How High-Precision GNSS Positioning Is Changing Slope Greening Construction Management

Slope greening is an important construction activity that establishes vegetation on slopes along roads, on developed land, and on levees to prevent soil erosion and improve the landscape. However, in slope greening projects, quality control to verify that the as-built condition after construction matches the design is indispensable. If the slope angle, surface irregularities, or thickness of the greening materials do not meet standards, erosion prevention effects may be insufficient, potentially affecting slope stability and safety. Variations in quality also affect aesthetics and may disrupt harmony with the surrounding environment. Therefore, in slope greening, confirming and managing the as-built condition and quality is extremely important to ensure the construction objectives are achieved.

Traditional surveying and as-built verification methods for slopes have presented many challenges. Workers entering steep slopes to measure heights with tape measures or leveling rods, or using a transit or level to measure the crest and toe elevations to check cross-sectional shapes, involved arduous, labor-intensive work and hazards. Measuring slopes by hand on unstable terrain carries risks of falls and rockfall, making worker safety a major concern. Moreover, because the number of measurable points is limited, it was inevitable that only a subset of points along cross-sections could be checked, leaving ambiguity in understanding the entire slope’s shape or inconsistencies. As-built management typically samples a few points such as the top and bottom of the slope at set intervals, but that means differences from the design hidden between measurement points can be missed. With traditional methods, even with considerable time and manpower, it was difficult to comprehensively guarantee critical quality.

The use of high-precision GNSS positioning and digital technologies is attracting attention as a technology that addresses these field surveying and as-built management challenges and dramatically improves quality control for slope greening. In particular, centimeter-level GNSS positioning using Real-Time Kinematic (RTK) methods combined with 3D point cloud data and AR (augmented reality) technologies is transforming construction management from as-built verification to consensus-building. This article explains in detail the changes and advantages that high-precision GNSS positioning brings to slope greening construction management, comparing them with traditional methods.

Objectives of slope greening and the importance of quality control

First, let’s establish why slope greening is performed and what its effects are. The main purpose of slope greening is to prevent surface erosion and stabilize slopes. By planting herbaceous and woody vegetation on slopes, root systems help retain soil and prevent surface soil runoff and collapse caused by rain and wind. Properly vegetated slopes enhance long-term ground stability and contribute to reducing the risk of landslides and other soil-related disasters. Green vegetation cover also reduces exposed concrete and bare ground, contributing to landscape beautification and mitigation of the urban heat island effect. As part of a regional ecological network, slope greening can also promote biodiversity, making it valuable from an environmental conservation perspective.

To fully realize these effects, quality assurance during construction is paramount. For example, in topsoil spraying works, if the specified thickness of the vegetation substrate is not applied uniformly, erosion may start from thin spots. Incorrect seed or fertilizer mixing ratios and improper application rates can also cause poor greening. Ensuring that slope gradients and shapes conform to design is essential for safety. If the slope is steeper than designed, surface soil is more likely to slide; if too shallow, additional material may be required and drainage problems can arise. Therefore, the client sets as-built management standards and checks whether finished dimensions and gradients fall within allowable tolerances. If slope greening does not meet these as-built standards, it will not pass final acceptance—so the success or failure of quality control can decisively affect the overall evaluation of the project.

Traditional surveying and as-built verification methods and their issues

Conventional verification of slope as-built conditions has centered on point surveying by survey technicians in the field. After construction, elevations at several points are measured from reference points using total stations or levels with staffs, then compared to the design cross-sections. Specifically, heights at the upper slope (crest) and lower slope (toe) are measured at regular intervals to calculate gradients from those distances and to check deviations from the design line on cross-sections. Craftsman-style inspections—such as placing long straightedges or layout lines across the slope to check unevenness—have also been performed. These traditional methods relied heavily on the intuition of experienced technicians, tending to make finish evaluations subjective and qualitative.

Several problems accompany these manual measurement-centered approaches. First, there is the safety risk. Installing staffs and performing visual checks on steep slopes is constantly accompanied by the danger of falling or slipping. On unstable ground, such as disaster recovery sites, surveying itself can become life-threatening. Second, these methods require huge amounts of labor and time. Survey crews enter after heavy equipment work is completed, meaning inspection and construction take place sequentially and duplicate time is needed, resulting in overall project delays. High-elevation measurements limit the daily measurable area, and personnel costs become significant. Third, there are limits to coverage and accuracy of data. As noted above, measuring only a few points is insufficient to understand the entire as-built condition. For example, deciding “we measured three points in the section and all were within tolerance, so it’s accepted” might overlook local defects between those points. As-built drawings and photographic records are also prepared manually, introducing risk of human error; there are cases where later inspections find discrepancies and cause frantic corrections. Traditional methods carried the risk of rework and disputes due to missed measurements or recording errors.

