The LiDAR Revolution in Construction Management – Achieving Accuracy and Efficiency Simultaneously with LRTK

Innovations in surveying technology are changing the conventional wisdom of construction management. As digitization of construction sites progresses, one technology attracting particular attention is LiDAR. LiDAR stands for "Light Detection and Ranging." It is a sensor technology that irradiates laser light onto targets and derives distances from the return time of the reflected light, acquiring the surrounding shapes as three-dimensional data. The advent of LiDAR has dramatically streamlined site surveying, which traditionally required considerable time and manpower. In recent years, starting with the Ministry of Land, Infrastructure, Transport and Tourism’s promotion of i-Construction, the use of 3D point cloud data in construction management has rapidly expanded. This is because 3D as-built data enables highly accurate understanding of site conditions and topography, which can dramatically improve construction quality and efficiency.

The main advantages of 3D scanning using LiDAR include the following:

• Measure large areas in a short time: Because a wide area can be scanned at once from a distance using lasers, surveying work that used to take several days can be completed in just a few hours.

• High-density, detailed point cloud data: Hundreds of thousands to millions of range points per second can be acquired, producing detailed 3D data that captures fine features of terrain and structures.

• Non-contact, safe measurement: Because measurement is non-contact using laser light, remote measurement is possible even in areas where people cannot enter or on steep slopes. This reduces the need to erect scaffolding or climb to high places, improving worker safety and efficiency.

• Labor reduction and improved work efficiency: With LiDAR equipment and a tablet, one person can perform surveying without transporting heavy equipment or allocating many personnel. This has significant effects on labor-short sites and contributes to labor-saving in surveying operations.

• Advanced use of digital data: Acquired point cloud data can be widely used for model checking against design models, cross-section creation, earthwork calculations, and more. Because the entire site can be digitally recorded, it is easy to extract needed information later and share it with stakeholders, contributing to improved construction management quality.

With the introduction of LiDAR, site condition comprehension has become dramatically more efficient, and a revolutionary change is occurring in construction management. Next, let’s look at how LiDAR point clouds are specifically used in construction management tasks and what effects they produce.

Examples of Point Cloud Utilization in Construction Management

LiDAR point cloud data is powerful in a wide variety of scenarios including as-built verification, slope surveying, structure measurement, pavement inspection, buried utility recording, disaster response, infrastructure maintenance, and AR visualization. Below we explain each example and the accuracy and efficiency benefits from using LiDAR.

Use in As-Built Verification

In civil works and land development, as-built verification to confirm that completed terrain and structures match the design is indispensable. Traditionally, staff used surveying instruments to measure critical heights and dimensions along control points and compared them with drawings, but this method risked overlooking shape variations between measured points.

By scanning the entire site with LiDAR, the ground and structures can be acquired as point cloud data without omission. For example, by modeling the finished terrain of embankments or excavations in 3D and overlaying it with the design surface, small excesses or deficiencies can be recognized at a glance. Cross-sections and as-built management drawings can be automatically generated from point clouds, so inspection work can be performed more quickly and accurately than before. Because many points can be obtained in a single scan, measurement time is greatly reduced and the personnel required for inspection can be decreased. LiDAR adoption has dramatically improved both the measurement accuracy and work efficiency of as-built verification.

Use in Slope Measurement

LiDAR is also effective for shape management of slopes formed by cutting or filling. It is difficult and often dangerous for people to enter steep or collapse-prone slopes for surveying, and measuring a few points from a distance was the best that could be done. This made it hard to grasp the entire slope state and posed safety management challenges.

Using LiDAR, the entire slope can be measured remotely in a short time, yielding accurate 3D shapes that include fine surface undulations. Deviations from design gradients and local bulges or depressions can be easily found from the acquired point cloud data. You can also create arbitrary cross-sections from the point cloud to confirm slope angles or calculate surface area and earthwork volumes. Since high-altitude measurements that are difficult manually can be done safely, there are major benefits in reducing worker burden and improving the reliability of survey results.

