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

Challenges of Earthwork Volume Management in Mega-Solar Site Development

Constructing a mega-solar (large-scale solar power plant) facility requires extensive site development (civil earthworks). Securing a flat site is often difficult, especially when planned in mountainous or sloped areas, where large-scale cut-and-fill operations are needed to level the ground for solar panel installation. A critical factor in this process is accurate earthwork volume management.

The volumes of soil handled in mega-solar earthworks are enormous; combined cut-and-fill volumes often reach tens of thousands of cubic meters. Managing such quantities accurately requires advanced planning and meticulous onsite supervision. Misestimating earthwork volumes can lead to excess or insufficient truckloads of soil being moved, causing not only financial losses but also environmental impacts.

Errors in estimating cut or fill volumes can create various problems. For example, if more soil is excavated than planned, disposal costs for surplus soil increase. Conversely, if there is a shortage of backfill material, procuring soil from offsite incurs additional costs. Over-excavating slopes beyond design can raise the risk of landslides and adversely affect the surrounding environment. Therefore, precise earthwork volume planning and construction management are indispensable.

Miscalculations in earthworks also directly affect schedules and budgets. Delays in earthworks impact subsequent foundation work and the entire panel installation process, influencing overall project progress. The accuracy of earthwork volume management in mega-solar site development is thus a critical issue not only for quality and safety but also for schedule adherence and cost control.

Conventional Methods and Their Limitations (volume calculations, onsite surveying, recording errors, etc.)

Traditionally, earthwork volume management has involved labor-intensive surveying and calculations. The common practice is to conduct on-site surveys before and after construction, generate cross-sections or meshes from the elevation data, and calculate volumes from the drawings. Surveyors would traverse slopes and the site, measuring heights at several dozen points to estimate volumes.

However, these conventional methods have several limitations. Key issues include:

• Because the number of measurable points is limited, fine surface irregularities can be overlooked, leading to errors in volume calculation.

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

• Transcription errors or calculation mistakes in survey data can introduce discrepancies in reported volumes.

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

As a result, conventional methods tend to be person-dependent, making it difficult to achieve both efficiency and accuracy in earthwork volume management.

Benefits of Using Point Cloud Data and Heat Mapping

A recently noted solution to these challenges is earthwork volume management using 3D point cloud data. Point cloud data are 3D datasets representing terrain and structures as a vast collection of points, acquired via laser scanners or photogrammetry. High-density point clouds that cover the ground surface comprehensively can reproduce the current terrain model with great precision. While traditional survey methods measured only several dozen points, point cloud datasets can contain millions of points, capturing even subtle terrain details and enabling more accurate volume calculations than before.

By creating a current terrain model from point cloud data and comparing it with the design terrain, differences in cut and fill can be captured spatially. Visualizing these differences with color coding produces an "earthwork heat map." For example, areas higher than the design (excess fill) can be colored red and areas lower than the design (over-excavated) can be colored blue, allowing users to instantly see where and how much earth needs to be moved.

The advantage of heat maps is that they make site conditions intuitively understandable. Shortages or surpluses that used to be inferred from numbers and cross-sections become clear at a glance with a color-coded map. This makes it easier even for less experienced staff to identify problem areas and facilitates smooth information sharing among stakeholders. Because the data are derived from point clouds, quantity calculations are highly accurate and small surface variations are not overlooked. As a result, planners and managers gain reliable data to support decisions about plan adjustments or additional work, improving construction management quality.

In verification comparisons between volumes calculated from point clouds and volumes calculated by traditional cross-section methods, differences have been found to be within 1%, confirming sufficient accuracy. At the same time, work time can be dramatically reduced, making point cloud-based volume management an approach that balances quality and efficiency.

At one site, introducing point clouds reportedly reduced the manpower and time required for surveying by more than half compared to traditional methods. In a construction industry facing severe labor shortages, point cloud technology enables efficient earthwork management with fewer people, contributing significantly to improved workstyles.

Acquisition Methods Using Smartphones and Drones, and Examples

How is this point cloud data captured? One representative method is photogrammetry using drones (UAVs). A small unmanned aerial vehicle equipped with a camera photographs the entire site from above. Specialized software generates a 3D point cloud model from the collected aerial photos. Even very large planned mega-solar sites can have their current terrain captured in a short time, and steep slopes can be measured safely without personnel entering hazardous areas. Sites that introduced drone surveys have reported substantial efficiency gains—for example, survey and volume calculation tasks that used to take more than a day can now be completed in a few hours.

More recently, methods for easily acquiring point clouds using smartphones equipped with LiDAR sensors have started to spread. With the latest smartphones and dedicated apps, you can scan surrounding terrain and convert it into a 3D point cloud. For example, a site supervisor can scan a small embankment or spoil heap with a smartphone and immediately calculate its volume. The ability for site staff to collect terrain data routinely 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 extensive terrain, while smartphone scans are effective for detailed checks or frequent progress monitoring. In either method, acquired point cloud data are processed and compared using specialized software or cloud services and used as earthwork heat maps or numerical reports. The flexibility to choose the measurement method according to site conditions is one of the strengths of digital measurement.

Note that drones can measure large areas at once but are subject to aviation regulations and weather conditions. Smartphone measurements are convenient on site but have a limited measurement range, making them unsuitable for very large sites. Considering the strengths and weaknesses of each, it is important to select and combine the optimal methods for the site.

