What can RTK AR do? Five on-site use cases and benefits of implementation

In civil engineering and construction sites, the use of AR (augmented reality) technology is advancing, with initiatives such as overlaying design models onto actual scenery to visualize construction and displaying survey results in real time. However, conventional smartphone AR often suffers from positioning errors of several meters (several ft), which was insufficient for construction management and surveying that require millimeter-level precision (approximately 0.04 in). That is why the combination with RTK (Real-Time Kinematic) methods using satellite positioning GNSS has attracted attention. By applying RTK corrections, positioning errors can be reduced to a few centimeters (a few in), enabling high-precision AR displays.

This “RTK AR” technology is expected to become a new solution supporting DX (digital transformation) in the construction industry. Within the trends of the Ministry of Land, Infrastructure, Transport and Tourism-promoted *i-Construction* and construction ICT, it is increasingly recognized as contributing to the advancement and efficiency of on-site work. In this article we will explain, from a professional perspective, what can be done on-site with RTK AR, five on-site use cases, and the benefits of implementation.

Pile driving guidance (AR pile driving navigation)

Pile driving is the process of installing piles into the ground as the foundation of a structure, and it is a critically important step that determines the safety of the structure. To install piles at the correct positions and depths, the staking-out work that indicates pile positions on site based on coordinates on the drawings before construction is indispensable. Traditionally, this staking-out has typically been performed by surveying teams using total stations or tape measures to measure distances from reference points and placing batter boards or stake marks on the ground. However, manual staking-out requires highly skilled techniques and considerable time and effort, and surveying itself can be difficult depending on terrain or weather. In addition, small measurement errors or positional shifts by humans can occur and pose a risk of construction mistakes.

Using RTK AR radically streamlines this pile position staking work. Through a smartphone or tablet screen, a virtual pile (AR pile) designated by the design can be displayed, allowing workers to move intuitively to the target point while viewing markers superimposed on the real scenery. Like an in-construction-site car navigation system, arrows and distances are displayed on the device screen in real time to guide workers to the designated pile position. As you approach the correct position, fine distance displays such as “○○ cm left” appear, and when you reach the target the virtual pile and the real-world mark line up exactly so you know it is the designated point.

This AR pile-driving guidance enables even inexperienced staff to identify pile positions accurately without getting lost. Staking-out work that used to rely on the intuition and skill of veteran workers is replaced by a digital guide, making it possible for anyone to complete pile positioning in a short time. On sites that have implemented RTK AR, reports indicate that the time required for pile position marking has been greatly reduced compared with traditional methods and that one person can mark multiple piles in succession. This leads to reduced personnel and costs, and because positions can be established with centimeter-level accuracy (half-inch accuracy), little rework is required in subsequent processes. Safety is also improved because pile positions can be confirmed on-screen from a safe distance, even in dangerous heavy-equipment operation areas or on unstable footing. AR displays allow accurate positioning even on concrete where physical stakes cannot be placed or on steep slopes.

As-built management (immediate AR inspection of construction results)

In civil engineering, as-built management to confirm that completed structures or regraded land conform to the design shapes and dimensions is important. Traditionally, after work completion, surveyors would measure heights and positions on site and compare them with drawing data to verify quality. This process takes time and requires taking measurement data back for analysis.

With RTK AR, much of as-built management can be performed on site in real time. For example, design 3D models or reference surfaces can be AR-displayed over the actual object on site, allowing verification by overlaying them on the constructed structure. In embankment work for roads, the designed finished line can be projected onto the ground with AR, enabling the equipment operator to confirm continuously that the embankment matches that line as work proceeds. There are cases where operators were guided by AR instructions such as “keep adding soil until the design is no longer visible,” allowing embankment work to proceed without relying on intuition. After finishing, the completed terrain can be overlaid with the design model in the smartphone camera view to visually check for hollows or shortages. Discrepancies of a few centimeters (a few in) that were easy to miss before can be spotted at a glance with AR, and corrective instructions can be issued immediately.