Use in 3D Measurement of Structures

LiDAR point cloud measurement is used for as-built inspection of buildings and civil structures themselves. Scanning structures such as building frames, bridges, and tunnels makes it possible to digitize the entire shape and compare it in detail with design models and drawings. Previously, only critical dimensions could be measured and verified, risking missed slight distortions between measurement points. With point cloud data, dimensions and positional deviations across the entire surface of a structure can be checked, virtually eliminating oversights.

For example, the squareness and flatness of concrete structures or the deformation of tunnel cross-sections can be quantitatively evaluated by analyzing acquired point clouds. Even complex curved surfaces and intricate structures can be captured completely by LiDAR in a short time. This speeds up verification of construction accuracy and contributes to improved quality control by enabling early detection and correction of problem areas.

Use in Pavement Measurement and Inspection

3D point cloud data is also powerful for as-built inspection of roads and pavements. By acquiring point clouds of newly paved surfaces and gradients along clothoid curves, you can evaluate pavement quality in detail over a wide area. Traditionally, inspections involved placing a straightedge to check local unevenness or measuring heights every few meters, but using point clouds makes it possible to visualize even small elevation differences across the entire pavement.

For example, scanning the subgrade and finished surface before and after paving allows verification of uniformity of compaction and paving thickness. Point clouds are also effective when determining rut depth and distribution after opening to traffic. Because the road surface can be continuously measured in a single pass, rapid quality checks after nighttime construction become feasible. Using LiDAR for pavement management simultaneously improves inspection accuracy and reduces work time.

Use in Recording and Managing Buried Utilities

LiDAR is beginning to be used for location recording of structures buried underground in infrastructure works. Scanning exposed trenches before backfilling and installed pipes and cables makes it possible to store accurate 3D positional data of buried elements.

Traditionally, after construction, depths and offsets of buried utilities were measured with tape measures or surveying instruments and recorded on paper drawings. This method depended on the skill of the recorder and risked omissions. Point cloud data acquired by LiDAR can comprehensively measure piping and allow accurate later verification of depth and slope at arbitrary locations. Because the data is digitized, it can be immediately used for future renovation work or maintenance, greatly improving efficiency in locating and verifying buried utilities. Recording buried utilities with LiDAR increases the precision of construction records and enhances the safety and efficiency of future site work.

Use in Disaster Situation Assessment

In disasters such as landslides, slope failures, and river flooding, 3D point clouds are a powerful tool for assessing the situation. Scanning a disaster site with LiDAR quickly reveals volumes of collapsed material and extent of damage, aiding prompt decision-making.

Dangerous areas where people cannot enter can be safely measured using drone-mounted LiDAR or remotely operated laser scanners. For example, at a large landslide site, comparing pre- and post-collapse terrain data allows accurate calculation of soil loss. Analyzing slope angles from point clouds of collapsed slopes helps assess secondary disaster risk. Even in cases where on-site inspections or partial survey data previously had to be used to infer conditions, point cloud data enables objective, high-precision assessment. LiDAR use in disaster response has dramatically improved the speed and accuracy of damage assessment and recovery planning.

Use in Infrastructure Maintenance

LiDAR point cloud measurement is also used in maintenance of social infrastructure such as bridges, tunnels, and roads. 3D scanning during periodic inspections allows quantitative tracking of deformation and damage progression over time.

Previously, visual inspection or measurements of certain sections were used to judge structural health, but comparing point cloud data over time makes it possible to capture behavior of the entire structure down to millimeter-level (0.04 in). For example, calculating displacements of tunnel inner walls or road surface settlement trends from multi-temporal point clouds enables quantitative evaluation of deterioration. Because LiDAR can measure large areas in a short time, road closures and work times associated with inspections are minimized. Accumulation of such 3D data directly supports preventive maintenance and more sophisticated repair planning. Using LiDAR for maintenance achieves both improved accuracy and efficiency in infrastructure inspection.

