Using Point Cloud Heat Maps for Mega-Solar Earthworks – Streamlining Earthwork Volume Management

Challenges of earthwork volume management in mega-solar site development

Construction of mega-solar (large-scale solar power plants) requires extensive site earthworks. Securing flat land is particularly difficult, and when sites are planned in mountainous or sloped areas, large-scale cut-and-fill earthworks are required to level the ground for solar panel installation. In this context, "earthwork volume management" becomes critically important.

The volumes of soil handled in mega-solar earthworks are orders of magnitude larger than typical projects; combined cut-and-fill can easily reach tens of thousands of cubic meters. Managing such quantities accurately requires sophisticated planning and meticulous on-site supervision. Misestimating earthwork volumes can lead to surplus or shortage of soil moved by hundreds of dump trucks, resulting not only in economic losses but also environmental impacts.

Mistakes in estimating cut or fill volumes can cause various problems. For example, if more soil is excavated than planned, disposal costs for surplus soil increase. Conversely, if there is a shortage of fill material, costs arise from sourcing soil externally. Excessive removal of slopes beyond design can increase the risk of landslides and negatively affect the surrounding environment, so accurate volume planning and construction control are indispensable.

Errors in earthwork estimation also directly affect schedules and budgets. Delays in earthworks impact subsequent foundation and panel installation phases, influencing overall project progress. The accuracy of earthwork volume management for mega-solar site development is therefore an extremely important issue not only for quality and safety but also for schedule compliance and cost control.

Traditional methods and their limitations (volume calculations, field surveying, recording errors, etc.)

Traditionally, earthwork volume management involved labor-intensive surveying and calculation. Pre- and post-construction field surveys were conducted, and elevation data obtained were used to create cross-sections or meshes on drawings to calculate volumes. Surveyors would traverse slopes and sites and measure heights at several dozen points to estimate earthwork quantities.

However, these traditional methods have several limitations. The main issues are:

• Because the number of surveyable points is limited, fine irregularities in the terrain are easily overlooked, often causing errors in volume calculation.

• Surveying large areas manually requires significant time and personnel, making high-frequency surveys (daily or weekly) practically difficult.

• Errors in transcribing survey data or calculation mistakes can cause discrepancies in reported earthwork volumes.

• Survey results are typically shared as numerical tables or cross-section drawings, making it difficult to intuitively grasp the overall site situation and hard to establish a common understanding among stakeholders.

Thus, traditional methods tend to make earthwork volume management person-dependent, and it is difficult to achieve both efficiency and accuracy.

Benefits of using point cloud data and converting it into heat maps

A recently emerging solution to these challenges is earthwork volume management using 3D point cloud data. Point cloud data are three-dimensional datasets that represent terrain and structures as a collection of countless points, acquired by laser scanners or photogrammetry. Using high-density point clouds that cover the ground surface in detail, you can precisely reproduce the current terrain model. While conventional surveys used only several dozen points, point cloud data can reach millions of points, enabling detection of fine terrain features without omission. This allows earthwork volume calculations to be performed with greater accuracy than before.

By creating a current terrain model from point cloud data and comparing it with the designed terrain, differences in cut and fill can be determined across the surface. The result visualized with colors is a "soil volume heat map." For example, areas higher than the design (excessive fills) can be shown in red and lower areas (over-excavated spots) in blue, visually indicating where and by how much the ground level deviates, so you can immediately see how much soil needs to be moved and where.

The advantage of heat maps is that they allow intuitive understanding of site conditions. Where previously surpluses or shortages in soil had to be inferred from numbers or cross-sections, a colored map makes them clear at a glance. This enables even less-experienced staff to identify problem areas easily and facilitates smoother information sharing among stakeholders. Since the data originate from point clouds, quantity calculations are highly accurate and subtle undulations are not missed. As a result, reliable data support decisions on plan revisions or additional work, improving construction management quality.

In fact, verification comparing volumes calculated from point clouds with volumes calculated by traditional cross-section methods has shown differences within 1%, confirming sufficient accuracy. At the same time, processing time can be drastically reduced, making point-cloud-based earthwork management an approach that balances quality and efficiency.

