4 Steps to Use Drone Surveying to Verify Pile Positions at Solar Power Plants

In the construction of solar power plants, the positions of the piles that support the racking have a major impact on construction quality. If pile positions deviate from the design, they can affect rack alignment, panel layout, cable routes, drainage plans, and the widths of access walkways, potentially resulting in rework in later stages. Especially on large prepared sites or sloped terrain, checking pile alignments one by one from the ground makes it difficult to grasp overall displacement or row irregularities, placing a heavy burden on site personnel.

One practical method is drone surveying of solar power plants. By recording the site from above with drones and organizing the data into orthophotos, point clouds, and materials close to as-built drawings, it becomes easier to verify the relative positions of piles across the site. However, drone surveys are not万能 (not万能?)....

Table of Contents

• Why Drone Surveying Is Useful for Verifying Pile Locations at Solar Power Plants

• Step 1 Organize the design coordinates and site conditions and determine the scope of verification

• Step 2 Set up reference points and shooting conditions before flight

• Step 3 Record the positional relationships around the stakes using drone surveying

• Step 4: Cross-check the drawings with the deliverable data to inform construction decisions

• Practical Points for Maintaining Accuracy and Safety in Pile Position Verification

• Summary: Streamlining pile position verification at solar power plants using drone surveying

Why Drone Surveying Is Useful for Confirming Pile Positions at Solar Power Plants

In checking pile positions at a solar power plant, you need to verify not only whether each pile is close to its design position but also the straightness of entire rows, the spacing between mounting racks, the continuity of the panel surfaces, and how they interface with walkways and drainage facilities. A pile's position does not make sense in isolation; it is meaningful only in relation to adjacent piles and the row as a whole. If you only look at individual measurements for each pile, you can overlook site-wide alignment irregularities or tendencies for a particular area to be shifted in one direction.

Using drone surveying, you can capture large sites from above, making it easier to visually grasp the alignment of pile rows. From the ground, sightlines can be obstructed by uneven terrain, vegetation, temporary materials, and the positions of heavy machinery, but aerial images make it easier to check the flow of the rows and any unevenness in the construction area. Because solar power plants have large site areas and many piles, being able to view the whole site at a glance is a major advantage.

Moreover, verifying pile positions is meaningful not only after construction but also during the construction stage. If a large positional deviation is discovered after pile driving has progressed, it can affect racking assembly and panel installation processes. By conducting drone surveys at an early stage and comparing them with the design drawings and planned pile centers, you can consider revising construction methods or reference lines before the deviation widens. It is especially important to perform checks while keeping records when the ground conditions after site preparation differ from those assumed in the design or when on-site fine adjustments occur.

The results of drone surveying also help with information sharing on site. Because construction personnel, managers, designers, and clients can check the situation while looking at the same images and drawings, it becomes easier to explain spatial relationships that are difficult to convey verbally. For example, issues such as "a portion of the pile rows on the north side are shifted toward the walkway" or "only the rows near the slope have changed their distance from the design line" can be explained by overlaying them on aerial images, which reduces discrepancies in understanding.

However, the positions of stakes visible in drone surveys vary in accuracy depending on shooting conditions, analysis conditions, the setting of control points, and how the stake heads appear. When stake heads are small, hidden in shadows, covered by grass, or similar in color to the surroundings, they can be difficult to interpret in images. Therefore, for confirming stake positions at solar power plants, it is realistic to use drone surveying as the main approach for wide-area checks while performing additional ground checks at important or suspicious locations.

Step 1 Organize the design coordinates and site conditions and determine the scope of verification

The first step is to organize the design information and site conditions before flying the drone. If you conduct imaging while the purpose of verifying pile positions is unclear, you may fail to capture the required area or be unable to reconcile the images with the drawings used for comparison. Rather than simply photographing the entire site, it is important to decide in advance which pile rows to check, which design drawings to compare with, and what degree of deviation you want to detect.

First of all, what you should confirm are the drawings and coordinate data that serve as the reference for pile locations. In a solar power plant, multiple drawings are involved, such as panel layout drawings, racking layout drawings, pile layout drawings, site development drawings, drainage plan drawings, and maintenance aisle plans. Even if you only look at the pile locations, if the interfaces with the racking and aisles are not clear, it becomes difficult to use them for construction decisions. Before developing the surveying plan, confirm which drawing will be treated as the authoritative reference, whether the drawings are the latest versions, and whether site changes have been reflected.

Next, clarify how coordinate systems and reference points will be handled. Depending on whether the design coordinates are public coordinates or a site-specific local coordinate system, the way you align them with the survey deliverables will differ. If control points, temporary benchmarks, or offset stakes remain on site, confirm that they are still reliable. If earthworks or the movement of heavy equipment may have displaced reference points, using old references as-is can make the entire drone survey output appear shifted.

