Table of contents

• Challenges in underground infrastructure maintenance

• Technology to visualize buried pipes with AR

• Centimeter-level accuracy enabled by RTK-GNSS

• Workflow for 3D scanning, recording and AR visualization of buried pipes

• Expected benefits for infrastructure inspection and construction

• Field case studies and future developments

• Conclusion: simple surveying and AR display enabled by LRTK

• FAQ

Challenges in underground infrastructure maintenance

The most frightening accidents during road works or site excavation are those in which buried water pipes, gas pipes, or power and communication cables are accidentally damaged. Breaking an aging water main can lead to a large-scale leak; damaging a gas pipe risks leaks or explosions. Cutting power or communication lines can cause local blackouts or service outages, severely disrupting social life. In fact, many accidents involving damage to underground utilities are reported every year domestically, and in many cases the cause is that people “did not know exactly what was buried there.”

To prevent such accidents, great care has long been taken in managing buried pipes. During installation, positions and depths of the pipes are surveyed and recorded before backfilling, and photos and drawings are archived. On site, workers rely on those drawings and ground markings, and experienced staff proceed with excavation by estimating “there should be a pipe around here.” Where necessary, ground-penetrating radar is used to locate buried objects, or trial excavations are performed for direct confirmation. However, management that depends on paper drawings and veteran intuition has limits, and it is not easy to mentally keep track of the exact positional relationships of pipes that intersect underground in complex ways. Especially in urban areas that have undergone repeated renovations, the information on drawings often differs from the actual buried conditions on site, and there are frequent cases where an unexpected pipe appears at a depth where people thought “there shouldn’t be anything here,” prompting close calls.

In short, the fundamental challenge in infrastructure maintenance is “how to make the invisible visible.” If subsurface structures could be visualized intuitively, not only could excavation-related incidents be avoided, but inspections and replacement planning for aging pipes could be made dramatically more efficient. That is why AR (augmented reality) technology for visualizing buried pipes is now attracting attention.

Technology to visualize buried pipes with AR

AR (Augmented Reality) is a technology that overlays digital information such as CG onto real-world imagery seen through a camera. Using AR, buried pipes and cables can be virtually displayed in a way that is visible on site. For example, if you point a smartphone or tablet camera at the ground, the screen can depict underground water or gas pipes as if you were seeing through the surface. Workers can intuitively understand “what is buried directly beneath this spot and how it runs,” allowing verification of underground structures on site as if viewing the real thing rather than relying on drawings or guesswork.

However, accurately “seeing through” to buried objects with AR requires advanced alignment technology. If you rely 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 required for “seeing through” and could even cause dangerous misidentification. Conventional AR systems also required placing markers (alignment targets) at each site or manually adjusting model positions at the start. For managing long stretches of road or buried utilities, deploying markers or performing manual adjustments at each location is impractical.

To solve these problems, a markerless high-precision AR approach combining smartphone + LiDAR + RTK-GNSS has emerged. Modern smartphones include advanced AR platforms that track device motion in space using camera imagery and IMU (inertial measurement unit) data. Higher-end models also incorporate compact LiDAR (light detection and ranging) sensors that can acquire the surrounding environment as real-time 3D point clouds. LiDAR enables high-precision measurement of ground and structure shapes and distances, allowing virtual objects (such as underground pipe models) to be stably overlaid on the real world and naturally rendering occlusion when objects are hidden behind others. In other words, smartphones can now instantly build a three-dimensional map of their surroundings in addition to camera imagery, greatly strengthening the foundation for AR rendering.

The final piece is accurately knowing “where the device itself is.” This is where high-precision positioning technology RTK-GNSS (Real-Time Kinematic satellite positioning) plays a crucial role. As mentioned, standalone phone GPS can have meter-level errors, but with RTK correction information the positioning error can be reduced to the centimeter level. RTK has long been used in surveying, and recent miniaturization and weight reduction of receivers have produced RTK-capable GNSS receivers that can be attached to smartphones. Combining such external high-precision GNSS with a smartphone makes it possible to determine the device’s position in a global coordinate system with centimeter-level accuracy, minimizing the discrepancy between virtual models and the real world.

