Fusion of RTK GNSS and AR: Next-generation positioning solutions advancing on construction sites

Table of Contents

• What is AR (Augmented Reality)?

• What is RTK GNSS positioning?

• New possibilities created by fusing RTK GNSS and AR

• Expected use cases on construction sites

• Benefits of introducing RTK GNSS and AR

• Simple surveying and high-precision AR display realized with LRTK

• FAQ (Frequently Asked Questions)

(Introduction) In recent years, positioning and surveying technologies in the construction industry have been evolving rapidly. Traditionally, surveying has been dominated by transit and total stations, optical distance meters, and GPS, but with ICT adoption and DX promotion, new technologies such as high-precision positioning using RTK-GNSS and drone surveying are becoming prevalent on sites. In particular, GNSS positioning using the Real-Time Kinematic (RTK) method has attracted significant attention in construction management and as-built measurement because it can reduce errors from on the order of several meters (several ft) to several centimeters (several in). The Ministry of Land, Infrastructure, Transport and Tourism’s promotion of *i-Construction* also emphasizes the use of 3D surveying and ICT construction, increasing the demand to utilize high-precision positional information on site.

Moreover, in recent years next-generation solutions that combine centimeter-level RTK positioning and Augmented Reality (AR) have emerged. By attaching a high-precision GNSS receiver to a smartphone and enabling on-site overlay of design data and survey information, tasks that previously required skilled surveying teams can now be performed intuitively by site staff themselves. In fact, there are reports that with just a smartphone, teams were able to complete everything from control point surveying to as-built point cloud measurement and AR-based comparison with design models on the same day, heralding a revolutionary era in which a smartphone essentially transforms into an “all-purpose surveying instrument.”

This article provides a detailed introduction to the latest construction positioning solutions enabled by the fusion of RTK GNSS and AR, from basic technical explanations to on-site use cases and the benefits of adoption. Finally, we will touch on a simple surveying method using our smartphone-based high-precision positioning system “LRTK,” proposing a way for anyone to easily incorporate RTK GNSS and AR on site.

What is AR (Augmented Reality)?

AR (Augmented Reality) is a technology that overlays digital information on real-world imagery through devices such as smartphones, tablets, and smart glasses. By compositing CG models, text information, and the like in real time onto scenes captured by a camera, it virtually augments the scene in front of the user. AR technology is increasingly used in the construction industry—for example, overlaying a model of the completed building on an actual site view or projecting piping routes from drawings onto structures under construction for verification. In practice, a major construction company, Shimizu Corporation, developed a proprietary system called “Shimz AR Eye,” which overlays BIM data onto real-world imagery to allow AR-based inspection of equipment piping and structural elements. This has been used to visualize concealed piping that is not visible before finishing to prevent construction errors, and to display upcoming process plans on site images for stakeholder sharing. In this way, AR technology is effective on construction sites for visually sharing information and intuitively grasping the finished image, contributing greatly to operational efficiency and the prevention of human error.

What is RTK GNSS positioning?

RTK GNSS positioning refers to Real-Time Kinematic positioning technology that uses GNSS (Global Navigation Satellite Systems). This method observes satellite signals simultaneously at one reference station (base station) and a rover (mobile station), then transmits positioning error corrections obtained at the reference station to the rover in real time to determine the current position with very high accuracy. Standalone GNSS positioning or simple augmentation (SBAS or DGPS) can produce errors on the order of several meters (several ft), but RTK can reduce errors to a few centimeters (a few in). This enables GNSS to be used for tasks requiring high precision such as ground elevation surveys and setting out structural positions. The RTK mechanism involves equipping the rover with a high-performance GNSS antenna and receiver, receiving correction data distributed from the base station via the internet or radio, and applying those corrections to its own position. Previously, it was necessary to set up a dedicated reference station near the site, but recently networked RTK services using the Geospatial Information Authority of Japan’s permanent GNSS reference network (VRS, etc.) and centimeter-class augmentation services from Japan’s Quasi-Zenith Satellite System “Michibiki” (CLAS) have been established, making centimeter-class positioning possible without users having to set up their own base stations. By utilizing these high-precision positioning services, accurate positioning data can now be obtained by anyone with a mobile device, not just licensed surveyors. RTK is becoming an indispensable technology for civil infrastructure measurement and machine guidance of heavy equipment in the civil engineering and construction fields.

