Complete with a smartphone! The RTK surveying revolution that changes solar construction

In solar construction sites, surveying is a crucial process that supports safe and reliable construction. Accurate surveying data are indispensable at every stage—for deciding solar panel and pile-driving locations, understanding terrain before site preparation, and verifying as-built conditions after construction. However, for solar power plants with vast grounds (mega-solar sites), conventional surveying methods have required large amounts of time and personnel, posing challenges for construction schedules and costs.

A recently spotlighted approach combines smartphones with RTK (real-time kinematic) positioning technology to create a new surveying method. “Smartphone RTK,” which equips a smartphone with a small high-precision GNSS receiver to enable centimeter-level positioning (cm-level (half-inch accuracy)), is ushering in an era in which a single person can perform precise surveying tasks. This article explains in detail the importance of surveying in solar construction and the challenges of traditional methods, how RTK surveying works and key points for improving accuracy, and how smartphones × RTK are transforming construction sites. It also describes the concrete workflow for one-person pile-driving, as-built and site surveys, and the benefits of managing point clouds, photos, and coordinates in the cloud, and concludes with an introduction to the LRTK smartphone construction support tool.

The importance of surveying in solar construction

In solar power facility construction, surveying plays an important role from the planning stage through construction and management. For example, high-precision surveying is required in the following situations.

• As-built/site survey: Before construction begins, the existing terrain, slopes, and solar irradiation conditions of the planned site are measured. Accurate terrain data form the basis for earthwork planning and layout design.

• Pile-driving and layout staking: This is the process of setting out the positions of piles that serve as foundations for the racks on which solar panels are installed. In large mega-solar sites, hundreds to thousands of piles must be installed at accurate positions and heights. Insufficient surveying accuracy can cause pile misplacement that leads to assembly problems with the racks, so precision control down to the millimeter level is required.

• As-built verification: After construction is complete, inspections verify that the actual constructed elements (piles, racks, panel placements, etc.) are at the designed positions and heights. The results of as-built surveying are used for inspection records and handover documents; if deficiencies are found, corrective work or additional costs may be necessary, so high-accuracy verification is important.

• Earthwork volume calculation: When large-scale site formation is involved, survey data are used to calculate cut-and-fill volumes. Accurate earthwork measurement directly affects reliable earthwork planning and cost control.

Thus, surveying is an indispensable element that affects quality and efficiency in solar construction. The higher the accuracy of the survey data, the more it contributes to optimizing construction planning and preventing post-construction problems. On the other hand, traditional surveying methods have various challenges that have caused inefficiencies and rework on site. Next, let’s look in detail at those issues.

Challenges of traditional surveying: two-person work, errors, rework

Traditional surveying work is performed using total stations (optical surveying instruments) or general-purpose GNSS surveyors and has typically been carried out by teams of two or more people. Surveying an entire large solar site can take several days, imposing significant labor and scheduling burdens. The following issues have also been identified.

• High labor and time burden: Surveying that requires one person to hold a pole-mounted prism while another operates the instrument necessitates multiple staff members on site. In mountainous or otherwise obstructed terrain, efficiency further declines, and surveying alone can prolong the project schedule.

• Risk of rework due to errors: Manual surveying leaves room for human error such as reading mistakes or recording errors. If pile positions are measured incorrectly, misalignment of racks or panels may be discovered after construction, leading to pile redriving or rework. Such mistakes can cause schedule delays and additional costs.

• Dependence on experienced technicians: Setting up total stations, planning surveys, and adjusting data require advanced expertise. Sites must rely on experienced surveyors, and with worsening labor shortages, securing such personnel is increasingly difficult. If work becomes highly person-dependent on certain veterans, the site can stall when those individuals are absent.

• Inefficiencies in data processing and sharing: Traditionally, survey data collected in the field were handwritten into field books, then manually entered into PCs back at the office for drawing and calculations. For large-area surveys, the volume of data can be enormous, and manual entry and organization are time-consuming. Also, information obtained on site could not be immediately shared with designers or other departments, creating time lags before survey results were reflected in drawings and plans.

As described above, surveying operations for solar construction face a dual challenge of the “burden of vast sites” and “inefficiency of traditional methods.” So what is RTK surveying, the technology attracting attention as a solution to these problems?