Setting the inspection area is also important. Decide whether to photograph only areas where piles have already been installed or to include uninstalled sections, material storage yards, heavy-equipment access routes, and areas around drainage facilities. Because deviations in pile positions affect not only individual piles but also the distances to adjacent structures, it is easier to make judgments later if you include surrounding areas in the photographs as needed. In particular, piles located near property boundaries, slopes, existing roads, drainage ditches, retention basins, and planned fence locations have little margin and are therefore worth including in the inspection targets.

On-site conditions to assess include terrain, slope, grass overgrowth, muddy ground, snow cover, temporary storage of materials, and the operating status of heavy equipment. If pile heads are not visible, it becomes difficult to confirm their positions from aerial imagery. If the tops of piles are hidden by soil or protective coverings, or if surrounding weeds make them hard to distinguish, preparations are needed before photographing to make them more visible. When placing markers, you must consider that they should not be blown away by wind, should not interfere with work, and should be easy to identify in the images.

At this stage, it’s efficient to decide in advance what will ultimately be delivered as the final output. Whether aerial photos alone are sufficient, whether to overlay stake plan lines on orthophotos, whether to cross-check with a coordinate list, or whether to compile it into a report for construction records will change the required capture accuracy and analysis work. The level of control required differs between a purpose that is only site verification and one that is organized in a form close to inspection documentation. Working backward from the intended use in later stages to determine the area to capture and the items to check is the first step to reducing rework.

Step 2: Prepare reference points and imaging conditions before the flight

The second step is pre-flight preparation. In drone surveying of solar power plants, the arrangement of reference points and capture conditions determines the usability of the results more than the image capture itself. When using it to verify stake positions, having clear images alone is not sufficient. You need to set up reference points, the capture area, flight altitude, image overlap, and weather conditions so that positional relationships can be confirmed when overlaid on the design drawings.

When placing reference points, choose locations that have good visibility on site, are unlikely to obstruct construction, and are easy to identify in the captured images. Because reference points are involved in the overall positional alignment of the outputs, take care not to place them too unevenly. If reference points are concentrated in only one part of the site, it can leave uncertainty when verifying positions in distant areas. For large solar power plants, consider arranging them to support the entire area, such as at the four corners of the imaging area and near the center.

Before photographing, check that the pile head and any markers are visible in the images. If the pile color is similar to the ground or the pile head is small, the images may be difficult to interpret afterwards. If necessary, clean around the pile head or attach conspicuous marks within limits that do not interfere with work so it will be easier to confirm later. However, if the marker is placed offset from the pile center, it can instead cause misunderstanding. It is important to make clear whether you are indicating the pile center or the outline of the pile head.

Flight altitude and shooting conditions should be determined according to the size of the target you want to check. Increasing altitude allows you to capture a wider area efficiently, but it reduces the legibility of each individual stake. Lowering altitude makes details easier to see, but increases the number of photos and the processing workload, and takes more time on large sites. When confirming stake positions, you need to consider both the goal of checking overall rows and alignments and the goal of reading stake heads, and choose conditions suited to the site.

Weather also affects results. During strong winds, not only is flight safety reduced but images can blur and flight paths can be disturbed. In rain, fog, or strong backlight, it may be difficult to interpret pile heads and the ground surface. Solar power plants are often located in open areas and are therefore susceptible to the effects of sunlight and shadows. During times when shadows from racks, piles, and temporary structures are long, pile heads can be hidden in shadow. Choosing times when the target objects are as visible as possible is important for maintaining inspection accuracy.

Pre-flight safety checks are essential. There may be workers, heavy machinery, temporary power supplies, overhead lines, and material storage areas on site. If the flight area overlaps with the work area, notify personnel on site and, if necessary, implement access controls or adjust flight times. Drone surveying can help improve efficiency, but because it is conducted on an active construction site, safety management cannot be put on hold. It is important to coordinate with the site manager whether work should be stopped for filming or the flight scheduled during periods with less activity.

Step 3 Record the positional relationships around the stakes using drone surveying

The third step is to actually carry out the drone survey and record the positional relationships around the stakes. At this stage, the objective is to photograph the entire planned area without omissions and to collect imagery that can later be compared with the design drawings. While shooting, be mindful not only of the number of images but also whether the rows of stakes, reference points, surrounding structures, and site boundaries are adequately captured.

When verifying pile positions at a solar power plant, it’s easier to judge if you photograph them together with surrounding features and construction reference points rather than taking tight shots of the piles alone. If there are access paths, drainage ditches, slopes, planned fence locations, or site boundaries near a row of piles, recording those as well lets you check for conflicts later. Even if a pile is slightly offset from its design position, it may not cause construction problems if there is sufficient clearance around it. Conversely, in locations close to boundaries or drainage facilities, even small deviations may require attention.