New possibilities created by fusing RTK GNSS and AR

Combining the high-precision position information from RTK with AR visualization opens up new on-site applications that were previously impractical. Typical smartphone AR apps require initial calibration such as marker placement or plane detection to align the virtual model with reality, and models can drift when the user moves. However, by using centimeter-precision self-position coordinates obtained from RTK-GNSS, virtual models in AR can be anchored to the earth coordinate system, allowing stable display without shifting from their real-world positions even when a user moves around the site. In other words, it becomes possible to display AR based on absolute coordinates linked to surveying coordinates. This eliminates the cumbersome initial alignment process and enables instant, accurately positioned overlays of 3D models of structures you want to show on site. For example, on vast embankment sites with no nearby visual landmarks, design fill and cut lines can be drawn on the ground pinpointed by AR, enabling immediate understanding of where and how much to excavate or fill. RTK also provides highly accurate heading (bearing) information for the user, so AR display position and orientation remain correct from various viewing angles while walking around. This RTK GNSS × AR fusion enables “AR that exactly matches real-world coordinates,” which was previously difficult. Tasks that had to be carried out in the field for setting out and verification can be simulated and reproduced accurately in virtual space, minimizing discrepancies between plan and construction. If design drawings and BIM model information can be visualized directly on site, communication and shared understanding between construction personnel and designers become much smoother, and all stakeholders can proceed with construction while sharing the expected finished image—leading to early detection of errors and reducing rework.

Expected use cases on construction sites

High-precision AR technology that combines RTK GNSS and AR is expected to have many applications in civil engineering and building construction. Here are some representative use cases.

Navigation for pile-driving work (improving efficiency of pile positioning)

To install foundation piles at the correct location and depth, it is essential before construction to mark pile positions on site based on coordinates on the drawings—this is called pile positioning (layout). Traditionally, survey crews used total stations and tape measures to measure distances from control points and installed pile markers or batter boards on the ground. However, manual layout requires high skill and considerable time and effort, and surveying can be difficult in uneven terrain or adverse weather. Human operations also carry the risk of slight measurement errors or marking misalignments that can lead to construction mistakes. By using RTK GNSS and AR, pile positioning can be revolutionized. Through a smartphone or tablet screen, virtual markers or pile models (AR piles) can be displayed at the positions specified in the design, so workers are guided intuitively to the exact spot while viewing the overlaid mark on the real scene. It works like a site-specific car navigation system, with arrows and remaining distance shown in real time on the device screen to guide the user to the designated pile position. As the user approaches the correct position, fine distance information such as “remaining ○cm” is displayed, and when the target is reached the virtual pile and the physical ground mark align perfectly, clearly indicating the correct location. With AR pile-navigation, even inexperienced staff can accurately mark pile positions without hesitation. The manual layout work that used to rely on veteran intuition and experience is replaced by a digital guide, enabling anyone to perform pile marking in a short time. On sites that introduced RTK AR technology, time required for pile marking was greatly reduced compared to conventional methods, and reports indicate a single worker could set multiple pile points rapidly. This contributes to labor reduction and cost savings, and centimeter-level accuracy minimizes the need for rework in subsequent processes. Safety also improves because pile positions can be confirmed from a safe distance via the screen, even in areas with hazardous heavy equipment or poor footing. AR can reliably indicate positions on asphalt or concrete where physical markers or batter boards cannot be placed, or on steep slopes.

Advanced as-built management and quality checks

On civil and earthworks sites, “as-built management”—verifying that completed structures and terrain match the design shapes and dimensions—is important. Traditionally, as-built checks were performed after construction by surveyors measuring heights and thicknesses on site and comparing the data to drawings, a process that takes time and often requires returning measurement data to the office for analysis. Combining RTK GNSS and AR enables as-built management processes to be performed on site in real time. For example, the finished ground surface or structures can be scanned with a smartphone or tablet equipped with a LiDAR scanner, and the resulting point cloud data can be overlaid and compared with the design 3D model in AR. Since the point cloud data acquired with RTK include accurate geodetic coordinates (world geodetic system coordinates), separately measured point clouds and design data automatically align. This allows the previously laborious task of comparing measured data to drawings to be done intuitively and instantly on site. For instance, in road paving, measuring the post-repair road surface on the spot and overlaying it with the design profile line in AR allows immediate checks of flatness and drainage slope compliance. In embankment or land development, scanning the finished surface and comparing it with the design model makes it easy to spot depressions or shortages at a glance. Errors of a few centimeters (a few in) that were previously easy to miss can be visually identified with AR, enabling immediate instructions for additional fill or trimming. This speeds up as-built inspections and prevents rework, achieving both quality assurance and construction efficiency. Advanced features are also appearing, such as generating a color-coded “heat map” of differences between acquired point cloud data and design models and displaying it in AR on site. If an as-built inspection heat map can be overlaid on the real scene, it becomes intuitive to identify defective areas for immediate repair. These state-of-the-art technologies are ushering in an era when daily quality management tasks can be completed on site.

