GNSS Rover × AR Integration for On-Site Visualization! A New Era of As-Built Verification

Introduction: Challenges in As-Built Verification and the Necessity of Digital Transformation

As-built verification (as-built management) is a quality control process in civil engineering and construction that involves measuring and confirming whether completed structures and terrain have been constructed according to the design drawings. After construction is finished, survey instruments and scales are used to measure heights, thicknesses, slopes, and other prescribed points, and the measured values are compared with the design values to determine pass or fail. This is an important step to guarantee on-site quality, but traditional methods have many issues.

• Time consumption: Staff must painstakingly measure each survey point with an auto level, total station, or tape measure, so when sites are large or there are many points, it takes a tremendous amount of time. Recording measurement results and returning to the office to compare them with drawings and prepare reports can mean that as-built inspections take several days.

• Dependence on personnel and skilled technicians: Accurate measurement and evaluation require the skills of experienced surveyors. However, the construction industry suffers chronic labor shortages and an aging skilled workforce, making it difficult to allocate sufficient personnel to every site. Surveying is often carried out by teams of two, which increases labor costs and logistical burden.

• Equipment costs: High-precision as-built measurement requires expensive dedicated equipment such as total stations and RTK-GNSS receivers, incurring large initial investments and maintenance costs. Small and medium contractors face high barriers to adoption and find it difficult to benefit from the latest technologies.

• Risk of human error: Manual measurement processes are prone to measurement errors and recording mistakes, and transferring handwritten numbers to drawings can introduce errors. Discovering such errors later may require re-measurement and rework.

• Delayed problem detection: For example, deficiencies such as insufficient concrete thickness or improper slopes may not be detected on the spot using traditional methods; they are sometimes only discovered after data is brought back and processed into drawings. By the time problems become apparent, the concrete may have already hardened or heavy equipment may have been removed, making corrections more laborious and costly.

• Burden of reporting: As-built management requires preparation of inspection drawings and reports based on measurement results to be submitted to the client. Manual data organization, drawing creation, and photo ledger compilation are labor-intensive and place a heavy burden on site staff.

As described above, traditional as-built verification is often inefficient and lacks immediacy, and constraints in personnel and cost have driven the need for improvement. On actual sites, for example, procedures often involve photogrammetrically recording the location of buried pipes before backfilling and converting the data to CAD later. However, such methods take time to understand and record site conditions, and the data obtained often ends up as mere attachments in reports rather than being fully utilized.

To solve these issues, new methods that enable accurate and intuitive as-built assessment in real time on site are necessary. One promising solution gaining attention in recent years is on-site DX (digital transformation) through the use of digital technologies. Initiatives such as the Ministry of Land, Infrastructure, Transport and Tourism-led " [i-Construction](https://www.mlit.go.jp/tec/i-construction/) " involve industry, government, and academia promoting smart construction that utilizes ICT and three-dimensional data. Among these, solutions that combine GNSS positioning technology and AR (augmented reality) technology for on-site as-built verification hold significant potential and are attracting industry attention.

Basics of GNSS Rovers and Precision Improvement in Coordinate Management with RTK

One of the technologies supporting on-site DX is high-precision positioning using GNSS rovers. GNSS refers to Global Navigation Satellite Systems (such as GPS, GLONASS, and the QZSS called Michibiki), and a GNSS rover is a mobile unit that receives signals from these satellites to determine its position. Standalone positioning traditionally has errors on the order of several meters, which is insufficient for the strict position management required in public coordinate systems used in civil engineering surveys. That’s where RTK (Real Time Kinematic), a high-precision positioning technique, is used.

In RTK, both a base station installed at a known position and a rover simultaneously receive GNSS signals, and the relative errors with respect to the base station are corrected in real time, enabling centimeter-level positioning. For example, by using network RTK or correction information services utilizing continuously operating reference stations, the rover can receive correction data via the internet and perform positioning. This allows high-precision positioning with horizontal and vertical errors within a few centimeters, and in some cases down to several millimeters of accuracy.