Moreover, systems like LRTK utilize smartphone-integrated LiDAR scanners or photogrammetry to obtain high-precision 3D point cloud data on site instantly. The acquired point clouds include geocoordinates, making them easy to compare with design data, and cloud-based automatic calculations of volume and cross-section differences are possible. Even for complex terrains, you can quickly get analysis results such as “where and by how many centimeters to cut or fill.” By combining AR and data analysis, the accuracy and speed of as-built management are dramatically improved. Preparing drawings and reports for as-built inspections can be greatly simplified by using digital data directly, contributing to both improved reliability of quality control and increased efficiency.

Boundary visualization (displaying invisible boundaries on site)

Accurately grasping land boundaries and construction extents is an important task for surveying companies and municipal civil engineering departments. However, boundary lines are often represented only as lines or numbers on drawings and are not visible on site. Even if existing boundary stakes or markers exist, they may be hard to find due to vegetation or undulations, or boundary points may not be clearly indicated at all. Therefore, boundary confirmation can be time-consuming and misidentifications can lead to land disputes.

With RTK AR technology, map boundary lines can be visualized directly on site. If land boundary coordinate data are registered in the system in advance, simply pointing a smartphone camera on site will render the specified boundary line in AR in the space. Even on empty lots where nothing is present, the invisible boundary line is clearly displayed on the screen, allowing workers to immediately see “where the property begins and ends.” RTK provides centimeter-level positioning (half-inch accuracy), so boundaries based on cadastral maps or design drawings can be shown at the exact real-world location without error, eliminating discrepancies in on-site recognition.

This AR display of boundaries is useful in various contexts such as land surveying, land acquisition meetings, and pre-checks of construction extents. For example, in a road widening plan, it can be difficult for local residents to visualize the required land from drawings alone. By using RTK AR to display boundary lines and planned road widths on the actual ground, residents can intuitively understand the situation and consensus building becomes smoother. During construction, equipment operators referencing AR construction-area lines can avoid unnecessary excavation or encroachment. Making the otherwise “invisible” information of boundary lines visible greatly contributes to improved efficiency of boundary confirmation and prevention of disputes.

AR verification of design models (comparing 3D models with the site)

One purpose of using design models on construction sites is to “eliminate discrepancies between design and construction.” AR verification of design models involves overlaying design data (3D CAD, BIM/CIM models, etc.) onto the actual scene to directly compare with structures during or after construction. Because RTK AR ensures accurate alignment between the model and reality, you can immediately check on site whether something has been built according to the design.

For example, at a bridge construction site when installing columns or bolts, displaying a design-position guide on the smartphone AR screen prevents misalignment during component installation. For rebar layout or pipe routing, projecting the completed 3D model in AR enables workers to compare the model to the physical object as they work and install accurately. If position or height is off by even a few centimeters (a few in), a discrepancy between the model and the actual object becomes immediately apparent. While RTK AR does not provide millimeter-level exactness, it offers sufficient accuracy for determining on-site whether the work is within allowable tolerances for construction management.

Such AR verification allows early detection of construction errors and prevents rework. Deviations that previously were discovered only after taking survey results back to the office can now be detected and corrected on site, reducing waste such as removing and reattaching components later. If the client or site supervisor reviews the AR imagery together, misunderstandings that cause errors can also be prevented. Proceeding with construction while sharing a digital “finished form” enables data-driven construction management that does not rely on veteran intuition. Before construction begins, AR can also be used to project the completed model onto the site to check for clashes or to preview the final appearance, which is effective for on-site consensus building and quality assurance.

Overlay comparison with point cloud data (3D scan conformity verification)

Recently, 3D point cloud data from drones and laser scanners have been used in construction management. A point cloud is a collection of many measured points that represent the shape of terrain or structures in detail. Using RTK AR, this point cloud data can be AR-displayed on site and overlaid to compare with design models or the actual scene.

For example, after an operator finishes drilling or embanking, the site can be scanned with a smartphone LiDAR to acquire a point cloud. Because RTK assigns absolute coordinates to that point cloud, it is handled in the exact same coordinate system as the design ground model. If a tablet displays the design model and the acquired point cloud simultaneously in AR on site, protruding areas that have been overfilled or areas that are still lacking become apparent immediately as color or shape differences. The major advantage is that this can be visually confirmed on site rather than comparing point clouds and design at a desk after the fact.

