Centimeter Accuracy Even Outside Coverage! Smartphone GNSS Supporting Mountainous Mega-Solar Sites

What if, even at a remote mountain site where mobile signals don’t reach, you could achieve centimeter-level positioning using the latest GNSS positioning technologies? This article explains the benefits of smartphone GNSS that can operate outside cellular coverage, using a mountainous mega-solar construction site as an example, and the technologies that make this possible.

Site environment and communication infrastructure challenges for mountainous mega-solar construction

Large-scale solar power plants (so-called mega-solar) installed on slopes or cleared forests in mountainous areas have unique challenges due to their locations. One of these is insufficient on-site communication infrastructure. In mountain regions far from urban areas, “outside coverage” zones where mobile phone or internet signals don’t reach are not uncommon. Even when trying to use positioning devices or work terminals across a vast development area, communications may be unavailable, causing data transmission and reception to stall.

The terrain characteristics typical of mountainous regions also affect the site environment. In valleys and highly undulating terrain, visibility is poor and signals from base stations can be blocked. Communications issues can impede worker coordination and remote monitoring of heavy machinery operations. Particularly problematic is losing the network connection needed to receive real-time positioning correction information for tasks that require high-accuracy positioning. Mega-solar construction demands accurate position information for tasks such as site-wide surveying and checking stake positions for panel installation, but constraints in communication infrastructure can hinder these operations.

Of course, methods such as installing temporary relay antennas or using satellite communications are considered to supplement communications, but these can be costly or impractical. Ultimately, establishing a system that allows work to proceed regardless of communication infrastructure is a pressing on-site need.

Importance of high-precision positioning and conventional limits (RTK dependence and base station installation)

On large development sites like mega-solar, errors of even a few meters can cause serious problems. For example, if the placement of solar panels is off, spacing between adjacent panels can be disrupted, hampering rack construction or shading panels and affecting power generation efficiency. For this reason, surveying and positioning from site preparation through equipment installation must be performed with centimeter-level accuracy.

However, conventionally achieving such high-precision positioning on-site has involved various constraints. Standard GNSS (e.g., GPS) positioning alone yields errors on the order of 5–10 meters and cannot be used standalone without augmentation. The method typically used to compensate for this is RTK (real-time kinematic) corrections, but RTK positioning requires a pair of devices: a base station and a rover. When within network coverage, network RTK receiving public base station data via NTRIP over mobile lines can be used. In mountain areas where network connectivity is unstable, the approach has been to install a dedicated base station on-site and wirelessly communicate with the rover.

Installing a dedicated base station requires pre-surveying accurate base coordinates and limits operation to the radio range between the base and rover. RTK equipment itself is expensive and requires specialized configuration, making operation difficult without personnel skilled in surveying. Installing a base station or dispatching a surveying team for each mountainous mega-solar site is inefficient and costly. Although high-precision positioning is crucial, traditional methods present major hurdles in both communication infrastructure and equipment/personnel. There is also a post-processing method that records observation data when communications are unavailable and analyzes it later in the office, but this does not provide immediate on-site results and reduces work efficiency.

GNSS positioning technologies for out-of-coverage use (CLAS and smartphone receiver evolution)

Recently, new GNSS positioning technologies have emerged to solve these challenges. One key term is “CLAS (centimeter-level augmentation service).” CLAS is a positioning augmentation service provided by Japan’s Quasi-Zenith Satellite System (QZSS, Michibiki), delivering correction data calculated from the Geospatial Information Authority of Japan’s Continuously Operating Reference Stations (CORS) network via satellite. Simply put, instead of receiving correction data from a base station over the internet, users can receive correction data directly from satellites overhead. This makes it possible to achieve real-time centimeter-level positioning in out-of-coverage areas, as long as the sky is visible. The four QZSS satellites are planned to expand to a seven-satellite constellation in the latter half of the 2020s, which should provide more stable augmentation signals even in mountainous regions.

Another key point is the evolution of smartphone receivers. Historically, achieving CLAS-based high-precision positioning required dedicated large receivers. Today, however, small high-performance GNSS antennas and receivers can be used in combination with smartphones. The latest smartphones support multiple frequency bands such as L1/L5 and are compatible with multiple satellite systems including GPS, GLONASS, Galileo, and QZSS. Reductions in ionospheric errors and an increased number of tracked satellites have dramatically improved stability and accuracy. Additionally, with external GNSS receivers that connect to phones, surveying equipment that once weighed several kilograms can be condensed to pocket size. In other words, the “smartphone + GNSS” combination is making it a reality to obtain centimeter-level accuracy without a base station, even outside cellular coverage.

Practical on-site use cases (staking, point clouds, as-built verification)

So how can out-of-coverage-capable smartphone GNSS concretely help on mountainous mega-solar construction sites? Let’s look at several use cases.

• Positioning for stake driving: When installing foundations or posts for solar panels, stakes must be driven at precise locations. Smartphone GNSS can navigate to stake positions based on design coordinates. Workers can confirm their current location on the smartphone display, mark the specified position, and drive the stake on the spot. Traditionally, a surveyor would use a total station to position and then instruct workers, but smartphone GNSS enables one person to intuitively carry out stake-driving tasks. Moreover, height information obtained via GNSS can be used to check stake depth and level on-site, aiding foundation quality control.

