In recent years, the civil engineering industry has been undergoing significant changes due to the advancement of digital technologies. The widespread use of drones for aerial surveying and 3D laser scanners has made it possible to record detailed information about construction sites. Among these, point cloud data and RTK (Real-Time Kinematic), a high-precision positioning technology, have emerged as key factors in dramatically improving the accuracy and efficiency of surveying and construction management. Additionally, CIM (Construction Information Modeling), which can be considered the civil engineering version of BIM, has been introduced, and the use of 3D models for information sharing and management is increasing the productivity of entire projects.

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As labor shortages and the decline of skilled workers continue to be significant issues, there is a growing trend to integrate these digital technologies to streamline construction processes, improve quality, and reduce costs.

This article aims to explain how combining point cloud data, RTK, and CIM can transform civil engineering construction for general contractors. It will provide a clear explanation, starting with the basics of each technology, followed by practical examples, and concluding with an introduction to the latest tool, LRTK.

What is Point Cloud Data?
 

Point cloud data refers to 3D data that represents the surface of objects or terrain as a collection of countless points (point cloud). Each point holds coordinates (X, Y, Z) and, in some cases, additional information such as color or reflectivity. By densely collecting these points, the shape of the object can be accurately recreated. For example, if a mountain's terrain is converted into point cloud data, it can be visualized as a detailed 3D model, including trees and elevations, which can be useful for volume calculations and shape analysis.

There are several methods for acquiring point cloud data, which can be broadly categorized as follows:

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• Utilization of Laser Scanners (LiDAR): This method involves using ground-based 3D laser scanners placed on tripods to take measurements, scanning the surroundings while driving with mobile mapping systems (vehicle-mounted), or equipping drones with LiDAR sensors to survey large areas from above. Since the laser directly measures distances, it offers high accuracy and can acquire detailed data consisting of millions to hundreds of millions of points in a short amount of time.

• Utilization of Photogrammetry (SfM): This technique involves using numerous photos taken with a standard digital camera or drone, calculating the matching feature points, and reconstructing the 3D shape. This method generates point cloud data. It does not require specialized equipment, making it easy to capture large areas and process the photos into point clouds using post-processing software. However, the accuracy is affected by the resolution of the photos and the shooting method.

• Acquisition with Smartphones or Tablets: Recent smartphones are equipped with LiDAR sensors, enabling easy point cloud acquisition of the surroundings using dedicated apps. For small-scale structures, 3D scanning can be done conveniently. By combining this with RTK-enabled devices, high-precision point cloud surveying can be achieved even with a smartphone.

The accuracy of acquired point cloud data varies depending on the equipment and method used. However, the latest LiDAR equipment can achieve millimeter-level accuracy, while photogrammetry can yield accuracy within a few centimeters when performed correctly. Point cloud data is utilized in a wide range of fields, including the management of road and land development, displacement measurements for bridges and tunnels, volume calculations, and even the documentation of cultural heritage. By digitizing the entire construction site, point cloud data provides spatial information that cannot be captured by traditional 2D drawings or cross-sectional views, contributing to the optimization of construction planning and the efficiency of progress management.

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Combination of RTK Technology and Point Cloud Surveying

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RTK (Real-Time Kinematic) is a high-precision positioning technology that utilizes GNSS (Global Navigation Satellite System) for real-time positioning. By correcting satellite positioning error information between a fixed base station and a moving station (rover), RTK achieves centimeter-level accuracy in real-time. In traditional GPS standalone positioning, errors of several meters occur, but with RTK, precise surveying and staking (marking positions) required for civil construction can be achieved.

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Combining RTK technology with point cloud data acquisition offers significant advantages. For example, in cases where RTK is integrated with drone-based photogrammetry, it is possible to align the acquired point cloud and orthophoto to an existing coordinate system with high precision without needing to set up numerous known ground points (targets) for alignment. This reduces preparation time while also streamlining post-survey data processing. In practice, 3D models generated from aerial photos captured by RTK-equipped drones can achieve coordinate accuracy within a few centimeters, allowing them to be directly overlaid onto design drawings' coordinate systems.

