Solar Construction Earthwork Volume Management Made Easy with a Smartphone! Visualizing Cut-and-Fill Is Changing the Jobsite

In recent years, innovative earthwork volume management methods using smartphones have been attracting attention on solar construction sites. Managing cut-and-fill generated by large-scale site development is a critical task that can determine the success or failure of a project. However, traditional methods have relied heavily on huge amounts of labor and experience, leaving room for mistakes and rework. This article explains in detail the latest trends in simple, high-precision earthwork volume management using smartphones and how visualizing cut-and-fill (visualization) is producing dramatic effects on site.

The importance and challenges of earthwork volume management in solar construction

Large-scale land development is indispensable for building solar power plants (especially for mega-solar site development). In cases planned in mountainous or sloped areas where it is difficult to secure flat land, large-scale cut-and-fill (earthworks) are performed to level the ground for solar panel installation. Naturally, the amounts of earth handled are enormous, and it is not uncommon for totals to reach tens of thousands of cubic meters. Accurately managing such large volumes of soil requires meticulous planning and on-site supervision, making "earthwork volume management" a crucial issue for the success of solar construction.

If estimates or management of earth volumes are incorrect, various problems can arise. For example, if more soil is excavated than planned, disposal costs for surplus soil increase; conversely, if backfill soil is insufficient, additional costs arise to procure soil externally. Excessive cutting of slopes beyond design can also increase the impact on the surrounding environment and the risk of landslides. Therefore, the accuracy of earthwork planning and strict on-site volume management are required. In addition, miscalculation of earthwork volumes directly affects schedules and budgets. If earthworks do not progress as planned, subsequent foundation and panel installation work will be affected, potentially causing delays and cost overruns for the entire project. 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 problems

Traditionally, earthwork volume management at development sites has been conducted by time-consuming field surveys and volume calculations. Surveyors walk the site before and after construction, measuring heights at dozens of locations on slopes and within the site. The elevation data from those points are used to create cross-sections or mesh models on drawings to calculate cut and fill volumes—this is the common procedure. However, these largely analog methods have several limitations. Key issues include:

• Limited accuracy due to few measurement points: Manual surveying can only obtain a limited number of points, making it easy to miss fine terrain undulations. As a result, there is a risk of errors in volume calculations.

• Cannot frequently measure wide areas: Surveying large sites by manpower requires time and personnel, making it impractical to measure the current state at high frequency such as daily or weekly. This prevents close tracking of progress and makes it difficult to manage earth volumes using always up-to-date information.

• Risk of transcription and calculation errors: When notes are taken by hand or data are entered into spreadsheets manually, numbers can be transcribed incorrectly or calculations can be mistaken. This can lead to discrepancies in reported earth volumes.

• Information sharing is not intuitive: Survey results are often presented as lists of numbers or cross-sections, formats that make it hard to intuitively grasp the overall site situation. As a result, it can be difficult to establish a common understanding among field staff, management, and the client about "where and how much soil is in surplus or deficit," leading to time-consuming communication.

Because of these limitations, traditional methods tend to be person-dependent, and it is difficult to achieve both efficiency and accuracy in practice.

Visualizing cut-and-fill using point cloud data

To solve these problems, earthwork volume management using 3D point cloud data has been gaining attention in recent years. A point cloud is 3D data representing the shape of terrain or structures as a collection of countless points, obtained by laser scanners or photogrammetry. Using high-density point clouds that cover the ground surface in detail makes it possible to reproduce the current terrain model with extremely high precision. While traditional surveys could at best obtain elevation information at a few dozen points, point cloud data allow understanding of terrain undulations down to millions of points. This significantly improves the accuracy of volume calculations.

By overlaying the acquired current point cloud terrain model with the planned ground model, you can extract, area by area, the differences showing where and how much cut or fill is required. The visualization of those differences by color according to height differences is called a "volume heat map." For example, areas higher than the design surface (where excess fill remains) can be shown in red, while areas that have been over-excavated and are too low can be shown in blue, indicating height deviations by color. This allows anyone to intuitively see where and how much earth needs to be cut or filled at a glance.

The greatest advantage of heat map displays is that they make site conditions intuitively understandable. Terrain surpluses and deficits that formerly had to be imagined by interpreting numerical data or cross-sections become clear simply by looking at a color-coded map. Less experienced staff can visually grasp problem areas more easily, improving the ability of all stakeholders to share the situation. Because point-cloud-based data are used, volume calculations are highly accurate and reflect subtle undulations that traditional methods might have missed. This provides reliable data to support decisions on whether plan adjustments or additional earthworks are necessary, improving the quality of construction management.

