Solar Construction Earthwork Volume Management Made Easy with Your Smartphone! Visualizing Cut-and-Fill Changes the Jobsite

In recent years, innovative earthwork volume management methods using smartphones have been gaining attention at solar construction sites. Managing cut-and-fill across large-scale land development is a critical task that can determine a project's success. However, traditional methods have relied heavily on enormous labor and experience, leaving room for mistakes and rework. This article explains in detail the latest trends in easy, high-precision earthwork volume management using smartphones and how visualization of cut-and-fill (making it visible) can dramatically transform the jobsite.

Importance and challenges of earthwork volume management in solar construction

Land development is indispensable in the construction of solar power plants (especially megasolar land development). When sites are planned in mountainous or sloped areas where it is difficult to secure flat land, extensive cut-and-fill earthworks are carried out to level the ground for solar panel installation. Naturally, the volume of soil and sand handled is enormous, and it is not uncommon for the total to reach tens of thousands of cubic meters. Accurately managing such a large amount of earth requires meticulous planning and on-site supervision, making “earthwork volume management” a critical issue for the success of solar construction.

If volume estimation or management is mistaken, various problems arise. For example, if more soil than planned is excavated, disposal costs for surplus soil increase; conversely, if backfilling soil is insufficient, additional costs to procure soil externally will be incurred. Excessive excavation beyond design can increase impacts on the surrounding environment and raise the risk of landslide disasters. Therefore, high accuracy in earthwork planning and strictness in on-site volume management are required. Also, errors in earthwork volume directly affect the schedule and budget. If earthworks do not progress as planned, subsequent foundation work and panel installation can be affected, potentially causing project-wide delays and cost overruns. From the perspectives of quality, safety, schedule adherence, and cost control, improving the accuracy of earthwork volume management in solar construction is extremely important.

Traditional earthwork volume management methods and their issues

Traditionally, earthwork volume management at development sites has been conducted through time-consuming on-site surveying and volume calculations. Surveyors walk the site before and after construction and measure heights at dozens of locations on slopes and within the site. From the obtained elevation point data, cross-sections or mesh models are created on drawings to calculate cut and fill volumes—this is the common procedure. However, such analog-centered methods have several limitations. The main issues include the following points:

• Limited accuracy due to few measurement points: Manual surveying can only acquire a limited number of points, so fine terrain undulations tend to be overlooked. As a result, there is a risk of errors in volume calculations.

• Cannot frequently measure wide areas: Surveying a large site by manpower takes time and personnel, making it practically difficult to measure the current state at high frequency such as daily or weekly. Progress cannot be tracked in detail, and volume management cannot always reflect the most up-to-date conditions.

• Risk of transcription or calculation errors: There is a possibility of copying numbers incorrectly or making calculation mistakes in the process of taking notes manually or entering data into spreadsheets. This can lead to discrepancies in reported volumes.

• Information sharing is not intuitive: Survey results are often presented as lists of numbers or cross-sections, which makes it hard to intuitively grasp the overall site situation. Therefore, it can be difficult for site staff and upper management/clients to share a common understanding of “where and how much soil is in excess or deficit,” leading to time-consuming communications.

As shown, traditional methods tend to make volume management subjective and it is difficult to achieve both efficiency and accuracy.

Visualizing cut-and-fill using point cloud data

To solve these issues, 3D point cloud data–based earthwork management has attracted attention in recent years. A point cloud is 3D data that represents the shape of terrain or structures as a collection of innumerable points, obtained by laser scanners or photogrammetry. Using high-density point clouds that cover the ground surface thoroughly makes it possible to reproduce the current terrain model with extremely high precision. While traditional surveying could at best obtain height information at several dozen points, point cloud data can capture fine terrain undulations from millions of points. Consequently, the accuracy of volume calculations improves dramatically.

By overlaying the acquired current point cloud terrain model with the designed planned ground model and comparing them, you can identify in area terms where and how much cut or fill is required. The visualization of such differences by color according to elevation difference is called a “volume heat map.” For example, areas where the ground is higher than the design (still overly filled) can be shown in red, while areas that have been dug too deep and are lower than the design can be shown in blue, thereby indicating discrepancies in ground elevations by color. This allows anyone to visually grasp where and how much soil needs to be cut or filled at a glance.

