3D Surveying for Slope Greening Anyone Can Do with a Smartphone

Slope greening construction is the practice of planting vegetation on roadside slopes or dam faces to balance landscape and environmental conservation with prevention of soil erosion. In such projects, it is essential to survey the slope shape before construction for design, and to inspect the as-built shape (completed shape) after construction to verify it matches the design. However, surveying on steep slopes poses many challenges in terms of securing footholds, manpower burden, and safety, so it has traditionally been entrusted to specialized surveying technicians.

In recent years, construction sites have faced labor shortages and calls for workstyle reforms, driving the need for labor-saving and efficiency improvements. One promising approach is 3D surveying using smartphones. This article explains in detail how smartphone-based 3D surveying that anyone can perform brings benefits to surveying for slope greening construction.

The importance of surveying in slope greening construction and traditional challenges

In slope greening construction, accurate understanding of the on-site slope geometry determines success or failure. If the slope gradient (slope angle), steps, and area are not measured appropriately, it will be impossible to create the greening base according to design, which may cause problems with vegetation establishment and safety. Also, understanding the slope conditions before construction allows accurate calculation of the required seeds and topsoil quantities, and the area of materials to be used (such as greening mats and nets), which helps cost control and schedule planning. Furthermore, after construction, it is necessary to inspect whether the completed slope matches the design in shape and dimensions as part of as-built management, and compile the findings into a report for the client. Thus, surveying is a very important process in slope works.

However, there have long been several challenges in surveying on slopes. On steep slopes, workers have had to climb directly and operate tape measures or surveying instruments, increasing the risk of falls and other safety hazards. Setting up scaffolding or wearing safety belts required time and effort. Manual measurements can only capture a limited number of points at a time, making it difficult to grasp the detailed shape of a wide slope. Even if only main points are measured and compared with drawings, unexpected irregularities or differences from the design may remain in unmeasured areas, potentially resulting in a failed inspection later. In addition, manual methods are prone to human error such as missed photos or record mistakes. When survey results were handwritten on recording sheets, numbers could be recorded incorrectly, creating burden and stress on site.

Thus, traditional issues in slope greening surveying include “danger,” “tedious work,” and “limits to accuracy and coverage.” The smartphone-based 3D surveying method described next is expected to address these issues.

Background driving the need for labor-saving and efficiency in surveying

The construction industry as a whole is facing serious problems such as labor shortages and an aging skilled workforce. Especially in mountain and rural areas, it is difficult to secure personnel for surveying, forcing efficient work with a limited number of people. At the same time, on-site workstyle reform is being demanded, with correction of long working hours and reduction of hazardous tasks being important challenges. Slope surveying tends to involve strenuous work in the heat and hazardous high-place operations, so labor-saving and workload reduction have long been strongly desired to lessen worker burden and ensure safety.

Against this backdrop, the Ministry of Land, Infrastructure, Transport and Tourism is promoting a productivity improvement initiative for construction sites called *i-Construction*, encouraging the use of ICT (information and communication technology) and three-dimensional surveying technologies. Efforts are underway nationwide to use digital technology to streamline surveying and as-built management processes, which previously relied on manpower, enabling accurate measurements in shorter time with fewer personnel. A low-cost technology that is attracting attention for ease of adoption even by small contractors is the simple 3D surveying method using smartphones. Even on sites that cannot introduce the latest ICT devices or large drones, leveraging a handheld smartphone can greatly improve surveying efficiency.

Basics of smartphone-based 3D surveying and what it can do

So what exactly is smartphone-based 3D surveying? The basics involve using a smartphone’s camera and built-in sensors to scan the surrounding terrain and obtain a “point cloud” — a large collection of 3D points (cloud data). Some of the latest smartphones are equipped with LiDAR (light-based distance measurement) sensors; by launching a dedicated app and moving the phone to trace the slope through the camera, you can record countless points that define the slope shape with XYZ coordinates. The resulting point cloud is a digital “copy” that faithfully captures the slope’s irregularities. Traditionally, measurements were taken point by point with tape measures or total stations; the ability of a smartphone to capture the surface all at once is revolutionary.