Visualizing property boundaries and buried utilities

In infrastructure projects, accurately understanding property boundary lines and the locations of underground utilities is often a challenge. Boundary lines are usually represented as lines or coordinates on drawings and are not visible on site; even existing boundary markers may be hidden by vegetation and hard to locate. On older sites boundary markers may be lost altogether. Similarly, it is difficult to precisely locate buried pipes and cable routes using only drawing information. Combining RTK GNSS and AR is a powerful means of visualizing such “invisible information” on site. If you digitize property boundary point coordinates and buried utility route information beforehand and load them into a site app, you can simply point a smartphone at the scene to display virtual lines or markers indicating “the boundary is here” or “a pipe runs under the ground at ○m depth.” For example, at a road widening briefing, using AR to visualize road boundary lines on the actual ground—lines that previously could only be shown on paper—helps local residents intuitively grasp the plan. During construction, heavy equipment operators referencing AR-displayed no-dig zones or existing utility lines can avoid damaging other facilities or excavating beyond boundaries. Visualizing information that was not visible on drawings reduces misunderstandings among stakeholders and helps prevent problems before they arise.

AR-based verification of design data (comparing plan and construction)

One of the purposes of using design data (drawings or 3D models) at construction sites is to “eliminate discrepancies between design and construction.” With RTK GNSS and AR, if you can overlay design models or lines on site, it becomes easy to directly compare them with structures being constructed or just completed to check for deviations. For example, in concrete casting, displaying an AR model of the planned wall or beam positions allows confirmation during rebar installation that positions have not shifted. In railway rail replacement work, overlaying the post-replacement rail positions with the planned alignment in AR could allow adjustments to catch even centimeter-level misalignments. AR-based verification of design models offers the major advantage that you can immediately determine on site whether construction is being carried out according to design. Deviations that previously only became apparent after taking surveying records back to the office can be perceived visually on the spot with AR, enabling early corrective actions. With RTK GNSS accuracy ensuring alignment between model and reality, deviations within a few centimeters (a few in) are immediately apparent on site. While managing everything to the millimeter is difficult, the precision is sufficient to judge whether construction falls within acceptable tolerances for construction management. Using high-precision AR verification can prevent construction errors and minimize rework.

Benefits of introducing RTK GNSS and AR

As described above, RTK GNSS × AR can be effectively applied in many on-site situations. Let’s summarize the benefits of adopting these technologies.

• Significant improvement in work efficiency: Tasks that traditionally required multiple people and long hours, such as setting out and as-built inspection, can be drastically streamlined. With RTK AR, one person can complete surveying and verification quickly, directly contributing to shorter construction periods and reduced personnel. This is particularly valuable in the construction industry, which faces severe labor shortages; the effects of labor savings and productivity improvements are highly beneficial.

• Improved surveying accuracy and reliability: Centimeter-level positioning reduces small errors that previously arose from analog layout and visual checks. High-precision alignment on site suppresses variations in construction quality, decreasing the risk of rework and re-construction in later stages. As-built inspection data can be obtained and shared immediately, also improving record reliability.

• Enhanced safety: AR display enables more checks to be performed without entering hazardous locations. For example, surveying at heights or within heavy equipment operation areas can be done from a safe distance, improving worker safety. Displaying no-dig zones and underground utilities also helps prevent accidents.

• Knowledge transfer and surveying anyone can perform: Surveying and inspection tasks that relied on veteran experience are now guided by digital tools, enabling younger or non-specialist staff to perform tasks with consistent accuracy. Intuitive AR interfaces are easy for non-experts to understand, aiding skills transfer and alleviating the shortage of experienced technicians.

• Support for DX promotion: Aligning with the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction and construction DX trends, preparing to use 3D data on site is increasingly important. High-precision positional information and AR visualization directly support electronic deliverables and BIM/CIM use. Early adoption makes it easier to meet public project procurement requirements and enhances corporate competitiveness.