The greatest advantage of heat map display is that it allows intuitive understanding of site conditions. Where in the past one had to imagine terrain excesses or deficits from numerical data or cross-sections, a color-coded map makes them clear without mental extrapolation. Even inexperienced staff can easily visually identify problem areas, facilitating shared understanding among all stakeholders. Because the data are point-cloud-based, volume calculation accuracy is high and even subtle undulations that used to be overlooked are reflected. This yields reliable data that support decisions about whether plan revisions or additional earthworks are necessary, improving the quality of construction management.

In practice, comparisons between volumes calculated from point cloud data and those computed by traditional cross-section methods have shown differences of less than 1%, confirming the high accuracy of point cloud measurement. Moreover, processing time can be significantly reduced, making point cloud–based volume management a new method that balances quality and efficiency. At one site, introducing point cloud technology reportedly reduced the personnel and time required for surveying work to less than half of that previously needed. In the construction industry, where labor shortages are becoming more severe, the ability to conduct efficient volume management with a small team using point cloud technology has significant value from the standpoint of work-style reform.

Easy point cloud acquisition using drones and smartphones

So how can such high-density point cloud data be obtained on site? One representative method is drone (UAV) photogrammetry. A small unmanned aerial vehicle equipped with a camera takes many photos from above to cover the entire site. Specialized software analyzes those images to generate a 3D point cloud model of the current terrain. Even for vast planned solar power plant sites, the entire current condition can be captured in a short time, and steep slopes can be safely measured without people entering hazardous areas. On sites that have adopted drone surveying, surveying and volume calculation work that used to take a day or more can be completed in a few hours, dramatically improving efficiency.

In recent years, methods using smartphones equipped with LiDAR sensors to easily capture point clouds have also become widespread. By installing a dedicated app on the latest smartphones and scanning the surrounding terrain, you can generate a 3D point cloud on the spot. For example, site supervisors can quickly scan small fill piles or accumulated spoil on the site with a smartphone and instantly calculate volumes. The advantage is that staff can routinely collect terrain data without the large-scale equipment a drone requires.

Depending on site conditions and objectives, you can use drones and smartphones selectively. Drones are suitable for capturing wide areas at once, while smartphones are powerful for detail checks and frequent progress monitoring. Point cloud data obtained by either method can be processed and compared with dedicated software or cloud services to generate volume heat maps and export numerical reports. The flexibility to choose the optimal measurement method for each site is a major strength of digital surveying.

Of course, each method has caveats. While drones can survey wide areas at once, they are constrained by aviation law permissions and weather. Smartphone measurement offers ease of use, but the area that can be measured at one time is limited, so it is unsuitable for surveying an entire vast site. Considering the pros and cons of each method, it is important to select and combine the optimal approach based on the site's scale and conditions.

The Ministry of Land, Infrastructure, Transport and Tourism’s promotion of i-Construction has also been supportive, and ICT utilization in earthworks (so-called “ICT earthworks”) is spreading year by year. Photogrammetry by drones and as-built management by 3D laser scanners have already proven effective at many sites, and such advanced technologies are increasingly being introduced in solar power plant development as well. Point cloud heat map–based construction management is becoming not a special advanced case but a standard method on sites. The ministry is also actively promoting the introduction of 3D technologies for as-built management, and it is pointed out that submitting 3D data such as point clouds as deliverables may become standard in the future. As digital transformation (DX) accelerates across the construction industry, becoming familiar with digital surveying early will contribute to future competitiveness.

Accelerating on-site decisions using heat maps

Visualization via volume heat maps also greatly speeds decision-making on site. At one solar power plant development site, drones were used to scan conditions at the end of each workday to update heat maps, and instructions were issued at the next morning’s briefing or progress meeting based on the latest map. By looking at the heat map, it is immediately obvious which areas have been leveled to the design height and where significant excesses or deficits remain. The site supervisor can instantly issue specific instructions, such as prioritizing excavation with heavy machinery on red areas (excessive fill remaining, too high) and bringing in soil for blue areas (over-excavated and now too low). Decisions that previously relied on intuition or experience become accurate, data-driven judgments, directly improving site productivity.

Heat maps also provide quantitative difference amounts in addition to color, allowing you to estimate the required future work volume. Because you can make data-based decisions such as “if we export X more truckloads of soil, we will reach the design elevation,” planning for heavy equipment operation and arranging dump trucks becomes more precise. By tracking daily terrain changes with heat maps, you can quickly determine whether the earthworks are likely to finish within the scheduled period and take proactive measures such as increasing personnel or revising the schedule as needed.

