Navigate pile-driving coordinates for solar power generation with cm level accuracy (half-inch accuracy)｜LRTK opens up next-generation surveying

Introduction: The proliferation of solar power generation and surveying challenges

In recent years, the adoption of solar power generation as a mainstream renewable energy source has been progressing rapidly. From large-scale mega-solar projects to small facilities, plans to construct solar power plants are being announced across the country. Along with this, the importance of on-site tasks such as surveying and verifying stake locations has grown even further.

In the construction of solar power plants, it is necessary to accurately place numerous piles (support piles that serve as foundations) across a wide site. However, there are various challenges involved in the surveying and installation work for these pile-driving coordinates. In this article, we explain the real-world surveying challenges at solar power sites and the next-generation solutions offered by the smartphone-compatible high-precision surveying equipment "LRTK series" from a professional yet easy-to-understand perspective.

On-Site Reality: Why the Accuracy of Pile-Driving Positions Matters

At solar power plant construction sites, small deviations in pile-driving positions can have a significant impact on subsequent construction quality. The mounting racks that support the solar panels are assembled on numerous pile foundations, but if each pile is not driven to its planned coordinates, the racks and panels can shift and the layout can fail to match the design. For example, even a deviation of a few centimeters (a few inches) can cause uneven spacing between adjacent panels, and in the worst case panels may interfere with each other or the sunlight incidence (the way sunlight falls) may be altered, affecting power generation efficiency.

Furthermore, because the bolt hole locations on the mounting frames and the dimensions of connecting components are designed with precision, if the pile positions are off the members’ holes will not align and adjustment work will be required at the construction site. This can lead to schedule delays and additional costs, and may also adversely affect the stability of the structure. In particular, because solar panels are subjected to environmental factors such as wind loads, it is essential for the safe and long-term operation of the power-generating equipment that the support piles be installed at the planned positions and depths.

Thus, at solar power generation sites, "the positional accuracy of each individual pile" is demanded. For developers and construction managers, placing every pile at the coordinates shown in the design drawings is essential for ensuring quality, and the surveying and layout work required for that is a process that must never be compromised.

Limitations of traditional surveying methods (total stations, GPS, etc.)

How has the important task of determining pile-driving positions traditionally been carried out? Generally, surveyors or surveying personnel set out positions on site based on coordinates shown on the drawings. Specifically, they measure distances and angles from reference points with tape measures and angle-measuring instruments, and install markers on the ground such as stakes (kuihyō) and batter boards (chōhari). This work typically uses an instrument called a total station (an optical surveying instrument), but it requires setting up heavy equipment and operating it with a two-person team, making it extremely time-consuming to measure and install hundreds of piles across large solar sites.

Additionally, total stations require regular calibration and maintenance from the manufacturer, and their operation demands skilled personnel. In bad weather or on highly uneven terrain, setting up the equipment and securing line of sight can be difficult, and the surveying work itself may be delayed. Moreover, manual staking always carries the risk of surveying errors and marking mistakes. Even being off by only a few centimeters when marking stake positions can, as noted above, affect construction quality, so conventional methods required experienced workers to proceed with multiple layers of checks.

On the other hand, there are limits to trying to determine positions simply using GPS. The positional accuracy of ordinary smartphones and handheld GPS devices is at best a few meters, so they cannot be used to pinpoint the exact location of a single stake. You can also adopt expensive RTK-GNSS surveying equipment, but because it requires setting up a dedicated base station and operator training, in practice it poses a high barrier for small-scale sites and companies that are not surveying specialists.

The process of staking out coordinates that relied on conventional optical surveying and general GPS was thus time-consuming and labor-intensive, and a factor that constrained productivity. As the solar power generation business expanded, how to make this part more efficient while ensuring high accuracy became a major challenge.

What is LRTK? (cm-level positioning, using iPhones, cloud integration, etc.)

Introduced to solve the challenges described above is a next-generation surveying solution called the LRTK series. LRTK is a system developed by Refixia, a venture company originating from Tokyo Institute of Technology, and is an all-in-one on-site DX tool that uses smartphones to achieve centimeter-level high-precision positioning and intuitive guidance through AR (augmented reality).