When photographing, it is important to record the entire area uniformly. If only some areas have insufficient image overlap, or are difficult to see due to shadows or blur, you may not be able to verify those parts after the deliverables are produced. In particular, the edges of the site, places where slopes change, areas near material storage, and near the paths of heavy equipment are prone to missed coverage. After the flight, quickly check the images on site to confirm that rows of survey stakes and reference points are captured, which makes it easier to decide whether to reshoot.

Visibility of the pile head is extremely important when verifying pile locations. If the pile head blends into the ground, it becomes easy to get confused when trying to pick out piles after image analysis. When grass, shadows, mud, protective coverings, or temporarily placed materials overlap, there is a risk of misidentifying the pile position. Therefore, recording areas that are hard to see at the time of capture and organizing them as locations requiring later ground verification makes the results more practical to use. It is also an important outcome to clearly identify any uncertainties, rather than forcing a judgment based solely on drone survey results.

After image acquisition, we produce deliverables such as orthomosaic images and point clouds, and organize them so the positions of the piles can be verified. Orthomosaic images are aerial photographs corrected to be easily used like a map, making them suitable for comparing the alignment of pile rows with design lines. Point clouds help in understanding terrain and elevation, but how well they can represent small features such as pile heads depends on conditions. For pile position verification, focusing on visually intuitive orthomosaic images and combining height information and cross-section checks as needed makes it easier to apply the results in practice.

When organizing results, record the date of capture, the capture area, the reference points used, the weather, site conditions, areas not yet constructed, and any sections that are difficult to interpret, as this makes later review and judgment easier. Because construction of a solar power plant proceeds in stages, it is extremely important to know when the data were captured. The meaning of the same positional information changes depending on whether the data were taken immediately after pile driving, after mounting-frame assembly, or after changes to the earthworks. Maintaining awareness to keep a chronological record increases the value of the data for construction management and explanatory materials.

Step 4: Cross-check drawings with deliverable data to support construction decision-making

The fourth step is to cross-check the outputs produced by the drone survey with the design drawings and use that to inform construction decisions. It’s not enough to simply capture images; it’s important to compare the design stake positions, the on-site stake positions, and their relationship to surrounding facilities, and to identify where potential problems may exist. The goal here is not to finalize everything at once, but to efficiently narrow down the locations that need to be checked.

First, overlay the design pile locations and pile-row lines onto the ortho image and the as-built deliverables. If the coordinate system, scale, or drawing reference are not aligned at this stage, locations that are actually fine may appear displaced, or conversely, actual displacements may be overlooked. Before overlaying the design drawings, verify that the alignment is reasonable using control points or known ground features. By checking against features with relatively well-defined positions—such as site boundaries, roads, drainage structures, and existing installations—you can confirm any overall offset in the deliverables.

When comparing pile positions, it is important not to focus only on the deviation of each individual pile but to observe the overall trends across entire rows. Whether a single row is shifted in one direction, multiple rows are displaced in the same direction, or only the edge sections are irregular will change the inference about the cause. The background of such deviations can be varied: mistaken reference lines, mismatches in coordinate transformations, misrecognition of offset references during construction, and adjustments to installation positions due to ground conditions. Drone surveying results provide material for taking an overarching view of these trends.

The verification results need to be organized in a form that can be used on site. Indicate the areas of concern on the images and clearly identify the rows of piles or areas that require ground confirmation. To enable field personnel to act immediately upon seeing them, organize the area name, pile row numbers, nearby landmarks, and reasons for checking so that re-surveys and corrective decisions proceed smoothly. Simply handing over the information obtained from drone surveys can make it difficult to know what to verify on site. Converting the deliverables into construction decisions is an important operational step.

Critical locations will be rechecked by ground surveying. Even if a drone survey indicates a possible positional shift, one should avoid concluding a construction defect based solely on image interpretation. Apparent discrepancies can arise from the visibility of pile heads, image distortion, the accuracy of control points, terrain effects, and other factors. Piles that are critical for racking installation or inspection, piles near boundaries, and piles suspected of interfering with drainage or access routes should have their coordinates and offsets confirmed on the ground and be judged against design tolerances and construction standards.

When making construction decisions, separate items that require correction, those that only need to be monitored, and those that require drawing changes or consultations. Treating all deviations the same can lead to excessive on-site responses or bury truly important issues. In solar power plants, pile position deviations may fall within the adjustment range of the racking, while in other cases they may affect row spacing, aisle width, or drainage slope. It is reasonable to use drone survey results to grasp the overall picture and address the most critical areas first.

Practical Points for Maintaining Accuracy and Safety in Pile Position Verification

When using drone surveying to verify pile locations at solar power plants, maintaining accuracy requires not only post-flight analysis but also thorough on-site preparation. The basics are making sure pile heads are clearly visible, appropriately placing reference points, standardizing the version of design drawings, and recording the construction status at the time of imaging. If results are produced without these measures being adequate, even images that look neat may be difficult to use for construction decision-making.