At one site, introducing point clouds reportedly reduced the personnel and time required for surveying by more than half compared to conventional methods. In the construction industry, where labor shortages are severe, point cloud technology’s ability to manage earthwork efficiently with fewer personnel has significant value from a work-style reform perspective.

Acquisition methods using smartphones and drones, and practical examples

How are such point cloud data acquired? One representative method is photogrammetry using drones (UAVs). Small unmanned aerial vehicles equipped with cameras photograph the entire site from above, and dedicated software generates a 3D point cloud model from the multiple aerial images. Even for expansive mega-solar sites, current terrain can be captured in a short time, and steep slopes can be measured safely without personnel entering hazardous areas. On sites that implemented drone surveying, tasks that used to take more than a day for surveying and volume calculations were completed in a few hours, demonstrating significant efficiency gains.

Recently, methods using smartphones equipped with LiDAR sensors to obtain point clouds easily have also begun to spread. With modern smartphones and dedicated apps, you can scan surrounding terrain and generate 3D point clouds. For example, a site supervisor can scan a small fill or a pile of excavated soil with a smartphone and instantly calculate the volume. The ability for field staff to routinely acquire terrain data without large-scale equipment like drones is a major advantage.

Depending on the use case, drones and smartphones can be used complementarily. Drones are suitable for capturing wide-area terrain, while smartphone scans are powerful for detailed checks and frequent progress monitoring. In either method, acquired point cloud data are processed and compared using dedicated software or cloud services, and used as soil volume heat maps and numerical reports. The flexibility to choose measurement methods according to site conditions is a strength of digital measurement.

Note that while drones can measure wide areas at once, they may be subject to aviation regulations and weather constraints. Smartphone measurement is convenient on-site but has a limited measurable range and is therefore unsuitable for very large sites. Considering their respective strengths and weaknesses, it is important to select and combine the optimal methods for each site.

With the Ministry of Land, Infrastructure, Transport and Tourism promoting the i-Construction initiative, ICT use in earthworks (so-called "ICT earthworks") is becoming more widespread year by year. Photogrammetry by drone and as-built management using 3D laser scanners have already shown results on many sites, and such advanced technologies are increasingly being introduced in mega-solar earthworks. Using point cloud heat maps for construction management is no longer a special advanced case but is becoming a standard on-site method.

Furthermore, the Ministry of Land, Infrastructure, Transport and Tourism actively promotes the introduction of 3D technologies into as-built management, and it is suggested that submission of 3D deliverables such as point cloud data may become standard in the future. As DX accelerates across the industry, becoming familiar with these workflows early on will also enhance competitiveness.

Effects of difference visualization with heat maps on construction decisions

Visualization through soil volume heat maps has a significant impact on on-site decision-making. For example, at one mega-solar site, the current condition was scanned by drone at the end of each day and the heat map updated; the map was then used for work instructions at the next morning’s schedule meeting. By checking the heat map, it is immediately clear which areas have been leveled to the design elevation and where substantial surpluses or shortages remain. Site supervisors can quickly issue precise instructions—prioritize cutting in red areas (excessive fills) and add soil to blue areas (over-excavated low spots). Data-driven, rapid decisions improve site efficiency.

Because the magnitude of differences can also be quantified numerically, future required work volumes can be estimated quantitatively. Decisions such as "if we remove X more dump trucks’ worth of soil, we will reach the design elevation" become data-based, improving the accuracy of equipment and dump truck scheduling plans. Tracking daily changes with heat maps makes it possible to detect early whether earthworks will finish within the planned schedule and to take proactive measures such as increasing personnel or revising the schedule as needed.

Moreover, visualizing as-built differences with heat maps is useful for quality control. Excessive excavation or insufficient fill during construction can be detected at a glance, allowing early correction of variations in the finish. This helps eliminate nonconforming areas before final inspection, reducing rework and material waste. Real-time difference visualization accelerates the site PDCA cycle and enables efficient, waste-free construction.