The core product of the LRTK series, the LRTK Phone, is an ultra-compact RTK-GNSS receiver (satellite positioning antenna) that is attached to a smartphone or tablet. The receiver weighs approximately 150 g and is compact enough to fit in a pocket; simply attaching it to an iPhone or similar instantly turns your handheld smartphone into a high-precision surveying instrument. The smartphone and the LRTK device receive positioning information and correction data from satellites, enabling you to determine your current position in real time with horizontal positioning accuracy of approximately ±1–2 cm (±0.4–0.8 in) and vertical accuracy of approximately ±3 cm (±1.2 in) (typical GPS errors are around 5–10 m (16.4–32.8 ft), so this is truly an order-of-magnitude improvement in accuracy).

By combining the dedicated LRTK app (smartphone app) with the LRTK Cloud (web service), another feature is that you can carry out everything from surveying to data management seamlessly. On-site, the LRTK app on a smartphone is used for point positioning, taking photos, navigation to stake positions, etc., and the acquired coordinate data and recorded photos can be uploaded to the cloud immediately with the push of a single button. You can also pre-register the coordinate data of design drawings on the cloud, enabling real-time comparison between points measured on site and the design values, and allowing information to be shared with staff in the office. In other words, by introducing LRTK you can set up an environment where "everything from surveying to stake placement guidance and record management can be completed with just one smartphone."

In this way, LRTK is a revolutionary tool that makes it extremely easy to bring cm level accuracy (half-inch accuracy) positioning—previously expensive and difficult to handle—onto the worksite. In the next chapter, we will focus on LRTK's "Pile-driving Navigation" feature, which dramatically streamlines the staking out of pile positions, and examine its mechanism in detail.

Details of the Pile-Driving Navigation Feature

One of the functions where LRTK demonstrates its power on site is the Coordinate Navigation Function, which navigates to pile-driving coordinates. Put simply, this is like a car navigation system dedicated to pile-driving that guides the user to the configured target coordinates. Let's take a look at the specific workflow.

First, before construction, register the design coordinate data for the piles to be driven (a list, etc.) in the LRTK Cloud. Because each pile can be assigned a number or ID for management, you can organize the positions of hundreds of piles even for large-scale solar power plants. On site, simply select the desired pile number from the LRTK app on your smartphone and its coordinates will be set as the target.

When you select a target, an arrow and distance are displayed in real time on the smartphone screen, and guidance to the target location begins. For example, the direction and remaining distance are shown at the top of the screen, such as "Northeast 5.3 m (17.4 ft)," so you simply walk following that. At longer distances a general directional cue is displayed, and as you get closer it switches to more precise guidance like "20 cm (7.9 in) to go." When you reach the target stake position, marks (markers) overlap on the screen so you can tell "This is the target location!" Workers can reach the target coordinates pinpoint-accurately without getting lost simply by following their smartphone, even without specialized surveying knowledge.

Furthermore, the LRTK app also includes a feature that displays AR stakes (virtual stake markers) on the camera view. When you approach the target point and hold up your smartphone to look around, vivid virtual stakes appear to stand on the actual ground. If an AR stake aligns perfectly with the ground and your position, it is proof that the stake is being placed correctly according to the design. Even in dark locations or on a bare soil lot, the point where “place the stake here” is obvious through the screen, preventing missed markings. Also, on steep slopes where people cannot get close, or where physical stakes cannot be driven into concrete, you can safely confirm positions from a distance by displaying AR stakes.

This pile-driving navigation feature allows even inexperienced workers to accurately set out pile positions on their own. It eliminates the need to peer at drawings while operating surveying instruments or to take repeated measurements; by following the on-screen instructions and simply proceeding and confirming, the pile-driving work is completed, dramatically improving the productivity and accuracy of pile-driving operations.

Use cases in solar power plants (pre-construction, during construction, inspection and documentation)

LRTK can be utilized in various situations throughout the lifecycle of a solar power plant. Here, we will look at concrete ways to use it by dividing the process into three stages: "pre-construction", "during construction", and "post-construction inspection and record-keeping".

Before Construction (Planning and Site Survey)

In the pre-construction stage of a solar power plant, LRTK plays an active role in understanding current site conditions and verifying construction plans. For example, when conducting a topographic survey of a proposed development site, surveyors traditionally had to take survey points everywhere to create topographic maps, but with LRTK the person in charge can walk around the site with a smartphone in hand and measure key topographic points with high accuracy. By combining it with the iPhone's LiDAR capability to capture 3D point cloud data of the surface, it is also possible to quickly produce detailed terrain models and perform earthwork volume calculations (fill and cut).

