A New Era of Slope Revegetation 3D Surveying Completed with a Smartphone

Traditional slope revegetation surveying methods and challenges

"Slope revegetation" refers to the practice of covering artificially created slopes (cut or fill slopes) such as those along roads or in development sites with vegetation to stabilize them. In slope revegetation works, "as-built verification"—accurately surveying the slope shape and finish after construction to confirm that the work was executed according to design—is indispensable. However, conventional surveying methods have presented several challenges.

In general traditional methods, workers measured slope heights and slope lengths manually using tape measures and surveying staff, or measured the coordinates of individual points with a total station (TS). For example, workers would climb dangerous slopes to stretch a tape measure and measure the length from the slope crest to the slope toe, or use an inclinometer to check the gradient. These methods not only require considerable labor and time, but also carry a risk of falling on steep slopes. TS surveying typically requires two people to operate heavy equipment, making it a labor-intensive task. Moreover, the data obtained are limited to discrete points or cross-sections, making it difficult to grasp the slope as a whole.

In recent years, new methods such as point cloud acquisition using 3D laser scanners and photogrammetry with drones have emerged. These can capture terrain over wide areas, but they require specialized equipment and operational expertise and are expensive with high barriers to adoption, so they have not spread widely in small to medium-sized sites. As a result, many slope revegetation sites still rely on conventional manual surveying, facing issues in terms of accuracy, efficiency, and safety.

Importance of surface-based management using point cloud data

To accurately verify the as-built condition of slope revegetation, it is important to measure the slope as a surface. Traditional methods only reveal partial heights or gradients and tend to miss the overall picture. What has attracted attention is the surface-based management using point cloud data.

Point cloud data consist of many points that make up the surface of the slope, acquired as three-dimensional coordinates (X, Y, Z). If you obtain a point cloud that covers the entire slope, you can comprehensively record information such as the distribution of gradients, the surface area, and the slope length from crest to toe. In other words, it becomes immediately clear which parts of the slope are steeper than the design, whether there are local irregularities, and whether seeding or coverage has been applied uniformly across the surface.

Having surface data allows verification of details that were overlooked with conventional methods. For example, you can check whether the slope matches the design gradient across the entire surface or calculate whether the required area has been secured. Subtle undulations that cannot be seen from cross-sections connecting points are revealed by 3D data. Acquired point cloud data also serve as digital evidence, making it smooth to prepare as-built management reports and respond to inspections. They can be presented as objective evidence to clients or regulatory authorities, enhancing the reliability of quality control.

Efficiency, labor reduction, and safety realized by high-precision GNSS and smartphone RTK

A key technology to easily perform such surface-based 3D surveying on site is RTK positioning using high-precision GNSS combined with the use of smartphones. RTK positioning is a system that provides real-time corrections to GNSS satellite positioning errors to achieve centimeter-level position accuracy (half-inch-level). Traditionally, special GPS equipment was required, but recently it has become possible to turn a smartphone itself into a high-precision positioning device by attaching a small RTK-capable receiver to the phone.

Smartphone surveying combined with high-precision GNSS brings major efficiency improvements to slope revegetation surveying. First, because it can be performed easily by a single person, it leads to labor reduction. There is no need for two or more people to operate equipment like a TS or to transport heavy gear with machinery. Only a smartphone and a small device need to be brought to the site, resulting in light equipment and reduced burden on the slope.

Another advantage is that RTK correction maintains high accuracy at all times, so the acquired data are less likely to suffer from positional shift or distortion. Typically, scans with a smartphone alone tend to distort or lose scale as the range expands, but RTK provides accurate coordinates to each point, allowing a consistent point cloud even after walking across a wide slope. This makes it possible to confidently measure even large slopes.

Improving safety is another important benefit. Even when surveying at height or on steep slopes, a smartphone makes it easy to take measurements from safer positions below or at a distance from the slope. The need to carry heavy equipment and stand on hazardous slopes is reduced, lowering the risk of falls or trips. Shortening survey work also reduces the time spent on the slope, thereby mitigating risks such as heatstroke or falling rocks. Thus, the use of high-precision GNSS + smartphone RTK contributes not only to labor savings but also to onsite safety.

Procedure for 3D point cloud scanning using a smartphone

• Equipment preparation: Attach a small RTK-capable GNSS receiver to the smartphone used for surveying and launch a dedicated surveying app. First, receive GNSS correction information and start RTK positioning, and confirm that the position accuracy on the smartphone has improved to centimeter-level (half-inch-level) (FIX solution). Once ready, start the scan measurement.