By combining the LiDAR-derived ground shape point cloud from the smartphone with the global self-position provided by RTK-GNSS, practical-precision “AR透視 of buried pipes” has become feasible. For example, if you preload a 3D model of the buried pipes (or a 3D mesh generated from point clouds) into the smartphone, then when you later visit the site and point the camera at the ground, the underground model will be displayed precisely at its real subsurface location. Because the smartphone recognizes the ground itself as a mesh model from LiDAR measurements, virtual pipes are naturally occluded as if buried in soil, and their depth relationships are intuitively understandable. This markerless AR透視 technology, which keeps models from drifting even as you walk around freely, is turning previously black-box underground infrastructure into “visible information” on site.

Centimeter-level accuracy enabled by RTK-GNSS

High-precision positioning by RTK-GNSS is the fundamental technology supporting AR visualization of buried pipes. RTK (Real-Time Kinematic) is a method that dramatically improves GNSS positioning accuracy by using real-time correction information from a base station, enabling relative positioning to a fixed reference point and reducing positioning errors to within a few centimeters. While standalone GPS typically has meter-level errors, RTK provides accuracy on the order of a few centimeters both horizontally and vertically, which is why it has long been valued in civil engineering and surveying.

Making RTK easy to use on site has been enabled by the recent appearance of ultra-compact RTK-GNSS receivers. For example, a device developed by a startup from Tokyo Institute of Technology called the “LRTK Phone” enables RTK positioning simply by attaching a small receiver of about 165 g and about 13 mm thickness to the back of a smartphone. The built-in battery runs for about 6 hours, and it can be attached and detached as easily as a phone case. It also supports the centimeter-class augmentation service (CLAS) provided by Japan’s Quasi-Zenith Satellite System “Michibiki,” so it can maintain centimeter-level accuracy using satellite augmentation signals alone even in mountainous areas without cellular coverage. In urban areas, conventional network-based RTK correction services can be used, allowing positioning errors to be corrected to within a few centimeters in real time anywhere in Japan. In other words, integrating such high-precision GNSS devices with smartphones is making an era in which “anyone can carry a high-precision positioning tool in their pocket” increasingly realistic.

We can already see a future where each field technician carries a smartphone with a built-in high-precision GPS device, takes it out when needed, and uses it for surveying and AR display. In fact, modern systems present positioning results and navigation information on the phone screen with intuitive Japanese UIs, so they are designed to be usable without specialized knowledge. For example, stake-out work that used to require two people can now be done by one person carrying a lightweight monopod with a smartphone+RTK attached, following on-screen guidance to accurately set out positions. As high-precision GNSS positioning becomes easily usable by anyone, productivity and accuracy in surveying and construction management will dramatically improve.

Workflow for 3D scanning, recording and AR visualization of buried pipes

• 3D recording of buried pipes (during construction): For example, when installing new pipes under a road, scan the pipes and excavation area with a LiDAR-equipped smartphone before backfilling. With an RTK-capable GNSS receiver attached, the acquired point cloud data is automatically assigned high-precision world coordinates and uploaded to the cloud. The system automatically generates a 3D mesh model of the pipe segments from the point cloud, creating an accurate digital record of the buried pipe’s route, depth, and shape. Traditionally, teams measured dimensions after backfilling to create drawings or sprayed the temporary surface to mark pipe routes, but with this workflow detailed 3D records are completed simply by scanning.

• Data sharing and management: The point cloud and model data of the buried pipes are instantly shared via the cloud and can be viewed and utilized from office PCs or other devices. Importing the data into asset ledgers or GIS allows it to be stored as asset information, aiding future inspection planning and coordination with other works. Cloud-based analysis of point clouds enables measurements of diameters and burial depths at arbitrary cross-sections, automatic calculation of excavation and backfill volumes, and other advanced processing at the push of a button. Site supervisors can thus obtain needed numerical information without creating CAD drawings or doing manual calculations. Real-time sharing between the field and the office also enables office staff to give instructions while checking 3D models remotely, and to advance tasks like spoil handling or material procurement in advance.