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Furthermore, when point cloud scanning is conducted using RTK-enabled equipment, point cloud data with absolute coordinates can be instantly acquired. This means that the acquired point cloud is already aligned with map coordinates or design coordinates, eliminating the need for later transformations to match the entire point cloud to reference points. For instance, if a site is scanned with an RTK drone before excavation by heavy machinery, the obtained terrain point cloud model can be immediately compared to the design's 3D terrain model, allowing for immediate calculation of excavation or embankment volumes. Tasks that used to require survey teams to measure multiple heights on-site and calculate volumes manually can now be automated in a short time with high precision by combining point clouds and RTK.

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Additionally, RTK is also used for machine guidance and quality control in construction. By equipping bulldozers and graders with RTK-GNSS, operators can always accurately know the position of the machine’s blade, enabling automatic control for ground shaping according to the design surface. By understanding the current situation with point cloud data and determining precise positions using RTK, this powerful combination improves both the accuracy and efficiency of civil construction. This results in fewer errors due to misalignment or re-surveys, leading to reduced construction time and cost savings.

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Integration with CIM: The Future of 3D Model Utilization

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CIM (Construction Information Modeling) is an integrated management method that centers around the use of 3D models for civil engineering projects. It can be considered the civil engineering version of BIM (Building Information Modeling), which is used in the construction of infrastructure such as roads, bridges, and dams. CIM aims to utilize 3D models across all phases of a project, from planning and design to construction and maintenance. By implementing CIM, information sharing among project stakeholders becomes smoother, which improves the accuracy of design, optimizes construction planning, and provides the added benefit of using the model as a digital asset during maintenance.

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So, what can be achieved by integrating point cloud data with CIM? The key lies in combining the current site conditions (point cloud data) with the design information (CIM model). For example, if a structure under construction is regularly surveyed using point cloud data, and this data is overlaid with the design CIM model, the construction’s progress can be checked in real-time. Any discrepancies between the design model and the construction can be easily identified, allowing for early corrective action. Traditionally, surveying work was carried out after construction, where surveyors would measure key areas and compare them with the plans. However, by combining point cloud data with CIM, comprehensive construction inspections can now be done digitally.

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Moreover, the integration of point cloud data and CIM is also effective in the maintenance of completed structures. In regular inspections of bridges or tunnels, new point cloud data can be overlaid on previously created CIM models (or models with point cloud data from the completion phase) to detect signs of aging or structural changes. For example, by scanning the concrete lining of a tunnel every year, cracks and deformations can be quantitatively compared on the model, and repair history can be managed in 3D space. By pinning photos of deteriorated areas or inspection notes to the CIM model, all site information can be centrally managed as a digital ledger. In this way, the integrated use of point cloud data and CIM provides a forward-thinking management approach that utilizes data throughout the entire lifecycle, from construction to maintenance.

In practice, the Ministry of Land, Infrastructure, Transport and Tourism is promoting the use of BIM/CIM, with an increasing number of projects that include 3D models in bidding documents or encourage the use of point cloud data for construction quality management. In the future, digital construction, integrating point cloud data, RTK, and CIM, will likely become the standard.

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Practical Use Cases

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To help you grasp the concept of new technologies, here are a few examples of how point cloud data, RTK, and CIM integration are being utilized in actual civil engineering projects.

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Utilization of Point Cloud Data in Bridge Construction

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This image shows the use of a smartphone with LiDAR to scan the pier of a small bridge, displaying the point cloud data on the phone’s screen. Photos and notes of deteriorated areas can be linked to the acquired point cloud data for record-keeping.