With the MLIT-promoted i-Construction initiative, ICT use in earthworks (so-called "ICT earthworks") is being adopted more widely each year. Photogrammetry using drones and 3D laser scanner-based as-built management have already produced results at many sites, and the adoption of such advanced technologies for mega-solar site development is progressing. Using point cloud heat maps for construction management is no longer an exceptional advanced case but is becoming a standard approach on site.

Furthermore, the MLIT is actively promoting the introduction of 3D technologies into as-built management, and there is a possibility that submission of 3D deliverables such as point cloud data could become standard in the future. As DX accelerates across the industry, gaining familiarity with these technologies early on will also help improve competitiveness.

Effects on Decision-Making through Difference Visualization with Heat Maps

The "visualization" enabled by earthwork heat maps has a major impact on onsite decision-making. For example, at a certain mega-solar site, the current terrain is scanned by drone at the end of each day to update the heat map, which is 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 which areas still have large surpluses or deficits. Site supervisors can promptly issue precise instructions—prioritizing cutting of red areas (excess fill) with heavy machinery and adding soil to blue areas (over-excavated)—based on the map. Data-driven, rapid decisions improve site efficiency.

Because the magnitude of differences can also be quantified, required future work volumes can be estimated objectively. For example, decisions like "If another X truckloads of soil are hauled out, the design elevation will be reached" can be made based on data, improving the accuracy of arrangements for heavy equipment and dump trucks. By tracking daily changes with heat maps, it becomes possible to identify early whether earthworks will be completed within the planned schedule and to proactively respond by increasing personnel or revising the schedule if necessary.

Moreover, visualizing as-built differences with heat maps is beneficial for quality control. Excessive excavation or fill shortages can be detected at a glance during construction, allowing early correction of variations in finishing. This helps eliminate areas that would fail final inspection, reducing rework and material waste. In this way, real-time difference visualization accelerates the PDCA cycle on site and enables efficient, waste-free construction.

Such data-driven management has also produced substantial reductions in earthwork duration and costs. Improved overall schedule visibility reduces idle time and optimizes the allocation of machinery and personnel. Thus, heat map utilization directly contributes to shorter construction periods and cost savings.

Cloud Sharing and Strengthening Coordination with Management Departments

To maximize the benefits of point cloud data and heat maps, sharing information via the cloud is also important. Traditionally, survey results were shared via paper drawings or spreadsheets, but uploading 3D data to the cloud allows management staff and clients in the office to share site conditions in real time. Services have emerged that let users view point cloud models and heat maps in a web browser even if they do not have specialized software, creating environments where everyone can access the same up-to-date information.

Sharing site data via the cloud allows headquarters construction managers and engineers to understand conditions and issue instructions without traveling to the site. For example, headquarters can monitor development progress, continuously check intermediate states, and promptly revise construction plans as needed. Accumulating data in the cloud also streamlines progress history management and report generation. Stronger collaboration between site and management departments builds a sense of unity across the organization, contributing to improved construction quality and safety.

The advantage of remotely understanding site conditions proved useful during mobility restrictions such as during the COVID-19 pandemic. Being able to check as-built data online without visiting the site has established a new style of construction supervision.

Using cloud-hosted 3D models and heat maps also helps explain progress to clients and local residents. Visual materials convey site conditions more clearly than numbers alone, improving external trust and understanding.

Additionally, acquired 3D data can be used to update CIM models (3D construction design models) and create as-built drawings, enabling broad use by engineers both inside and outside the company. Recording terrain changes over time can serve as useful documentation for maintenance inspections after completion or for verification in case of landslide incidents.

Point cloud-derived progress quantity data also serve as objective evidence, smoothing progress reporting and settlement with clients. In the past, disagreements sometimes arose between site and management over survey results, but visual data that everyone accepts can help avoid unnecessary disputes.

Proposal: Smartphone-Only Point Cloud Scanning with LRTK and AR Heat Map Utilization

Finally, to make the point cloud heat map approach easy to apply on site as described above, we introduce a solution called LRTK. With LRTK, a single smartphone can complete the entire workflow from high-precision 3D point cloud measurement to earthwork heat map creation. It does not require dedicated surveying equipment or large systems and is characterized by an intuitive, simple operation that site technicians can use. No complicated software skills or specialized knowledge are needed—measurements can be completed by following prompts on the smartphone screen. 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 positioning information with the smartphone's built-in LiDAR to obtain high-accuracy point clouds. Volumes and heights can be automatically calculated on the spot from the acquired point clouds, and difference heat maps against the design can be generated with one tap. Generated heat maps can also be displayed in AR on the smartphone screen and overlaid on the ground in the field for verification. For example, holding up the phone can reveal red and blue overlays on the actual ground, letting users match the visualized deviations (in centimeters) to the real scene.

Because point clouds can be acquired in high-accuracy absolute coordinates, it becomes easy to accurately overlay them with design CAD data or boundary lines—something that used to be difficult. Measurements taken on different days can be managed in the same coordinate system, simplifying daily progress comparisons and evaluation of measured quantities.

These advanced features allow immediate on-site verification of as-built shapes and ensure that all necessary corrective work is identified. Measurement data are automatically saved to the cloud, and sharing a URL allows remote supervisors and subcontractors to check the 3D model and heat map.

Currently, from major general contractors to local construction firms, the use of tools like LRTK is spreading as part of site DX initiatives. As anyone can more easily handle high-precision point clouds, a productivity revolution in construction management is becoming realistic.

LRTK makes point cloud technology—which used to be difficult to adopt—practical from the site perspective, strongly supporting DX across civil construction, not just in mega-solar site development. Consider leveraging the latest technologies to streamline earthwork volume management and realize safer, smoother site operations.