• On-site use via AR visualization (during maintenance): Accumulated 3D data of buried pipes can be displayed on site using AR for future inspections or renovation work. For example, even years later when the same road must be excavated for other work, you won’t need to rely on old drawings or perform trial excavations to find pipe locations. With 3D record data, you can launch an AR app on your phone and point the camera to see the positions and routes of pipes beneath the road surface visually on site. Information such as “a single water pipe of diameter ○○ mm is running directly beneath this spot” or “a gas pipe runs parallel further in” can be shown as colored virtual pipe models overlaid on the real scene, making it obvious to anyone. Depth information is also presented as labels, so vertical position relationships such as “this water pipe is buried 1.2 m (3.9 ft) below the surface” can be shared on site. In this way, the task of locating buried objects—previously dependent on veterans’ intuition and archived records—becomes a visible process anyone can perform based on digital data.

This workflow digitally integrates the cycle from survey recording to data sharing and on-site AR confirmation. Because it preserves detailed 3D information that paper drawings or photo ledgers could not reproduce, the information does not degrade over time and high-precision spatial coordinate management is always possible. As a result, accuracy in buried infrastructure maintenance improves and contributes to accident prevention and more efficient planning in the future.

Expected benefits for infrastructure inspection and construction

• Preventing accidents involving buried utilities: By accurately confirming buried positions and depths with AR before excavation, the risk of damaging pipes with heavy machinery can be greatly reduced. Making “invisible hazards” such as gas pipes and power lines visible in advance significantly strengthens safety measures.

• Improved efficiency and reduced labor: Time spent comparing drawings and estimating positions on site is eliminated, allowing excavation and investigation to be performed efficiently where needed, which shortens work time. Multiple processes such as surveying, stake-out, and pipe recording can be completed with a single smartphone, which can reduce personnel requirements, shorten schedules, and cut costs.

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

• Advanced maintenance and inspection planning: AR can revolutionize renewal planning and periodic inspection of aging pipes. By overlaying current 3D data with past repair histories on site, sections to be replaced can be quickly and accurately identified and reinforcement measures considered. For instance, in sinkhole risk investigations, displaying ground-penetrating radar-detected cavities or sewer deterioration data in AR while marking the site can help identify risk locations without omission. Such data-driven inspection planning dramatically improves preventive maintenance efficiency.

• Improved information sharing and communication: AR visualization serves as a common language on site. In road projects involving multiple utility owners—water, gas, communications, etc.—integrating each party’s pipe data and displaying them together in AR lets everyone share the same “visible underground” information during joint site meetings. This reduces the need to compare paper drawings and prevents misunderstandings or miscommunication. When explaining to clients or nearby residents, you can intuitively show “these are the pipes under this road” through a smartphone, making understanding and consensus-building smoother.

• Promoting on-site DX: Introducing RTK×AR strongly promotes digital transformation (DX) at construction sites. It aligns with the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiative and is gaining attention as part of smart construction and infrastructure maintenance DX. Because seamless data-driven workflows from surveying to construction and maintenance become possible, overall business process efficiency and sophistication improve. Active adoption of digital technology can also help solve industry challenges such as labor shortages and skill transfer, and is expected to reduce life-cycle costs in the long term.

Field case studies and future developments

The RTK×AR technology for visualizing buried pipes is already being used on actual construction sites. Domestically, a startup has combined an RTK positioning unit with a tablet device to develop a system that displays underground pipelines in AR on site. Without unfolding drawings or performing trial excavations, crews can spatially grasp buried objects on the spot, contributing to improved safety and efficiency. Field trials have reported substantial benefits: records of buried pipe works were completed without photos or CAD drawings, and subsequent re-excavation work could immediately locate pipes using AR. Workers have praised the system, saying “finding buried objects no longer relies on intuition and anyone can do it” and “the operation is intuitive and usable without training,” indicating good prospects for adoption on sites.

Looking overseas, outdoor high-precision AR systems are drawing attention as world-first technologies in the construction industry. Systems combining high-performance GNSS receivers with AR can overlay 3D design models on real scenery with centimeter-level accuracy through a smartphone, enabling intuitive on-site sharing and verification of complex BIM models and underground utility information. In Japan and abroad, RTK×AR initiatives for construction DX and smart maintenance are accelerating, with adoption spreading across a wide range of projects from bridge construction to water and sewage maintenance.