What is RTK surveying? Differences in accuracy from traditional technologies and how it works

RTK surveying is a method that dramatically improves positioning accuracy by applying real-time error corrections to satellite positioning such as GPS. Ordinary smartphones or handheld GPS units can have positioning errors of several meters, but RTK (Real Time Kinematic) technology can reduce errors to a few centimeters (a few cm (about 1 in)). This is achieved by having the rover receiver (the surveyor’s device) receive correction information distributed from known reference stations such as the Geospatial Information Authority of Japan’s continuously operating reference stations, and correcting minute deviations in the satellite signals. Specifically, phase information of signals received from multiple GNSS satellites—GPS, GLONASS, and QZSS (Michibiki), for example—is compared to that of the reference station, and error factors are subtracted in real time to enable centimeter-level high-precision positioning.

Conventionally, such high-precision positioning required stationary high-cost GNSS survey equipment and base station sets. However, recently network RTK that delivers correction information via the Internet and services such as Japan’s QZSS-provided sub-meter augmentation (CLAS) have been developed, making RTK positioning easily accessible with just a small receiver and a communication environment. As a result, centimeter-level positioning via a combination of a smartphone and an inexpensive small GNSS receiver has become feasible without relying on survey-dedicated instruments. This is truly a groundbreaking technological innovation that lowers the barrier to surveying.

What changes with smartphones × RTK?

So, what changes on solar construction sites when smartphones are combined with RTK technology into “smartphone RTK”? The keywords are “high precision,” “labor reduction,” and “real time.” The main benefits expected from introducing smartphone RTK include:

• Surveying can be completed by one person: Survey tasks that previously required two to three people can be performed by one person with only a smartphone and a small GNSS receiver. Reducing personnel not only cuts labor costs but also enables surveying to proceed smoothly even on sites with labor shortages.

• Greatly improved work efficiency: There is no need to carry heavy tripods or surveying instruments or to repeatedly set up equipment at each survey point. You can measure and record required points simply by walking around the site with a smartphone, dramatically shortening surveying time. In practice, there are reported cases where work that took three people 20 minutes was reduced to one person in 10 minutes after introducing one-person surveying.

• Prevent rework with high-precision layout staking: Smartphone RTK constantly shows the accurate current position in global coordinates. Because designed coordinate values can be directly shown on site for pile-driving and marking, positional errors causing construction mistakes are minimized. For example, keeping pile-position errors within ±2 cm (±0.8 in) can prevent downstream corrections or rework.

• Operable without specialized knowledge: Intuitive smartphone app interfaces allow even non-experienced surveyors to perform surveying and layout staking easily. Coordinate navigation that displays guide arrows and distance to the target point on the screen, and AR (augmented reality) functions that overlay design positions on the camera, enable reliable surveying without relying on “intuition and experience.”

• Real-time data sharing: Measured coordinate data and photos can be uploaded to the cloud on site and immediately shared with managers and designers in the office. There is no need to return with data for later drawing conversion as in the past, so surveying results can be promptly reflected in construction plan adjustments and quality checks, accelerating the entire process.

By leveraging smartphones × RTK, surveying work in solar construction becomes dramatically more efficient and transforms into a high-precision process that does not depend on many people. Next, let’s look at how one person can proceed from surveying to pile-driving and as-built verification using smartphone RTK.

Workflow for one-person pile-driving, site surveying, and as-built verification

By utilizing smartphone RTK, each surveying process in solar construction can be performed seamlessly by one person. Below is a step-by-step explanation of that workflow.

• Site survey (terrain assessment before construction): Before construction, measure the site in detail. Walking while positioning with an RTK receiver attached to a smartphone enables efficient terrain data acquisition even on large sites. If you combine this with LiDAR scanners or 360° cameras built into modern smartphones such as iPhones, you can simultaneously record point cloud data of the ground surface and panoramic photos. The acquired site data are useful for preparing earthwork plans and shadow simulation analyses.