In the case of a small bridge repair project in a rural area, traditional bridge condition surveys required considerable effort. Engineers had to crawl under the bridge, sketch damaged areas in a paper field notebook, and take a large number of photos with a digital camera, which would later need to be organized. However, with the introduction of 3D scanning using a LiDAR-equipped smartphone and RTK receiver, the situation changed dramatically. By simply scanning the bridge piers and beams with a single smartphone, high-precision 3D point clouds can be captured on-site. Photos and comments can be pinned directly to the specific areas of concern on the point cloud, eliminating any confusion later about "which photo corresponds to which location." Using this method, inspection costs and time were reduced by approximately half, and the on-site survey record-keeping was completed with just a smartphone.
 

Since it’s possible to directly measure distances and areas on the point cloud data, for example, measuring the extent of damage to the underside of a bridge beam no longer requires using a tape measure, significantly improving both safety and efficiency.

The technology developed for bridge inspections and repairs has also been applied to the construction management of new bridges. After the concrete pouring for bridge piers and abutments, point cloud scans can be taken and compared with the design CIM model to check dimensions and shapes for construction accuracy. In large-scale bridge projects, drones are used to acquire point cloud data of the entire bridge, allowing for high-altitude inspections without the need for scaffolding. The integration of point cloud data and RTK is making quality management in bridge construction more precise and efficient.

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Collaboration with CIM in Road Construction

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In the field of road construction, the combination of point cloud data and CIM supports the site in various ways. For example, in a road widening project, a CIM model that could be shared by all parties, including the client, designer, and contractor, was created and fully utilized on-site. Specifically, before the project started, the current terrain was carefully assessed based on point cloud data obtained from drone photogrammetry and ground-based laser scanning. Then, a 3D model of the design (including the completed road and associated structures) was overlaid on top of the terrain data. During construction, this model was used to simulate excavation areas and embankment heights in advance, and the 3D completed design was shown to heavy machinery operators on tablets. This allowed them to intuitively understand the construction areas, which would have been difficult to convey with 2D drawings alone, helping prevent construction mistakes.

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There is also an advanced example using AR technology. On one site, the completed road and bridge models were overlaid on the actual scenery through the tablet screen, and this was used for meetings with the client and local residents.

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The completed image, which is hard to grasp from just the drawings, became clear and intuitive when projected onto the site using AR. This attempt to visualize the CIM model on-site helped facilitate agreement and was well-received in briefings. Furthermore, during construction, point cloud data obtained daily (for example, point clouds captured from drones flying overhead) was incorporated into the CIM model to visualize progress. By color-coding the work completed and displaying it on the model, managers could instantly see how much work had been done and how much was left, improving the accuracy of schedule management.

As demonstrated in the road construction example, integrating point cloud data with CIM enables smoother communication and more advanced construction management. From explaining to clients and providing information to the surrounding area to sharing data among on-site staff, the 3D model is increasingly becoming a common language.

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3D Point Cloud Surveying in Tunnel Construction

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3D point cloud surveying is also playing a key role in the construction of mountain tunnels. During tunnel excavation, rock is removed using blasting or tunnel boring machines, and it is necessary to check whether the excavated cross-section is in accordance with the design to ensure proper installation of supports and concrete linings. Traditionally, this excavation cross-section measurement involved on-site engineers using measuring poles inside the tunnel to measure radii at specified positions or manually measuring distances from a reference line called "chokume" (survey marker). However, the tunnel environment is dark and dusty, making it easy to overlook points during measurement. Today, after tunnel excavation, the entire tunnel cross-section is measured using a 3D laser scanner to capture point cloud data, which is then compared to the designed tunnel cross-sectional shape. Using point cloud data, it is possible to fully assess where the excavation exceeds the design (overbreak) or falls short (underbreak) by several centimeters. Based on this information, decisions can be made accurately regarding adjustments to shotcrete thickness or additional reinforcement in areas where excessive excavation has occurred.