Use in AR-Based Site Visualization

Combining augmented reality (AR) technology with point cloud data is also attracting attention as a next-generation construction management method. By overlaying design 3D models or acquired point clouds onto live site images on a tablet or other display, you can intuitively understand the completion image or current as-built on location.

For example, superimposing a design model in AR over a structure under construction makes slight deviations between actual and design immediately apparent on site. Mistakes or areas needing rework that are hard to notice from drawings alone can be easily found by comparing the real object and digital information in AR. Also, projecting the finished image on site before completion and sharing it with stakeholders facilitates consensus building with the client and smoother planning discussions. Combining AR and point clouds dramatically improves communication efficiency and construction accuracy, and is evolving the way sites are managed.

High-Precision GNSS (RTK) Positioning and the Fusion with LRTK

No matter how detailed the point cloud data, it is not useful in practice unless it corresponds to accurate positional coordinates. Therefore, high-precision georeferencing that ties LiDAR point cloud surveys to a map coordinate system is essential. The key here is GNSS positioning, especially the use of RTK (Real-Time Kinematic).

GNSS is a general term for global navigation satellite systems represented by GPS, measuring positions on Earth based on signals from satellites. However, standalone positioning usually produces errors of several meters and cannot be used as-is for precise surveying. RTK is a technology that uses correction information from a base station in real time to reduce positioning error to several centimeters (several inches). There are methods that set up a dedicated base station on site and network-based services that use internet-delivered corrections; in any case, RTK enables satellite positioning to achieve centimeter-level high-accuracy coordinates (half-inch-level accuracy).

Combining LiDAR measurement with RTK positioning makes precise point cloud georeferencing simple. Traditionally, point clouds acquired by laser scanners had to be registered to known control points in post-processing, but pairing RTK-capable GNSS allows accurate coordinates to be attached to point clouds during acquisition. For example, equipping LiDAR sensor units with RTK-GNSS receivers means point clouds acquired while scanning a site will inherently have geodetic coordinate values. We refer to this LiDAR+RTK approach here as LRTK. Utilizing LRTK makes high-accuracy 3D surveying easy without special large equipment.

In recent years, smartphones and tablets have been equipped with LiDAR sensors, and by pairing these with compact RTK receivers, a palm-sized point cloud surveying system can be built. The point cloud density and accuracy obtainable from smartphone-built-in LiDAR have reached levels practical for general construction management use. However, since built-in GPS in smartphones has large positioning errors, RTK correction is indispensable to secure absolute accuracy. LRTK technology enables point cloud data acquired with familiar devices like smartphones to be given centimeter-level accurate coordinates (half-inch-level accuracy).

With smartphone point cloud surveying using LRTK, you can walk around a large site scanning needed areas in 3D one after another and immediately overlay the data on drawings or BIM models for verification. Because it is highly mobile and wireless, it allows access to desired measurement locations even in obstacle-dense sites or indoor spaces. Another advantage is that systems can be constructed that are intuitive enough for non-specialist workers to operate, enabling site personnel themselves to conduct surveying tasks that previously required specialist technicians. The fusion of LiDAR and RTK is making point cloud surveying more accessible and faster.

Conclusion

Three-dimensional measurement using LiDAR is bringing unprecedented accuracy and efficiency to construction management. From as-built and slope inspections to infrastructure inspection and disaster response, the use of point cloud data is improving construction quality and safety while enabling labor savings.

Furthermore, the arrival of LRTK, combining GNSS/RTK and LiDAR, has made it easy for anyone to enjoy these benefits. Smartphone-based point cloud surveying allows small teams to perform high-precision construction management, embodying the productivity revolution that i-Construction aims for at the site level.

Smartphone point cloud surveying with LRTK achieves both labor reduction and accuracy improvement, and is a future-oriented construction management method that contributes to i-Construction. Let’s adopt cutting-edge technology in site operations and realize a new era of construction management that combines efficiency and quality.