Drone Point Cloud Surveying for Mega-Solar Construction! RTK Support Eliminates the Need for Ground Control Points

Surveying Challenges at Mega-Solar Sites and the Background for Drone Use

Construction of mega-solar (large-scale photovoltaic) plants requires surveying vast sites that can span tens of hectares and include steep, varied terrain. Traditional manual surveying over wide areas can take several days or more, and working on steep slopes or rough land before grading poses labor and safety challenges. Precise surveying to accurately capture land elevation differences and sunlight conditions is essential for efficient earthworks planning and maximizing generation efficiency. Against this backdrop, drone (unmanned aerial vehicle) surveying has attracted attention in the construction industry in recent years. Drone surveys can acquire large-area topographic data from the air in a short time, providing a countermeasure to the growing shortage of skilled personnel, and initiatives such as the Ministry of Land, Infrastructure, Transport and Tourism’s “i-Construction” promotion have helped drive innovation in surveying operations on large sites like mega-solar projects.

Advantages of Point Cloud Data and the Importance of Survey Accuracy

Drone surveying can generate a set of numerous 3D coordinate points known as point cloud data by analyzing aerial photographs. Point cloud data offers the following advantages:

• Because the entire vast site can be recorded as a high-density 3D point cloud, subtle terrain variations and structures can be captured without omission.

• After acquisition, heights, distances, and slopes at any points can be measured from the data, enabling various analyses without additional field measurements.

• Accurate 3D models and contour maps can be generated from point clouds, allowing overlay comparisons with design drawings and aiding earthworks planning simulations.

• It can be used for construction management tasks such as calculating fill and cut volumes and visualizing construction progress, providing an objective data-driven understanding of site conditions.

• For solar panel layout planning, terrain slopes and surrounding obstacles can be considered to run shading simulations from point clouds, helping optimize power generation efficiency.

However, to fully leverage the usefulness of such point cloud data, survey accuracy must be ensured. For example, if a terrain model has errors of several tens of centimeters, volumetric calculations for earthworks will produce significant discrepancies. Positional errors in panel or pile locations can cause misplacement of components during construction. Civil engineering works typically require centimeter-level accuracy, and the Ministry of Land, Infrastructure, Transport and Tourism’s as-built management standards set allowable errors on the order of ±5 cm. Therefore, point clouds acquired by drones must meet comparable accuracy. Traditionally, establishing this high accuracy required placement of ground control points, but more recently RTK-based methods have emerged. The next section first examines the challenges associated with conventional control points.

Challenges of Ground Control Points in Conventional Drone Surveying

As noted above, to obtain high-precision point cloud data it is necessary to tie the captured images to accurate coordinates. Conventional drone photogrammetry commonly used multiple known-coordinate markers on the ground called ground control points (GCPs) and synchronized them with aerial images. The coordinates of GCPs are measured in advance by GNSS surveying or total station, and during aerial image processing they serve as references for aligning and scaling the entire model.

However, there are the following challenges in installing GCPs:

• On large sites many GCPs are required, and simply installing them and accurately measuring their coordinates can take half a day or more.

• In forests or on steep slopes, installing GCPs can be difficult, and poor footing raises safety risks such as slips or falls for workers.

• Survey personnel entering an active construction site with heavy machinery requires coordination and safety measures, and sometimes the whole site’s operations must be paused.

• If terrain changes due to earthworks, existing GCPs may become unusable, requiring GCPs to be reinstalled for each survey.

• Installing and surveying GCPs requires personnel with specialized knowledge, increasing labor costs.

Thus, although preparing GCPs is necessary to ensure accuracy, the preparation work entails considerable effort and cost. RTK-capable drones, which can minimize or make GCPs unnecessary, are attracting attention as a solution to these challenges. The next section explains the surveying innovations brought by RTK-equipped drones.

Surveying Innovations with RTK-Equipped Drones

RTK stands for Real-Time Kinematic, a technique that enables centimeter-level positioning by correcting GNSS (satellite positioning) errors in real time. RTK-equipped drones carry high-precision GNSS receivers, and by receiving correction data from a local base station or network reference station during flight, they can improve the positional accuracy of each captured photo. This makes it possible to generate point cloud models in accurate coordinates without the many GCPs that were previously essential.

