AR visualization of contour lines transforms terrain management at solar power sites

On solar power plant construction sites, understanding and managing terrain is a key to project success. When installing solar panels on sloping land such as in mountain areas, it is essential to accurately understand which areas need earthwork and where equipment can be placed. What is used for that purpose are contour lines. Contour lines are basic information showing different elevations on a map, but reading curves on paper drawings or 2D screens and imagining the terrain is not easy. Unless experienced, it is difficult to intuitively grasp on-site elevation differences from contour lines on drawings, which can lead to on-site judgment errors and communication mistakes.

Recently, visualizing contour lines using AR (augmented reality) has attracted attention as a technology that solves this difficulty in terrain understanding and renews on-site management. It is becoming possible to overlay contour lines and ground models from design drawings onto live terrain imagery through a smartphone or tablet screen. As the construction industry accelerates DX (digital transformation), symbolized by the Ministry of Land, Infrastructure, Transport and Tourism–led "i-Construction", AR is poised to revolutionize terrain management at solar power sites as well. This article explains in detail the significance and benefits of being able to intuitively grasp contour lines on site with AR, expected use cases, and the concrete implementation method using a smartphone and RTK-GNSS (the workflow from simple surveying with LRTK to point cloud generation, contour extraction, and AR display). We deliver practical and forward-looking topics for construction managers, designers, clients, and surveying engineers interested in improving on-site productivity and leveraging DX.

Terrain management at solar power sites and challenges of contour maps

In large-scale solar power projects, the scale of earthworks and panel layout planning directly affect power generation efficiency and construction costs, so accurate terrain understanding is indispensable. On sites with complex undulations, it is first necessary to grasp on-site elevation differences and slopes, and then calculate the earthwork area and the volume of fill and cut based on that. The basic material used for this is the contour map. A contour map is a topographic map that expresses elevations within a site by connecting points at regular height intervals (e.g., 0.5 m (1.6 ft) or 1 m (3.3 ft) increments), and it serves as a guideline for earthwork plans and drainage planning.

However, traditionally it has not been easy to fully imagine the on-site situation by staring at contour maps alone. Especially for large sites or highly undulating terrain, one has to follow densely packed contour lines on paper drawings and mentally imagine a three-dimensional terrain, which is a task that relies heavily on the tacit knowledge of experienced personnel. For less experienced staff or clients, understanding the bumps and hollows of the site from lines on a drawing itself is a hurdle. When sharing terrain recognition between contractors, designers, and clients via drawings, differences in interpretation or lack of understanding can lead to communication losses. Gaps such as "it looks different from what I expected" or "the real thing doesn't match the image I was shown" can cause construction errors, rework, and additional costs.

Moreover, there has been the challenge that grasping the current terrain using traditional methods requires time and effort. Surveying with total stations or leveling instruments by surveyors required days to measure numerous point elevations across wide sites and create contour maps. Drone photogrammetry to create point clouds has increased recently, but it requires specialist operators, aviation law procedures, and high-performance PCs for image processing, and re-surveying often entails outsourcing arrangements again, creating inefficiencies. In this way, the field of terrain management has seen limits in traditional methods in terms of accuracy, efficiency, and information sharing. In response to these challenges, the approach of directly overlaying contour lines on-site using AR, rather than relying on paper or 2D screen contour maps, is expected to be the key to renewing terrain management.

Significance and benefits of on-site AR contour visualization

AR contour visualization has great significance in bridging the gap between drawings and the field and making terrain information intuitively understandable to everyone. When you hold up a tablet or smartphone, digital contour lines and planned ground models are drawn over the camera image of the actual terrain, so you can perceive elevation differences as if lines were drawn directly on the ground. This makes it possible to visualize undulations that previously could only be imagined in your head, enabling terrain understanding that does not depend on the ability to read survey maps.

AR contouring provides the following concrete benefits:

• Intuitive terrain understanding: Because contour lines are displayed along the actual ground surface, you can grasp the direction and steepness of slopes at a glance. For example, on steep sections contour lines are projected densely on the ground, and on gentle areas the contour spacing appears wider, so you can intuitively understand gradient conditions on site without referring to drawings.

• Faster decision-making: Because you can check terrain with AR while walking around the site, you can make construction decisions on the spot without spreading out drawings or conducting surveying measurements each time. Operators and site supervisors can make real-time fine adjustments to work by seeing through the camera things like "how many more meters to cut to reach the planned elevation" or "up to which line fill is required." This significantly shortens the process that traditionally waited for surveying results before making decisions.

