Disaster Recovery in Action! 3D Point Cloud Data Supporting Slope Greening

Japan is hit almost every year by landslides caused by heavy rains and earthquakes, with slope and hillside collapses occurring across the country. For example, the 2018 Western Japan heavy rains produced more than 2,000 landslide incidents, causing numerous slope failures in many locations. To safely restore collapsed slopes, covering the surface with vegetation—known as “slope greening”—is indispensable. Slope greening involves planting grasses and shrubs on inclined ground to stabilize the soil and prevent erosion or collapse due to rain and wind. In disaster recovery, quickly covering exposed bare ground with vegetation reduces the risk of secondary disasters and helps preserve the surrounding environment.

At the same time, applying the latest digital technologies has become essential to carry out slope greening work quickly and reliably. Especially noteworthy is 3D point cloud data obtained by drones, LiDAR, and similar tools. Point cloud data that records the slope’s current condition in detail provides major support at every stage from planning to construction in disaster recovery. This article begins with the relationship between slope greening and disaster recovery and explains how 3D point cloud data supports field operations. We will look step by step at surveying methods that overcome traditional challenges, improved safety, advanced design, AR-assisted construction support, cloud-enabled information sharing, and operational mobility for small sites. Finally, we introduce a new technology called LRTK that enables simple point cloud measurement and AR display with a smartphone, offering ideas to strengthen disaster response capabilities.

The Relationship and Necessity of Slope Greening in Disaster Recovery

Slope greening involves covering artificial slopes such as those along roads or on reclaimed land with vegetation to prevent soil collapse and runoff. While valued in normal times for landscape improvement and ecosystem conservation, its importance becomes even greater in disaster recovery. After landslides from heavy rain or cliff collapses from earthquakes, if the slope remains exposed, each rainfall can wash away topsoil and lead to further collapse. By applying emergency slope greening and using plant root systems to hold the soil, the risk of secondary disasters can be reduced.

In practice, early greening and prevention of topsoil erosion are key in disaster recovery work. Techniques such as seed spraying onto collapsed slopes or installing vegetation mats and vegetated sandbags make it possible to rapidly cover slopes with greenery even where heavy machinery cannot easily enter. This helps stabilize slopes during rains that occur during recovery works and can protect nearby residents and infrastructure. Restoring green landscapes also contributes to the psychological recovery of affected communities. Moreover, the concept of “green infrastructure,” which leverages plant functions instead of relying solely on concrete retaining walls or sprayed concrete, is attracting attention. In that regard, slope greening plays an important role in both disaster prevention and environmental preservation. Slope greening is an indispensable measure supporting both aspects.

The Importance of As-Built Surveying of Damaged Slopes and Challenges of Traditional Methods

When a slope collapse occurs, an accurate as-built survey is essential. Accurately grasping the terrain of the collapsed area allows you to determine how much soil has slipped and how much fill or reinforcement is required for restoration. When planning slope greening, knowing the inclination and volume of collapsed soil helps select appropriate methods and materials (such as seed types and quantities, or the scale of vegetation mats). If recovery work proceeds based on incorrect as-built information, the completed slope may not meet the designed gradients or heights, and lack of strength could lead to re-collapse. However, traditional surveying methods for investigating damaged slopes have posed many challenges.

Conventional surveying typically uses optical instruments such as total stations and levels, with personnel on-site measuring point by point. This approach has the following problems:

• Time-consuming: For wide slopes, the number of survey points becomes enormous. Traditional methods measure each point sequentially, so covering the entire collapsed area can require a massive amount of time. Even when a recovery plan must be produced urgently, surveying can become a bottleneck and compress the construction schedule.

• Labor-intensive: Total station surveys usually require a two-person team—one operating the instrument and the other holding a prism or leveling rod at the target points. In disasters with many scattered slope collapses, it is difficult for a limited number of surveyors to cover everything, and manpower shortages can delay investigations.

