Improving Safety in Slope Surveying: 3D Point Cloud Technology Reducing Hazardous Work Through Labor Saving

Introduction: Why is slope surveying hazardous?

"Nōmen" (slope face) refers to inclined surfaces formed artificially or naturally on roads, dams, and development sites. Accurately surveying these slopes is indispensable for construction planning and as-built management. However, slope surveying sites often involve steep slopes and unstable ground, making the surveying work itself highly hazardous. In fact, occupational accidents such as slipping and falling on unstable slopes or being struck by falling rocks from above have occurred. High-elevation and slope work on slope faces always carries the risk of falls and collapses, forcing surveyors to work under constant tension.

The dangers of slope surveying are present at every stage of construction. Pre-construction site investigations require stepping onto steep slopes to understand topography and geology, and during construction or final inspections there are occasions when measurements on the slope itself are needed. In other words, it becomes necessary to approach slopes repeatedly before, during, and after construction. How to carry out these tasks safely has long been a challenge.

Challenges of traditional methods: slope entry, high-elevation work, and manpower burden

Traditionally, slope surveying typically involved survey staff entering the slope directly to take measurements. For example, to measure points on a slope with a total station, an operator with a prism must climb the steep slope to the setup locations. Height measurements with measuring tapes or leveling staffs (rods) require personnel to move along the slope while taking readings. Such methods, in which people physically enter the slope to measure directly, always carried the risk of slipping or falling.

To work safely at height, conventional countermeasures such as installing safety lines (lifelines) and wearing safety harnesses are employed. However, no matter how careful one is, the risk can never be reduced to zero, and fundamentally reducing the amount of high-elevation work on slopes themselves has been seen as the solution. Slope surveying also imposes heavy physical demands, often requiring multiple personnel working in shifts. High accuracy often depends on experienced surveyors, the work takes time, and this became a heavy burden amid labor shortages.

Moreover, traditional methods can only measure a limited number of points, resulting in fragmentary data. To grasp the entire slope shape you need many points, but because of the danger and effort involved, teams sometimes had to compromise with a minimal sample of measurement points. This led to the risk of oversight and measurement errors, leaving issues in quality control as well.

Emergence of “non-contact × labor-saving” surveying with 3D point clouds

In recent years, advances in ICT have produced new surveying methods that achieve non-contact, labor-saving workflows. At the core of these is measurement using 3D point cloud technology. A point cloud is a collection of many three-dimensional coordinate points obtained by laser scanners or photogrammetry, digitally reproducing the shape of the target with high precision. By creating a point cloud of a slope, the entire slope can be recreated on a computer and required dimensions and gradients can be measured later as needed.

The major characteristic of 3D point cloud surveying is that data can be collected remotely without the surveyor physically touching the slope. Because distance and shape are measured with laser light or photography, personnel do not need to enter hazardous areas. Also, tasks that previously required several people become device-operation–driven, allowing measurement with fewer personnel. It is attracting attention as a revolutionary solution that truly combines "non-contact × labor-saving."

With initiatives like i-Construction and ICT-enabled construction promoted by the Ministry of Land, Infrastructure, Transport and Tourism (MLIT), adoption of 3D point cloud technology in the field is progressing. In slope works, examples of using three-dimensional measurement for pre-construction surveys and as-built management are increasing. By replacing dangerous on-slope work with digital technology, dramatic improvements in safety and work efficiency can be achieved.

Methods overview: when to use TLS, drones, or smartphone RTK scanning

Although we broadly call it 3D point cloud surveying, several methods are available for field use. Here we introduce three representative approaches—the terrestrial laser scanner (TLS), drone photogrammetry (UAV aerial photography), and the increasingly popular smartphone RTK scan—highlighting their features and appropriate use cases.

Terrestrial Laser Scanner (TLS)

A TLS (Terrestrial Laser Scanner) is a tripod-mounted laser measurement device that emits laser light from the ground directly to the target to acquire high-density point cloud data. TLS's strengths are millimeter-level measurement accuracy and long range—tens to hundreds of meters. By placing the instrument in a safe location below the slope and scanning the entire slope, you can obtain detailed terrain data without anyone climbing the slope.

Even on slopes with many trees or rocks, TLS can build models that include occluded areas by scanning from several vantage points with clear lines of sight and merging multiple point clouds. In practice, when comprehensive measurement is needed on steep terrain and drones are blocked by forest cover, TLS is often used to complement drone data. The equipment is large and requires expertise, but its precision and reliability make TLS valuable for as-built confirmation of slope shapes.