Key benefits (innovations) of RTK-equipped drones include:

• Significant reduction of GCPs: With RTK drones, surveying is possible with little to no placement of ground control points, dramatically reducing pre-survey preparation.

• Maintenance of high accuracy: Even without many GCPs, point cloud data can be acquired with accuracy comparable to traditional methods (horizontal and vertical errors on the order of several centimeters). Only a very small number of check points are needed for accuracy verification.

• Shorter working time: Because on-site preparation is almost unnecessary, the workflow can be completed with flight planning and data processing alone. Surveys that used to take several days can be completed with a single flight (tens of minutes) and a few hours of processing in some cases.

• Cost reduction: Reduced workdays and personnel requirements substantially lower surveying costs. There are reports of drone surveying reducing conventional costs to less than a quarter.

• Improved safety: There is no need for personnel to enter hazardous areas, allowing safe aerial surveying and reducing the risk of occupational accidents associated with surveying.

• High-frequency surveying: The low burden makes it feasible to survey as often as needed, enabling weekly or monthly checks and ad-hoc additional surveys aligned with construction progress.

The advent of RTK drones has dramatically improved surveying efficiency for large-scale mega-solar sites. The next section looks at concrete examples of how the high-precision point cloud data and 3D models obtained in this way can be used in earthworks, pile driving, and construction management.

Use Cases for Earthworks, Pile Driving, and Management in Mega-Solar Projects

On mega-solar construction projects, high-precision data obtained by RTK-equipped drones are being used in many scenarios. Below are main use cases for earthworks, pile driving, and construction management.

Earthworks use: During the earthworks phase, drone surveying is used before construction to capture the as-built terrain and support the drafting of design plans (grading plans). Point clouds can be used to create pre-construction terrain models and, by comparing them with planned design ground elevations, accurately calculate cut and fill volumes. After construction starts, regularly surveying the site with drones allows early detection of deviations from planned cross-sections and tracking of weekly or monthly volume changes. On expansive mega-solar sites it is difficult to understand earthworks progress across the entire site manually, but point cloud data can generate 3D maps that clearly show which areas have been graded according to design. This helps prevent unnecessary over-excavation and enables appropriate allocation of machinery according to progress, improving earthworks efficiency and quality.

Pile driving use: RTK and drone surveying are also powerful for pile-driving operations that support solar panel frames. Normally, accurately placing thousands of piles across a vast site requires survey teams to lay out reference marks and install stakes or markings. Using RTK-equipped devices greatly streamlines this layout process. If pile position coordinate data are prepared on design drawings and loaded into a GNSS-equipped terminal, the terminal can display the real-time deviation between the operator’s current position and the target pile position on site. Workers follow the on-screen guidance and mark the designated position, completing layout much faster and more accurately than before. Satellite positioning works even in low-visibility mountain areas or for nighttime work, making it efficient across large mega-solar sites. After pile driving, drones can re-measure pile heads in 3D to easily inspect whether all piles meet design position and elevation. If pile placement errors are found, corrective measures can be taken immediately, preventing accumulation of errors in later stages and ensuring smooth panel installation.

Construction management use: Point cloud data from drones are extremely useful for construction control and as-built verification. As-built inspections require comparing completed terrain and structures with designs to confirm they are within specified tolerances; high-precision 3D models from drone surveys enable comprehensive as-built checks in a short time. For example, surveying the ground model after earthworks and comparing it with the design model can visualize height and slope discrepancies, eliminating the need for laborious partial measurements. Dedicated software can analyze point cloud data to easily produce site-wide cross-sections and longitudinal/transverse profiles, reducing time spent creating reports and inspection materials.

Furthermore, detailed recorded data from drone surveys facilitate information sharing with clients and stakeholders. Site conditions that are hard to convey with 2D drawings can be intuitively understood using 3D models or orthophotos (top-down composite images), helping all parties share a common understanding. Using point cloud data for progress reports allows distant contractors or investors to view site conditions convincingly. Drone surveying is also useful for material management; for example, scanning stockpiles of soil or crushed stone enables periodic volume measurements to accurately track material consumption and remaining quantities.

After a mega-solar facility enters operation, drones also help streamline inspections. Aerial images can reveal panel contamination or failures, and combining point clouds can monitor shading risks from tree growth nearby, expanding applications in maintenance and management. In this way, point cloud surveying using drones can be applied across all phases of a mega-solar project—from surveying to construction and maintenance—delivering major improvements in both operational efficiency and data accuracy.