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In tunnel construction, RTK GNSS positioning cannot be used inside the tunnel, so instead, known points are surveyed using a total station to assign coordinates to the point cloud. This allows the point cloud data inside the tunnel to be connected to a coordinate system on the surface, providing it with absolute positioning. As a result, the point cloud data can be integrated with data from other structures or topographic maps and accurately reflected in the completed CIM model.

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Furthermore, point cloud data is also powerful in tunnel maintenance. By scanning the tunnel interior every few years, the aging process can be digitally archived. For example, by comparing point cloud data of the internal shape (deformation) over time, the sagging of the tunnel crown or the contraction of sidewalls can be quantitatively detected. Even small changes that are hard to notice with the naked eye can be identified through the data, allowing for the development of preventive maintenance plans. By combining point cloud data with CIM models, it will be possible in the future to digitally manage the placement of equipment and cables installed within the tunnel, and confirm their locations via AR displays when necessary. Even in the closed space of a tunnel, digital measurement and 3D models support safe and reliable construction and maintenance.

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Introduction to LRTK

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The LRTK Phone device (a compact RTK-GNSS receiver) attaches to a smartphone. When combined with the smartphone, it allows for easy high-precision positioning and 3D scanning.
 

Finally, let me introduce LRTK, an exciting tool that makes the use of point cloud data and RTK more accessible. LRTK is a pocket-sized universal surveying tool developed by Lefixea, a startup company spun off from Tokyo Institute of Technology. By attaching a dedicated small RTK-GNSS receiver to a smartphone or tablet, it allows for centimeter-level positioning with just one device. In other words, the smartphone transforms into a high-precision GNSS receiver, capable of conducting point cloud measurements, photogrammetry, and even displaying design data in AR—all in one device. Tasks that traditionally required expensive surveying equipment and specialized knowledge can now be easily performed by anyone, making it a revolutionary solution that truly supports the digital transformation (DX) of construction sites.

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With LRTK, you can easily acquire point cloud data with absolute coordinates. For example, by scanning embankment or excavation areas with a smartphone, a 3D point cloud model is generated on-site, and the volume is calculated. The entire process, from positioning to point cloud generation and volume calculation, is completed in real-time, with the results instantly displayed on the device. Additionally, the acquired data is integrated with cloud services, allowing high-precision location data, photos, and point clouds collected on-site to be uploaded to the shared company cloud for immediate viewing and sharing. This significantly reduces the time and effort needed to bring the information back to the office for drafting or report creation. Seamless information usage is also made possible, such as overlaying design drawings and construction plans with point cloud data on the cloud platform or sharing the latest on-site data with stakeholders.

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The biggest feature of LRTK is that it eliminates the need for complicated setups or coordinate alignment on-site. By attaching the receiver to a smartphone and launching the dedicated app, correction data is automatically obtained, and high-precision positioning begins. From there, all you need to do is walk to the desired measurement location and follow the on-screen instructions to move the smartphone, enabling point cloud scanning and positioning. Since the software covers much of the specialized knowledge and experience traditionally required for surveying, it is easy to use even for those who are not experienced professionals, which is a significant advantage. By allowing anyone on-site to handle high-precision data, it is expected that the digital transformation (DX) of the entire civil engineering industry will accelerate. In fact, as simple tools like LRTK become widespread, 3D surveying and CIM utilization will become more accessible even on small and medium-sized construction sites, leading to a major transformation in workflow.

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In conclusion, the integration of point cloud data, RTK, and CIM is bringing transformation to every stage of civil construction, including surveying, design, construction management, and maintenance. By effectively utilizing digital technologies, tasks that were previously reliant on manual labor can be streamlined, while also enhancing precision and reliability. For general civil contractors, these technologies are not something extraordinary but will serve as a powerful ally in improving site operations. We encourage you to embrace high-precision surveying with point cloud data and RTK, and 3D model management with CIM, to help improve productivity and ensure safety on future construction sites. The new form of civil construction that merges digital technologies with on-site operations is steadily becoming a reality.