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

Slope greening (norimen ryokka) is an important type of work that plants vegetation on slopes such as roadsides, reclaimed land, and levees to prevent soil erosion and improve the landscape. However, in slope greening work, quality control to verify that the as-built result matches the design after construction is indispensable. If the slope angle, surface irregularities, or thickness of the greening material do not meet standards, erosion prevention effects may be insufficient and the slope’s stability and safety may be compromised. Variations in quality also affect aesthetics and risk disrupting harmony with the surrounding environment. Therefore, in slope greening, confirming and managing as-built conditions and quality is extremely important to ensure the construction objectives are reliably achieved.

Traditional surveying and as-built verification methods on slopes have had many challenges. Tasks such as having workers enter steep slopes to measure heights with tape measures or staffs, or using a transit or level to measure the heights of the crest and toe of a slope to check cross-sectional shape, were extremely laborious and dangerous. Measuring slopes by hand on unstable footing carried risks of falls and rockfalls, making worker safety a persistent issue. In addition, the number of measurable points was limited, so only some points along cross-section lines could be checked, making it inevitable that the overall shape and unevenness of the slope could not be fully understood. As-built management typically selects a few points such as the top and bottom of the slope at regular intervals for measurement, but that approach can miss differences from the design hidden in unmeasured areas. Conventional methods therefore faced the problem that even with considerable manpower and time, it was difficult to comprehensively guarantee the essential quality.

High-precision GNSS positioning combined with digital technologies is attracting attention as a technology that solves these field surveying and as-built management problems and dramatically improves quality control for slope greening. In particular, centimeter-level GNSS positioning via Real-Time Kinematic (RTK) and the integration of 3D point cloud data and AR (augmented reality) technology are changing construction management from as-built verification to stakeholder consensus building. This article explains in detail the changes and benefits high-precision GNSS positioning brings to slope greening construction management, with comparisons to traditional methods.

Purpose of Slope Greening and the Importance of Quality Control

First, let’s review why slope greening is carried out and what its objectives and effects are. The main purpose of slope greening is to prevent surface erosion and stabilize slopes. By establishing herbaceous and woody plants on inclined ground, root systems firmly hold the soil, preventing runoff and collapse of topsoil due to rain and wind. Properly vegetated slopes increase long-term ground stability and contribute to reducing landslide risk. Vegetative cover reduces exposure of concrete and bare ground, contributing to landscape beautification and mitigation of the heat island effect. As part of the local ecological network, greening also promotes biodiversity, making it valuable from an environmental conservation perspective.

To fully realize these effects, ensuring construction quality during execution is paramount. For example, in soil spraying (topsoil spraying) work, if planting substrate is not sprayed uniformly at the specified thickness, erosion can start from thin spots. Incorrect seed or fertilizer mixing ratios or improper application rates can also cause greening failure. Ensuring the slope gradient and shape match the design is also essential for safety. If the grade is steeper than designed, topsoil can more easily slide off; if too shallow, excess material may be required and drainage issues may arise. Therefore, the client sets as-built management standards to confirm that finished dimensions and slopes fall within allowable tolerances. If slope greening work does not meet these as-built standards, it will not pass inspection, so the success or failure of quality control can, arguably, determine the evaluation of the entire project.

Traditional Surveying and As-Built Verification Methods and Their Challenges

Traditional as-built verification for slopes centered on site point surveying by survey technicians. After construction, a total station or level and staff were used to measure the elevations of several points from control points, and those measurements were compared with the design cross-section drawings. Specifically, heights at the slope crest (shoulder) and toe were measured at set intervals to calculate gradients from those distances and check deviations from the design line on cross-sections. Craftsman-style inspections such as applying long straightedges or chalk lines to the slope to check irregularities were also performed. These conventional methods relied heavily on the instincts and experience of skilled technicians, making finish evaluation prone to subjectivity and qualitative judgment.

There are several problems with such manual, labor-centered measurement. First is safety risk. Installing staffs or doing visual checks on steep slopes was always accompanied by the danger of slipping or falling. In disaster recovery sites with unstable ground, surveying itself could even become life-threatening. Second, it required enormous labor and time. Survey teams would enter the site after heavy equipment work was completed, so both construction and inspection consumed time and created schedule inefficiencies. Measurements at height were time-limited per day, and personnel costs were significant. Third, there are limitations in data coverage and accuracy. As noted, measuring only limited points is insufficient to grasp the entire as-built condition. For example, judging “the three points within a section are within spec, so it’s acceptable” might overlook localized defects between those points. As-built drawings and record photos were also prepared manually, introducing human error risk and leading to cases where discrepancies were flagged in later inspections. Conventional methods therefore carried risks of rework and disputes due to measurement omissions and recording mistakes.