What you should be particularly careful about is not to confuse the purpose of confirming stake positions with the accuracy requirements. Drone surveying is effective as a way to efficiently grasp the current conditions over a wide area, but it cannot always be substituted for the final measurement of each individual stake. The content that can be confirmed varies depending on the site’s shooting conditions and the method used to produce deliverables. While it is suitable for assessing overall alignment and extracting anomalous locations, strict as-built control and inspection decisions may require combining it with ground surveying or prescribed management methods.

From a safety perspective, consideration must be given to operating drones on an active construction site. On solar power plant construction sites, pile drivers, transport vehicles, racking components, and electrical work materials may be in operation. Ensure flight routes do not overlap the airspace above workers or heavy machinery, and share flight times and coverage with on-site stakeholders. To avoid disrupting work, it is advisable to separate flight areas as needed or to capture footage during periods of lower activity.

Also, when operating unmanned aircraft, it may be necessary to confirm not only site rules but also applicable laws and regulations, permits and approvals, and the placement of observers depending on the flight location, the aircraft, and the flight method. Solar power plants are often located in suburban or mountainous areas, yet they can be close to nearby roads, power lines, houses, and workers’ movement routes. It is important to confirm flight conditions at the survey planning stage and to avoid unreasonable flights in order to maintain safety.

When confirming pile positions, on-site communication also affects the quality of the deliverables. If the person in charge of drone surveying photographs without knowing which rows of piles are important, the extent of any changes, or which drawings are the latest, necessary information is likely to be missing. By having the construction manager, surveyor, and racking installer share the points to check in advance, you can reduce missed shots and misunderstandings.

Time-series management is also important. Conducting drone surveys before and after pile driving and before and after rack installation makes it easier to compare changes on site. In particular, if you check immediately after pile driving, you can more easily detect trends of positional shifts before rack assembly. If a problem is discovered after moving on to later stages, not only will corrections take longer, but schedule adjustments and consultations with stakeholders will increase. Keeping records at an early stage is effective not only for construction quality but also for schedule management.

It is also necessary to consider how to store the resulting data. If captured images, post-processed deliverables, overlay materials with design drawings, and on-site inspection notes are managed separately, it can become unclear which document is correct when reviewed later. By linking and managing the capture date, coverage area, drawing version, verifier, and assessment result, the materials become easier to use for internal reviews and explanations to the client. Drone surveying of solar power plants gains value when organized not as one-off captures but as part of the construction record.

Furthermore, it is important not to become overconfident in the results. Even if a pile is visible in the imagery, that does not necessarily mean it accurately indicates the pile center. There are multiple factors that can cause misjudgment, such as the pile head appearing at an angle, the presence of shadows, overlapping temporary materials, or alignment errors in the analysis. Use drone surveying to identify anomaly candidates, verify critical locations on the ground, and make the final decision based on site conditions and design requirements. By rigorously following this workflow, it becomes easier to maintain both efficiency and reliability.

Summary: Streamlining Pile Location Verification at Solar Power Plants with Drone Surveying

When checking pile positions at solar power plants, many piles are installed across large sites, so it can be difficult to grasp overall deviations or irregularities in the rows through ground inspections alone. By using drone surveying, it becomes easier to confirm the straightness of pile rows, their relationship to design lines, and any clashes with surrounding facilities from above, making it easier to identify potential problems at an early stage of construction. It is especially effective for wide-area current-condition assessment, overlaying drawings, and information sharing among stakeholders.

In practical use, first organize the design coordinates and drawing sheets, and clarify the scope and objectives of the verification. Next, set up control points and imaging conditions, and capture images so that pile heads and surrounding features are legible. Then, produce deliverables such as orthoimages, compare them with the design drawings, and identify trends in discrepancies and locations that require ground verification. Finally, combine ground surveying and on-site checks for critical locations and use the results to inform construction decisions.

Drone surveying does not automate all pile position checks. However, it is an effective means of understanding a large site holistically, narrowing down the areas that need to be checked, and reducing rework. In construction management of solar power plants, it is necessary to comprehensively consider the relationships between pile positions, racking layout, drainage, access paths, and boundaries. By appropriately incorporating drone surveying, it becomes easier to share site conditions and to improve both the speed of decision-making and the quality of records.

When incorporating drone surveying into pile location verification, it is important to consider operations not only in terms of ease of shooting but also including cross-checking with design drawings, on-site re-verification, and how records are preserved as construction documentation. At solar power plant sites, using drone surveying as an entry point for wide-area checks and combining it with ground surveying and on-site verification makes it easier to balance efficiency in pile location verification with safety in decision-making.