Enabling Labor Savings in Surveying with LiDAR – LRTK as a Solution to Labor Shortages

In recent years, labor shortages have become a serious issue on surveying and construction sites. With an aging population of skilled surveyors and a lack of younger professionals, there is an increasing need to carry out work efficiently with limited personnel. At the center of attention in this context is the labor-saving potential of laser-based LiDAR surveying technology. This article explains in plain terms the principles of LiDAR sensors and their application to surveying, highlights differences and advantages compared with conventional methods, and explores how a new workflow that combines smartphone-mounted LiDAR with high-precision GNSS (RTK corrections) can address the shortage of surveying personnel. Finally, we present various use cases such as automated point cloud acquisition and single-person surveying for slope management, and touch on applicability to public surveys and conformity with accuracy requirements. Let’s examine how the GNSS receiver that attaches to a smartphone, “LRTK,” can contribute as a cutting-edge solution that achieves both labor savings and high precision.

How LiDAR Sensors Work and Their Application to Surveying

LiDAR (Light Detection and Ranging) is a sensing technology that uses laser light to measure distances to targets and capture the shape of space in three dimensions. The basic principle is simple: a laser is emitted toward a target, and distance is calculated by measuring the time until the reflected light returns (the Time of Flight method). For example, terrestrial LiDAR units emit hundreds of thousands to millions of laser pulses per second into the surroundings and obtain numerous ranging points called a point cloud from the returned light. This enables dense collection of distance information that is not visible to the eye—such as building geometry and terrain undulations—and the creation of three-dimensional maps and models.

The expanded use of LiDAR in surveying stems from its ability to perform non-contact, high-speed measurements. Traditional surveying commonly used a total station and a staff (rod) to measure distance and height point by point. That approach typically required two or more personnel for each measurement point and demanded significant time and effort to cover wide areas. In contrast, LiDAR can be set up and scanned to measure the surrounding terrain as a surface all at once. It is also a major advantage that data can be acquired remotely and safely from steep or hazardous locations where people cannot safely enter.

Differences from Conventional Methods and Benefits of LiDAR Surveying

LiDAR surveying attracts attention because it offers various benefits not found in conventional methods. The main advantages are summarized below.

• Detailed surface measurement: Conventional surveying estimated terrain from a collection of discrete points, whereas LiDAR records terrain and structures as high-density point clouds that cover surfaces. Because it can capture surface irregularities and subtle changes, it contributes to improved accuracy in as-built (post-construction) verification and volume calculations.

• Labor savings and speed: Because large volumes of data can be acquired at once, LiDAR is overwhelmingly more efficient than taking measurement points one by one. Even on sites lacking experienced surveyors, the necessary surveying can be completed in relatively short time. Reducing personnel while cutting waiting time for surveys leads to overall process efficiency.

• Improved safety: LiDAR’s non-contact, long-distance measurement capability makes it ideal for surveying dangerous locations. Shape data of cliffs and slopes can be acquired with lasers from below without requiring personnel to climb onto slopes, greatly reducing worker risk and enhancing safety. Also, on sites with operating heavy machinery, scanning surroundings from a distance allows situation awareness while reducing the risk of contact accidents.

• Versatile data use: Obtained point cloud data can later be used to extract arbitrary cross-sections or converted into drawings and 3D models. Because a single measurement can serve multiple purposes—map creation, as-built management, displacement monitoring, etc.—it reduces duplicate surveys and streamlines work.

As described above, LiDAR surveying is an attractive labor-saving solution because it can cover large areas in short time, reduce personnel, and acquire high-density information. However, dedicated terrestrial laser scanners (TLS) are expensive and require specialized knowledge to operate. Recently, to make these advantages more accessible, small LiDAR sensors built into smartphones have begun to play an active role.

A New Surveying Workflow Enabled by Smartphone LiDAR and RTK GNSS

Some of the latest smartphones and tablets include small LiDAR sensors on the rear in higher-end models. Using these, a user can perform a 3D scan of the surroundings simply by pointing their phone, without preparing special surveying equipment. However, smartphone-only LiDAR measurement has several challenges. First, the point cloud obtainable is limited in range and accuracy; compared with professional laser scanners, the point cloud density is coarse and errors of several centimeters (several in) may occur. In addition, a smartphone’s built-in GPS has positioning errors on the order of several meters, so even if a point cloud is obtained it cannot be tied to accurate coordinates. That makes it unsuitable as surveying data by itself.

The solution is a new workflow combining smartphone LiDAR + high-precision GNSS. GNSS refers to satellite-based positioning systems in general; among them, RTK (Real-Time Kinematic) GNSS positioning uses correction information from a reference station to reduce positioning errors to within a few centimeters. If a small RTK-GNSS receiver that can be attached to a smartphone (a device like LRTK) is installed, the smartphone can obtain centimeter-level coordinates in real time.

