Using cm-level GPS for land surveying at solar power plants｜Precise positioning anyone can do with LRTK

In recent years, solar power generation (mega-solar) installations have been progressing nationwide. Along with this, land surveying for the construction of solar power plants has become increasingly important. Accurately understanding the area, topography, and elevation differences of a prospective site directly affects panel layout planning, construction efficiency, and safety. However, conventional surveying required specialized knowledge and time, posing a significant burden for small and medium-sized operators. At the center of attention, therefore, is high-precision positioning technology using centimeter-level GPS. This article explains the benefits of using cm-level GPS (RTK technology) for land surveying of solar power plants and introduces a solution called LRTK that makes it easy for anyone to use.

Why land surveying for solar power plants is important

For the construction of a solar power plant, it is essential first to accurately grasp the current condition of the site. If area, boundary locations, elevation differences, and slope angles are not surveyed in advance, problems may arise such as planned panel layouts not fitting the actual land. For example, a situation where “during the planning stage it was thought the panels would fit within the site, but after construction began inaccurate land surveying caused panels to protrude” must be avoided. Especially for large-scale mega-solar projects, even slight surveying errors can have a major impact on the overall plan.

Elevation difference data of the site also affects the design of mounting structures and earthwork volume calculations. If the terrain is measured correctly, panel placement can be adjusted so the modules receive sunlight at optimal angles, and the required quantities of fill and cut can be calculated accurately. Conversely, insufficient surveying information can lead to rework during construction—such as “ground being more sloped than expected, requiring changes to the mounting height” or misestimating soil transport—which in turn causes increased costs and schedule delays. In this way, accurate on-site understanding through pre-construction land surveying forms the foundation for the success of a solar power plant.

Conventional surveying methods and their challenges

However, conducting accurate conventional surveying required specialized skills and expensive equipment. Typically, surveyors use a total station (an optical surveying instrument) or high-precision GNSS receivers to establish control points and measure the land in detail. This approach involves the following challenges:

• Equipment cost and preparation burden: Assembling a full set of high-precision surveying equipment requires a large investment, sometimes on the order of millions of yen. The equipment is also heavy, and transporting and setting up tripods and batteries at the site is time-consuming. In addition, preparatory work is required to install reference stakes that serve as known points and to set their coordinates.

• Dependence on specialized personnel: Accurate surveying requires experienced surveyors and technicians, so if a company lacks such personnel it must outsource to a surveying firm. Outsourcing increases costs and requires schedule coordination, making it difficult to respond quickly when surveys are needed in the planning stage.

• Limits to positioning accuracy: Standard handheld GPS or smartphone GPS functions have errors of around 5–10 m (5–10 ft), making them unusable for surveying large sites or for precise positioning. Traditionally, to compensate for such errors, laborious measures such as detailed transit surveys or repeated coordinate transformation calculations were necessary.

• Lack of real-time capability: With conventional methods, the final result is not visible until the field data is taken back to the office and drawn into maps. If omissions or mistakes are discovered on-site, inefficient repeat visits for re-measurement occur.

Because of these problems, the demand grew for ways to obtain high-precision surveying results more easily and quickly. Especially for solar projects that require rapid surveying at sites nationwide, conventional methods relying on specialized equipment and personnel posed high cost and time barriers.

High-precision positioning using centimeter-level GPS (RTK)

RTK (Real-Time Kinematic) positioning, a centimeter-level GPS technology, emerged to solve these issues. RTK can reduce satellite positioning errors to the order of several centimeters (a few inches). While standalone positioning (a single receiver) typically yields errors of several meters (several ft), RTK positioning can reduce that by about a factor of 100—i.e., to a range of several centimeters (a few inches)—through an error correction mechanism. (cm level accuracy (half-inch accuracy))

The principle of RTK is to receive satellite signals simultaneously at two points—a reference station and a rover station—and have the reference station send its error information to the rover in real time for correction. Specifically, a reference station whose precise coordinates are known in advance is installed near the site, or correction information from public reference points or private correction services is used. The error data computed at the reference station is sent to the rover (the receiver carried by the surveyor) via radio or the Internet, and the rover’s measurements are corrected to achieve high accuracy.

Because this processing is performed in real time for each measurement every second, a major feature of RTK is that the rover can obtain centimeter-level positions even while moving. Accuracy is also more stable when the distance to the reference station is short because error sources can be common between the two. Recently, network RTK (such as VRS), which allows users to obtain correction information online from surrounding reference point networks without installing their own reference station, has become widespread. Japan has a nationwide network of reference points, and by using them one can easily obtain cm-level positioning results in a global coordinate system. Additionally, mechanisms that improve positioning accuracy by receiving correction signals directly from satellites—such as the centimeter-level augmentation service (CLAS) provided by the Quasi-Zenith Satellite System (QZSS or “Michibiki”)—have appeared. With these technological foundations in place, RTK positioning has become far easier to use than before.

Benefits of using cm-level GPS for surveying solar power plant sites

The advantages that centimeter-level positioning brings to the field are immense. In land surveying for solar power plants in particular, there are many situations where high-precision position information from RTK is advantageous. Here are the main benefits.

• Improved layout accuracy: High-precision surveying enables panel layout plans to be realized at the designed positions and spacings. Knowing positions at the centimeter level allows accurate marking for pile driving and mounting structure installation, ensuring all panels are placed in the intended layout. This maximizes power generation efficiency and prevents problems such as “arrays being misaligned so some panels are shaded.”

• Efficiency of surveying work: Using RTK-GPS, one person can rapidly gather survey points across a large site. Compared with traditional methods where a surveying crew spends days measuring with tapes and a total station, current conditions can be collected in a short time. Even on undulating terrain, a person can efficiently obtain topographic data including elevation differences simply by walking around, greatly reducing labor.