Prospects for Point Clouds, 3D Models, and AR Use

With detailed 3D data from drones becoming easier to obtain, expectations are rising for augmented reality (AR) technologies that leverage those data on site. Combining point clouds and 3D models with AR makes it possible to overlay digital design information onto the real world. For example, if a smartphone or tablet is held over a graded site after earthworks, the screen could display the planned equipment layout or design elevation lines, enabling intuitive sharing of the finished appearance that may be hard to grasp from drawings alone. For pile layout, projecting design points onto the ground in AR lets workers place piles at the correct points without confusion. Displaying buried cable conduits in AR after completion can also reduce the risk of accidental damage during future maintenance.

Moreover, such 3D data use extends to machine operation assistance. Machine guidance and machine control technologies, which equip excavators and bulldozers with GPS receivers and 3D design data to display target excavation elevations and slopes on in-cab monitors, are becoming more widespread. Operators can perform accurate cutting and filling following display instructions without visually checking grade stakes. By using 3D models across both humans and machines, construction accuracy and efficiency improve dramatically.

The Ministry of Land, Infrastructure, Transport and Tourism is promoting on-site digital transformation (DX), and it officially introduces low-cost 3D surveying methods that combine smartphone-integrated LiDAR sensors with RTK receivers. Whereas 3D surveying previously required expensive laser scanners or advanced surveying equipment, it is becoming feasible with the simple combination of a smartphone and RTK. For example, by attaching a compact RTK-capable GNSS device to a smartphone to obtain centimeter-level positioning while scanning the surroundings with the phone’s camera or LiDAR, point clouds can be generated on the spot and displayed in AR. These technologies are ushering in an era of “smartphone-only surveying,” where site staff themselves can perform necessary surveys and layout immediately when needed. The next section introduces LRTK, a solution that strongly supports smartphone-based surveying.

Convenience of RTK Data Integration with LRTK and Smartphone-Only Surveying

As described above, drones and RTK have greatly improved surveying efficiency on mega-solar sites, and LRTK further simplifies on-site operations. LRTK is our company’s solution for achieving high-precision positioning and surveying using smartphones. By attaching a high-precision GNSS receiver called the “LRTK Phone” to the back of a smartphone or other mobile device and linking a dedicated LRTK app with a cloud service, anyone can easily use centimeter-level positioning, point cloud measurement, and AR features.

With the LRTK system, you can perform additional measurements and layout on a smartphone in the same coordinate system as the orthophotos and point cloud models created by RTK-capable drones. For example, if you want to mark an arbitrary point on a 3D model created by drone surveying, you can import that coordinate into the LRTK app and simply walk the site following guidance on the smartphone screen to reach the exact location. For pile driving and layout tasks, LRTK’s coordinate guidance function enables quick identification of reference points or pile positions without specialized surveying equipment. Point cloud data and design drawings can be displayed on a smartphone via the cloud, allowing confirmation of the planned completion image through AR. These features are provided through an intuitive app UI, so on-site staff without surveying expertise can use them easily.

LRTK is also strong in mountain sites where internet connectivity is unavailable. The LRTK Phone supports augmentation signals from Japan’s quasi-zenith satellite system “Michibiki,” allowing it to receive correction information directly from satellites and maintain high-precision positioning even outside cellular coverage. In remote, trail-less forest areas or distant mega-solar construction sites, LRTK enables real-time, accurate position awareness during work.

In this way, LRTK is highly compatible with data obtained from drones and contributes to further labor savings and sophistication of surveying and construction management on mega-solar sites. By surveying wide areas with RTK-capable drones and using LRTK for detailed measurements, pile-driving guidance, and AR verification, tasks that were previously outsourced or left to heavy machinery can be handled by on-site personnel themselves. As a result, not only will schedules and costs be reduced, but on-site decision-making speed will also improve. We expect the trend toward smartphone-only surveying to expand across the civil engineering and construction industries, not just in mega-solar construction. If you are interested in these new surveying methods, please also visit the [LRTK product page](https://www.lefixea.com/phone). The combination of smartphones and RTK technology could become a powerful force that changes on-site practices.