In the construction industry, the evolution of digital technologies is significantly changing the management methods on construction sites. The Ministry of Land, Infrastructure, Transport and Tourism is promoting the introduction of ICT in all processes, from surveying to maintenance, through the "i-Construction" initiative, aiming to improve construction productivity. In particular, the use of 3D data (point cloud data) obtained from drones and 3D scanners has become essential for accurate as-built management and efficient work planning. By visualizing the site in three dimensions, it is possible to improve the accuracy of volume calculations during the design phase and contribute to maintenance after construction.

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Against this background, a new 3D visualization technology that combines point cloud data, AR (Augmented Reality), and RTK (Real-Time Kinematic) is gaining attention. AR technology allows digital information, such as design models, to be overlaid onto real-world footage, enabling intuitive site checks. This has increased expectations for preventing construction errors and improving project efficiency. In fact, there have been reports in infrastructure projects where the use of AR has facilitated smoother communication between designers, contractors, and clients.

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On the other hand, traditional AR applications have faced challenges such as slight discrepancies (position errors) with the real world and data consistency issues, requiring solutions for full implementation. The key to addressing these issues is the integration of RTK, a high-precision positioning technology. RTK uses satellite positioning to achieve centimeter-level accuracy in real-time, and when combined with AR, it can eliminate the positional discrepancies between digital information and the physical site. The fusion of point cloud data, AR, and RTK is expected to significantly improve the efficiency of construction management and surveying.

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This article will first explain the basics of point cloud data and its acquisition methods, then explore the use cases of combining AR and point cloud data, and discuss the importance of RTK in providing high-precision positioning information. Additionally, it will touch on the latest technology that integrates these elements, "LRTK," and introduce specific examples and benefits of its application in construction management, as-built management, and maintenance.

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2. What is Point Cloud Data?

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Point cloud data is a collection of countless points in space, each consisting of three-dimensional coordinates (X, Y, Z) and other information such as color data. When objects or terrain are measured using laser scanners or photogrammetry, the positions of numerous points on the surface are captured. These points, when plotted in 3D, form point cloud data, which can accurately reproduce the shape of the object. In recent years, with advancements in sensor technology and the promotion of national policies, the measurement and utilization of 3D point cloud data have rapidly become more widespread.

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There are various methods for acquiring point cloud data. One of the most common methods is laser surveying (LiDAR). By scanning terrain and structures with ground-based or mobile laser scanners, or LiDAR-equipped drones, high-density point clouds can be obtained. Photogrammetry is also widely used. By taking numerous photos with drones or DSLR cameras and using image analysis to reconstruct 3D shapes, point clouds can be generated. In some cases, underwater surveying using sound waves is also utilized. Because point cloud data can be obtained using multiple methods, such as laser light or photography, it is possible to create 3D data for a wide range of civil engineering sites, from vast terrains to specific sections of bridges.

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The main uses of point cloud data in the civil engineering industry include the following:
 

• Current Surveying and Design Support: By converting the terrain into point cloud data before construction begins, accurate volume calculations and planning assessments can be made during the design phase. Traditionally, volume estimation was done through sectional surveys, but with point clouds, volumes can be directly calculated in 3D, improving both accuracy and efficiency. This method also helps optimize planning by providing a comprehensive understanding of the terrain and structure layouts.

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• Application in Construction Management: Point cloud data is also effective for tracking progress and verifying as-built conditions (final shapes) during construction. For example, by capturing excavation or embankment progress using drones and converting the data into point clouds, it can be used for daily volume and schedule management. Tasks that previously required on-site measurements at specific points can now be verified with minimal checks by comparing point clouds.

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• As-built Inspections and Quality Control: If the completed structure is measured with point clouds, as-built inspections can be performed efficiently by comparing the data with the design model. By overlaying point clouds and color-coding the discrepancies, it becomes easy to identify which parts align with the design and where errors exist. This helps prevent missed mistakes and enables early detection of areas that need repairs. Tools that comply with the Ministry of Land, Infrastructure, Transport, and Tourism’s “Guidelines for As-built Management Using 3D Measurement Technology” are now available, and point cloud-based as-built management is becoming more widely adopted in practice.

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• Maintenance and Infrastructure Inspections: Point cloud data is also used in inspections of infrastructure such as bridges and tunnels. By scanning the entire structure, deformations like cracks and sagging can be detected by comparing current data with historical records. Previously, damage documentation was done through visual inspections or 2D drawings, but now it can be precisely captured by marking on the point cloud. Additionally, analyzing the acquired point cloud data allows for the assessment of deterioration progression and helps prioritize repairs, contributing to preventive maintenance.