With the smartphone LiDAR + RTK GNSS workflow, the smartphone becomes both a “3D scanner” and a “high-precision GPS surveying instrument” in one. Specifically, the user runs a LiDAR scanning app on the phone while the LRTK-like receiver performs RTK positioning. The user simply walks around the site with the phone; the LiDAR sensor acquires surrounding point clouds while the RTK-GNSS simultaneously records the phone’s trajectory and the positions of point cloud blocks with high accuracy. As a result, the acquired point cloud data are tied from the outset to accurate coordinates in real-world reference frames such as public coordinate systems.

What makes this approach revolutionary is that it can be handled with less specialized surveying skill. Traditionally, obtained point clouds would require post-processing to align with known control points or integration with separately measured GPS points—tasks that demand advanced work. With a smartphone and LRTK combined, location information is automatically attached to the point cloud on site, greatly reducing data processing workload. A single operator can complete the job by walking the site with a smartphone in hand, overturning the conventional notion of surveying as a “two-person” task. This is a major boon for sites struggling with labor shortages.

Moreover, RTK-secured coordinate accuracy helps offset the accuracy concerns that were a weakness of smartphone LiDAR. Although smartphone LiDAR itself has ranging errors of several centimeters, accuracy can be improved by extracting planar surfaces such as walls or the ground from the point cloud and averaging them. If RTK-GNSS provides firm positional reference, scan data from multiple locations can be overlaid without misalignment. In short, by complementing each other—“shape from LiDAR, position from RTK”—a workflow that balances ease-of-use and accuracy becomes feasible.

Thanks to these new technologies, even less-experienced personnel are increasingly able to conduct high-precision as-built surveys using smartphones. As a force to make up for the decline in veteran surveyors, smartphone surveying that anyone on site can operate is highly promising. Now, let’s look at concrete use cases where smartphone LiDAR + GNSS can improve site work efficiency.

Field Use Cases

Using smartphone LiDAR and RTK positioning can streamline a variety of surveying and measurement tasks. The main use cases and their effects are as follows.

• Efficiency through automated point cloud acquisition: Tasks that used to require manual selection of measurement points can be automated by the device for 3D scanning. With a single pass of the smartphone, complex terrain and structures can be captured as a whole in point cloud data in a short time. For example, scanning the existing pavement surface before paving work allows later analysis of needed cross-sections and elevation differences. The approach reduces measurement omissions and forgotten spots, cutting down on additional re-measurement work.

• Slope management enabled by single-person surveying: Previously, surveying steep slopes or embankments required multiple people and hazardous work. With smartphone LiDAR, an operator can scan from a safe location and acquire the entire slope’s geometry. A single person can grasp slope gradients and detect collapse points, dramatically improving the efficiency of frequent patrol inspections and post-construction slope as-built management. Even on sites with limited personnel, one person can survey multiple slopes in a short time, aiding early detection of anomalies and formulation of repair plans.

• As-built recording and inspection of structures: Even large structures such as tunnels, bridges, and dams can have their surface geometry thoroughly recorded with smartphone LiDAR. For verifying as-built (deviations from design), conventional practice measured values at fixed points and compared them with drawings. With point clouds, the entire structure can be preserved as a digital as-built model, allowing verification of deviations from design at any location. If a single person scans comprehensively, detailed as-built inspections can be performed later in the office, improving the efficiency of preparing inspection materials. Point clouds can also be used for before-and-after renovation comparisons and crack detection, contributing to DX-driven infrastructure maintenance.

• Emergency surveying at disaster sites: Rapid and safe situation assessment is required at landslide or earthquake collapse sites. Smartphone LiDAR can provide rough estimates of collapsed earth volume and three-dimensional damage extents by scanning from a distance without personnel remaining long in hazardous areas. A single operator can quickly survey unstable terrain shortly after a disaster, reducing the risk of secondary disasters while supplying data necessary for emergency recovery planning. For example, a 3D model of a collapsed slope can be created immediately and shared among stakeholders to show where debris is deposited and whether dangerous overhangs exist. This speeds initial response decisions and enables faster life-saving and recovery operations.

• Support for infrastructure maintenance and management: Point cloud data are powerful tools for maintaining infrastructure such as roads, rivers, and water/sewer systems. Using smartphone LiDAR, inspection items such as road subsidence, riverbank deformation, and tunnel lining deterioration can be recorded as quantitative 3D data. Items previously judged by visual inspection or 2D measurement can be understood as precise displacement values from point clouds. Regularly scanning the same locations makes it easy to quantify aging-related changes and show deterioration progression numerically. Even when manpower is insufficient for frequent patrols, acquiring wide-area data at once reduces the chance of missing warning signs at critical locations. The result contributes to improved preventive maintenance and more accurate planned repairs.

• Combination with AR navigation: Point cloud data acquired by smartphone can be linked directly to on-site AR (augmented reality) applications. For example, a 3D model generated from a point cloud can be overlaid on the real-world view on a smartphone screen to visualize the invisible. This can support excavation work by showing the locations of underground utilities in AR, or overlay design BIM models on the as-built state for construction management. The combination of high-precision position information (RTK) and real-time point clouds makes AR-based site navigation practical. This enables intuitive instructions and as-built checks for workers, reducing communication loss and preventing construction errors.

