construction errors, sometimes leading to rework.

There are also challenges when confirming on site whether work is proceeding according to the design during construction. Traditionally, positions and heights have been measured with a tape measure and level and checked one by one against drawing dimensions. This is time-consuming and labor-intensive and prone to human error. In complex equipment piping work, there are cases where the actual installation position is off by several centimeters from the drawing, or piping interferes with other elements, and such issues are discovered later requiring urgent rework. A means to bridge the gap between 2D and the field and directly utilize model information on site was needed.

A solution by combining AR and high-precision positioning (RTK-GNSS)

A promising solution to these issues is the fusion of AR (augmented reality) technology and high-precision positioning. AR overlays 3D models and annotation information onto real-world video captured by a smartphone or tablet camera. Because it can visualize the completed image and equipment layouts that were previously only visible at the design stage by superimposing them on the actual site, it is expected to be widely used for pre-construction simulation and verification of as-built conditions.

However, conventional AR faces limitations: the built-in GPS in smartphones has meter-level accuracy, making it difficult to overlay large structures or entire buildings precisely. AR displays based on device gyros and camera tracking (ARKit/ARCore, etc.) have local stability but tend to drift slightly as you move over a wide area. The key to solving this is centimeter-class high-precision positioning using RTK-GNSS (real-time kinematic satellite positioning). With RTK-GNSS, you can determine your position with about 1–2 cm accuracy, avoiding the large deviations typical of standard GPS. By using a high-precision GNSS receiver that connects externally to a smartphone, RTK positioning can now be realized on site.

Combining high-precision positioning with AR makes it possible to project a 3D model onto the site at the correct location and scale according to the design. For example, if you have a 3D model of the building aligned to reference points in advance, you can simply point your camera on site and see walls and columns appear exactly where they should be according to the design. Previously, it was necessary to set up AR markers or manually align the model on site, but high-precision positioning eliminates that extra work. In Japan, interest is growing in the AR+RTK combination within initiatives such as i-Construction and the push for construction DX, and precision AR construction management is becoming a realistic option.

How LRTK displays 3D models in AR (from loading to display)

So how does a high-precision positioning–compatible AR system like “LRTK” display 3D CAD models on site in AR? Here is the basic workflow.

• Preparing model data: First, prepare the 3D model data of the building or equipment (BIM models or 3D CAD drawings). If the model contains a design coordinate system (such as grid-based coordinates or latitude/longitude), subsequent alignment will go more smoothly. If the model is not aligned to survey coordinates, you can specify reference points on the model and link them to measured coordinates to compensate.

• Uploading to the cloud: Next, upload the model data to the LRTK cloud system. The LRTK cloud is a service that centrally manages various drawing and point cloud data, and uploaded models can be synchronized with smartphones on site. It supports common formats like DWG and IFC, allowing you to register multiple data sets as needed—such as equipment piping models or architectural finish models.

• On-site positioning and model selection: On site, power on the LRTK device connected to your iPhone (a positioning device with a high-precision GNSS receiver) and start receiving correction information from satellites to begin positioning. Within several tens of seconds, the RTK solution typically reaches a fixed state (Fix), allowing the smartphone’s current position to be determined with an accuracy of about ±2 cm. Launch the LRTK app and select the project and model data you want to display.

• Executing AR display: When you start “AR display” mode in the app, the selected 3D model is superimposed on the camera image. Because the model is placed based on absolute coordinates obtained via RTK-GNSS, there is no need to set special markers or perform manual alignment—the model matches the real-world position exactly. For example, if you select a piping model, the virtual pipes are displayed along floors and walls as if they had already been installed. You can then walk around the site with your smartphone or tablet to observe the model from any angle.

• Accuracy checks and fine adjustments: While the model projection is principally based on GNSS-provided absolute accuracy, you can, if needed, align the model to known site control points (such as building corner positions) and perform fine adjustments to further verify accuracy. LRTK includes functionality to check the discrepancy between the model’s overlay and real structures during AR display and to correct the model’s position as required. Following these steps completes the process from loading the model to AR display on site.

On-site AR use cases for BIM and piping models (clash detection, opening checks, virtual verification of installation positions, etc.)

Once 3D models can be displayed in high-precision AR, various use cases become possible in construction management. Below are specific examples particularly effective in building and equipment construction.

• Clash checks for pipes and ducts: Display equipment piping and duct models in AR and check for interference with structural elements or other equipment beforehand. For example, even where pipes cross in the ceiling space, displaying both models simultaneously in AR makes it easy to judge at a glance whether the clearances are sufficient. Issues in interfaces that are easy to overlook on drawings become easier to spot when full-scale models are overlaid on site.