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In this way, point cloud data serves as a comprehensive 3D foundation that can be widely utilized from the beginning to the end of construction, and even in maintenance. Despite its vast amount of information, recent advancements such as smartphone-mounted LiDAR have made measurement tools more accessible, making it easier for anyone to use. Today, "just turning the site into a point cloud" can be considered the first step toward efficient site management.

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3. Fusion of AR and Point Cloud Data

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By combining AR (Augmented Reality) technology with point cloud data, the real world and digital information can be seamlessly integrated. By overlaying and comparing the point cloud data (current 3D) captured on-site with 3D models from the design phase or construction information, differences that were difficult to perceive using only floor plans or cross-sectional drawings can now be intuitively understood. Here, we will introduce examples of how AR and point cloud data are applied in various phases of civil construction.

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• Application in Construction Management: During construction, by overlaying the design 3D model with AR onto the actual site, the current construction status can be directly compared with the planned final shape. For example, displaying the completed 3D model of the structure in AR during construction makes the progress (completed work) instantly visible. The differences from the plan can be immediately identified, allowing for early adjustments to the schedule or additional arrangements as needed, ensuring that all stakeholders share the same understanding. Additionally, by cross-checking with the design data, surveying or construction errors can be detected in advance. By constantly comparing the AR-displayed design 3D data with the actual structure on-site, construction errors due to misreading drawings or positional shifts can be prevented. This creates an environment where even less experienced technicians can perform work accurately without relying on the intuition of seasoned professionals, leading to reduced rework and ensured quality.

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• Application in As-built Management: The fusion of AR and point cloud data also proves powerful in as-built inspections and quality checks after construction. By continuously verifying whether construction aligns with the design in real-time, the risk of needing significant revisions after completion is reduced. For example, once a section is completed, point cloud data can be immediately scanned and compared with the design model, or the completed model can be overlaid in AR to check for discrepancies beyond acceptable limits. Previously, the process involved as-built surveying, drafting, and checking differences from design values, but by confirming "the actual and design match almost perfectly" in AR, the inspection process can be significantly streamlined. By confirming as-built conditions in AR in the presence of stakeholders, corrective actions can be shared and directed on the spot, improving both the speed and accuracy of as-built management.

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• Efficient Infrastructure Maintenance: The fusion of AR and point cloud data can also be utilized in inspecting and maintaining infrastructure facilities such as bridges and tunnels. By comparing point cloud data obtained during regular inspections with previous data from when the structure was in good condition or with design BIM data, and then displaying the results in AR on-site, areas of degradation or damage can be highlighted directly on the structure. For example, by extracting differences in the deflection of a bridge beam or deformations in the tunnel interior from point cloud data, and projecting these differences onto the actual structure using AR glasses, even minor changes that might be missed by the human eye become visible. This allows inspectors to intuitively grasp hidden internal damage or aging changes on-site, leading to better prevention of oversight and more accurate diagnosis. Additionally, by attaching digital tags to previously recorded damaged areas during inspections and displaying them in AR during the next inspection, changes since the previous check can be accurately assessed. This method enhances deterioration prediction and makes it easier to optimize repair planning (deciding when and where repairs should be made). As a result, this approach becomes an effective way to extend the lifespan of infrastructure while working within limited budgets.

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As seen above, the fusion of AR and point cloud data proves effective in a wide range of situations, from the planning stage of construction to completion inspections and maintenance. By directly comparing the 3D model with the actual site, it significantly reduces discrepancies between the site and the drawings, enabling smart construction that doesn't rely on the experience of seasoned professionals. For younger engineers, this approach reduces the burden of imagining the completed structure from drawings, and by working with the completed model in AR, their learning curve can be shortened. In the future, as tablets and AR glasses become more widespread, the combination of point cloud data and AR is expected to become an accessible tool even on small-scale projects in regional areas.

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4. The Importance of High-Precision Positioning with RTK

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The core technology supporting the use of AR is high-precision positioning through RTK (Real-Time Kinematic). RTK is a method that corrects the error factors in satellite positioning and provides centimeter-level position coordinates in real-time. In typical GPS (GNSS) positioning, errors in satellite signals can cause deviations of several meters. However, with RTK, the usual GPS error of 2 to 5 meters can be reduced to within a few centimeters. This is achieved by calculating the difference between the observation data at a known reference point (base station) and sending the error correction data to the mobile station.

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To briefly summarize the differences between RTK positioning and standard GPS:

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• Positioning Accuracy: While standard standalone positioning has an error of about 5 meters, RTK positioning achieves accuracy within 2 to 3 cm. This high-precision positioning enables automatic control of construction machinery and precise surveying.

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• Positioning Mechanism: Standalone positioning only measures the distance (pseudo-distance) to each GPS satellite, whereas RTK performs relative positioning using carrier phase data received by both the base station and mobile station. This cancels out satellite orbit errors and atmospheric errors, allowing for highly reproducible positioning.