The introduction of RTK-GNSS has dramatically improved the precision of coordinate management in construction management. Because coordinates obtained on site directly match public coordinates (survey reference coordinates), comparing them with design drawings and other process data becomes straightforward. Previously, temporary reference points were sometimes established at each site to manage local coordinate systems, but with RTK the site and design can be directly connected in the same coordinate system. In Japan, the QZSS “Michibiki” centimeter-class augmentation service (CLAS) has also been developed, and with compatible receivers it is possible to achieve high-precision positioning from satellite signals alone even in mountainous areas where network connection is difficult. Thus, GNSS rovers plus RTK provide the foundation for obtaining high-precision location information anywhere.

Recently, GNSS rover devices themselves have become smaller and lower-cost. RTK positioning that once required dedicated equipment costing several million yen is now becoming available in compact GNSS receivers that can pair with smartphones and tablets. In addition to conventional fixed base stations, regional correction distribution services and cloud reference stations make it possible to perform centimeter-precision positioning without installing large equipment at each site. These technological advances make it possible for positioning tasks that previously required specialists to be performed by a single person in a short time, making GNSS utilization for as-built verification and simple surveying a realistic option.

On-Site Application of AR Technology — An Era of “Viewing” Drawings

Alongside GNSS, AR (Augmented Reality) technology is key to on-site DX. AR overlays digital information (3D models, text, etc.) onto real-world images, and with recent improvements in smartphone and tablet performance it has become much more accessible. Modern mobile devices often have high-performance cameras and LiDAR sensors, and AR apps that leverage these capabilities make it possible to use AR in everyday construction management tasks.

Traditionally, construction drawings and specifications were reviewed on paper or PDFs, and workers had to visualize how the drawings corresponded to the site in their heads—imagining “this is the point shown on the drawing.” Unless one was experienced, it was difficult to imagine the finished form from the drawings, which contributed to mistakes and rework. With AR, however, you can project the drawings directly onto the site and “see” them. For example, through a smartphone or tablet screen you can display CAD lines or 3D models of the expected finished structure aligned with the actual site view. This allows information that was only available on drawings to be overlaid on the real scene, enabling intuitive understanding and sharing.

AR applications are increasing on construction sites. In areas called “AR surveying,” surveying data and design models are displayed on site with AR, advancing initiatives to visualize onsite verification tasks that were previously done on drawings. Specifically, BIM/CIM 3D design models of buildings and civil structures can be overlaid at the work location, allowing intuitive confirmation of placement and dimensions. AR can be used for setting out by displaying the planned structure on the ground before construction, or to compare the placement of columns and walls during construction to ensure they match the design. AR makes it possible to instantly recognize discrepancies between the design image and the field in physical space—discrepancies that are difficult to grasp with drawings or measuring instruments alone.

In the field of as-built inspection, efforts are also beginning to compare acquired three-dimensional as-built data (point clouds and 3D models) with design data and display deviations as color-coded heat maps on site. If a heat map automatically generated in the cloud by comparing the design 3D model and the as-built point cloud is downloaded to a tablet and overlaid on the camera view, it becomes immediately apparent which areas are higher or lower than the design. For example, evaluating the finish of an embankment as a surface and instantly correcting defective areas helps accelerate the PDCA cycle.

AR’s applications are broadening to include visualization of underground buried utilities and assistance for heavy equipment operation. For instance, in pipe installation work, pipes can be 3D scanned before backfilling and then confirmed via AR after burial to check their positions and depths as if viewed through the ground. Pointing a smartphone at the road can display underground piping routes, which aids future maintenance and eliminates the need for immediate marking after burial, improving construction efficiency. Experiments have also been conducted in machine work to guide operators by displaying height reference planes and excavation areas in their view. In training, AR has been used to recreate site spaces to practice safety procedures. As a technology that accelerates on-site DX, AR is becoming indispensable.

Practical Methods for As-Built Verification by Combining GNSS Rovers and AR

How does the field of as-built verification change when high-precision positioning from GNSS rovers is combined with AR display? Here we consider practical methods.

The greatest advantage of combining GNSS and AR is that digital design information and real construction results can be spatially overlaid with precision. Using centimeter-level current position and elevation obtained by a GNSS rover, a design drawing or 3D model can be accurately projected into real space within an AR app. This enables on a tablet screen direct side-by-side comparison of design data and the as-built condition.

The concrete workflow is to first import 3D models or drawing data created during the design phase into a compatible app. On site, use GNSS rover positioning to accurately calibrate your position and orientation so that the digital data aligns with the field coordinates. Then, viewing the site through the camera, the designed finished form and reference lines will be overlaid on the real scene. Workers can check on the spot, by looking at the screen, whether the constructed elements are deviating from the design—for example, whether a structure’s corner is offset from the planned location or whether the finished height of an embankment matches the design.

