Visualizing Buried Pipes with RTK AR! Smart Infrastructure Inspection

Buried pipes such as water supply pipes, gas pipes, and power cables are essential lifelines of social infrastructure, but because many of them are buried deep underground and therefore invisible, they pose significant challenges for maintenance and construction sites. Damaging buried utilities by mistake can lead to major accidents such as water leaks, gas leaks, or power outages. However, in recent years, RTK (Real-Time Kinematic) high-precision GNSS positioning combined with AR (augmented reality)—so-called RTK AR—has made it increasingly possible to visualize underground pipelines on-site as if seeing through the ground. This new technology, which “makes the invisible visible” at infrastructure inspection and construction sites and enables safer, more efficient work, is attracting attention. This article explains in detail the basic technology for visualizing buried pipes using RTK AR, the workflow of positioning, scanning, and recording, applications in infrastructure inspection, effects on accident prevention for underground structures, integration with point cloud data and maintenance ledgers, minimization of positional errors by RTK accuracy, benefits of adoption, and field examples, and concludes with an example of simple surveying and AR display using LRTK.

Challenges in Underground Infrastructure Maintenance and Management

The most feared accident during road works or site excavation is inadvertently damaging existing underground pipes or cables. Breaking an aging water main can lead to a large-scale leakage incident; damaging a gas pipe risks gas leakage or explosion. Cutting power or communication lines can cause local power outages and communication failures, severely disrupting social life. In fact, many incidents of buried-utility damage are reported nationwide every year, and in many cases the cause is that people “did not accurately know what was buried there.”

To prevent such accidents, meticulous care has long been taken in the maintenance and management of buried pipes. During installation work, positions and depths of the pipes are surveyed and recorded before backfilling, and information is preserved through photographs and drawings. On site, workers rely on those drawings and ground markings, with experienced personnel proceeding with excavation guided by intuition such as “there should be a pipe around here.” When necessary, ground-penetrating radar is used to investigate the position of buried objects, or trial excavations (digging holes to directly verify) are conducted. However, management based on paper drawings and veteran intuition has limitations, and it is not easy to mentally visualize the precise positional relationships of pipes that intersect complexly underground. Especially in urban areas with repeated renovations, discrepancies between drawing information and actual on-site conditions are common, and there are many near-miss cases where an unexpected pipe appears from a depth where “there should be none.”

In short, the fundamental issue in infrastructure maintenance management is how to “make the invisible visible.” If the underground structure could be intuitively understood, not only could excavation-related troubles be avoided, but inspection and replacement planning for aging pipes could be made dramatically more efficient. AR (augmented reality) technology for visualizing buried pipes is therefore expected to play a major role.

Technology for Seeing Through the Ground with AR

AR (Augmented Reality) overlays digital information such as CG onto real-world images seen through a camera. Using this technology, it becomes possible to display virtually the pipes and cables buried underground in a visible form on-site. For example, pointing a smartphone or tablet camera at the ground can render gas pipes or water pipes below the surface on the screen as if the ground were transparent, allowing workers to intuitively grasp “what is buried directly beneath these feet and how it is laid out.” In this way, one can verify underground structures on-site visually without relying on drawings or guesswork.

However, accurately rendering buried objects via AR requires advanced alignment technology. If one relies only on a phone’s built-in GPS or electronic compass, horizontal positioning errors of several meters can occur, causing virtual pipe models to be displayed far from their actual buried locations. This is far from the precision needed for “seeing through” and could even create hazards through misidentification. Also, conventional AR systems typically required placing markers (registration marks) on-site or manually calibrating model positions initially. For large areas such as roads and utility networks, placing markers or manually calibrating at every location is impractical.

To solve these issues, “markerless high-precision AR” using the combination of smartphone + LiDAR + RTK-GNSS has emerged. Modern smartphones come with advanced AR platforms that track device movement from camera images and IMU (inertial measurement unit) data to follow spatial position. Higher-end phones also include small LiDAR (laser scanners), enabling real-time acquisition of the surrounding environment as 3D point cloud data. Because LiDAR can accurately capture the shape and distance of the ground and structures, virtual objects (for example, underground pipe models) can be stably overlaid onto the real world and occlusion—naturally hiding virtual objects behind real ones—can be represented. In other words, smartphones can now instantly build a 3D map of their surroundings in addition to camera images, greatly strengthening the foundation for AR display.