From a quality-control perspective, visualizing as-built status with heat maps is beneficial. If excessive excavation or insufficient filling occurs during construction, it can be detected at a glance and corrected early, reducing uneven finishes. This can prevent items from failing final inspection and reduce rework and material waste. Real-time difference visualization accelerates the jobsite PDCA cycle, enabling efficient construction without waste.

Data-driven management has also reported outcomes such as significant schedule reductions and cost savings for earthworks as a whole. With a clear overall picture, idle waiting time is reduced and the deployment of machinery and personnel can be optimized. The use of heat maps therefore directly contributes to shorter schedules and lower construction costs.

Cloud integration for information sharing and remote management

To maximize the benefits of point cloud data and heat maps, cloud-based information sharing is indispensable. Previously, survey results were exchanged on paper drawings or Excel sheets, but uploading 3D data to the cloud allows office-based management staff and clients to share site status in real time. Services are emerging that allow those without specialized software to view point cloud models and heat maps via a web browser, ensuring everyone can check the latest information.

Sharing site data via the cloud enables headquarters construction managers and engineers to grasp the situation and issue instructions without traveling to the site. For example, headquarters can monitor development progress at any time and promptly revise construction plans as needed—facilitating rapid follow-up. The accumulation of data in the cloud also streamlines progress history management and report creation. Close coordination between the site and management via data fosters a sense of unity across the organization in supporting the project, contributing to improved construction quality and safety.

The ability to remotely monitor the site proved powerful during movement restrictions such as the COVID-19 pandemic. Being able to check as-built data online without visiting the site has established a new supervisory workflow. In addition, cloud-based 3D models and heat maps are useful for explaining construction to clients and local residents. Visual materials make it easier to convey site conditions that are hard to explain with numbers and technical terms alone, improving external credibility.

Furthermore, acquired 3D data can be used to update CIM models (3D design models for construction) and to create as-built documentation. Because in-house and external engineers can effectively use the data, consistent information management across the lifecycle from design to construction and maintenance becomes possible. Time-series recording of terrain changes can be useful for post-completion maintenance inspections or as verification material in the event of landslide disasters. Also, as-built quantities derived from point clouds serve as objective evidence, facilitating client reporting and settlement tasks. In the past, discrepancies sometimes arose between site and management over interpretation of survey results, but clear visual data visible to all can prevent unnecessary disputes.

Smart construction management using smartphone RTK surveying and point cloud heat maps [LRTK]

Finally, as a solution that makes it easy to apply point cloud heat maps on site as described above, we introduce LRTK. With LRTK, a single smartphone alone can perform everything from high-precision RTK positioning–based 3D point cloud measurement to generating volume heat maps. No specialized heavy machinery is required, and the system’s simplicity allows site technicians to operate it intuitively. You don’t need to learn complicated software or acquire surveying expertise—just follow the smartphone screen guidance to complete the survey. With brief training, anyone can use it, facilitating smooth adoption at sites.

LRTK consists of a compact device attached to a smartphone and a dedicated app, combining high-precision GNSS satellite positioning with the phone’s built-in LiDAR scanner to acquire point cloud data with millimeter-level precision (0.04 in). The point cloud captured on-site automatically calculates volumes and heights and can generate a design comparison heat map with a single tap. Another major advantage is that the generated heat map can be displayed in AR on the smartphone screen. When you point the phone, colored overlays appear on the ground in front of you so you can visually correlate how many centimeters (inches) higher or lower each location is compared to the design.

Because LRTK always acquires point cloud data in a high-precision absolute coordinate system, it is easy to accurately overlay design CAD data and boundary lines—tasks that were difficult until now. Survey results from multiple days can be managed in the same coordinate system, enabling smooth daily progress comparisons and volume calculations. These advanced features allow you to verify as-built conditions and comprehensively identify areas needing rework while remaining on site. Measurement data are automatically saved to the cloud, and by issuing a sharing URL you can online share 3D models and heat maps with distant supervisors and partner companies.

Currently, from major general contractors to regional construction firms, adoption of smartphone RTK surveying and point cloud utilization tools like LRTK is spreading in pursuit of site DX (digital transformation). As everyone gains the ability to handle high-precision 3D point cloud data easily, a productivity revolution in construction management is becoming a reality. LRTK makes previously high-threshold point cloud technology practical from a field perspective, strongly supporting DX promotion across civil engineering and construction—not only for solar development but for general earthworks. Why not consider introducing visualized earthwork volume management using just a smartphone at your sites?