GNSS rover + AR systems also enable real-time as-built inspection. Defects that previously were only discovered after bringing measurement data back to the office can be detected on the spot, allowing immediate correction. By comparing the AR-displayed design model with the actual condition, workers can identify “this area is low” or “that area protrudes” and promptly perform additional filling or trimming. This lets you run the PDCA on site and minimize rework.

Another innovation of GNSS × AR-based as-built verification is that surveying, inspection, and recording can be completed with a single smartphone. Integration of high-precision coordinate measurement (GNSS) and visual confirmation (AR) eliminates the need to carry paper drawings or multiple surveying instruments. For instance, to measure the elevation at a point, a worker can simply align a virtual target shown on the smartphone screen with the physical point and press a button to record the measurement; the app will automatically display the difference from the design value. Even workers without specialized surveying knowledge can complete inspection tasks by following on-screen guidance. This prevents as-built verification from becoming person-dependent and enables the whole team to share data while working.

Furthermore, sharing AR-displayed information among stakeholders smooths consensus-building with clients. Traditionally, inspections with clients involved explaining by comparing drawings and as-built records, but AR allows clients themselves to visually confirm the completed image and inspection results on site. Statements such as “this area is finished X cm lower than the design” become obvious when viewed together with a color-coded heat map on the screen. Intuitive visualization makes it easier to share situational awareness between client and contractor, facilitating quick agreement about whether additional corrections are necessary. In this way, as-built verification using GNSS and AR simultaneously enables on-site correction and smooth communication among stakeholders.

Practical Scenarios: Pavement Thickness Checks, Structural Placement Confirmation, and Client Consensus

Here are several scenarios where GNSS rover + AR as-built verification is especially effective.

• Pavement thickness checks: In roadworks, confirming that subgrade and pavement thickness meet the design specifications is crucial. Traditionally, after compaction staff measured elevations at various points and estimated thickness from differences to the design elevation. With an AR-capable GNSS rover, crew can measure finished elevations at each point with a smartphone immediately after subgrade work and upload them to the cloud to instantly check whether the required thickness is met. If thickness is insufficient, such locations are detected on the spot, allowing additional material or compaction before the pavement is laid, preventing rework. For completed pavement surfaces, overlaying the designed longitudinal and transverse grade lines in AR lets you detect and correct slight unevenness or irregularities. Being able to judge pass/fail on site right after construction greatly aids early recovery and quality assurance.

• Confirmation of structure and landscape placement: For works such as parking lots, park development, and building foundations, it is necessary to confirm that facilities are placed according to the design plan. Traditionally, layout lines and batter boards were used to set positions and heights, then re-measured after completion to compare to drawings. With GNSS × AR, you can project the design drawing itself at the site and check the finish, so even complex shapes can be judged at a glance. For example, displaying curved walkways or lot boundaries in AR lets the whole crew verify that the paved curve follows the planned line, preventing misunderstandings and construction errors. On building sites, AR guides can be used to confirm column and beam placement during installation, or to compare post-pour structures with design models to check for core offsets. Subtle alignments that relied on skilled intuition can be performed accurately by anyone with AR visual assistance.

• Client consensus building: As-built verification is directly connected to final inspections and payment agreements with clients. Visualizing construction results with AR allows clients to confirm the finished form on site during inspection, preventing disputes due to differing perceptions. For example, when explaining whether the widened section of a road curve matches design, overlaying the design line and the actual condition in AR makes it immediately understandable. If nonconformances are found, sharing the subtle deviations on site instead of only through photos or numbers makes it easier to reach agreement on the scope of corrective work or additional work. Clients gain peace of mind by spatially grasping the as-built quality, and the inspection process is likely to be expedited.

Data Integration: Connecting the Construction Cycle with the Cloud and Public Coordinates

To further enhance as-built management using GNSS and AR, data integration with cloud services is essential. By uploading positioning data, point cloud models, photos, and other site records to the cloud immediately, and sharing them with office support staff and stakeholders, the overall construction cycle efficiency can be improved.