• Performing the scan: Select the 3D scan function in the app and begin acquiring point cloud data of the target slope. Using the smartphone camera or built-in LiDAR sensor, walk slowly while pointing the camera at the slope to capture images. To cover the entire slope, it is important to shoot from various positions while changing the angle from the foot of the slope to the mid-slope and upper parts. During the scan, the acquired point cloud is displayed in real time on the smartphone screen, allowing you to proceed while checking for any blind spots with missing points. For example, the upper part of the slope may be hard to see from the foot, so devise approaches such as shooting at an upward angle from a slightly distant position to capture data over the entire slope surface.

• Data saving: When you have scanned a sufficient area, end the measurement and save the point cloud data on the smartphone. Because positioning has already been performed by RTK, the obtained point cloud is assigned accurate coordinates from the outset. You can preview the acquired 3D data on site to check for omissions. If necessary, you can also perform simple analyses immediately on the smartphone, such as measuring distances or areas and estimating gradients.

• Data sharing: Saved point cloud data can be sent to office PCs via the cloud or shared with stakeholders. If needed, upload using a mobile network on the spot and pass it to subsequent processes (details of cloud sharing are described later).

With the above steps, you can obtain detailed 3D data of the entire slope with a single smartphone. Even for large slopes, scanning is completed simply by walking while shooting, so it can be finished in a matter of minutes. At sites that used to take a full day to measure dozens of survey points, smartphone scanning completes the task in a short time, dramatically improving onsite productivity.

Using point cloud data in construction management

Point cloud data obtained by smartphone can be used in many ways in subsequent construction management tasks. First and foremost is the application to as-built management (post-construction finish verification). Using the acquired 3D data, you can thoroughly examine discrepancies with the design shape.

For example, you can extract longitudinal and cross sections of the slope at arbitrary locations from the point cloud data and compare them with the cross-section lines on the design drawings to check the finish. Traditionally, field cross-section measurements were taken at fixed intervals, but with point clouds you can create cross-section drawings anywhere in the office. This prevents rework such as returning to the field due to missed measurements, and makes it easy to add required cross-section information later.

From point cloud data, you can also calculate the average slope and local gradients and accurately compute the surface area of the slope. These are important indicators when checking quality during as-built inspection. For example, if a design specifies a slope of 1:1.5, you can determine from the point cloud whether the slope across the entire area falls within that gradient range or whether parts are too shallow or too steep. Moreover, by calculating the actual revegetated area, you can verify that the amount of vegetation mat laid or the area covered by seed spraying matches the instructions, which also helps verify the work quantity (completed quantity).

Quantity management is essential in civil engineering, and using point cloud data allows efficient earthwork quantity calculations. In slope shaping works related to slope revegetation, the terrain is adjusted by excavation and embankment. By comparing the as-built terrain model (point cloud) with pre-construction original terrain data, excavation and fill volumes can be reconciled with high precision. This is more reliable than estimates based on cross-sectional area calculations and can reduce discrepancies in understanding between client and contractor.

Thus, point clouds obtained by smartphone are effective in many aspects of construction management, from as-built verification to quantity calculation. As needed, measurement results from the point cloud can be converted into drawings, exported as CAD data, and attached to reports. Utilizing digital data simultaneously increases both the accuracy and efficiency of site management.

Design verification and visual confirmation of as-built using AR technology

Another innovative aspect of smartphone surveying is that combining it with AR (augmented reality) technology allows design data and measurement data to be visually confirmed on site. With a dedicated app’s AR function, you can overlay and display the design model or the acquired point cloud model on the actual slope as seen through the smartphone screen.

With AR-based design verification, design lines and finished surfaces from drawings can be projected onto the actual site scenery, allowing intuitive recognition of deviations from the design during construction. For example, when viewed through the smartphone, the ideal slope gradient and shape can be displayed as a semi-transparent guide, making it immediately clear whether the current slope has been overcut or overfilled. Information that was traditionally indicated by batter boards or survey stakes can be shared more understandably with site workers using AR.

AR is also powerful when confirming the as-built condition after construction. If you overlay past point cloud data (the 3D survey results immediately after construction) onto the completed slope, you can, for example, color-code areas that were constructed according to plan and areas that require correction. The acceptability of the as-built condition, which is difficult to grasp from paper drawings or numerical lists, can be intuitively evaluated by comparing the real object and the virtual model on site.