As described above, the fusion of smartphone LiDAR and GNSS technology holds potential not only to save labor in surveying tasks but to accelerate digitalization across construction sites. Can this approach be applied to formal surveying work such as public projects? Next, we consider accuracy requirements and regulatory positioning.

Considerations on Application to Public Surveys and Accuracy

Under the Ministry of Land, Infrastructure, Transport and Tourism’s push for “i-Construction,” ICT adoption on sites is accelerating. Simple 3D measurement using smartphone LiDAR has gained attention as part of this trend, and in recent years there have been moves to adopt it as a method for as-built management on small-scale ICT construction sites. In the 2020s, the Ministry’s guidelines included “as-built measurement using LiDAR mounted on mobile devices” as a case study, and field trials have been conducted. The initiative aims to supplement three-dimensional surveying—previously requiring expensive laser scanners or drones—with low-cost equipment usable by small and medium-sized contractors.

That said, fully applying smartphone LiDAR to official public surveying (such as cadastral surveying or design surveys) currently requires careful verification and conditional operation. Japan’s public surveys set accuracy standards for equipment and methods under the “Guidelines for Work Procedures.” Because smartphone LiDAR is a new method, it does not directly fit existing rules. Its use requires creating a site-specific work manual under Article 17’s special provisions, undergoing accuracy verification, and obtaining approval.

So what is the actual accuracy? Although high-performing, smartphone-mounted LiDAR is inferior to laser scanners and generally includes errors on the order of several centimeters (several in). One verification reported that modeling from point clouds obtained by consumer smartphones/tablets produced errors of approximately ±5 cm (±2.0 in) (whereas high-precision TLS yields ± a few mm). Conversely, in indoor environments scanning objects on the scale of a few meters (several ft), some cases showed differences from ground-truth measurements of less than several centimeters (less than several in); results vary by environment and target. At present, it is unrealistic to use smartphone LiDAR for applications demanding millimeter-level precision, and it is more practical to view it as a technology for quickly grasping approximate shapes.

However, combining with RTK-GNSS position correction dramatically improves absolute coordinate accuracy. Even if a smartphone LiDAR point cloud’s global location is uncertain, RTK positioning reduces initial coordinate offsets and allows multiple scans to be correctly integrated. This makes it possible, for instance, to acquire 3D data for small-scale site surveys with practical accuracy (errors on the order of a few centimeters). In fact, some prefectures and municipalities have published trial results using tablet-type LiDAR for as-built measurement and reported that “sufficiently practical accuracy was obtained.”

There are, however, practical constraints to be aware of in field use. First, the effective range of smartphone LiDAR is limited to around 5 m (16.4 ft), making it unsuitable for measuring vast sites in a single pass. Sensors may not function well under direct sunlight outdoors, so operation is ideally in shaded areas, evenings, or cloudy conditions. Also, raw point clouds often contain substantial noise and may be difficult to use directly for drawing production, requiring post-processing in software to remove unnecessary points and approximate planes and lines. When measuring, moving the smartphone too quickly can coarsen point sampling or distort shapes, so some practice and technique are needed. Given these factors, phased introduction with use-case limitations is realistic for adoption into public surveying. For example, employ it for purposes with relatively high tolerance for accuracy—such as pavement or structure as-built checks—while continuing to use conventional methods for precision-critical tasks like control point surveys or boundary determinations.

Conclusion: LRTK Enables High-Precision Smartphone Surveying for Everyone

In surveying and construction sites where labor shortages are acute, LiDAR technology can greatly contribute to labor savings and improved safety. In particular, the latest solution combining smartphone LiDAR sensors and RTK-GNSS is opening an era in which anyone can easily perform high-precision surveying. By introducing a small GNSS receiver that attaches to a smartphone—LRTK—centimeter-level positioning that once required specialized equipment and personnel becomes possible with a single smartphone, enabling on-site acquisition of point cloud data. This helps cover the decline of veteran staff, increases individual productivity, and contributes to resolving chronic labor shortages.

Furthermore, the spread of such easy 3D measurement aligns with the promotion of i-Construction. i-Construction emphasizes ICT-based as-built and construction management, and point cloud surveying with smartphone + LRTK embodies that philosophy. When anyone can obtain high-precision existing-condition data, construction delays due to waiting for surveys are reduced, and design, construction, and inspection processes connect seamlessly.

As smartphone LiDAR and GNSS technologies advance, accuracy and applicable scope will continue to improve. As intuitive tools for site personnel, solutions like LRTK may help consign the era in which surveying was a bottleneck to the past. Adopt smartphone surveying that achieves both labor savings and high precision, and promote smart sites where everyone can make data-driven decisions. This could become the new standard for the construction industry in an era of labor shortages and the key to on-site DX and productivity improvement.