Specifically, coordinates of points measured by the GNSS rover and captured site photos are saved to the cloud with high-precision location information, timestamps, and notes. This allows the office to review as-built data in real time and provide immediate feedback. For example, when embankment thickness measurements for a section are synced to the cloud, the quality control manager can review the data and immediately instruct the field team to add material where needed. This cloud synchronization ensures uninterrupted circulation of information between site and office, enabling rapid decision-making and corrective actions.

Data stored in the cloud can also be integrated and managed with design data and other process data. Because GNSS rover measurement data are based on the public coordinate system, there is no need for the extra step of aligning the acquired point clouds or as-built models with the design 3D model. In the earlier heat map example, the difference can be color-coded automatically in the cloud simply by comparing the design model and the as-built point cloud—this is possible because the raw datasets share a common coordinate foundation. When as-built and design data align without discrepancies, the digital inspection results can be readily repurposed as deliverables for electronic submission.

The Ministry of Land, Infrastructure, Transport and Tourism is promoting 3D as-built management guidelines (draft), which standardize surface-based as-built evaluation methods using point clouds from drones and laser scanners. As-built data obtained with GNSS rovers + AR also meet these guidelines in terms of accuracy and format and can be exported in formats such as LandXML and SIMA. Some cloud systems are even developing features to automatically generate as-built inspection reports with a single click from on-site visualized heat maps and measurement results. Through such data integration and automation, an end-to-end digital workflow from construction to inspection to electronic submission is becoming attainable.

In short, seamlessly linking on-site data acquired with GNSS and AR to the cloud and public coordinates dramatically improves the speed and accuracy of the construction PDCA. This benefits both clients and contractors, and suggests that the standard for as-built management may shift toward 3D data and AR utilization.

Case Study: Labor-Saving As-Built Management Using AR × GNSS with LRTK Phone

Finally, as an example of actual on-site implementation of the GNSS rover and AR fusion, we introduce the LRTK Phone (a GNSS rover). LRTK Phone is a small high-precision GNSS receiver device that attaches to a smartphone, transforming an ordinary smartphone into a centimeter-class surveying instrument. It connects to the phone via Bluetooth or Wi‑Fi and performs RTK positioning through a dedicated app. Whereas the smartphone’s built-in GPS may have meter-level errors, using this GNSS rover allows obtaining the current position with centimeter-level accuracy. By integrating with the phone’s camera and LiDAR scanner, it becomes a versatile surveying tool capable of 3D surveying (point cloud measurement) and AR-based overlay of design data on site—everything on a single device.

For example, introducing LRTK Phone enables site staff to quickly perform as-built management tasks that previously required specialized surveying equipment and teams, using only a smartphone. One civil contractor trialed the system in a road improvement project to streamline subgrade thickness checks and as-built recording. Immediately after subgrade work, workers measured various points with a smartphone and instantly saw on the screen whether thickness was insufficient, allowing immediate additional work. Previously, deficiencies might only have been discovered the next day and required rework, but with LRTK the team achieved same-day correction and same-day inspection, greatly reducing rework. In another project, LRTK Phone was used to record buried pipe installation. Pipes were scanned with a smartphone before backfilling to obtain high-precision point clouds, and saving this to the cloud allowed accurate pipe locations to be retrieved via AR from the surface after backfilling. This provided highly valuable 3D records for client explanations and future maintenance.

Smartphone-connected GNSS rovers like LRTK Phone also have the advantage of low adoption barriers. The device is lightweight, compact, and battery-powered; simply attaching it to a smartphone allows anyone to start using it immediately. Initial costs are a fraction of those for expensive dedicated equipment, and no special controller is required since a worker’s own smartphone is used. Intuitive app operation covers positioning through data sharing, enabling site staff with no surveying background to operate it after brief training. LRTK Phone has been featured on the Cabinet Office page introducing CLAS-compatible devices, and is gaining attention from public bodies. It aligns with the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiatives and is expected to simultaneously improve site surveying accuracy and productivity.

Thus, labor-saving as-built management using AR × GNSS is already at a practical stage on worksites. Next-generation GNSS rover technologies such as LRTK Phone have lowered the barrier between as-built verification and surveying, allowing less experienced technicians to perform high-quality inspections with digital tools. Site inspections that were once paper-based and manual are set to transition to smart inspections using tablets and cloud services. The combination of GNSS rovers × AR is poised to bring a new era of on-site visualization and quality control, and is likely to spread to more and more worksites in the future.