Furthermore, AR can be applied to safety management. For instance, displaying the location information of anchors buried inside the slope or hazardous spots in AR allows you to inspect the underground situation as if seeing through the ground. During inspections, displacements since the previous measurement can be emphasized in AR, enabling detection of minute deformations on the spot. Because these functions can be realized with just a smartphone without special equipment, AR becomes a useful tool for routine patrols and inspections.

Remote verification, data sharing, and record storage through cloud integration

3D data acquired by smartphone can dramatically enhance information sharing between the site and the office by integrating with cloud services. Uploading point cloud data to the cloud enables remote as-built verification. Site managers, designers, and clients can view as-built data while in the office, check quality, and exchange opinions.

Cloud-hosted 3D data can be displayed and manipulated through a browser, making it easy to share with parties that do not have dedicated software. For example, a field technician can share the slope point cloud scanned that day to the cloud and hold a meeting with supervisors or partner companies while viewing the same data. This reduces communication loss and accelerates responses.

The cloud also serves as a data archive. By storing as-built data and survey results in the cloud, they can be used for post-construction maintenance and future construction planning. Past slope shapes at construction stages can be retrieved at any time for comparison and review, aiding in assessing deterioration during annual inspections or understanding damage in the event of a disaster. Unlike paper documents, there is no worry about deterioration or loss, and data can be accumulated as a long-term digital asset.

Advanced cloud services also support automatic measurements and report generation from uploaded point cloud data. For example, you can calculate slope earth quantities with one click on the web or overlay multiple datasets to compute changes. Efficiently processing digital information collected in the field on the cloud and immediately sharing results with stakeholders further enhances the speed and accuracy of construction management.

Flexibility for small sites, steep slopes, and disaster response

Smartphone-completed 3D surveying is expected to be used across various sites due to its ease and versatility. It is effective not only for large infrastructure projects but also for small sites. Even small slope works that were previously given up as not warranting a dedicated surveying team can be quickly surveyed by the site person in charge using a smartphone, enabling rigorous quality control regardless of scale.

Mobility is another feature. Even on steep mountainous slopes or sites where moving equipment and materials is difficult, surveying can be completed with just a smartphone and a portable device, allowing for agile response. On unstable slopes or places with poor footing, data can be acquired with minimal personnel and equipment while ensuring safety.

Moreover, smartphone 3D surveying is useful in disaster response. For example, when a slope collapses due to heavy rain, personnel can go to the site and scan the damage with a smartphone to quickly generate a 3D model without waiting for heavy machinery or surveying equipment. This enables rapid estimation of collapsed soil volumes and identification of locations at risk of secondary disasters, providing decision-making material for initial response. In fact, smartphone surveying is being adopted by municipalities and is beginning to be used for terrain recording and damage assessment at disaster sites.

Thus, smartphone-completed surveying technology has the strength of being flexibly deployable regardless of site scale or conditions. Where three-dimensional surveying was previously avoided due to cost and effort, it has become possible to easily perform digital measurements using a familiar smartphone, opening up new possibilities in construction management.

Conclusion: The future of slope revegetation 3D surveying opened by LRTK

3D surveying using smartphones and RTK is revolutionizing surveying and as-built management in slope revegetation. As described above, the era has arrived in which surface-based management with point cloud data and visual verification with AR can be realized with a single smartphone. This advances not only efficiency, labor reduction, and safety improvement but also the visualization of construction quality and data utilization.

One solution that makes it easy to introduce this new era is the smartphone surveying system "LRTK". With LRTK, you can perform high-precision point cloud surveying with a smartphone and use that data for AR-based design comparison and as-built checks. In addition, the system’s coordinate guidance function can navigate to design target points and lines on site, enabling all-in-one support from surveying to as-built verification and stakeout. With the ease of not relying on dedicated equipment and dependable accuracy, it is a next-generation surveying tool that anyone can use.

By adopting such technology, safe, efficient, and high-quality construction management can be achieved. In the digitizing construction industry, advanced initiatives that align with industry DX promotion trends such as the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction are likely to become standard in the future. Please consider the smartphone-completed point cloud surveying "LRTK" at this opportunity. As a reliable partner that balances reduced onsite burden with improved quality, it should provide new value to slope revegetation sites.