Drone photogrammetry (UAV aerial photography)

Drone-based photogrammetry captures the site from above and converts it into a point cloud. A camera-equipped UAV photographs terrain including slopes, and photogrammetry techniques generate a 3D model from multiple images. The biggest advantage of drone surveying is that it can cover wide areas in a short time. Large-scale slope surveys that would take people days can have point cloud data collected in a short flight.

Drone photogrammetry achieves complete non-contact surveying because there is no need for surveyors to enter the slope; capture is done from the air. Drones can photograph hard-to-see sections from above or oblique angles, so complex terrain can be recorded comprehensively. However, slopes densely covered with vegetation make it difficult to extract the ground surface from photos, so combining drone data with ground-based TLS is effective. Also, drone flights must consider conditions such as battery life and wind, but under suitable conditions they are a highly efficient and safe surveying method.

Smartphone RTK scan (smartphone surveying)

Recently introduced smartphone RTK scanning combines a smartphone with a high-precision GNSS (RTK) receiver to obtain point clouds. Modern iPhones and iPads include LiDAR sensors, and when combined with RTK centimeter-level positioning, anyone can easily perform 3D surveying. By using a dedicated smartphone app and walking around the site while scanning, you can generate a real-time point cloud of the area around your walking path.

The smartphone+RTK advantage is mobility and ease of use. Because you use a smartphone that fits in your pocket, heavy equipment and special piloting skills are unnecessary, and surveying can be done on the spot whenever needed. Each person can carry one device for surveying, making it especially effective for small slopes or for supplemental detailed measurements. RTK ensures high-precision absolute coordinates are attached to the acquired point cloud, facilitating smooth georeferencing in post-processing. In locations where drone flight is difficult or where bringing TLS is unnecessary, smartphone scanning provides a new option.

On-site safety effects: zero contact, fewer personnel, no scaffolding

The safety benefits that 3D point cloud surveying brings to the field are immeasurable. Here we summarize three particularly important points: "zero contact," "reduced personnel," and "no scaffolding."

• Zero contact: The greatest benefit is that survey staff do not need to enter hazardous areas. Because data can be acquired without physically touching the slope using laser scans or drone photography, the risk of slipping or collapse is greatly reduced. Even on slopes where collapse risk prevents people from approaching, remote measurement enables safe current-condition assessment. Making surveying itself non-contact dramatically lowers the risk of occupational accidents on site.

• Reduced personnel: Slope surveying that used to require multiple people can be done with a minimal crew by using point cloud technology. For example, drone surveys can cover wide areas with one operator and one observer, and TLS can be operated and data-collected by one to two people. Reducing the number of personnel exposed to risk lowers the number of people in danger. Also, because surveys can be completed in shorter time with fewer people, prolonged high-elevation work is avoided and the physical and mental burden on workers is reduced.

• No scaffolding: Introducing point cloud surveying can eliminate the need to erect temporary scaffolding or use aerial work platforms solely for surveying. Traditionally, temporary scaffolds or lifts were installed to access slopes safely, and these scaffold erection operations themselves carry accident risks. Switching to non-contact surveying removes the need for such scaffolding and suspended equipment, saving the associated effort and risks. Site preparation is simplified and peripheral safety measures are reduced, improving overall safety levels.

In this way, 3D point cloud technology fundamentally removes situations where people are exposed to danger and realizes safer surveying operations. This not only allows surveyors to perform work safely but also reduces risks for surrounding workers and third parties, contributing to the overall safety management of the site.

Automating reports with point clouds: reducing the burden on construction managers

Once 3D point cloud data are acquired, subsequent data processing and report generation can be dramatically streamlined. Traditionally, verifying slope as-built conditions required plotting measured points on drawings, calculating differences from design values, and compiling reports. Using point cloud data, much of this work can be automated by software.

For example, to check final slope gradients you can extract arbitrary cross-sections from the point cloud and overlay them with design sections to analyze differences. What was difficult with dozens of manual measurements—performing surface-based as-built evaluations—can be accomplished with a single scan. As-built management software can compare point clouds and design 3D models to color-code areas with insufficient thickness or automatically compute cut-and-fill volumes. Construction managers can validate quality based on objective point-cloud evidence and address defects early.

Point cloud technology also greatly aids report creation. By sharing point cloud data in the cloud, detailed analysis and drawing creation can be done on office PCs. Extracting required figures from large field point clouds and automatically reflecting them in reports prevents calculation and manual-entry errors. Photo management and records in survey notebooks also become digital, reducing time spent on paper-based organization.