Advantages Brought by High-Precision GNSS Positioning

High-precision GNSS positioning has recently begun to spread as a trump card to solve these challenges. Satellite positioning such as GPS previously had errors on the order of meters, but the advent of RTK (real-time kinematic) positioning dramatically improved accuracy to the centimeter level. In RTK, a base station installed at a known position and a rover station that moves while receiving signals exchange data via radio or network; observational differences between them are used to correct error factors. This enables real-time millimeter- to centimeter-level positioning, allowing staking positions and slope as-built conditions to be numerically confirmed to nearly drawing-level accuracy.

GNSS positioning’s advantages are not limited to accuracy. Because it uses radio waves from artificial satellites, it can provide positioning over wide areas without line-of-sight constraints. Instruments requiring direct line of sight between instrument and prism, like total stations, tend to have blind spots on curved slopes or in obstructed sites, but GNSS can measure seamlessly across the entire slope as long as the sky above is open. Positioning results are obtained as coordinates in a global geodetic system, making it easy to correlate with design coordinates on drawings and other survey data and facilitating integration with digital construction data. Without laying out baselines, a GNSS receiver carried by hand can identify arbitrary design points with “coordinate guidance,” enabling staking and as-built inspections that previously required experience to be performed by anyone. In short, introducing high-precision GNSS makes on-site surveying safe and easy for a single person while enabling reliable numerical management.

Revolutionary Surface Verification and Construction Management via Point Cloud Surveying

In addition to precise single-point GNSS measurements, point cloud surveying that captures the entire slope as three-dimensional surface data has advanced dramatically in recent years. Point cloud data obtained by laser scanners (LiDAR) or photogrammetry create a digital copy that covers the slope shape with countless measurement points. This detailed topographic information, distinct from traditional point surveying, dramatically improves the accuracy and efficiency of construction management when applied to as-built control. Key benefits of point cloud surveying include:

• Precise, comprehensive as-built records: Point clouds capture the slope’s entire surface irregularities without omission. Because undulations are recorded, even minute unevennesses that were previously missed can be detected. By capturing the surface in a spatial, three-dimensional manner that manual methods could never fully collect, the precision of quality control is greatly enhanced. If the internal slope structure (such as fill layer thickness) is digitized immediately after construction, it becomes a highly reliable record for future proof.

• Reduced surveying labor and faster work: Using 3D scanners or drone photogrammetry, large extents of slope can be scanned in a short time to acquire vast point cloud datasets. What once took a surveying team a full day to climb and measure on a slope can sometimes be completed in tens of minutes by setting up laser equipment. Because measurement is contactless, heavy equipment operation need not be suspended, enabling efficient inspection. The Ministry of Land, Infrastructure, Transport and Tourism’s ICT construction initiatives report that introducing 3D surveying and machine guidance reduced overall civil engineering work time by about 30%. Point cloud utilization therefore contributes significantly to shortened schedules and improved productivity.

• Improved safety: Point cloud surveying allows remote or automated data acquisition, greatly reducing occasions when surveyors must enter dangerous slopes. For example, flying a drone from above the slope to photograph the terrain keeps people away from unstable areas. This enables safe surveying with fewer personnel, effectively addressing chronic labor shortages and reducing onsite accident risks.

• Digital recording and shareability: Acquired point cloud data can be freely analyzed and used on a computer. Creating required cross-sections or calculating slope length and gradients can be done with clicks, eliminating situations where “we forgot to measure a spot and have to return to the site.” Creation of as-built documentation can be semi-automated, and submission of 3D data instead of photo logs is already beginning. Uploading to the cloud allows stakeholders to check the same 3D model remotely, so clients and inspectors can perform remote inspections from the office. Electronic data are easy to store long-term and search, making them far more manageable than paper.

By introducing point cloud surveying, as-built management for slopes can be conducted “more accurately, faster, safer, and with less effort.” It prevents human errors and oversights while strengthening the evidentiary power of objective data, enabling a level of construction management that is a different dimension from traditional methods.

Consensus Building and Visual Quality Checks Using AR

AR (augmented reality) technology has also been gaining attention for field use. By combining high-precision GNSS with point cloud data, design drawings and 3D models can be overlaid onto real space. When a tablet is held up at the construction site, the camera view can display the designed finished appearance and any as-built deviations in real time. This allows intuitive on-the-spot checks to see whether the finished slope matches the plans, and it smooths recognition sharing between clients and contractors. Information that was hard to convey with paper drawings or strings of numbers becomes obvious to anyone via AR, dramatically speeding up on-site consensus building and decision-making.

Specific AR use cases include:

• Design phase: Displaying a projected finished image in AR to facilitate consensus building with clients and local residents. Being able to preview the slope greening’s post-construction appearance helps stakeholders understand and accept design and planting plans.

• Construction phase: Projecting the design model on-site during work allows accurate construction without relying on intuition. For example, with soil spraying at a specified thickness, following AR-projected guides helps prevent inconsistencies. If the locations of buried utilities are pre-scanned into a point cloud and shown transparently in AR, machine operators can avoid pipes during excavation.

