A New Era of Smartphone-Only 3D Surveying for Slope Greening

Conventional slope greening surveying methods and their challenges

"Slope greening" refers to efforts to stabilize artificial slopes (cut or fill slopes) created for roads or land development by covering them with vegetation. In slope greening works, "as-built verification"—accurately surveying the slope shape and finish after construction to confirm it was built according to design—is indispensable. However, conventional surveying methods have several challenges.

Typical traditional methods involved manually measuring slope heights and lengths with tape measures or surveying staff, or using total stations (TS) to measure coordinates point by point. For example, workers would climb hazardous slopes to stretch a tape measure from the slope crest to the slope toe to measure length, or use an angle meter to check gradients. These methods are not only labor- and time-intensive, but on steep slopes they carry a risk of falls. TS surveying typically requires two people to operate heavy equipment, imposing a large personnel burden. Moreover, the data obtained are often limited to discrete points or cross-sections, making it difficult to understand the entire slope.

In recent years, new methods such as point cloud measurement with 3D laser scanners and photogrammetry with drones have emerged. While these can capture wide areas of terrain, they require specialized equipment and operational expertise and are expensive and difficult to adopt, so their use has been slow at small- to mid-sized sites. As a result, many slope greening sites still rely on traditional manual surveying, facing challenges in accuracy, efficiency, and safety.

The importance of surface-based management using point cloud data

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

Point cloud data are many points that make up the slope surface, acquired as three-dimensional coordinates (X, Y, Z). If a point cloud covering the entire slope is obtained, information such as the slope's gradient distribution, surface area, and slope length from crest to toe can be recorded in full. In other words, it becomes immediately clear which parts of the slope are steeper than designed, whether there are local irregularities, and whether seeding or coverage has been applied uniformly across the whole surface.

Having surface-based data allows verification down to details that were previously overlooked. For example, you can check across the entire slope whether the gradient matches the design or calculate whether the required surface area has been secured. Subtle undulations that cannot be detected by connecting discrete points in cross-sections are revealed by 3D data. Also, because acquired point cloud data serve as digital evidence, creating as-built management reports and responding to inspections become smoother. You can present objective evidence to clients and regulatory authorities, improving the reliability of quality control.

Efficiency, labor savings, and safety achieved with high-precision GNSS and smartphone RTK

A key technology that makes surface-based 3D surveying on-site easy is RTK positioning using high-precision GNSS combined with the use of smartphones. RTK positioning is a method that corrects GNSS satellite positioning errors in real time to achieve centimeter-level position accuracy. Previously, special GPS equipment was required, but recently it has become possible to convert a smartphone itself into a high-precision surveying device by attaching a compact RTK-capable receiver to the phone.

Smartphone surveying combined with high-precision GNSS brings major efficiency gains to slope greening surveying. First, because measurements can be taken easily by a single person, it leads to labor savings. 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 site—a lightweight setup—reducing the burden when working on slopes.

Another advantage is that RTK position corrections maintain high accuracy, so the acquired data are less prone to positional drift or distortion. Normally, scans taken with a smartphone alone tend to become distorted or lose scale as the range increases, but RTK provides accurate coordinates for each point, enabling consistent point clouds even when walking around large slopes. This makes it possible to confidently survey large slopes.

Improved safety should not be overlooked. Even when surveying at height or on steep slopes, a smartphone makes it easier to take measurements from safer locations below the slope or from a distance. The need to carry heavy equipment onto hazardous slopes is reduced, lowering the risk of falls and slips. Shortening surveying time on the slope itself also reduces risks such as heatstroke and rockfall. In this way, high-precision GNSS plus smartphone RTK contributes not only to labor savings but also to improving on-site safety.

Procedure for 3D point cloud scanning using a smartphone

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

• Performing the scan: Select the 3D scan function in the app and start acquiring the point cloud of the target slope. Use the smartphone camera or built-in LiDAR sensor and walk slowly while pointing the camera at the slope to capture images. To cover the entire slope, it is important to photograph from various positions with changing angles from the slope toe through the mid-slope to the upper slope. During scanning, the acquired point cloud is displayed in real time on the smartphone screen, allowing you to proceed while checking for dead spots where points are missing. For example, the upper part of the slope can be hard to see from the toe, so take oblique upward shots from a slightly distant location to capture the entire surface.

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

• Sharing the data: The saved point cloud data can be sent to office PCs via the cloud or shared with stakeholders. If needed, upload via the mobile network on site and pass the data to subsequent processes (details of cloud sharing are described later).

By following these steps, detailed 3D data of the entire slope can be obtained with a single smartphone. Even for wide slopes, scanning is completed in just a few minutes because you only need to walk while shooting. On sites that once took a whole day to measure dozens of survey points, smartphone scanning can finish the work in a short time, dramatically improving on-site productivity.

Using point cloud data in construction management

Point cloud data acquired with a smartphone can be used in various construction management tasks afterward. First and foremost is the application to as-built management (post-construction finish verification). Based on the acquired 3D data, you can examine discrepancies from the design geometry in detail.

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

From point cloud data you can also calculate the slope's average gradient and local gradients, and compute the slope surface's accurate area. These are important indicators for quality checks during as-built inspections. For instance, if the design specifies a 1:1.5 gradient, you can determine from the point cloud whether the slope falls within that gradient range across the entire area or whether parts are too shallow or too steep. Calculating the actual vegetated area can verify whether the placement of erosion-control mats or the extent of seed application matches the instructions, and it also helps verify measured quantities.