• Topography recording via point clouds: In mountainous development, it is important to accurately record and manage terrain changes from cutting and filling. Combining a smartphone camera or LiDAR sensor with GNSS allows acquisition of site terrain as point cloud data. For example, walking around with a phone to scan the ground surface can complete wide-area 3D surveying in a short time. Because the collected point clouds are tied to geospatial coordinates (absolute coordinates), they can be used directly for as-built management and earthwork volume calculations. The ability to digitally record terrain with a single smartphone, without hauling heavy laser scanners, is a major advantage. For distant areas beyond the smartphone LiDAR’s direct reach, photogrammetry from multiple photo positions can supplement the data. Combining LiDAR and camera data as needed enables precise digital measurement of extensive mountainous terrain.

• As-built measurement and quality control: After site formation is complete, high-precision GNSS is powerful for as-built measurement to verify that shapes and dimensions match design. Distances and elevation differences between remote points can be measured immediately on-site and compared against design values using a smartphone. For example, the height and tilt of panel-supporting racks can be checked with GNSS positioning, and any discrepancies can be corrected immediately. Real-time measurement and verification prevent rework and help ensure quality. Measuring multiple points in succession allows quick assessment of the overall site finish. Because measurement results are automatically recorded digitally, preparing inspection reports becomes easier and improves efficiency in quality control.

As described above, smartphone GNSS usable outside coverage supports various processes from surveying to construction management. The ability to complete tasks that previously required separate equipment or steps—such as stake placement guidance, terrain point cloud acquisition, and as-built accuracy checks—with a single smartphone can dramatically boost on-site productivity.

Portability and simplicity unique to smartphone GNSS

The attention smartphone-based GNSS positioning is receiving is also due to its portability and ease of use. Conventional high-precision GNSS surveying equipment requires tripods or mounting apparatus, making transport and setup time-consuming. In contrast, smartphone GNSS fits in the palm of your hand, making it easy to carry into mountainous sites on foot. Equipment can be handled with one hand even on steep slopes, allowing mobile work at measurement points. Being lightweight significantly reduces the burden of transporting equipment on steep terrain without trails.

User-friendly smartphone apps mean non-specialists can operate the system intuitively. Real-time display of your position on a map, navigation to target points, and cloud features for saving and sharing measurements on the spot are smartphone conveniences that support fieldwork. For example, arrows or bearings shown on the phone screen guide you to specified measurement points so you won’t get lost even in complex terrain. You can also record photos and notes while positioning, removing the need to carry paper drawings or multiple devices.

Additionally, smartphone GNSS systems make power management easier. Conventional equipment often required batteries or generators, but a smartphone paired with a small receiver consumes little power and can run for long periods using mobile battery packs for convenient charging during work. This portability and simplicity enable continuous surveying and monitoring across vast mega-solar development sites.

Ripple effects on labor reduction, safety, and real-time management

Introducing smartphone GNSS usable outside coverage delivers not only direct efficiency gains on-site but also various positive effects in adjacent areas. One is its contribution to labor reduction. Traditionally, surveying and positioning required teams of multiple people, but smartphone GNSS allows more tasks to be completed by a single worker. This reduces personnel needs and helps mitigate shortages of skilled technicians, enabling a limited workforce to cover more sites.

Improved safety is another important benefit. Reducing the need for people to set up surveying equipment or enter hazardous or unstable areas lowers the risk of falls and accidents. Using smartphone camera functions or AR displays, you can perform necessary positioning or monitoring from a safe distance, allowing workers to understand the situation from secure locations.

Moreover, if positioning data are shared to the cloud in real time, site supervisors and remote managers can instantly grasp the situation. This enables real-time progress and quality management and rapid response when issues arise. Remote specialists can also review cloud data and provide immediate guidance, facilitating collaborative work in real time.

Furthermore, such digital efficiencies contribute to shorter construction schedules and cost reductions. Accumulated surveying and construction data stored in the cloud can be analyzed for advanced planning and knowledge sharing across sites. Smartphone GNSS adoption thus goes beyond improving positioning accuracy; it helps drive changes in construction workstyles and promotes smart construction through digital transformation.

Field deployment proposal: LRTK for out-of-coverage operation, cloud integration, and AR guidance

As described above, there are many benefits to high-precision positioning and smartphone GNSS use outside coverage at mountainous mega-solar sites. Finally, we introduce “LRTK” as one solution to achieve these benefits. LRTK is a high-precision GNSS positioning system designed to work with smartphones, providing out-of-coverage RTK positioning, cloud service data integration, and AR-based visual guidance.

One feature of LRTK is its compatibility with QZSS Michibiki’s CLAS signals. This enables centimeter-level positioning without an internet connection even at sites outside cellular coverage, such as mountainous areas. Positioning data, acquired point clouds, and photos can be stored and shared in the cloud, delivering site information to the office immediately and promoting collaborative work. Additionally, AR overlays of design drawings or measurement points on the smartphone screen can provide intuitive guidance to workers. For example, visualizing stake positions or excavation limits for heavy machinery through the screen can reduce on-site mistakes and enhance safety.

LRTK offers these cutting-edge technologies in an all-in-one package that lowers the barrier to on-site adoption. By simply attaching a compact dedicated device to a smartphone, anyone can handle survey-grade accuracy, allowing untrained workers to perform on-site positioning tasks. The confidence of obtaining centimeter accuracy outside coverage, combined with cloud and AR-enabled smart site management, means LRTK can make mountainous mega-solar construction more efficient, safer, and more reliable. In fact, LRTK is already being introduced in mountainous civil surveying and solar farm construction, steadily making high-precision positioning achievable where it was previously difficult. These initiatives align with the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction and construction DX (digital transformation) policies, and the spread of smartphone GNSS–based smart construction is expected to accelerate. Bringing a smartphone and a small GNSS device into a remote mountain area will soon allow you to complete everything from high-precision surveying to construction management—such a future is just around the corner.