The final piece is for the device itself to know precisely where it is. This is where high-precision positioning technology RTK-GNSS (Real-Time Kinematic satellite positioning) proves powerful. As noted, standalone smartphone GPS can have meter-level errors, but with RTK correction information the positional error can be reduced to the centimeter level. RTK positioning has long been used in surveying, and recently receivers have become smaller and lighter, allowing RTK-capable GNSS receivers to be attached to smartphones. Combining such external high-precision GNSS with a smartphone makes it possible to determine the device’s position in a public coordinate system with centimeter-level accuracy, minimizing the discrepancy between the virtual model and the real world.

Combining the ground-shape point cloud data acquired by a smartphone’s LiDAR with the global self-positioning information obtained by RTK-GNSS enables practical-precision “AR see-through” of buried pipes in the field. For example, if a 3D model of buried pipes (or mesh data created from point clouds) acquired in advance is loaded into a smartphone, then on a later site visit the underground model will align precisely with the actual position under the ground simply by pointing the camera. Because the ground itself is recognized by the device as a mesh model from LiDAR measurement, the virtual pipes will appear buried in the soil and be appropriately occluded, allowing intuitive understanding of depth relationships. This markerless AR see-through that remains aligned even when freely walking around is turning previously black-box underground infrastructure into on-site visible information.

Centimeter-Level Positioning Enabled by RTK-GNSS

High-precision positioning by RTK-GNSS is a key element supporting AR visualization of buried pipes. RTK (Real-Time Kinematic) uses correction information from a base station in real time to enhance GNSS positioning accuracy, enabling relative positioning to a fixed reference point within a few centimeters of error. While standalone GPS often includes meter-level errors, RTK can achieve centimeter-level accuracy both horizontally and vertically, and has long been valued in civil engineering and surveying.

Making RTK positioning easy to use in the field has been facilitated by the appearance of ultra-compact RTK-GNSS receivers. For example, a device called the “LRTK Phone,” developed by a startup originating from Tokyo Institute of Technology, enables RTK positioning simply by attaching a small receiver weighing about 165 g and about 13 mm (0.51 in) thick to the back of a smartphone. It runs on an internal battery for about 6 hours and can be attached to a phone case with one touch for convenience. It also supports the Japan Quasi-Zenith Satellite System “Michibiki” centimeter-class augmentation service (CLAS), allowing stable centimeter-level accuracy to be maintained using satellite augmentation signals alone even in mountainous areas where mobile communications are unavailable. In urban areas, conventional RTK correction services via the internet can be used, enabling real-time correction to within a few centimeters anywhere in Japan. In other words, with these high-precision GNSS devices integrated with smartphones, the era in which “anyone can carry a high-precision positioning tool in their pocket” is becoming a reality.

Envision a future where each field technician carries their own smartphone with a high-precision GPS device, quickly taking it out for surveying or AR display when needed. Current systems display positioning results and navigation information with intuitive Japanese UIs on the smartphone screen, making them easy to operate without specialized expertise. For example, tasks that once required two people—such as laying out staking positions—can now be performed by one person holding a lightweight monopod with a smartphone + RTK, following on-screen guidance to accurately mark positions. By making high-precision GNSS accessible to everyone, surveying and construction management productivity and accuracy can improve dramatically.

3D Scan Recording of Buried Pipes and AR Visualization Workflow

Combining centimeter-level RTK positioning with smartphone AR enables end-to-end digitalization from pipe installation records to maintenance management. Below is the workflow for how 3D scanning and AR display of buried pipes are typically performed.