• Smoother communication: Terrain information shared via AR is clearer than explanations with words or drawings. Showing a client or site staff the smartphone screen allows you to visually share the current terrain and planned finished elevations. Terrain undulations and earthwork extents that were hard to convey with paper maps can be aligned on the spot, making explanation of design intent and consensus building smoother.

• Reduced errors and rework: By overlaying contour lines and design models on site for confirmation, it becomes easier to notice discrepancies or misunderstandings during construction. For example, if fill is insufficient, the design line will appear floating above the ground in AR; conversely, if too much has been cut, the line will appear sunk below the surface. This visual feedback helps prevent situations where "the finished result turned out different from the drawings," enabling early corrective actions. This leads to improved quality assurance, shorter schedules, and reduced unnecessary costs.

Terrain information that was previously captured only in planar drawings and numbers now appears on site in an understandable form thanks to AR. This is like visualizing and sharing the experienced image that veteran workers hold in their heads using digital technology. By introducing AR contouring, terrain management will shift from a person-dependent task reliant on experience and intuition to an objective and efficient process.

Main scenes where AR contour lines are useful

On-site projection of contour lines via AR is expected to be useful in various terrain-related situations. Below are the main use cases anticipated at solar power sites.

• Site reconnaissance and terrain confirmation: At the pre-survey stage of a planned site, you can check the contour lines of the current terrain through your smartphone. Even ground that appears flat can be checked for subtle gradients, valleys, or rises. Capturing terrain features in initial site surveys helps in considering appropriate earthwork policies and panel layout plans.

• Construction planning: AR contour lines are also powerful when drawing up specific earthwork plans. For example, decisions about how far to cut with machinery or where to set fill boundaries can be considered with the AR contour lines as a guide. By displaying the design ground model in AR and simulating construction steps while checking differences from the existing terrain, you can create plans with less unreasonable work or waste.

• Explanations to clients: Even clients or stakeholders without technical knowledge can have terrain conditions intuitively explained via AR. If they attend the site and view the landscape with contour lines on a tablet screen, points such as "where and how much will be cut" or "how flat it will be when completed" become immediately clear. Information that was difficult to convey with paper contour maps or numbers can be explained convincingly with visual information.

• Consensus building among stakeholders: When designers, contractors, and clients conduct on-site checks together, AR helps form a common understanding. For example, in an intermediate stage of earthworks you can overlay the planned lines on the current terrain and confirm together, "We have completed earthworks up to here, and another ◯ m (◯ ft) of excavation is needed." Everyone can view the same image while discussing, reducing interpretation gaps and making it easier to agree on corrective measures or plan changes on the spot.

• As-built management and inspection: AR contour lines can also be used when verifying whether finished work matches the design after construction completion. By overlaying design contour lines or models on the completed ground, you can visually check deviations in finish. For example, you can immediately confirm on site whether the foundation heights for solar panel racks match the planned levels or whether slope gradients conform to design values. This can improve the efficiency of inspections and the accuracy of records.

As described above, AR contour display supports the site across a wide range of phases from planning to construction and post-completion inspection. Its impact is particularly large on projects such as solar power plants with wide sites and significant elevation differences.

AR contour display realized by smartphone + RTK + point clouds

How is AR contour visualization like this achieved? The key is the combination of a smartphone, RTK-GNSS, and point cloud data.

Recent smartphones and tablets come standard with AR capabilities that allow overlaying three-dimensional data on camera images. However, to draw contour lines accurately on the terrain, positional and elevation data in the digital model must match real space exactly. Ordinary smartphone GPS has errors of several meters (several ft), so contour lines would be displayed misaligned if used as-is. Here, the satellite positioning technology known as RTK (Real Time Kinematic) is powerful. By using a small high-precision GNSS receiver attached to a smartphone, real-time corrections can be applied to positioning information from satellites, reducing positional errors to a few centimeters or less (a few inches or less). If you attach an RTK-capable device to a smartphone and link it with a dedicated app, the smartphone instantly becomes a surveying instrument that can measure its current position with cm level accuracy (half-inch accuracy). Because of this high-precision self-positioning, digital contour data can be overlaid on the real terrain without misalignment.

Next, the terrain itself must be digitized. You need to have the shape of the current terrain or the design target ground in a computer and calculate and render contour lines from it. A commonly used digital representation of terrain is the 3D point cloud data. A point cloud records many points that make up the ground surface or structures as XYZ coordinates and can be regarded as a digital model that almost directly copies the real shape. In addition to photogrammetry using a drone or smartphone camera, recently some high-end smartphones equipped with small LiDAR sensors can also acquire point cloud data on site. By walking the earthwork area while scanning with a LiDAR-equipped smartphone, you can create a point cloud consisting of millions of points that indicate ground undulations in a short time.