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• Implementation Methods: There are two main methods: using a base station on-site (local RTK) or using correction data provided by an electronic reference point network (network RTK). In Japan, high-precision positioning environments can be easily established using services like NTT Docomo’s GNSS correction information service and the CLAS (Centimeter-level Augmentation Service) transmitted by the Quasi-Zenith Satellite "Michibiki."
   

Why is high-precision positioning information important on construction sites? The main reason is to integrate all data using correct coordinates. For instance, point cloud data, design 3D models, and AR displays, as mentioned earlier, are meaningless if their alignment is off. Traditionally, there was the tedious process of converting and adjusting data to local coordinate systems for each site. However, by using RTK to acquire and manage all data in global coordinates (such as the World Geodetic System), point clouds measured separately or design models can be aligned perfectly without additional alignment work. This eliminates the need for complex adjustments when exchanging data between the site and the office, providing significant support for driving digital transformation (DX).​

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Moreover, high-precision positioning with RTK contributes to both the quality and efficiency of construction itself. For example, in surveying and staking tasks, what used to require multiple people using a total station for reference setup can now be done quickly by one person using an RTK-compatible GNSS receiver. In earthworks and paving with heavy machinery, there are increasing examples of GNSS guidance reducing labor while ensuring precise work. Furthermore, by combining RTK with AR solutions, accurate AR displays can be achieved without the need for markers, and there is no risk of model misalignment when moving the device.

For instance, in traditional AR, it was necessary to place markers on the ground or manually align the initial position, which caused problems when the user moved and the model shifted. By using RTK for position synchronization, the 3D model will always maintain the correct position in the real world as the device moves, ensuring that high-precision alignment is consistently maintained in AR. In this way, RTK not only enhances positioning accuracy but also serves as a crucial foundation for supporting the digital twin of the construction site.

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5. What is the Latest Technology "LRTK"?

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One of the latest technologies combining point cloud data, AR, and RTK solutions is the innovative "LRTK." LRTK is an all-in-one site DX tool developed by Lefixea, a startup spun off from Tokyo Institute of Technology. It consists of a small RTK-GNSS receiver and a smartphone app. In simple terms, it is a "pocket-sized universal surveying device" that can perform positioning, point cloud measurement, staking, photogrammetry, and AR display all by simply attaching it to a smartphone (iPhone/iPad).

 

Figure: Example of the LRTK device, which turns a smartphone into a centimeter-precision surveying tool (an ultra-small RTK receiver attached to the back of an iPhone). With a compact size that fits in your pocket and weighing only about 125g, it is lightweight and comes with a built-in battery, making it easy to carry and use on-site. The receiver can be easily attached or removed with one touch using the dedicated smartphone case, and once attached, positioning starts on the dedicated app, allowing centimeter-level positioning information to be obtained.

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What sets LRTK apart from traditional point cloud measurement methods and AR tools is its ease of use and integration. The main features are as follows:

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• No On-Site Coordinate Alignment for AR: The standout feature of LRTK is its ability to provide accurate AR projections without the need for coordinate alignment on-site, thanks to the high-precision positioning data from RTK. Traditional AR software required marker placement and manual alignment, but with LRTK, the design 3D model can be displayed directly at global coordinates, and the model remains aligned even when the device is moved. This allows anyone to easily and immediately confirm construction details using AR.

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• Point Cloud Scanning with a Smartphone (3D Scanning): If you have an iPhone equipped with a LiDAR sensor, LRTK allows you to acquire high-precision point cloud data on-site using the LRTK app. The acquired point cloud data is displayed in real-time on the smartphone and can be instantly uploaded to the cloud for verification and sharing as a 3D model. It’s groundbreaking because you can perform 3D scanning of the current site with just your smartphone, without needing specialized 3D scanners.

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• Coordinate Guidance (Staking): LRTK also allows you to perform staking (marking design positions) digitally. By specifying target coordinates in the app, arrows and distance information are displayed on the smartphone screen, guiding the user to the designated location. This enables tasks like pile driving or string lining, which used to require two people, to be carried out efficiently and precisely by one person.

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• Positioning Photos and Records: With LRTK, photos taken with a smartphone can be saved with high-precision location coordinates and orientation data. For example, by simply taking a photo of the construction site, the exact location and direction of the photo are recorded with centimeter accuracy, allowing the photo to be later plotted on a map or drawing. This feature makes photos serve as measurement records, reducing the effort required to create report documents.

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• Instant Cloud Sharing: Positioning and point cloud data are automatically uploaded from the smartphone to the LRTK cloud. On the cloud platform, the acquired data is visualized as maps or 3D models, and can be immediately shared with stakeholders. For example, the measured coordinate points can be plotted on a web map along with point names, timestamps, and notes. Generating a shareable link for internal and external data sharing is also simple, making it easy to share real-time, on-site data with stakeholders and receive feedback.