1\. Three-dimensional recording of buried pipes (during construction): For example, when burying new pipes under a road, scan the pipes and the surrounding excavation area with a smartphone equipped with LiDAR before backfilling. If an RTK-GNSS receiver is attached to the smartphone, the acquired point cloud data is automatically tagged with high-precision absolute coordinates (in a global geodetic coordinate system) and the point cloud is saved directly to the cloud. The system can automatically generate a 3D mesh model of the pipe portion from the point cloud, digitally recording the exact position (route and depth) and shape of the buried pipe. Previously, dimensional measurements and drawing production or spraying pipe routes on a temporarily restored road surface were necessary, but with this workflow a detailed 3D record is completed simply by scanning.

2\. Data sharing and management: The point cloud and model data of the buried pipes obtained after measurement are immediately shared via the cloud and can be viewed and used from office PCs and other devices. By importing the data into maintenance ledgers or GIS as asset information, it becomes useful for future inspection planning and coordination with other works. Point cloud data can be analyzed in the cloud to measure diameters and burial depths on arbitrary cross-sections or automatically calculate excavation and backfill volumes with a single button click. This allows site supervisors and construction managers to obtain needed numerical information immediately without creating drawings in CAD or doing manual calculations. Because data can be shared in real time between the site and the office, office staff can give instructions while confirming the point cloud model remotely, or proceed with arrangements for spoil disposal and equipment in advance.

3\. On-site use via AR visualization (during maintenance): The accumulated 3D data of buried pipes can be used for AR on-site display during future inspections or renovation works. For example, if after some years the same road must be excavated again for another project, the conventional process would involve digging out old drawings and guessing pipe locations with trial excavations for verification. With 3D record data, however, simply starting the smartphone AR app and pointing the camera allows the positions and routes of pipes beneath the road surface to be visually displayed on-site. Information such as “a water pipe with a diameter of ○○ mm (○○ in) runs directly below here” or “a gas pipe runs parallel on the far side” appears as colored virtual pipe models overlaid on the real scene, making it instantly obvious to anyone. Depth information can also be shown as labels, so vertical relationships such as “this water pipe is buried 1.2 m (3.9 ft) below the surface” can be shared on-site. The former practice of searching for buried objects using veteran intuition and historical records is transformed into a democratized digital “visible” work based on data.

This workflow integrates measurement (surveying), recording, data sharing, and on-site AR confirmation, enabling precise 3D information that paper drawings and photo ledgers could not reproduce. Because high-precision spatial coordinate management is preserved digitally, information does not degrade over time and can always be accessed. As a result, the accuracy of buried infrastructure maintenance management improves, contributing to future accident prevention and more efficient planning.

Expected Benefits for Infrastructure Inspection and Construction

Using the RTK AR technology described above brings various benefits to infrastructure inspection and civil engineering sites. The main effects are summarized below.

• Prevention of accidents involving buried utilities: By accurately understanding buried locations and depths via AR before excavation, the risk of pipe damage from mis-excavation by heavy equipment can be greatly reduced. Making invisible hazards such as gas pipes and power lines visible in advance significantly strengthens safety measures.

• Increased efficiency and labor savings: Eliminating the need to compare drawings and on-site conditions to guess positions reduces unnecessary work, enabling digging and investigation only where needed and shortening work time. Multiple processes such as surveying, staking, and pipe recording can be completed with a single smartphone, enabling reductions in manpower, shorter schedules, and cost savings.

• Improved recording accuracy: Digital records from point cloud scans can preserve the positions and shapes of buried objects to millimeter-level precision. This results in far more accurate data than paper drawings or oral transmission, providing a reliable foundation for future maintenance ledgers. Because data is stored in the cloud, there is no worry of loss or degradation.

• Advanced maintenance and inspection planning: AR brings innovation to renewal planning and periodic inspection of aging pipes. By overlaying current 3D data with past repair histories on-site, sections that need replacement can be identified and reinforcement measures considered quickly and accurately. For example, in sinkhole risk surveys, displaying the locations of cavities found by ground-penetrating radar and the degradation data of sewer pipes in AR while marking the site can ensure that no risk points are overlooked. Such data-driven inspection planning dramatically improves preventive maintenance efficiency.