It can also be used to verify the layout shown on design drawings at the site. By displaying on-site via AR the panel layout drawings and pile position data registered in the cloud, you can perform on-the-spot checks such as “placing according to the plan would put a pile at this location — are there any issues with the ground conditions?” For example, even if an obstacle exists on-site that was not noticed during the design phase, because you can overlay the design positions onto the real object in AR, you can identify problems before construction begins and quickly make design revisions. On-site surveys using LRTK contribute greatly to improving the accuracy of construction planning and streamlining preparatory work.

During Construction (Pile Driving and Construction Management)

During the construction phase, the aforementioned pile-driving navigation feature takes center stage. When installing foundation piles for solar panels, site supervisors and workers use LRTK to mark pile positions one after another. Traditionally, a surveying team would set up batter boards and the heavy-equipment operator would visually confirm and drive each pile one by one, but after adopting LRTK, a single site staff member can accurately indicate multiple pile positions in a short time. For the pile-driving machine operator, work also proceeds smoothly because they only need to align the heavy equipment with the locations indicated by markers or AR piles. As a result, the overall time required for pile-driving operations is significantly reduced, leading to improved construction productivity.

LRTK is also useful for interim inspections and as-built (dekigata) management during construction. For example, once pile driving in a section is complete, if you quickly measure the actual coordinates of each pile using LRTK, you can immediately identify any deviations from the design values on the spot. Even if some piles are slightly misaligned, performing corrective work before racking installation can prevent problems in subsequent processes. In this way, LRTK also functions as a real-time quality control tool during construction and supports on-site management of solar power plants.

Inspections and Records (Completion Inspection and Report Preparation)

Even after all piling and panel installation are complete, LRTK plays an important role. During the as-built inspection at completion, when verifying whether each pile and major structure is located in its designed position, measurements from LRTK become a strong ally. By surveying a series of piles with LRTK and comparing their coordinate data to the design values stored in the cloud, you can instantly check for any deviations.

Moreover, if you use the LRTK app to take and record photos for each pile location, you can later digitally track which pile was installed at which location and in what condition. All of this data is organized and stored in the cloud, making the preparation of the final construction report smooth. As submission materials for the client, you can easily create a coordinate list for each pile and a layout map with photos, providing highly reliable evidence.

Thus, LRTK consistently supports on-site operations from pre-construction through post-construction of solar power plants. From preliminary ground surveys and pile-driving work to final inspection and documentation, it can be regarded as a reliable tool that contributes to the digitalization and streamlining of on-site operations.

Practical benefits (labor savings, personnel cost reduction, quality improvement, report generation)

The introduction of LRTK provides the following practical benefits for on-site operations at solar power plants.

• Labor savings: Because surveying and stake-out of pile positions can be carried out with a small crew in a short time, the workload is greatly reduced even on large sites. Surveying work that used to be physically demanding has shifted to being primarily smartphone-operated, reducing worker burden and improving safety.

• Reduced labor costs: The number of personnel in surveying teams can be kept to a minimum, and the frequency of outsourcing to external surveying contractors can be reduced. By expanding the range of tasks a single worker can handle, reductions in labor and travel expenses can be expected. Because site staff can handle tasks without relying on seasoned specialists, this also helps mitigate the risk of future labor shortages.

• Quality improvement: Because pile positions can always be managed with positioning with cm level accuracy (half-inch accuracy), construction accuracy is dramatically improved. The risk of rework due to surveying errors and of racking installation defects caused by misaligned pile positions is reduced, resulting in higher overall quality and reliability of solar power installations. In addition, making quality management data-driven makes it easier to run the site PDCA cycle (plan, do, check, act).

• Automated reporting: Because surveying data and photographic records are automatically accumulated in the cloud, creating various forms and reports becomes simple. As-built documents that were previously organized manually are maintained on the cloud almost in real time when using LRTK, greatly reducing the effort required to format final documents. Having digital data as backing also increases the credibility of the documentation and makes explanations to clients and inspection agencies smoother.

Frequently Asked Questions (accuracy in outdoor environments, handling when out of coverage, supported devices, etc.)