Recently, efforts combining point cloud data with AR (augmented reality) for visualization have attracted attention. Viewing the site through a tablet, you can overlay an expected finished model based on the point cloud in situ, making it easy to intuitively grasp discrepancies between design and current conditions. This allows not only "checking as-built by numbers" but also "confirming as-built visually," facilitating explanations to clients and stakeholders.

Automation and visualization using 3D point clouds reduce the workload of construction managers and improve as-built management accuracy. Freed from tedious data processing and report creation, engineers can devote more time to creative tasks and overall project management.

Compatibility with client inspections: smoother inspections with 3D data

Point cloud data acquired for as-built management also positively affect client-side inspection work. Traditionally, final inspections involved the client verifying the site based on drawings and measurements submitted by the contractor and remeasuring as necessary. With the objective digital record of a 3D point cloud, inspectors can evaluate as-built conditions by directly examining the data, making the inspection process smoother.

For example, if point cloud data are submitted at the time of final inspection for a slope project, the client can freely view the slope geometry on an office PC and check required cross-sections and gradients. Areas that are difficult to see on site can be easily checked in virtual space, reducing the risk of "missing points that should be inspected." Also, if comparison results between point clouds and the design model (such as color-coded heatmaps) are available, the acceptability of as-built conditions can be judged at a glance, streamlining communication until inspection approval.

The MLIT’s "Guidelines for As-Built Management (draft): Slope Work" also present methods for as-built management using three-dimensional measurement technologies, recommending the use of point cloud data as final deliverables. This indicates that the foundation for clients to accept 3D data as official deliverables is being established. In practice, some sites that adopted point-cloud-based as-built management are using electronic deliverables in place of paper drawings for inspections.

By sharing 3D data between contractors and clients, "data-driven transparent inspections" become possible. For clients, the need to physically access hazardous slopes to check details is reduced, enabling efficient and safe quality verification. Ultimately, data-mediated trust is built, accelerating inspections and smoothing consensus-building.

Conclusion: protecting survey safety and quality through labor saving

Utilizing 3D point cloud technology in slope surveying is revolutionizing work that was once performed amidst danger. Through non-contact measurement and labor saving, surveyor safety is secured while detailed data acquisition improves survey quality—two goals that were once difficult to achieve simultaneously. By supplementing and replacing manual tasks with technology, we can protect workers’ lives and health while raising the level of construction management and quality assurance.

Safety improvements and efficiency gains go hand in hand. Reducing hazardous work decreases occupational accidents, preventing project interruptions and personnel loss. Using high-precision as-built management based on point clouds also reduces rework and additional corrections. In other words, the slack created by labor and effort savings generates a virtuous cycle that boosts overall site productivity and quality.

As the construction industry faces chronic labor shortages and an aging skilled workforce, DX tools such as 3D point cloud technology will become increasingly important. To create kinder worksites that do not expose people to dangerous tasks while ensuring reliable quality, consider adopting these new technologies.

Bonus: Start safe point cloud surveying with smartphone × LRTK

For those who feel that procuring the latest equipment is a high hurdle, there is good news. Recently, solutions enabling easy point cloud surveying with smartphones have emerged. A representative example is surveying with smartphone + LRTK. LRTK involves attaching a compact RTK-GNSS receiver to a smartphone, turning the phone into a centimeter-accurate surveying device.

Using a smartphone and LRTK, 3D measurement of slopes that used to require expensive specialized equipment can be performed easily by one person. For example, points on the upper portion of an otherwise inaccessible steep slope can be targeted and positioned from the ground by capturing them with the smartphone camera, allowing coordinates to be obtained while remaining in a safe location. Scanning with the smartphone's built-in LiDAR scanner while walking the site can yield point cloud data of the slope in minutes. Because RTK provides absolute coordinates to the point cloud, no additional georeferencing is required later for comparison with design drawings or as-built calculations.

Smartphone surveying with LRTK is attractive because it realizes labor saving, safety improvement, and reporting efficiency using a small device. Acquired point cloud data can be uploaded to the cloud immediately for sharing, enabling office-based volume calculations and drawing production or 3D viewer–based reviews with stakeholders. AR features can overlay the design model onto the current point cloud for on-site as-built confirmation and consensus building. Survey tasks that formerly relied on specialized technicians are becoming doable with a smartphone in hand.

As a first step toward safe and efficient slope surveying, consider smartphone × LRTK point cloud surveying. By skillfully incorporating the latest technologies, you can protect site safety and quality while improving productivity.