Simple surveying and high-precision AR display realized with LRTK

Finally, as a concrete, easy-to-deploy solution for bringing RTK GNSS and AR to site, we introduce our product LRTK. LRTK is an all-in-one site DX tool that realizes centimeter-level positioning and AR display with a single smartphone. By attaching a dedicated ultra-compact RTK-GNSS receiver to a smartphone and obtaining correction information from networked RTK services or Michibiki’s CLAS satellites, the smartphone instantly becomes a high-precision surveying instrument. No complicated equipment operation or complex initial setup is required: bring it to the site, power it on, and in about several tens of seconds the receiver acquires a “Fix solution” and the device screen displays the current position with centimeter-level accuracy. Since its launch in 2022, the LRTK series has been used on various construction and civil engineering sites. For example, on one project, an iPhone equipped with LRTK was used to survey control points, then the as-built area was scanned and a heat map comparing it to design data was created in the cloud and instantly checked via AR display. Tasks that previously required days—using a total station, laser scanner, and desktop analysis—were completed in a single day with just LRTK and a smartphone. On other sites, CAD data of planned excavation areas was loaded into an LRTK-compatible app and virtual guide lines were displayed on the actual ground while operating heavy equipment, enabling accurate earthworks without installing batter boards. By using LRTK, surveying through construction verification can be performed entirely on a smartphone, dramatically improving surveying accuracy and work efficiency on site. LRTK also provides cloud services: uploading point cloud data and design models captured on site for automatic analysis enables functions such as heat map generation for as-built management, cross-section volume calculations, and one-click report output—streamlining site management tasks. Combining these features dramatically simplifies daily surveying and inspection work, enabling site personnel to complete everything from surveying to quality checks on the spot—realizing a “simple surveying” workflow. LRTK, which leverages centimeter-level positioning and AR visualization, is a next-generation solution that strongly promotes DX on construction sites. Please refer to the LRTK official site and case study pages for more details.

FAQ (Frequently Asked Questions)

Q: What is RTK-GNSS positioning? How is it different from GPS? A: RTK-GNSS positioning is a technology that achieves far higher accuracy than typical GPS by correcting satellite positioning errors in real time. Standalone GPS positioning normally produces position errors of several meters (several ft), but RTK uses correction data from a base station to reduce errors to a few centimeters (a few in). Therefore, it is used where centimeter-level accuracy is required, such as civil surveying and machine position control.

Q: Why is centimeter-level positioning necessary for AR? A: Typical smartphone AR has large alignment errors, and virtual objects can appear offset from reality by several meters (several ft). On construction sites, AR must accurately visualize pile positions and structural dimensions, so meter-level offsets are unacceptable. With RTK-GNSS providing centimeter-level self-positioning, models displayed in AR can be made to match real-world coordinates precisely, enabling a seamless fusion of real space and virtual information. High-precision positioning is the indispensable foundation for practical AR in construction.

Q: Do I need to set up a dedicated base station to use RTK positioning? A: Not necessarily. Recently, networked RTK services provided by national or private entities that distribute correction information over the internet have become widespread. In Japan, receiving centimeter-class augmentation signals such as CLAS from the Michibiki QZSS also enables high-precision positioning without a local base station. Using these services allows users to benefit from RTK positioning without owning a base station. Of course, it is possible to set up and operate your own base station, but for small sites or mobile work, using networked correction services is more convenient.

Q: Can a smartphone really perform centimeter-level surveying? A: Yes. Combining the latest smartphones with an external high-performance GNSS antenna makes it possible. For example, using a small RTK-capable receiver that attaches to an iPhone (such as our LRTK), the smartphone becomes a surveying instrument capable of centimeter-level positioning. In practice, control point surveys and as-built measurements have been performed with smartphones and RTK systems, achieving accuracy comparable to total stations. The critical factors are a GNSS chipset that supports high precision and appropriate correction information. Under proper conditions, a smartphone can achieve positioning accuracy comparable to dedicated surveying instruments.

Q: What kind of system is LRTK? A: LRTK is our proprietary solution that enables RTK-GNSS positioning and AR display using a smartphone. An ultra-compact RTK receiver with an integrated antenna attaches to the phone, and a dedicated app integrates satellite positioning and AR functionality. By acquiring RTK correction data over the network, you can measure centimeter-level current positions even while mobile. LRTK leverages that accuracy to support AR display of drawing data, comparison with point cloud scans, generation of as-built heat maps, and other on-site tasks, all on a single device. With LRTK, you do not need to carry specialized surveying equipment to perform high-precision positioning and AR-based on-site verification easily. As an all-in-one tool that promotes DX on construction sites, LRTK has been adopted by many companies and projects.