Quantity management is essential in civil engineering, and using point cloud data makes earthwork volume calculations efficient. In slope shaping associated with slope greening, the terrain is adjusted by cutting or filling. By comparing the as-built terrain model (point cloud) with the pre-construction original terrain data, you can perform precise settlement of excavation and fill volumes. This is more reliable than traditional cross-sectional area estimations and can reduce discrepancies in understanding between client and contractor.

Thus, point clouds acquired with a smartphone are effectively usable in many aspects of construction management, from as-built verification to quantity calculation. If necessary, measured results from the point cloud can be converted into drawings and exported as CAD data to attach to reports. Leveraging digital data simultaneously improves the accuracy and efficiency of site management.

Design comparison and visual verification of as-built conditions using AR technology

Another revolutionary aspect of smartphone surveying is that combining it with AR (augmented reality) technology allows visual verification of design and measurement data on-site. With the AR function of a dedicated app, you can overlay design models or acquired point cloud models onto the actual slope as seen through the smartphone screen.

With AR-based design comparison, design lines and finish surfaces from drawings can be projected onto the site scenery, enabling intuitive recognition of deviations from design during construction. For example, when viewed through a smartphone, the ideal slope gradient and shape can be displayed as a semi-transparent guide, so you can immediately see whether the current slope is overcut or overfilled. Information that used to be indicated by staking or layout marks can be shared more understandably with on-site workers through AR.

AR also excels when verifying as-built conditions after construction. Overlaying past point cloud data (3D survey results taken immediately after construction) onto the completed slope allows you to color-code areas that match the plan and those that need correction. The quality of the finish, which is hard to grasp from paper drawings or lists of numbers, can be intuitively evaluated by comparing the real object with the virtual model on site.

Moreover, AR can be applied to safety management. For instance, if the locations of anchors buried inside the slope or hazardous spots are displayed in AR, you can effectively "see through" the ground to check subsurface conditions on site. During inspections, displacements since the previous measurement can be highlighted in AR so that even small deformations are detected on the spot. Because all of this can be realized with just a smartphone and no 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 improve information sharing between site and office when integrated with cloud services. Uploading point cloud data to the cloud enables remote as-built verification from distant locations. Site managers, designers, and clients can view the as-built data from the office to check quality and exchange opinions.

Cloud-hosted 3D data can be viewed and manipulated through a web browser, so parties without dedicated software can still easily share the data. For example, a site staff member can upload a slope point cloud scanned on site to the cloud the same day, and hold a meeting with supervisors and subcontractors while viewing the same data. This reduces communication losses and speeds up responses.

The cloud also serves as a repository for data storage. By accumulating as-built data and survey results in the cloud, they can be used for post-construction maintenance and future work planning. Past slope shapes from construction stages can be retrieved at any time for comparison, aiding judgments about deterioration in annual inspections or assessing damage after disasters. Unlike paper documents, cloud storage eliminates concerns about degradation or loss, allowing accumulation as a long-term data asset.

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

Flexibility for small sites, steep terrain, and disaster response

Smartphone-only 3D surveying is expected to be used widely because of its ease and versatility. It is effective not only for large infrastructure projects but also for small-scale sites. Small slope works that previously were not worth calling a dedicated surveying team for can now be surveyed quickly by the site staff themselves using a smartphone, enabling consistent quality control regardless of scale.

High mobility is another feature. In mountainous steep terrain or sites where transporting equipment is difficult, surveying can be completed with just a smartphone and a portable device, enabling a light-footed response. Even on easily collapsed slopes or places with poor footing, data can be collected safely with minimal personnel and equipment.

Furthermore, smartphone 3D surveying is valuable in disaster response. For example, when a slope collapses after heavy rain, responsible staff 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 collapse volume and identification of areas at risk of secondary disasters, providing timely information for initial response decisions. In fact, local governments and others are beginning to adopt smartphone surveying for terrain recording and damage assessment at disaster sites.

In this way, smartphone-completed surveying technology has the flexibility to be deployed across site sizes and conditions. The ability to perform 3D surveying easily with an everyday smartphone opens new possibilities for construction management, even in scenarios where three-dimensional surveying was previously avoided due to cost or effort.

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

3D surveying using smartphones and RTK is transforming surveying and as-built management in slope greening. As described above, the era in which surface-based management with point cloud data and visual verification with AR can be realized with a single smartphone has arrived. This advancement dramatically promotes efficiency, labor savings, and safety improvements, as well as the visualization of construction quality and data utilization.

One solution that makes this new era easy to adopt is the smartphone surveying system "LRTK." With LRTK, you can perform high-precision point cloud surveying with a smartphone and use AR to compare design models and check as-built conditions based on that data. In addition, the coordinate guidance feature can navigate workers to design target points and lines on site, enabling an all-in-one workflow from surveying to as-built verification and layout. With the convenience of not relying on dedicated equipment and reliable accuracy, it can be considered a next-generation surveying tool that anyone can use.

Adopting such technologies enables safe, efficient, and high-quality construction management. As digitalization progresses in the construction industry and initiatives like the Ministry of Land, Infrastructure, Transport and Tourism's i-Construction promote DX, these advanced practices are likely to become standard. Consider smartphone-completed point cloud surveying with "LRTK" as an opportunity: it should provide new value to slope greening sites as a dependable partner that reduces site burden while improving quality.