However, point clouds acquired by a smartphone alone could be inaccurately referenced or distorted over wide-area scans. Here again, high-precision positioning from RTK is effective. By combining accurate coordinates obtained by RTK with smartphone AR self-positioning, you can record undistorted, precise point clouds even during long-duration, wide-area scans. From the acquired point cloud data you can generate a ground surface model and slice it at fixed elevation intervals to extract contour lines. Whereas contour generation used to be done on desktop PCs with GIS software, recent cloud services and dedicated apps have automated and accelerated this processing.

In summary, the combination of smartphone + RTK-GNSS + point cloud technology made on-site AR contour display a reality. Precisely measuring your own position, acquiring 3D terrain data, and overlaying contour lines from that data in real time into space—the fusion of surveying and AR is underpinning on-site DX.

Workflow from simple surveying with LRTK to AR display

By using the technologies mentioned above, anyone on site can easily experience AR contour display. Specifically, by using LRTK, a smartphone-complete high-precision surveying solution, the following steps can be performed consistently from terrain data acquisition to AR display.

• Acquire high-precision positions (surveying): Attach an RTK-GNSS receiver (LRTK device) to a smartphone and launch a surveying app. This instantly turns the smartphone into a cm-accurate positioning terminal, allowing measurement of coordinates (latitude, longitude, elevation) at arbitrary points on site. The person in charge can measure desired points by simply pressing a button, enabling high-precision terrain surveying that previously required specialized equipment. Even on wide sites, one person can efficiently obtain many survey points and grasp the terrain framework.

• Generate point cloud data: Next, perform point cloud scanning of the site using the smartphone camera or LiDAR. Because LRTK’s high-precision positioning continuously corrects your location during scanning, you can obtain an absolute-coordinate 3D point cloud in a short time simply by holding up the smartphone and walking. A dedicated app can build the point cloud in real time, generating and confirming a 3D model on the spot that includes terrain undulations and the shape of in-progress earthworks.

• Extract contour data: The acquired point cloud data is automatically processed in the cloud or within the app, and within minutes a surface mesh and contour data are generated. For example, you can specify output of a contour map at 50 cm (19.7 in) intervals, giving you an up-to-date terrain map on site quickly. Tasks that required specialized skill in reading contour lines are now at a stage where digital processing can instantly visualize them.

• On-site visualization with AR: When preparations are complete, display contour lines over the site in AR mode on the smartphone. Because the LRTK positioning information allows the contour data on the smartphone screen to align precisely with the actual terrain, contour lines appear in correct positions and elevations relative to the site scenery. This makes it possible to walk the site with just a smartphone and understand and evaluate the terrain without carrying paper drawings.

That a single smartphone can complete surveying, data processing, and AR visualization is revolutionary. The process that once had surveying crews take data back for drawing and then waited days to make decisions has been reborn into a workflow that provides immediate on-site feedback. This simple surveying and AR linkage using LRTK is dramatically changing terrain management at solar power sites.

Conclusion: AR contour lines and LRTK surveying accelerate on-site DX

AR visualization of contour lines holds the potential to dramatically streamline and improve the quality of terrain understanding and consensus-building processes in solar power site management. Compared to the era of relying on paper drawings, being able to directly view digital information on site has significantly sped up the basic actions of "seeing," "measuring," and "verifying." This brings not only shorter schedules and cost savings but also improved planning accuracy and enhanced site safety.

The important point is that these advanced technologies are no longer exclusively for specialists. By adopting the easy LRTK surveying solution using a smartphone and RTK introduced here, anyone on site can readily obtain high-precision terrain data and enjoy the benefits of AR contour lines. By stepping into on-site DX without being bound by traditional habits or analog methods, productivity in construction management and design work can dramatically improve.

In civil engineering and construction fields, including solar power, the fusion with digital technology is becoming the new norm. The combination of AR contour display and LRTK surveying is a representative example of this trend. If you feel challenges in terrain management or surveying at your site, consider trying this new approach. By using [LRTK surveying](https://www.lrtk.lefixea.com/blog-js/taiyoukou2) that can be completed with just a smartphone, you may be able to take the first step toward DX as soon as tomorrow. Embrace cutting-edge AR technology and an easy surveying solution and work toward forward-looking site improvements.