In practice, comparisons between volumes calculated from point cloud data and those calculated by the traditional cross-section method have shown differences of less than 1%, confirming the high accuracy of point cloud measurement. At the same time, work time can be significantly reduced, making point-cloud-based earthwork volume management a new method that balances quality and efficiency. Some sites report that introducing point cloud technology reduced the personnel and time required for surveying to less than half of what was previously needed. In the construction industry, where labor shortages are becoming more severe, the ability of point cloud technology to enable efficient earthwork volume management with fewer personnel has significant value from a work-style reform perspective.

Easy point cloud acquisition using drones and smartphones

So how can such high-density point cloud data be acquired on site? One representative method is drone (UAV) photogrammetry. A small unmanned aircraft equipped with a camera captures multiple images from above the whole site. Specialized software analyzes those images to generate a 3D point cloud model of the current terrain. Even for large solar power plant sites, you can quickly capture the whole current situation, and steep slopes can be measured safely without personnel entering hazardous areas. Sites that adopted drone surveying reported dramatic efficiency gains—for example, surveying and earthwork calculation tasks that used to take a day or more were completed in a few hours.

More recently, methods that allow easy point cloud acquisition using smartphones equipped with LiDAR sensors have begun to spread. By installing a dedicated app on a modern smartphone and scanning the surrounding terrain, you can create a 3D point cloud on the spot. For example, a site supervisor can quickly scan a small mound of fill or a pile of excavated soil with a smartphone and instantly calculate the volume. The fact that site staff can routinely and conveniently acquire terrain data without the large-scale equipment required for drones is a major advantage.

Depending on site conditions and objectives, it is also possible to use drones and smartphones in combination. Drones are suitable for capturing wide areas at once, while quick smartphone scans are effective for detailed checks and frequent progress monitoring. Point cloud data obtained by either method can be processed and compared using dedicated software or cloud services to generate volume heat maps and output numerical reports. The ability to flexibly choose the optimal measurement method for each site is a major strength of digital measurement.

Of course, each method has caveats. Drones can survey wide areas at once but are subject to aviation regulations and weather conditions. Smartphone measurements are attractive because anyone can use them quickly, but their coverage per scan is limited, making them unsuitable for surveying extremely large sites all at once. Considering each method’s strengths and weaknesses, it is important to select and combine approaches that best fit the site scale and conditions.

The national Ministry of Land, Infrastructure, Transport and Tourism’s push for i-Construction has also been a tailwind, and the use of ICT in earthworks (so-called "ICT earthworks") is becoming more widespread year by year. Photogrammetry by drone and as-built management by 3D laser scanners already have track records at many sites, and the adoption of such advanced technologies in solar power plant site development is progressing. Point cloud data heat-map-based construction management is no longer a special advanced case but is becoming a standard method on sites. The ministry is actively promoting the introduction of 3D technologies into as-built management, and in the future it may become common practice to submit 3D data such as point clouds as deliverables. As digital transformation (DX) accelerates across the construction industry, familiarizing yourself with digital measurement early on will help improve future competitiveness.

Speeding up on-site decisions with heat map use

Visualizing with volume heat maps also greatly speeds up decision-making on site. At one solar power construction site, the team scanned the current condition by drone at the end of each workday, updated the heat map, and used the latest map for morning briefings and schedule meetings the next day. By looking at the heat map, it is immediately clear which areas have been leveled to design height and which areas still have significant surpluses or deficits. The site supervisor can instantly give specific instructions—for example, to prioritize cutting the red areas (where excess fill remains and heights are too high) with heavy equipment, or to add soil to the blue areas (where over-excavation has made the ground too low). Decisions that previously depended on intuition or experience become data-driven, accurate choices, directly improving site productivity.

In addition, heat maps allow differences to be quantified numerically, so required future work can be estimated quantitatively. Decisions like "if we remove X more dump truck loads of soil, we will reach the design elevation" can be made based on data, improving the accuracy of heavy equipment scheduling and dump truck arrangements. By tracking terrain changes daily with heat maps, you can quickly determine whether earthworks are likely to finish within the planned schedule and take preemptive actions such as increasing personnel or revising the schedule when necessary.