Here are frequently asked questions and answers for when you are considering implementation.

• Q. Can surveying really achieve cm level accuracy (half-inch accuracy) at large outdoor sites? A. Yes. The LRTK is equipped with a high-performance GNSS receiver that supports multiple frequencies and multiple satellites (not only GPS but also GLONASS and Michibiki, etc.), and in open outdoor environments with good visibility it can stably determine positions with horizontal accuracy of about ±1–2 cm (±0.4–0.8 in). Accuracy may be slightly reduced under trees or in mountainous areas where satellite signals are harder to receive, but in actual use it has been confirmed that high-precision positioning can be performed without problems at open sites such as solar power plants.

• Q. Can it be used deep in the mountains where there is no mobile phone reception? A. Rest assured. In addition to correction data via the Internet (RTK networks), LRTK also supports the Quasi-Zenith Satellite System "Michibiki"’s centimeter-level augmentation service (CLAS). Even if the site is outside mobile coverage, correction signals can be received directly from satellites overhead, enabling centimeter-level positioning (cm-level accuracy; half-inch accuracy) even in environments without communication infrastructure (available wherever CLAS signals reach across Japan). Therefore, even at solar power plants in mountainous or remote areas with unstable communications, you can take advantage of LRTK’s high-precision surveying capabilities.

• Q. What devices can it be used on? A. At present, it is primarily available on iOS (iPhone and iPad) devices. A dedicated LRTK device connects to the smartphone via Bluetooth and operates with the LRTK app downloadable from the App Store. Please check the product's official website for the latest information. Note that as long as you have an iPhone or iPad, no special dedicated hardware is required; you can start operating with only the LRTK receiver unit itself and a software service contract (for access to correction information and cloud services).

Summary and Future Outlook

We've reviewed the challenges in on-site surveying and pile-driving work for solar power generation and LRTK as a solution. The determination of pile coordinates, which traditionally relied on manual labor and experience, is becoming something anyone can perform quickly and accurately with the advent of LRTK. Despite its simple configuration of a smartphone and an ultra-compact GNSS receiver, LRTK achieves centimeter-level accuracy and AR-based visual guidance, making it a game changer not only for the solar power industry but for construction surveying as a whole.

Looking ahead, digital surveying technologies including LRTK are expected to become more widespread and on-site DX (digital transformation) is likely to accelerate further. The momentum of initiatives such as the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction will also act as a tailwind, and new construction methods centered on LRTK — such as complete digital management of construction records and linkage with automated heavy equipment operation — will be established. In addition, possibilities for technological expansion are broadening, including hands-free stakeout guidance via AR glasses and integration with drone-based wide-area surveying.

In any case, as a key to achieving both "high accuracy × efficiency" in the development and construction of solar power plants, solutions like LRTK are likely to become increasingly important going forward. Next-generation surveying methods that break free from conventional wisdom are expected to dramatically improve on-site productivity and reliability, contributing to the development of the industry as a whole.

A Natural Introduction for Those Considering Adoption (A Recommendation for Simple Surveying with LRTK)

For everyone involved in the development and construction of solar power plants, streamlining and upgrading surveying and pile-driving work is an issue that cannot be avoided. Some may worry, "We'd like to introduce it at our company, but will we really be able to master it?" However, as we have introduced, LRTK features a simple equipment setup and intuitive operation, and is designed to be used on site without special qualifications or extensive training. On sites that have actually implemented it, feedback includes: "The time spent on surveying has been greatly reduced, allowing personnel to be reassigned to other important tasks," and "Concerns about pile-driving accuracy have disappeared, giving us more flexibility in construction planning."

It may be a good idea to start with small-scale projects or parts of a workflow to experience its convenience and effectiveness. The LRTK series can be put into use immediately once the necessary equipment and service contracts are in place, and the initial barriers to adoption are not high compared with conventional surveying instruments. The fact that, with just a smartphone, you can achieve professional-quality positioning while performing "simple surveying" is likely to greatly change conventional practices in field operations.

In the solar power business, construction that combines speed and accuracy is a source of competitive advantage. If you feel there are challenges in the surveying or pile-driving processes, please consider next-generation simplified surveying using LRTK. By incorporating the latest technology, you can achieve both improved on-site productivity and quality assurance, helping to improve project success rates.