With point cloud data obtained by a smartphone, various measurements and analyses can be performed on the spot. For example, a dedicated app can easily measure the distance between any two points or check elevation differences at the touch of a button. If the slope angle and elevation differences can be confirmed in real time, checks for whether the required gradient is maintained or whether there are steps or unevenness can be performed immediately. It is also possible to calculate area or earthwork volume from scanned data. For instance, by scanning the current condition during embankment or excavation, you can instantly determine whether the target earth volume has been reached by comparing with design values. In this way, a single smartphone can serve as a flexible analysis tool that covers most measurements needed on site.

Moreover, smartphone 3D surveying is a powerful tool for as-built inspection. Scanning the completed slope and creating a point cloud allows detailed digital recording of the finished shape. Acquired data can be compared with three-dimensional design data (BIM/CIM models, etc.) or design drawing values to accurately verify whether the design gradient and thickness are ensured and whether there are insufficient fills or overhangs. While traditional as-built judgments were limited to a few inspection points, point clouds allow checking of the entire slope, dramatically improving quality control accuracy. Some smartphone apps offer advanced features such as color-coded display of differences from the design on the spot or automatic extraction of areas exceeding tolerances. This enables anyone to make objective pass/fail decisions based on data without relying on a veteran engineer’s intuition.

Examples of point cloud data use: design comparison, quantity calculation, report creation

Point cloud data acquired with a smartphone can be used in various ways for construction management. Major uses include:

• Comparison with design data: Overlaying the point cloud of the scanned current condition with a prepared design model or design cross-section allows instant judgment of whether the as-built matches the design. For example, it is possible to display the differences from design elevation at various slope locations as a colored heatmap or extract areas outside standards. The “surface-based comparison” unique to point clouds ensures small discrepancies are not overlooked.

• Quantity calculation (volume/area): Point cloud data can automatically calculate volumes of fills/cuts and the surface area of slopes. Work that used to involve manual earthwork calculations based on drawings or measured points can now be calculated accurately at the touch of a button using point clouds. If a sudden design change requires additional topsoil, scanning the site lets you immediately estimate the needed soil. Quantity calculation is essential for progress and as-built management in civil works, and point cloud utilization dramatically streamlines this process.

• Report creation: Acquired point clouds serve as a “3D record” of the site that can be used later for detailed analysis and drawing creation. For example, you can extract arbitrary cross-sections from point cloud data to create before-and-after cross-section comparison drawings, or attach a 3D model view of the slope to a report. A cloud-based point cloud viewer enables sharing data with clients and internal stakeholders so they can check measurement results online. Information that is hard to convey with photos or paper drawings alone can be presented more convincingly using 3D data.

Accelerating pre-construction checks and on-site consensus with AR

Data obtained by smartphone 3D surveying and design models can be combined with AR (augmented reality) technology to greatly enhance pre-construction confirmation tasks. Using the AR function of a smartphone or tablet, you can overlay and display design-stage 3D models or drawing information on the actual site scenery. For example, showing the placement range of vegetation mats or the height of topsoil to be placed as AR on the terrain allows intuitive sharing of the completed image before construction. Finish images that were hard to imagine from drawings alone can be visually confirmed as life-size CG models, preventing mismatches of expectations.

AR also aids consensus-building with the client. Parts that used to rely on completion renderings or verbal explanations can be shown on site through a smartphone, enabling all stakeholders including clients and nearby residents to reach agreement before starting work. Since slope greening affects the landscape, being able to preview the post-greening appearance provides reassurance. Even if a design change occurs during construction, displaying a new model in AR on site allows instant sharing and easier agreement on changes. Visual sharing via AR reduces time spent on explanations and dramatically speeds up decision-making.

Furthermore, combining AR with cloud services makes remote site checks easy. If photos of AR displays or point cloud data captured on site are uploaded to the cloud and shared, clients can confirm current progress and as-built status from the office. Real-time information sharing without physically visiting the site can greatly shorten lead times for consensus-building. By combining smartphone surveying and AR, communication quality and speed from pre-construction through post-construction are dramatically improved.

Flexibility to handle small sites, steep slopes, and disaster recovery

Smartphone 3D surveying is highly adaptable to various site conditions due to its ease of use. For small sites or short slope sections, arranging large-scale drone surveys or expensive laser scanners may not be justified. With a smartphone, you can quickly take it out and survey alone when needed, saving cost and setup time. Its mobility allows free movement even in confined sites, enabling data capture of fine areas that were difficult to measure with traditional equipment.