Advantages brought by high-precision GNSS positioning

Recently, high-precision GNSS positioning has begun spreading as a trump card to solve these problems. Satellite positioning such as GPS once had errors on the order of meters, but the emergence of RTK (Real-Time Kinematic positioning) has improved accuracy dramatically to the centimeter level. RTK uses a base station placed at a known position and a rover station that moves while receiving data via radio or network communication; the difference in observations between the two is used to correct error factors. This enables real-time positioning to millimeter- to centimeter-level accuracy, allowing stakeout positions and slope as-built conditions to be numerically verified at nearly design-level accuracy.

The advantages of GNSS positioning extend beyond accuracy. Because it uses radio signals from satellites, it can position over wide areas without line-of-sight constraints. Instruments requiring a direct line of sight between the instrument and a prism, like total stations, often have blind spots on curved slopes or in sites with obstacles, but GNSS can measure seamlessly across the slope as long as the sky above is open. Positioning results are obtained as coordinates in the global geodetic reference frame, making it easier to align with design coordinates and other survey data and facilitating smooth integration with digital construction data. Without the need for baseline layout, simply walking with a GNSS receiver can identify any design point—enabling “coordinate guidance”—and traditional staking and as-built inspections that once required experience are becoming tasks that anyone can perform. In short, the introduction of high-precision GNSS has made it possible for field surveying to be done safely and easily by a single person while enabling reliable numerical management.

Surface verification and construction management innovation through point cloud surveying

In addition to precise single-point measurements with GNSS, point cloud surveying—which captures the entire slope as 3D surface data—has also advanced rapidly. Point cloud data obtained from laser scanners (LiDAR) or photogrammetry is a digital replica of the slope’s shape, covering it with countless measured points. Unlike traditional point surveys, this detailed topographic information, when applied to as-built management, can dramatically improve the precision and efficiency of construction management. Let’s summarize the main advantages point cloud surveying brings.

• Precise, comprehensive as-built records: Point clouds capture the entire surface irregularities of a slope without omission. Because even subtle undulations are recorded, previously overlooked minor unevenness can be detected. The surface- and volume-based as-built understanding that human measurements cannot achieve greatly enhances quality control accuracy. If internal slope structures (such as fill layer thicknesses) are digitized immediately after construction, they can serve as reliable evidence in the future.

• Reduced survey labor and faster work: Using 3D scanners or drone-based photogrammetry, large slopes can be surveyed and large volumes of point cloud data acquired in a short time. Tasks that once required survey crews to climb slopes for an entire day can, in some cases, be completed by setting up laser equipment in minutes. Because measurements are non-contact, heavy equipment operation need not be suspended, enabling efficient inspections. The Ministry of Land, Infrastructure, Transport and Tourism’s promoted ICT construction has reported that introducing 3D surveying and machine guidance reduced overall civil engineering work time by about 30%. Point cloud utilization contributes significantly to shortening schedules and improving productivity.

• Improved safety: Point cloud surveying allows remote or automated data acquisition, greatly reducing situations where surveyors must enter hazardous slopes. For example, flying a drone from above the slope to capture imagery avoids placing people near unstable areas. Fewer personnel and safer surveying are possible, addressing chronic labor shortages and reducing on-site accident risk.

• Digitization of records and ease of sharing: Point cloud data can be freely analyzed and used on a computer. Cross-sections, slope lengths, and gradients can be generated by clicks, preventing scenarios like “we forgot to measure a spot and must return to the site.” Creation of as-built deliverables can be semi-automated, and submitting 3D data instead of photo albums is beginning. Uploading to the cloud allows stakeholders to review the same 3D model remotely, making it feasible for clients and inspectors to perform remote checks from the office. Electronic data is easier to store long-term and search than paper, which is another major advantage.

With point cloud surveying, slope as-built management becomes “more accurate, faster, safer, and less labor-intensive.” By preventing human error and oversight while strengthening the objective evidentiary power of data-based quality assurance, construction management reaches a level far beyond traditional methods.

Consensus-building and visual quality checks using AR

Another recent focus is the on-site use of AR (augmented reality) technology. By combining high-precision GNSS with point cloud data, design drawings and 3D models can be overlaid onto the real world. When a tablet is held up at the construction site, the camera view can display the designed completed image and any as-built deviations in real time. This allows immediate, intuitive checks of whether the finished slope matches the drawings, and it smooths recognition sharing between clients and contractors. Information that was hard to convey with paper drawings or lists of numbers becomes immediately obvious to anyone via AR, accelerating consensus-building and decision-making on site.

Specific AR use cases include the following:

• Design stage: AR displays the projected completion image to aid agreement with clients and local residents. Being able to preview the landscape after slope greening makes it easier to obtain stakeholders’ understanding and approval of design and vegetation plans.

• Construction stage: Projecting the design model on site during work enables accurate, non-guesswork construction. For example, when spraying topsoil at the specified thickness, following AR-projected guides can prevent uneven application. Additionally, by measuring the positions of buried utilities in advance with point clouds and displaying them in AR, machine operators can avoid pipelines and other infrastructures during excavation.

• Inspection stage: Overlaying design data onto the completed slope and checking with AR makes it easy to find minute defects not visible to the naked eye. Contractors and inspectors can view the same image on site to discuss issues, enabling quick corrective actions and shortening the time to inspection approval.