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With these features, LRTK covers all aspects of on-site operations, from surveying and construction management to as-built management and maintenance, all with a single device. For example, in construction management, even without a surveyor, the construction manager can scan the current site and verify the as-built conditions by comparing it with the design model in AR. In as-built management, by measuring and recording each completed section with LRTK as soon as it’s finished, all the necessary data will already be available for smooth inspection during the final check. In maintenance, inspection personnel can regularly measure and compare structures using LRTK, allowing them to conduct 3D measurements continuously in-house, a task that was previously outsourced to specialists, and detect deterioration trends early. Moreover, the operation is simple, requiring no specialized knowledge—just connect the smartphone to the receiver to start using it. The app automatically handles the averaging of positioning data and coordinate system transformations, eliminating the need for complex settings.
 

LRTK is compatible with CLAS (Centimeter-level Augmentation Service) provided by Japan's Quasi-Zenith Satellite "Michibiki," enabling centimeter-level positioning even in areas beyond communication networks, such as mountainous regions (left photo). In fact, during the 2023 Noto Peninsula earthquake, LRTK played a crucial role in the affected area where large equipment could not be brought in and mobile communication was disrupted. It was instrumental in providing high-precision records of the damage and enabling rapid sharing. In disaster situations, having a portable LRTK device allows for immediate digital measurements of the site, which can then be shared with stakeholders via the cloud, contributing to faster initial response times. In this way, LRTK demonstrates its capabilities not only in regular construction sites but also in extreme environments like disaster surveys.

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Currently, LRTK is the only AR tool on the market that does not require coordinate alignment on-site, making it a revolutionary solution for easy implementation. Its price is set to be very reasonable compared to traditional surveying equipment, and the concept of having one device per person is becoming increasingly realistic. If everyone on-site can carry high-precision positioning and 3D measurement tools, and instantly measure and share data whenever needed, the style of construction management will undergo a significant transformation. As a solution that embodies the digital transformation (DX) of civil engineering sites, LRTK is expected to receive growing attention in the future.

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6. Conclusion

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In this article, we discussed the on-site 3D visualization technology resulting from the fusion of point cloud data, AR, and RTK. To recap the key points, they are as follows:

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• Point Cloud Data: High-density 3D data obtained through laser scanning or photogrammetry, which allows for precise reproduction of the site’s terrain and structures. It is an essential foundational technology for enhancing construction planning, improving the efficiency of as-built management, and advancing infrastructure inspections.

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• AR (Augmented Reality): A technology that overlays design models onto the real-world site, enabling intuitive decision-making and progress tracking. It offers numerous benefits, including early detection of construction errors, real-time verification of as-built conditions, and improved communication among stakeholders.

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• RTK Positioning: Real-time high-precision positioning technology using GNSS. By positioning the site with centimeter-level accuracy, it eliminates discrepancies between data points, supports the integration of 3D data, and improves the accuracy of machine-assisted construction. The issue of misalignment in AR applications is also resolved with RTK.

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• LRTK: The latest tool that combines the three elements above into one package. With a smartphone and a super-small RTK receiver, it enables point cloud measurement and AR functionality, accelerating on-site digital transformation (DX) with ease of use for anyone. With "AR without the need for coordinate alignment" as its key feature, it can be widely used in surveying, construction management, and maintenance.

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By utilizing these digital technologies, tasks that traditionally relied on the intuition and experience of craftsmen will evolve into objective and efficient processes based on data. Specific benefits include the prevention of rework by reducing construction errors, improved as-built accuracy, labor-saving in surveying and inspection tasks, addressing labor shortages, and faster decision-making through accelerated information sharing among stakeholders. It also contributes to improved site safety by reducing unnecessary survey entries and heavy machinery guidance, thus lowering the risk of accidents.

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In the future, technologies such as point cloud data, AR, and RTK will continue to evolve, with new developments such as automatic detection and control through AI analysis becoming increasingly apparent. For regional civil contractors, there is no reason not to leverage these technologies. By adopting solutions like LRTK, which are easy to implement even on small-scale sites, they can achieve productivity and quality that rival larger companies. Indeed, "the future of the site will be dramatically transformed by AR and RTK."

If you are interested in introducing these technologies to your construction sites, please feel free to check out the detailed information. For LRTK, you can request free materials or consult about demos. Harness the power of point cloud data, AR, and RTK, and bring innovation to your construction management starting tomorrow. We strongly recommend using the latest technologies as the first step in riding the wave of on-site digital transformation (DX), significantly enhancing accuracy and efficiency.