• Checking wall and slab opening positions: Confirm the positions of openings (holes) in walls and floor slabs using AR. Before coring holes in concrete, showing the opening size and position according to the design through your smartphone lets you accurately understand relationships with actual columns and beams. This prevents mistakes such as “the hole was offset” or “it hit an unexpected brace.” You can also perform accurate layout marking by using AR display as a guide.

• Simulating equipment installation locations: Before bringing in and installing large HVAC units or pumps, simulate the installation space and access routes. By showing equipment models at full scale in AR, you can intuitively check whether there is enough clearance from surrounding piping and walls and whether there is sufficient space for maintenance. It’s also possible to project the model of an overhead crane and verify its motion range within the actual building to ensure no interference.

• Verification and inspection against as-built conditions: AR is useful for comparing the as-built condition with the design model after construction. For example, overlaying the design BIM model on a concrete structure after placement lets you check on site for distortions or positional deviations in the finished form. You could also display point cloud data of buried underground piping in AR to virtually “see through” the pavement and confirm buried elements. Keeping digital records of parts that become hidden after completion and enabling AR visualization later can be powerful for future maintenance.

Practical benefits (shorter inspection time, fewer construction errors, improved explanation to clients)

Using 3D CAD models on site via AR brings the following practical benefits to construction management.

• Shortened verification time: Traditional tasks of comparing drawings and site conditions are greatly streamlined. Instead of holding a paper drawing and taking measurements step by step, you can check consistency on the spot by viewing the model in AR. In one example, a site used a tablet’s AR function to visualize rebar and piping design positions, and marking and position-checking tasks that even experienced workers had previously spent half a day on were completed quickly. By reducing the effort required for checks, construction managers can allocate time to other important tasks.

• Reduction in construction errors and rework: AR helps prevent errors during construction. For example, displaying design position guides in AR when installing pipes or cables enables less experienced workers to install accurately, stabilizing finish quality. Continuously checking the model against reality during construction lets you detect and correct deviations down to millimeter scales on the spot, preventing major issues like “pipes don’t fit” or “equipment mounting positions are wrong” later on. Sites that adopted AR systems for equipment piping reported a significant reduction in verification burden and fewer human errors compared to when they relied on paper drawings. Such error reduction contributes to fewer reworks, shorter schedules, and cost savings.

• Improved ability to explain to clients: AR is also effective when explaining the finished image or construction details to clients (owners). Spatial impressions that are hard to convey with models or perspective drawings become instantly clear when the client sees a full-scale model overlaid on site. For example, at pre-completion walkthroughs, having the client view the completion model through a smartphone helps them understand details, and projecting a bridge’s completed image onto the road for a community briefing can ease concerns. AR enables intuitive sharing of construction intent and the finished form, speeding up consensus building and strengthening trust with clients.

Introduction to LRTK’s simple surveying and AR-guidance features and a natural rollout suggestion (as case-style options)

Finally, let’s touch on LRTK’s simple surveying and AR guidance features, which are effective approaches for introducing the system on site. LRTK combines high-precision positioning with a smartphone and includes functions useful for everyday construction management beyond AR display.

First, the simple surveying capability: with LRTK, one person can easily perform site measurements. By leveraging the iPhone’s built-in LiDAR sensor and camera, you can 3D-scan terrain and structures and convert them into point cloud data. This enables quick completion of tasks such as measuring excavated volumes or recording as-built shapes. You can later analyze distances, elevation differences, and cross-sectional shapes on the point cloud, or use the LRTK cloud to automatically calculate volumes and areas with a single touch. Surveying tasks that previously required a total station and multiple people can be completed with just a smartphone, resulting in major efficiency gains.

Next, AR-based coordinate guidance (support for stakeout and layout marking) functions: on building and civil engineering sites, tasks such as stakeout and layout marking place elements on site according to coordinates from drawings. LRTK provides an AR navigation function that guides users toward pre-registered coordinate points. Arrows and guides are displayed on the smartphone screen, and when you approach the specified point it notifies you that “this is the designated position,” so even non-experts can accurately identify points. In one case, using this AR guidance to mark anchor bolt locations allowed a task that used to take two experienced workers half a day to be completed by one person in under an hour. High-precision coordinate guidance dramatically reduced human error and eliminated mistakes in setting out points.

LRTK’s ability to be deployed in stages—“start with surveying and measurement or layout marking, then gradually expand to AR model display”—is another advantage. In practice, some sites introduced it initially as an as-built measurement tool, and as teams recognized its convenience, use expanded to AR-based construction checks and discussions. Because it can be used immediately on site with just a smartphone and a small device, site staff were able to use it intuitively without pre-training, making it easy to integrate into workflows. LRTK, which realizes high-precision AR construction management, is no longer an exotic cutting-edge technology but is becoming an option anyone can use. If your company is considering leveraging 3D CAD or BIM data for site DX, you might consider adding this type of smartphone-based high-precision AR system to your list of options.