Thus, AR becomes a powerful tool for smoothing communication among stakeholders from design through construction to inspection and for deepening common understanding of quality. In slope greening projects, visualizing digital data on site can be expected to reduce rework and raise as-built standards.

Improved responsiveness and safety in difficult or disaster recovery sites

Slope greening sites often involve harsh working environments such as rugged terrain or unstable slopes immediately after disasters. In such sites, it can be difficult or impossible to have people physically enter to conduct surveying and inspection as in traditional methods. In disaster recovery for slope collapse caused by heavy rain or earthquakes, rapid assessment and remedial work are needed, but there was a dilemma: detailed on-site surveys could not be done quickly because of the risk of secondary disasters.

Combining high-precision GNSS, point cloud technology, and drone aerial photography makes it possible to digitally record terrain conditions immediately even under such severe conditions. Even at collapse sites where people cannot enter, a few minutes of flight can capture a 3D slope model from above. Sharing that data via the cloud allows all stakeholders, including experts not present on site, to discuss recovery plans. Near-real-time visualization of conditions shortens lead times from emergency measures to full recovery.

Furthermore, surveying equipment with GNSS receivers can achieve centimeter-level positioning even in mountainous areas without cellular coverage by using satellite-based augmentation services (for example, CLAS service from the Quasi-Zenith Satellite System). This enables stable positioning and measurement anywhere without relying on terrestrial communication infrastructure. Overall, digital technologies are a trump card for ensuring rapid response while protecting lives during surveying and construction management in difficult sites.

An integrated surveying, point cloud, and AR solution with LRTK

As described above, GNSS positioning, point clouds, and AR technologies open new possibilities for slope greening construction management. However, some may worry that fully leveraging these technologies on site requires expensive specialized equipment and advanced analysis skills. That is where an integrated solution called LRTK has emerged. LRTK was developed as an innovative tool that realizes surveying, point cloud acquisition, AR display, and cloud sharing on a single platform.

With LRTK, field personnel can measure and record slope as-built conditions with high precision using only a palm-sized GNSS receiver and a smartphone. A compact positioning device that attaches to a smartphone obtains centimeter-level position information in real time, and by moving the phone’s built-in LiDAR scanner or camera, point cloud data with absolute coordinates is generated. No complex operations or special training are required—anyone can intuitively perform 3D surveying. The acquired point cloud is visualized on the phone screen on site, and comparison with design data is just a tap away. Deviations in as-built condition are color-coded, making it immediately clear where corrective work is needed. Switching to AR mode overlays the design model and correction areas on the actual slope so differences between reality and data can be verified in situ.

LRTK also supports cloud integration, allowing survey results to be uploaded to the cloud with a single tap. This enables managers and clients in the office to instantly share and view data. Without installing dedicated software or preparing high-performance PCs, stakeholders can view 3D point clouds and AR views via a web browser, facilitating remote inspections and discussions. LRTK, which covers everything from surveying to data delivery in an all-in-one package, is attracting attention as an integrated solution that powerfully supports on-site digital transformation (DX).

Ease of adoption even for small slopes and short schedules

Traditionally, 3D scanners and high-precision GNSS equipment were expensive and required expertise, making them feasible mostly for large projects. However, with LRTK, even small-scale slope works and short-term projects can readily adopt advanced technologies. The hardware is lightweight and compact with built-in power, so it can be transported to the site and used immediately. By launching a smartphone app and attaching the device, positioning starts without complex setup, making it easy even for first-time users. The intuitive interface automates processes from surveying to point cloud generation and analysis, allowing site staff to operate it without a dedicated specialist.

Short-term sites often lack time for detailed measurement planning and post-processing, but with LRTK, point cloud acquisition, as-built checks, and report sharing can be completed within the same day. For example, on the final day of construction one can scan the slope with LRTK, immediately assess acceptance criteria, perform corrective work if needed, and upload inspection materials to the cloud for the completion inspection. Since only a smartphone and a small device are required, even remote slopes can be brought in by vehicle with heavy equipment and the quality check completed on site without arranging an additional survey crew. This ease of operation is particularly valuable for small-scale sites.

Conclusion: The future of slope greening construction management opened by LRTK

To reliably achieve slope protection and landscape enhancement—the main objectives of slope greening—more precise and efficient construction management than ever before is required. The use of digital technologies, led by high-precision GNSS positioning, is key to dramatically improving on-site safety and productivity and raising the level of quality control. The integrated nature of LRTK is groundbreaking because it packages these advanced technologies into an easy-to-use on-site form. Shifting slope construction management from reliance on the intuition and experience of skilled workers to a data-driven approach will enable anyone to reliably achieve high-quality work in a short time, which is the on-site DX vision LRTK promises.

As society increasingly demands greater efficiency in infrastructure maintenance and changes in work styles, the adoption of such smart construction management tools will likely accelerate. If you currently face challenges in surveying or inspecting slope greening works, LRTK may offer a practical solution. By proactively adopting the latest technologies, we can promote safe, resilient infrastructure development and environmental conservation while advancing on-site digital transformation and quality improvement.