• Improved information sharing and communication: AR visualization functions as a common on-site language. In road works where multiple utility operators for water, gas, communications, etc., are involved, integrating each party’s pipe data and displaying it together in AR allows everyone in joint on-site meetings to share the same “visualized underground” information. This reduces time spent comparing paper drawings and prevents misunderstandings or communication errors. When explaining to clients or nearby residents, pointing a smartphone to show “these are the pipes running under this road” intuitively facilitates understanding and consensus building.

• Promotion of on-site DX: Introducing RTK AR strongly supports digital transformation (DX) of construction sites. This aligns with the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiatives, contributing to productivity improvements and advanced safety management through ICT and 3D data. Tasks that were once based on experience and intuition become data-driven, enabling anyone to make accurate decisions and perform work via visualization. This leads to reduced defects and rework, and is expected to help reduce lifecycle costs in infrastructure maintenance and management.

Field Examples and Future Developments

RTK × AR visualization technology for buried pipes is already being used in the field. Domestically, a startup developed a system that combines a tablet with an RTK positioning unit to display underground buried pipes in AR on-site. Without spreading out drawings or conducting trial excavations, users can grasp the positions of buried objects in three dimensions on-site, contributing to improved safety and work efficiency. Trials at actual construction sites reported that pipe installation records were completed without photographs or CAD drawings, and that during subsequent excavation the pipes could be immediately located by AR display—demonstrating significant benefits. Workers have praised the system, saying things like “identifying buried objects no longer relies on intuition and is doable by anyone” and “operation was intuitive and usable without training,” indicating promising on-site adoption.

Globally, outdoor high-precision AR systems are also gaining attention as world-first technologies in construction. Systems that combine high-performance GNSS receivers and AR can overlay 3D design models onto real-world scenes with centimeter-level accuracy through a smartphone, allowing complex BIM models and underground utility information to be shared and verified intuitively on-site. Both in Japan and abroad, initiatives for construction DX and smart maintenance using RTK × AR are accelerating, and adoption is expanding across a wide range of projects from bridge construction to water and sewer maintenance.

Going forward, this high-precision AR technology is likely to become more generalized and simplified, becoming a new industry norm. A future where workers routinely point smartphones on-site to check design drawings and underground utilities via AR is approaching. Without relying on expensive surveying equipment or specialized skills, everyone will be able to handle accurate, real-time spatial information, further accelerating the productivity revolution in construction and infrastructure sectors.

Conclusion: Simple Surveying and AR Display Enabled by LRTK

Visualizing buried pipes with RTK AR has the potential to fundamentally change infrastructure maintenance and civil construction. By overlaying digital data onto the real world with centimeter-level positional accuracy, tasks that once depended on expert intuition are shifting toward data-driven smart construction. The cutting-edge solution attracting attention for making this advanced technology easy to use on-site is LRTK.

LRTK is an integrated system that combines a compact RTK-GNSS receiver that attaches to a smartphone with a dedicated app to enable anyone to perform centimeter-level positioning and AR visualization easily. While many AR surveying tools require prior marker placement or complex initial calibration, LRTK powers up and achieves RTK Fix in seconds, allowing immediate start of high-precision AR without any special calibration work—its ease of use on the job site is a major feature. Cloud integration enables seamless operations such as downloading design data or point cloud survey data on-site for AR display and uploading measured data for immediate sharing. Designed for intuitive use by non-experts, there are reports that one person with one smartphone was able to handle surveying, staking, inspection, photo recording, and AR simulation.

By using LRTK, sites can dramatically improve productivity and safety without expensive equipment or large teams. Beyond see-through display of buried pipes, it can be applied to verification of as-built shapes (construction completion shapes), construction navigation, and other wide-ranging uses—truly a “universal surveying tool” and a trump card for on-site DX. Surveying firms, municipal civil departments, and construction companies can adopt this cutting-edge RTK AR technology to step into a new stage of smart infrastructure inspection. For product information and case studies, see the [LRTK official site](https://www.lrtk.lefixea.com/). Bring your site to the next stage with LRTK.