There are also applications such as observing long-term changes by overlaying point clouds acquired periodically for displacement measurement of existing structures. Although complex point cloud data are usually analyzed with specialized software, overlaying them in AR enables differences to be understood with on-site intuition. Of course, the point cloud data themselves can be used in the cloud for detailed analysis and volume calculations, and AR display serves as an intuitive complementary inspection method. Point cloud comparison and verification with RTK AR is a powerful tool to quickly detect discrepancies between design and actual conditions and further improve the accuracy of quality control and as-built inspections.

Benefits of implementing RTK AR

Below is a summary of the main benefits obtained by introducing RTK AR on site.

• Improved surveying accuracy: By using centimeter-class high-precision GNSS (half-inch accuracy), the reliability of location information displayed in AR is dramatically increased. This enables boundary lines and structure positions to be established without error and allows detailed construction control that was difficult before. Accurate work backed by data can be achieved without relying on the intuition of veteran craftsmen.

• Operational efficiency and labor savings: The time required for surveying, staking-out, and as-built verification can be greatly reduced. AR guidance enables work to proceed by the most efficient route, increasing situations where one person can perform the work of many. For example, pile position staking that traditionally required several people and half a day could be completed by one person in a short time. As a result, labor costs can be reduced and construction schedules shortened.

• Improved safety: AR use reduces the risk of workers entering hazardous areas. As described earlier, there is no need to enter heavy-equipment operation zones to stake out, and positions can be safely guided from a distance. Also, by completing surveying and verification tasks in a short time, work in bad weather or at night can be reduced, contributing to on-site safety management.

• Smoother communication and consensus building: Digital information can be shared intuitively on site, facilitating smooth communication among stakeholders. Showing clients, site staff, and local residents the finished image or boundaries in AR produces the effect that “seeing is believing.” Spatial images that were difficult to convey with drawings can be shared on the spot, preventing rework and complaints caused by misunderstandings.

• Data utilization and promotion of on-site DX: Introducing RTK AR itself greatly advances on-site digitization and ICT use. Positioning data, point clouds, and photo records are centrally managed in the cloud, reducing the time spent organizing data after returning to the office. Accumulated data can be used directly for analyses and reports linked to BIM/CIM models, contributing to DX across the workflow. Also, being able to handle 3D data on site as an i-Construction–compatible approach matches requirements for future public works and helps strengthen competitiveness.

Simple surveying and high-precision AR display realized by LRTK

Finally, as a concrete solution to easily introduce RTK AR on site, we introduce LRTK. LRTK is an all-in-one on-site DX tool that achieves high-precision positioning and AR display with just a smartphone. By attaching a dedicated ultra-compact RTK-GNSS receiver (weighing about 125g) to a smartphone and launching the supported app, an ordinary smartphone instantly becomes a surveying instrument with centimeter-level accuracy. No complicated initial calibration or marker installation is required; turn on the power and high-precision AR is available immediately.

LRTK uploads design coordinates and survey data to the cloud and synchronizes them with on-site devices for use. For example, if a list of pile coordinates is registered, selecting it on site starts AR navigation and anyone can perform virtual pile display and coordinate guidance. Similarly, importing linework from drawings allows AR display of boundary or planned lines, and uploading point cloud data enables on-site comparison with the as-built condition. These operations are provided through an intuitive UI designed so that even non-specialist survey technicians can use them.

By using LRTK, which completes surveying measurement to AR visualization with a single smartphone, on-site operations can be executed on a one-person-per-device basis. Tasks that previously required separate equipment and software (surveying, staking-out, as-built scanning, photo records, design verification, etc.) can be integrated on a single platform with LRTK, achieving dramatic efficiency gains. On sites that adopted LRTK, comments such as “even junior staff could perform surveying and pile driving without issues” and “real-time cloud recording made reporting much easier” have been heard. The fact that expensive dedicated equipment is not required makes it easy to introduce, so small contractors and municipal offices that previously had little access to ICT-based construction can use it casually.

To fully realize the potential of RTK AR, choosing tools that are easy to use on site is key. LRTK is a representative example, offering a practical solution that balances simple surveying and high-precision AR display. If you are considering adopting RTK AR, please also consider LRTK and experience next-generation smart construction.