Also, smartphone surveying can record terrain within the reachable range even on steep slopes or slopes surrounded by forest, where other survey methods struggle. Drones face challenges flying in strong winds or under trees, and laser scanners can be difficult to transport and set up in adverse conditions, but a smartphone can be carried to scan points while climbing and descending the slope. Of course safety measures are necessary, but the burden is much less than having a surveyor carry heavy equipment for long periods. Because smartphone surveying generally does not require qualifications or flight permits, regulatory hurdles are low, allowing flexible use regardless of terrain or environment.

Smartphone surveying is also useful for emergency response immediately after disasters. At sites where slopes have collapsed due to heavy rain or earthquakes, it is necessary to quickly grasp the affected area and collapsed soil volume to plan restoration. In such cases, site personnel can scan the collapse with a smartphone before specialized contractors arrive, enabling rapid analysis of damage. Point cloud data can be used to estimate collapsed soil volume or present dangerous areas as 3D models for information sharing with relevant agencies. With its flexibility and rapid response capability, smartphone 3D surveying is a tool that can support a wide range of situations from small-scale sites to urgent disaster recovery.

Improving on-site record accuracy through cloud sharing and automated forms

Survey data captured by smartphone can be saved and shared directly to the cloud. Cloud linkage allows scanned point clouds, photos, and measurement results to be viewed instantly from the office or remote locations, smoothing information flow. Multiple stakeholders — construction managers, designers, clients — can always share the latest data, eliminating discrepancies such as “it was like this on site but not communicated to headquarters.” Since data is accumulated in the cloud, past survey records can be easily retrieved when needed, aiding long-term record management.

Using digital data also enables automated creation of various report forms. Traditionally, as-built management documents and reports were compiled by manually entering measured numbers into drawings and tables. By linking point clouds and measurement results from smartphone surveys with software via the cloud, difference lists from design values, cross-sections, and quantity summary tables can be auto-generated. This eliminates manual transcription errors, dramatically improving record accuracy while reducing office work. For example, Ministry of Land, Infrastructure, Transport and Tourism surveys report that the time required to create as-built documents in earthworks was significantly reduced after introducing 3D surveying and ICT construction. Cloud and data integration make the sequence of “measure, compile, and communicate” seamless, improving both site productivity and record accuracy.

An integrated solution: smartphone surveying + AR + point cloud + cloud via LRTK

As described above, smartphone 3D surveying brings significant benefits to slope greening construction sites. To realize this on site, however, a system supporting high-precision positioning and data processing in addition to the smartphone itself is necessary. This is where a solution called LRTK comes in. LRTK consists of an ultra-compact high-precision GNSS receiver attached to a smartphone and a dedicated app, providing RTK positioning for centimeter-level position information (cm-level accuracy; half-inch accuracy), smartphone 3D scanning, AR display, and cloud linkage in an integrated package. It is, so to speak, a site DX tool that enables “measure, view, compare, and share” in one suite.

With LRTK, anyone can easily perform high-precision point cloud measurements and on-the-spot analysis. Complicated survey coordinate setup and post-processing are automated, allowing intuitive smartphone operation to complete 3D surveying without specialized knowledge. Acquired point clouds are tagged in real time with positioning information, clearly indicating where each slope point sits in a map coordinate system. This enables instant overlay and comparison of on-site data with design drawings or CIM data, allowing as-built management, quantity calculations, and AR-based confirmation of the finished image all on a single platform. Measurement data can be saved to the cloud with one click, eliminating the need to copy to USB or send emails after returning to the office.

Systems like LRTK that can be started with only a smartphone are attractive because they are easy for small to medium contractors or sites without a dedicated surveying department to introduce. On sites that have adopted LRTK, reports show substantial effects such as reducing as-built slope surveys that used to require 2–3 people to one person in a short time, and using point cloud measurements for routine progress management to eliminate waste. Improvements in safety and the training of young technicians have also been noted. Combining smartphone surveying + AR + point cloud + cloud in this integrated solution can make surveying and management for slope greening construction dramatically smarter.

Introducing advanced technology to the field may seem like a high hurdle, but with the emergence of LRTK, “3D surveying anyone can do” is already becoming a reality. If your company is considering labor-saving measures or DX for your sites, consider a surveying solution using LRTK that can be started with a single smartphone. Tasks that have traditionally been time-consuming, such as slope greening, can become highly efficient with the power of cutting-edge technology.