• Real-time on-site verification: RTK survey data can be used immediately on site. Acquired coordinates can be plotted on maps on a tablet or smartphone to visualize boundaries and planned installation positions. This eliminates the traditional time lag of “measuring but not knowing the result until later drawing,” allowing immediate checks for omissions or inconsistencies on site. From the measured terrain data, simple earthwork volume estimates can also be performed in real time to help plan construction.

• Cost reduction: Being able to perform precise surveying quickly in-house can reduce outsourcing fees and the costs of additional work. Fewer construction interruptions due to waiting for surveying and the ability to adapt plans flexibly on site lead to overall project cost savings. With accurate initial site survey data, materials ordering and selection of construction methods can be properly balanced, eliminating waste.

By incorporating centimeter-level GPS positioning into land surveying for solar power plants, you gain benefits in accuracy, speed, and cost. So how can this high-precision positioning be made easy for anyone to use? One answer is the new surveying device called LRTK, introduced next.

Precise positioning anyone can do: the arrival of LRTK

Although RTK surveying is highly useful, its operation traditionally required specialized equipment and advanced skills. Enter the groundbreaking device “LRTK unit”, which enables centimeter-level positioning easily using a smartphone. LRTK is a small high-precision GNSS receiver that attaches to a compatible smartphone or tablet. By connecting to the phone via Bluetooth or similar and launching a dedicated app, anyone can immediately start centimeter-level positioning that previously required surveying equipment costing hundreds of thousands of yen. (cm level accuracy (half-inch accuracy))

The strengths of the LRTK unit are its combination of high precision, low cost, and portability. Its accuracy rivals that of conventional stationary RTK-GNSS equipment, achieving horizontal positioning errors of about 1–2 cm (0.4–0.8 in) and vertical errors of about 3–4 cm (1.2–1.6 in). Because it can perform reliable positioning compliant with domestic satellite positioning standards, it can even meet public surveying accuracy levels. Yet the device is compact enough to fit in a pocket, eliminating the need to transport heavy surveying equipment to the site. All that is required is a smartphone, the LRTK unit, and a communication environment. There is no burden of carrying heavy loads into forests or remote sites, making it easy to survey even distant locations.

Furthermore, the ease of use is a major advantage. With LRTK, even those without specialized knowledge can perform surveys intuitively via smartphone operation. Communication settings with the reference station and complicated coordinate system settings are supported by the app, so users need not worry. For example, conversion to Japan’s coordinate system (the World Geodetic System) is processed automatically, allowing the data to be used directly in digital maps or CAD drawings. A mechanism for obtaining correction information in real time is also built in, and models capable of receiving Michibiki (QZSS) satellite augmentation signals can maintain stable high precision even in mountainous areas without cellular reception. Because of these conveniences, LRTK is attracting attention as a new tool for on-site DX and is making high-precision positioning familiar in construction and surveying sites.

Examples of using LRTK on solar power plant sites

So what does the actual workflow look like when using LRTK for land surveying of a solar power plant? Here is one example.

• Measuring the existing terrain: First, walk around the prospective site holding a smartphone equipped with LRTK and take positions at key points of the terrain. Pick up and measure boundary lines, corner points, and locations with large elevation differences, plotting points in real time on the app’s map. This allows visual on-site understanding of the land’s shape and slope.

• Reflecting survey data in design: The high-precision point data obtained can be shared immediately with designers. For example, send it to the office PC via the cloud and create detailed topographic maps or contour maps in CAD software. Based on these, optimize the panel layout. Adjust mounting heights and row spacing to suit the terrain, and use the data to examine layouts that maximize solar exposure.

• Marking pile-driving and installation positions: Once the layout is decided, import the coordinate data back into the LRTK app and mark pile-driving positions on site. Following the app’s guidance to the specified coordinates indicates where the mounting structure should be installed. Pile positions that were previously measured using drawings and tape measures can now be positioned with navigation to centimeter-level accuracy. One person can identify the position by looking at the smartphone while another marks it, efficiently and accurately indicating all pile locations across a wide site.

• On-site verification and adjustment during construction: LRTK continues to be useful as construction progresses. After installation, measure the actual pile positions and immediately check on site for any deviation from the planned coordinates. If there are slight discrepancies, they can be discovered early and corrected before panel installation. Additionally, during earthwork, LRTK can be used to periodically measure ground elevation to check whether excavation and fill meet planned heights. Real-time recalculation of earthwork volumes and adjustment of heavy equipment deployment improve construction management accuracy.

As shown above, using LRTK enables consistent use of high-precision positioning from land surveying through construction management for solar power plants. It smoothly connects the traditionally segmented processes of “surveying → design → construction” and speeds information sharing between the field and the office.

Conclusion: Making solar power plant surveying accessible with LRTK

Accurate land survey data is a crucial factor that determines the success or failure of planning and construction in solar power projects. The introduction of RTK surveying using centimeter-level GPS has transformed precise positioning—once entrusted only to professional surveyors—into a more accessible and routine task. Accelerating this trend are user-friendly high-precision positioning devices like LRTK.

By using LRTK, companies can quickly grasp site conditions in-house even without a dedicated surveying team. Consistent precision management from site investigation through pile driving allows for rapid response to design changes and troubleshooting. As a result, the overall quality and speed of solar power plant construction projects improve, and unnecessary costs can be reduced.

Now that precise surveying has become a technology within everyone’s reach, it is worth leveraging its benefits in the solar field. If you have an opportunity to survey land for a solar power plant, try the easy, high-precision positioning provided by LRTK. You will likely be surprised by its simplicity and accuracy. LRTK, leading the new era of high-precision positioning, should become a reliable ally for your solar projects.