From a quality control perspective, visualizing as-built conditions with heat maps is also useful. If excessive excavation or insufficient fill occurs during construction, it can be detected at a glance and corrected early, preventing uneven finishes. This reduces rework and prevents material waste before final inspections, reducing the chance of failing final acceptance. In this way, real-time visualization of differences accelerates the site PDCA cycle and enables efficient construction with minimal waste.

Data-driven management has also been reported to produce major reductions in overall schedules and costs for earthworks. With a clearer overall picture, idle time is reduced and heavy equipment and personnel deployment can be optimized. Thus, heat map use directly contributes to shorter schedules and lower construction costs.

Cloud integration for information sharing and remote management

To fully leverage point cloud data and heat maps, cloud-based information sharing is indispensable. Traditionally, survey results were exchanged on paper drawings or Excel sheets, but uploading 3D data to the cloud allows management staff in the office and the client to share the site situation in real time. Services have emerged that let even those without specialized software view point cloud models and heat maps via a web browser, creating an environment where everyone can check the same up-to-date information.

Sharing site data on the cloud means that headquarters construction managers and engineers can grasp the situation and give instructions without traveling to the site. For example, headquarters can continuously monitor development progress and promptly revise construction plans as needed—enabling rapid follow-up. Also, accumulated cloud data streamlines progress history management and report preparation. Tight coordination between the field and management departments through shared data fosters an organizational sense of unity in supporting the project and contributes to improved construction quality and safety.

The advantage of remotely monitoring the site proved particularly effective under movement restrictions during the COVID-19 pandemic. Being able to confirm as-built data online without visiting the site has led to new styles of supervision work. Cloud-based 3D models and heat maps are also useful for explaining construction to owners and local residents. Visual materials make construction status easier to understand than numbers or technical terms alone, helping build external trust.

Furthermore, the acquired 3D data can be used to update CIM models (3D design models for construction) and create as-built documentation. Because internal and external engineers can utilize the data, consistent information management across the lifecycle from design to construction and maintenance becomes possible. Recording terrain changes over time can aid post-completion maintenance inspections or serve as verification material in the event of a landslide. Also, quantities derived from point clouds serve as objective evidence, smoothing progress reporting and settlement tasks with clients. Where disagreements over survey interpretations once occurred between the field and management, clear visual data that anyone can understand helps prevent unnecessary disputes.

Smartphone RTK surveying and point cloud heat maps for smart construction management [LRTK]

Finally, as a practical solution that makes the point cloud heat map approach easily applicable on site, we introduce LRTK. With LRTK, a single smartphone alone can perform the entire process from high-precision RTK positioning-based 3D point cloud measurement to creation of earthwork volume heat maps. No specialized heavy equipment is required, and the system’s simple, intuitive operation is a major feature for field technicians. Users do not need to learn complicated software or acquire surveying expertise—just follow the on-screen guidance on the smartphone to complete measurements. With brief training, anyone can master it, which facilitates smooth adoption on sites.

LRTK consists of a small device attached to a smartphone and a dedicated app, combining high-precision GNSS satellite positioning with the smartphone’s built-in LiDAR scanner to acquire point cloud data with millimeter-level accuracy. It automatically calculates volumes and elevations from the acquired point cloud on the spot and can generate a design-difference heat map with a single tap. Another major advantage is that the generated heat map can be displayed on the smartphone in AR. When you point the smartphone at the ground, colored overlays of red and blue appear on the real surface, letting you match which locations are centimeters higher or lower than the design with the real-world view.

Because LRTK always acquires point cloud data in a high-precision absolute coordinate system, accurate overlay with design CAD data and boundary lines—previously difficult—becomes easy. Survey results from multiple days can be managed in the same coordinate system, simplifying day-by-day progress comparisons and calculation of measured quantities. These advanced features allow you to verify as-built conditions immediately on site and comprehensively identify areas requiring rework. Measurement data are automatically saved to the cloud, and sharing a URL lets remote supervisors and partner companies view 3D models and heat maps online.

From major general contractors to regional construction firms, movements to introduce smartphone RTK surveying and point cloud utilization tools like LRTK are spreading as part of site DX (digital transformation) efforts. As anyone can easily handle high-precision 3D point cloud data, a productivity revolution in construction management is becoming tangible. LRTK makes point cloud technology—which used to have high barriers to entry—user-friendly from a site perspective, strongly supporting DX in civil engineering and not just solar site development. Why not consider introducing visualized earthwork volume management with just a smartphone to your company’s sites?