This data-driven management has produced concrete results such as significant reductions in earthwork duration and cost savings. Better visibility of the entire process reduces idle time and enables optimal allocation of heavy machinery and personnel. Thus, heat map utilization directly contributes to shorter schedules and lower costs.

Cloud sharing and strengthening collaboration with management departments

To maximize the benefits of point cloud data and heat maps, sharing information via the cloud is also important. Previously, survey results were shared on paper drawings or spreadsheets, but uploading 3D data to the cloud allows office-based management staff and clients to share site conditions in real time. Services now allow those without specialized software to view point cloud models and heat maps in a web browser, making it possible for everyone to confirm the same up-to-date information.

Sharing site data in the cloud enables headquarters construction managers and engineers to understand site conditions and issue instructions without traveling to the site. For example, headquarters can check the progress of earthworks in detail and rapidly adjust construction plans as needed. Accumulating data in the cloud also streamlines progress history management and the creation of reports. Stronger collaboration between site and management departments fosters a sense of unity in supporting the project across the organization and contributes to improved construction quality and safety.

The advantage of remote site visibility was especially evident during movement restrictions such as those imposed by the COVID-19 pandemic. Being able to confirm as-built data online without visiting the site has helped establish a new style of construction supervision.

Also, cloud-based 3D models and heat maps are useful for explaining progress to clients and local residents. Construction status that was difficult to convey with numbers alone can be more easily understood when presented visually, improving external credibility.

Acquired 3D data can also be used to update CIM models (3D construction design models) and create as-built drawings, allowing technical staff both inside and outside the company to leverage the data. Keeping a time-series record of terrain changes can be useful for maintenance inspections after completion and as verification material in the unlikely event of a landslide.

Furthermore, quantities derived from point clouds serve as objective evidence, smoothing reporting of progress and payment settlement with clients. Disputes between site and management over survey results have occurred in the past, but visual data that everyone accepts can help avoid unnecessary trouble.

Proposal for smartphone-only point cloud scanning with LRTK and AR heat map utilization

Finally, as a practical way to easily implement point cloud heat map utilization on-site, we introduce a solution called LRTK. With LRTK, a single smartphone can complete everything from high-precision 3D point cloud measurement to creation of soil volume heat maps. It requires no dedicated surveying equipment or large systems and features an intuitive interface that site technicians can operate easily. No complicated software operation or specialized knowledge is necessary—measurements are completed simply by following on-screen guidance. With minimal training, anyone can use it, facilitating smooth on-site adoption.

LRTK consists of a small device attached to a smartphone and an app, combining GNSS (satellite positioning) and the smartphone’s built-in LiDAR to acquire high-accuracy point clouds. Volumes and heights are automatically calculated on-site from the acquired point cloud, and difference heat maps relative to the design can be generated with a single tap. Moreover, the generated heat map can be displayed in AR on the smartphone screen and overlaid on the actual ground. For example, when you point the smartphone at the ground, red and blue color distributions appear on the real surface, allowing you to match where and how many centimeters (inches) higher or lower the surface is in the real view.

Because point clouds can be obtained in high-accuracy absolute coordinates, precise overlay with design CAD data and boundary lines—which was difficult using traditional methods—is now easy. Measurement results taken on different days can be managed in the same coordinate system, making daily progress comparisons and evaluation of quantities straightforward.

With these advanced features, it is possible to verify as-built conditions on-site instantly and identify all required corrective areas. Measurement data are automatically saved to the cloud and can be shared via a URL, allowing remote supervisors and partner companies to view 3D models and heat maps.

Currently, from major general contractors to regional construction firms, the move to use tools like LRTK for site DX is spreading. As high-precision point cloud handling becomes accessible to everyone, a productivity revolution in construction management is becoming realistic.

LRTK makes point cloud technology—which used to have high barriers to entry—easy to use from a site perspective, and strongly supports DX (digital transformation) across civil engineering construction, not just for mega-solar earthworks. Why not leverage the latest technology to streamline earthwork volume management and achieve safer, smoother site operations?