• Safety risks: It is extremely dangerous for people to enter destabilized slopes. Approaching a collapse site in poor footing while carrying heavy survey equipment increases the risk of secondary collapses or falls. In large disasters, aftershocks or heavy rains are likely, raising the risk of accidents during surveying. Additionally, reference points (known survey benchmarks) may be washed away in disasters, or power outages can render equipment unusable, meaning conventional instruments may not function adequately in emergencies.

Given these challenges in “time,” “personnel,” and “safety,” traditional surveying methods sometimes cannot meet the initial response needs of disaster recovery. A new approach that can measure damaged conditions more efficiently and safely was therefore required to enable faster recovery.

Area-Based Understanding and Safe Remote Surveying Enabled by Point Cloud Measurement

Enter 3D point cloud surveying. Point cloud data is a collection of countless 3D coordinate points obtained by laser scanning or photogrammetry, recording terrain shapes at high density. Point clouds can be generated from aerial photos taken by drone-mounted cameras, obtained by ground-based LiDAR scanners, or even captured by LiDAR sensors built into modern smartphones—various methods exist. Using point cloud measurement makes it possible to achieve area-based as-built understanding and safe remote surveying, which were difficult with traditional methods.

For example, photographing a collapsed slope from above with a drone can generate a detailed 3D model of a wide area in a short time. There are cases where surveying that used to take three days can be completed in less than half a day with drone photogrammetry. Likewise, LiDAR-capable smartphones such as iPhones can record the terrain by scanning from below without anyone climbing the dangerous slope. With short time and few personnel, the entire site’s shape can be digitized, and because surveyors do not need to remain on-site for long periods, safety is dramatically improved.

The greatest advantage of point cloud measurement is that it can record the slope surface exhaustively. The number of points humans can measure manually is limited, but point clouds can capture hundreds of thousands of measurement points so every nook and cranny of the slope is covered. This enables detection of irregularities or unstable blocks that might be missed by the naked eye. Since surveying can be done from a safe distance or remotely, worker burden and risk are greatly reduced. A surface digital terrain model obtained this way provides comprehensive information needed to plan recovery work.

Advanced and Faster Design Planning Using Acquired 3D Data

Detailed as-built models obtained from point cloud data are extremely powerful for recovery design planning. Because the data is digital, designers can analyze slopes freely on a computer. For example, if the volume of collapsed soil is accurately calculated from the point cloud, numerical considerations of fill plans—where and how much soil to place—become possible. Where volume estimates were once made by reading plans and sections manually, using point clouds enables rapid and accurate quantity calculations.

Moreover, overlaying the as-built point cloud with the design plan (the completed model) streamlines evaluation of optimal recovery options. If pre-disaster slope shape data or design drawings are compared with the current collapsed terrain point cloud, you can immediately see which parts have collapsed and by how much. From those differences you can compute backfill volumes or the amount of rock to be removed, making required work quantities instantly clear. It is also easy to try multiple recovery plans and compare excavation/fill volumes and slope gradients for each directly on the point cloud.

By using 3D data at the design stage, you can create advanced plans grounded in actual site conditions. Precision terrain-based design reduces the risk of over- or under-provisioning materials and minimizes rework during construction. Digital information is easy to share among stakeholders, so when design changes occur you can quickly verify them using point cloud data and devise countermeasures. As a result, you can produce higher-quality recovery plans in a shorter period, enabling earlier commencement and completion of work.

Visual Construction Support Combining Point Cloud Data and AR

Even during the construction phase after designs are finalized, 3D point cloud data provides various supports. Especially useful is combining it with AR (augmented reality) technology. When you hold an AR-capable smartphone or tablet on site, you can overlay design models or lines onto the camera view. This lets you intuitively confirm the intended finished slope and work extents by superimposing them on the real scene.

For instance, if vegetation mats are to be laid on a slope for greening, highlighting the mat areas in AR at their design positions makes it immediately clear to workers how far to install them. Being able to share the final greening image on site before construction makes it easier to explain plans to clients and local residents. Images that are hard to convey on drawings alone can be shown in situ using AR, smoothing the consensus-building process. During construction, you can also overlay the design model with the current point cloud to compare the as-built status in real time. This allows on-the-spot checks that gradients and thicknesses match the design, helping prevent mistakes and rework. As a form of visual construction support, point cloud × AR deepens site understanding and greatly reduces communication loss.