Going forward, it is highly likely that these high-precision AR technologies will become more generalized and easier to use, becoming the industry’s new normal. A future where each worker routinely points a smartphone at the site to confirm design drawings and underground conditions in AR is approaching. When everyone can handle accurate, real-time spatially referenced information without expensive equipment or specialized skills, a productivity revolution in construction and infrastructure is expected to accelerate.

Conclusion: simple surveying and AR display enabled by LRTK

Visualizing buried pipes using RTK×AR has the potential to greatly change infrastructure maintenance and civil engineering practices. By overlaying digital data on the real world with centimeter-level accuracy (cm level accuracy (half-inch accuracy)), tasks once dependent on skilled workers’ experience are beginning to shift to data-driven smart construction. One solution that makes these advanced technologies easy to use on site is LRTK.

LRTK is an integrated system that enables anyone to achieve centimeter-level positioning and AR visualization using a small RTK-GNSS receiver attached to a smartphone and a dedicated app. Many AR surveying tools require pre-placed markers or complicated initial calibration, but with LRTK RTK can fix within tens of seconds after powering on the device, allowing high-precision AR to begin immediately. No special calibration is required, and the ease of use on site is a major feature. Cloud integration allows seamless operations such as downloading design data or point-cloud survey data to display in AR on site, and immediately uploading and sharing data measured at the site. The system is designed to be intuitive for users without specialized knowledge, and there are reports that “one smartphone per person was sufficient for surveying, stake-out, inspection, photo recording, and AR simulation.”

Using LRTK, sites can dramatically improve productivity and safety without expensive equipment or large teams. Beyond visualizing buried pipes, LRTK can be applied to as-built verification of structures, construction navigation, and many other uses—truly a “universal surveying instrument” and a trump card for on-site DX. Surveying companies, municipal civil departments, and construction contractors are encouraged to adopt this cutting-edge RTK×AR technology in their operations and step into a new stage of smart infrastructure inspection. For more information, product details and case studies are available on the [LRTK official site](https://www.lrtk.lefixea.com/). If you are interested, please take a look. Let LRTK evolve your sites to the next stage.

FAQ

Q: What equipment and preparation are required to display buried pipes in AR on site? A: You need a smartphone or tablet and an AR app. Recent iPhones and iPads have AR functionality (ARKit) built in, so they can be used without additional hardware, but to improve alignment accuracy it is recommended to use a high-precision GNSS receiver such as the LRTK Phone. Also, upload the design data you will use (3D models of buried pipes or drawing files) to the cloud in advance so the device can select them, and if necessary adjust the coordinate system beforehand for a smooth start.

Q: Can AR display be used with only 2D drawing data, or is a 3D model required? A: AR display is possible even with only plan (2D) drawings. Without a 3D model, you can project pipeline routes drawn on plans onto the ground or show virtual markers and symbols at important points. For example, you can lay a CAD plan (DXF) or an image of a plan as a background in AR and check for discrepancies with the site. However, 3D data includes height information and enables full three-dimensional interference checks, so preparing 3D data is preferable when possible.

Q: How accurate is AR positioning for buried-pipe display? A: Standalone phone GPS or basic AR can have offsets ranging from tens of centimeters to meters. That may be acceptable for rough checks but is insufficient for pinpointing exact excavation locations. By contrast, high-precision positioning such as LRTK can reduce horizontal and vertical errors to within a few centimeters (cm level accuracy (half-inch accuracy)), allowing virtual overlays to match buried pipes with near-exact precision suitable for actual construction.

Q: Is specialized knowledge or training required? Can site staff use it? A: No advanced CG software skills are required. Generally, anyone can use the system by following the smartphone app prompts. LRTK’s UI is designed for users with limited surveying experience, allowing positioning and AR display via button operations. With brief on-site training, staff can quickly apply it to daily construction management.

Q: Do I need to place markers or reference points in advance for AR display? A: When using LRTK, you generally do not need special markers. The GNSS makes the device itself a reference, allowing models to be automatically displayed at prescribed coordinates. However, in GPS-denied environments such as indoors, you will need to rely on ARKit plane detection or visual markers. In those cases, placing clear reference features (for example, a corner of a wall or a distinct floor pattern) to align the model can improve accuracy. For outdoor wide-area sites, LRTK coordinate alignment is the most efficient approach.