• Pile-driving and staking (foundation installation): Based on the pile layout coordinates specified in the design drawings, mark pile-driving locations on site. Smartphone RTK can display in real time the deviation from the pre-entered design coordinates. The operator simply follows the navigation arrows on the smartphone screen to reach the target point and drives piles or inserts marking pins at the specified positions. Without the need for tape measures or extra personnel for staking, one person can accurately indicate and install piles one after another, allowing pile-driving work for large solar power plants to be completed in a short period.

• As-built verification (post-construction inspection): After all pile-driving and installation tasks are complete, perform as-built surveying to verify construction results. By measuring the coordinates and heights of pile tops and panel corners with smartphone RTK, deviations from design values can be checked immediately. Because measurements are shared to the cloud as they are taken, the office can monitor as-built conditions in real time. If deviations beyond acceptable ranges are found, corrective actions can be taken early. Such rapid feedback helps ensure quality and prevents rework.

As described above, smartphone RTK enables a single person to carry out surveying, pile-driving, and inspection in an integrated manner. Next, let’s look at how cloud integration for managing point clouds, photos, and coordinates further supports this workflow and reduces management workload.

Cloud integration of point clouds, photos, and coordinates reduces management workload

Survey data obtained with smartphone RTK contribute greatly to improving management efficiency when integrated with cloud platforms. Traditionally, organizing survey results and producing drawings required a lot of effort, but the following cloud-based mechanisms make information sharing and data management between site and office much smoother.

• Immediate sharing and visualization of survey data: Coordinate values and photos of survey points acquired by the smartphone app can be uploaded to the cloud with a tap and instantly shared with the office over the Internet. Uploaded data are automatically plotted on maps or 3D views, allowing office staff to visualize site progress in real time.

• Centralized management of point cloud data: Point cloud (3D scan) data acquired during site surveys or construction can be stored and managed in the cloud. Since these are linked with precise position information for each measured point, it is easy to extract cross-sections or calculate volumes later as needed. Large numbers of point cloud files and photo assets are organized in the cloud, eliminating concerns about lost or misfiled files.

• Streamlined document creation: Cloud-based survey data can be used directly for reports and drawing creation. For example, you can immediately compile on-site reports using automatic distance and area calculation functions between measured points, or quickly create as-built drawings. Digital centralization of data avoids transcription errors and duplicate entry, reducing administrative workload for managers and improving work quality.

With such cloud integration, the survey data management cycle in solar construction is dramatically streamlined. Because all information collected on site is immediately shared and stored, communication loss among stakeholders is reduced and decision-making and overall construction optimization are accelerated.

Introduction and proposal for the smartphone construction support tool LRTK

Finally, as a concrete solution to realize the smartphone RTK surveying revolution described above on-site, we introduce LRTK. LRTK is a smartphone-mounted RTK positioning device and cloud service developed by Refixia Co., Ltd., a startup originating from Tokyo Institute of Technology, and is a smartphone construction support tool that turns a smartphone into a high-precision surveying instrument. It consists of a small GNSS receiver called “LRTK Phone” that magnetically attaches to the back of an iPhone or iPad, an easy-to-use dedicated app, and a cloud service for storing and sharing data—together enabling one-person surveying and data management as described in this article.

By introducing LRTK, you can utilize not only centimeter-level positioning through smartphone RTK (cm level accuracy (half-inch accuracy)), but also features tailored to field needs such as coordinate navigation that guides you to the point you want to measure, cloud management of acquired point clouds, photos, and survey point information, and AR guidance that overlays virtual models and guides onto camera images. For example, simply pointing the device at the point you want to measure can automatically record coordinates and upload them to the LRTK cloud on the spot for team sharing. The dedicated app emphasizes intuitive operability, so even those without surveying expertise can use it without difficulty.

LRTK is already being used in civil engineering construction and infrastructure inspection sites, and practical examples of one-person surveying in mega-solar construction are increasing. With centimeter-precision positioning and AR-enabled visualization, anyone can become immediately effective on site for surveying and pile-driving tasks. As a smartphone construction support tool that can achieve both improved surveying accuracy and labor reduction, LRTK can greatly contribute to solving surveying challenges in solar construction. If you are struggling with inefficiencies or labor shortages in surveying for solar power plant construction management, we recommend considering the introduction of the smartphone RTK solution LRTK. A surveying revolution that can be completed with a smartphone may soon arrive at your site.