Rapid Information Coordination through Cloud Sharing

Another major advantage of digital information like point clouds and photos is that they can be shared instantly via the cloud. Recovery projects require information not only by contractors but also by local government disaster management staff, design consultants, and many other stakeholders. Traditionally, compiling survey results into drawings and reports and explaining them in meetings took time. But if data is uploaded to the cloud, everyone can check the latest status from the site right away.

For example, if point clouds and photos captured at the site are uploaded to a dedicated cloud and a sharing link is issued, personnel at a distant head office or government office can view the 3D damage status in a browser. The overall extent of damage, which is difficult to convey with text or still images alone, can be grasped three-dimensionally online, enabling faster decision-making. Because everyone can discuss design changes or construction methods while viewing the same 3D data, misunderstandings are less likely and consensus-building time is shortened. Cloud utilization realizes rapid information coordination that makes the distance between field and office negligible, thereby speeding up and improving the efficiency of the entire recovery process.

Mobility That Works Even on Small Sites and Emergency Works

3D point cloud measurement and smartphone-based surveying technologies are powerful not only for large-scale disasters but also for small sites and emergency responses. Because advanced surveying used to require time and expense, small landslide sites were sometimes handled by simple visual inspection. However, with portable small equipment and drones, any site can be measured immediately. Even for one-sided collapses in mountainous areas or small slope failures beside roads, a person with a smartphone and a drone can arrive and acquire detailed terrain data within the day and consider response measures.

High mobility of equipment means strong initial response capability right after a disaster occurs. Drones that fit in a truck bed and pocket-sized surveying devices are easy to carry and allow teams to move between multiple sites. Even without heavy machinery or large surveying teams, one person can quickly digitize the damaged conditions, making the results immediately useful for emergency work decisions and temporary repair planning. Digital surveying techniques that can be flexibly applied from small collapses to wide-area disasters will likely become standard equipment at all disaster sites. In fact, the Ministry of Land, Infrastructure, Transport and Tourism is promoting efforts to spread these technologies to small and medium-sized projects, bringing an era where anyone can use digital surveying close at hand.

Introducing the Smartphone Surveying Tool “LRTK” That Excels in Disaster Response

As described above, leveraging 3D point cloud data and the latest technologies brings major benefits to disaster recovery work including slope greening. One solution that makes these benefits easy to obtain is LRTK. LRTK (pronounced “L-R-T-K”) is a compact surveying device attached to a smartphone that combines RTK-GNSS centimeter-level positioning, the smartphone’s LiDAR camera for point cloud scanning, and even AR display in a single unit.

For example, simply walking around a collapsed slope with an iPhone equipped with LRTK can produce a high-precision 3D point cloud model of the entire site within minutes. Because the acquired point cloud is automatically georeferenced to global coordinates, you can perform on-site volume calculations to estimate the required backfill immediately. Measurement data can be shared to the cloud with one tap, allowing office staff to grasp the site situation instantly. With AR functionality, you can overlay design models on the real scene via the smartphone screen and easily share the intended finished image with stakeholders. The fact that this entire workflow can be accomplished with just a smartphone—without special expertise—makes it extremely valuable for disaster response. Site personnel can carry out measurement, verification, and recording themselves without relying on specialized equipment, dramatically improving the speed and quality of recovery works.

Portable and able to operate even where power or communications infrastructure is down, LRTK is a true next-generation surveying tool that lets you “measure anytime, anywhere.” It enables even small teams to safely and quickly move from as-built slope assessment to greening plan and construction, making it a reassuring asset in times of need. To minimize disaster damage and realize rapid recovery, consider introducing such cutting-edge technologies. By advancing DX through the use of the latest technologies, we can build a safer, more disaster-resilient social infrastructure.