• Inspection phase: Overlapping design data on the completed slope in AR makes it easy to detect minute defects that are not visible to the eye. Contractors and inspectors can view the same imagery on-site and discuss, enabling rapid correction of issues and shortening time to acceptance.

AR thus becomes a powerful tool to smooth communication and deepen shared understanding of quality across design, construction, and inspection stages. In slope greening, visualizing digital data on site can reduce rework and raise as-built standards.

Required Rapid Response and Improved Safety in Difficult Areas and Disaster Recovery

Slope greening sites often involve harsh working environments such as steep terrain or unstable slopes immediately after disasters. In such sites, it can be difficult to have people enter for surveying and inspection as in traditional methods. In recovery sites after heavy rain-induced slope collapse or earthquake-induced landslides, it is necessary to quickly grasp the damage and execute countermeasures, but the danger of secondary disasters makes it impossible to spend time on detailed field surveys.

Combining high-precision GNSS, point cloud techniques, and drone aerial photography makes it possible to digitally record terrain conditions quickly even under these difficult conditions. Even where humans cannot enter a collapse site, a few minutes of drone flight from above can acquire a 3D slope model. If that data is shared via the cloud, all stakeholders, including specialists not on site, can examine recovery plans together. Because conditions can be visualized at near real-time speed, this directly shortens lead times from emergency measures to full recovery.

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

Integrated Surveying, Point Cloud, and AR Solutions with LRTK

As described above, technologies such as GNSS positioning, point clouds, and AR bring new possibilities to slope greening construction management. Some may worry that fully utilizing these in the field requires expensive specialized equipment or advanced analysis skills. That is where LRTK, an integrated solution, comes in. 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 accuracy using only a palm-sized GNSS receiver and a smartphone. A compact positioning device that attaches to the phone acquires centimeter-accurate location information in real time, and simply moving the phone’s built-in LiDAR scanner or camera generates point cloud data with absolute coordinates. No complex operation or special training is required; it is designed so anyone can intuitively perform 3D surveying. Acquired point clouds are visualized on the phone screen on site, and comparison with design data is one touch. Deviations are color-coded so it is immediately clear where the slope needs correction. Switching to AR mode overlays the design model and correction areas onto the actual slope, allowing on-site confirmation of differences between the physical object and the data.

LRTK also supports cloud integration and allows survey results to be uploaded with a single button. Office-based managers and clients can instantly share and view the data. Without installing dedicated software or preparing a high-performance PC, stakeholders can view 3D point clouds and AR views via a web browser, making remote inspections and consultations easy. By handling surveying to data delivery in an all-in-one workflow, LRTK is attracting attention as an integrated solution that strongly promotes on-site digital transformation (DX).

Ease of Adoption Even for Small Slopes and Short Schedules

Historically, 3D scanners and high-precision GNSS equipment were expensive and required expert operation, so adoption was often limited to large-scale projects. However, with the advent of LRTK, the environment is becoming ready for even small slope jobs and short-schedule sites to easily adopt advanced technologies. The hardware is lightweight and compact with built-in power, so it can be carried to the site and used immediately. Starting the smartphone app and attaching the device initiates positioning with no complicated setup, so even first-time users will not be confused. The intuitive interface automates surveying through point cloud generation and analysis, enabling site staff to operate it without a dedicated operator.

On short-term sites there is no time to plan detailed measurement schedules or perform extensive post-processing, but LRTK can complete point cloud acquisition, as-built checks, and report sharing in the same day. For example, scanning a slope with LRTK on the final construction day, immediately judging pass/fail, performing any touch-up work, and submitting inspection documents to the cloud for final acceptance becomes a realistic, speedy workflow. With only a smartphone and a small device required, even a remote mountain slope can be transported by vehicle with heavy equipment and complete quality checks on site without arranging an additional surveying team. This ease of operation will be particularly valued on small sites.

Conclusion: The Future of Slope Greening Construction Management Opened by LRTK

To reliably achieve slope protection and landscape improvement—the objectives of slope greening—more precise and efficient construction management than ever before is required. Utilizing digital technologies, starting with high-precision GNSS positioning, is the key to dramatically enhancing site safety and productivity and raising the level of quality control. In particular, LRTK is groundbreaking in integrating these advanced technologies into an easy-to-use field solution. Shifting slope construction management from reliance on the intuition and experience of seasoned workers to data-driven processes so that anyone can reliably achieve high-quality construction in a short time—that is the field DX that LRTK promises.

As society increasingly demands more efficient infrastructure maintenance and work-style reform, adoption of such smart construction management tools will accelerate. If you currently face challenges in slope greening surveying or inspection, using LRTK may provide the solution. By proactively adopting the latest technologies, we can promote on-site DX and quality improvement while achieving both safe, resilient infrastructure and environmental conservation.