Table of Contents

• The problem of underground buried pipes being "invisible"

• Technology to visualize buried pipes with AR

• Workflow for using AR display of buried pipes

• Benefits of improved construction efficiency through AR use for buried pipes

• Field cases and future developments

• Conclusion: Simple surveying and AR display made possible by LRTK

• FAQ

Buried infrastructure such as water mains, gas pipes, and power cables that support social infrastructure are hidden underground and are not normally visible, making the presence of buried items a major problem at construction sites. If a pipe is accidentally damaged, it can lead to serious accidents such as water leaks, gas leaks, or power outages. Traditionally, buried pipes have been managed using drawings, markings on the ground, and the experience of veteran workers, but it is not easy to fully grasp the positions of complex, intersecting underground structures, and unforeseen excavation accidents continue to occur.

In recent years, AR (augmented reality) has attracted attention as a technology to "make the invisible visible." In particular, "AR display of buried pipes" combined with high-precision positioning technology RTK-GNSS makes it possible to visualize deep underground pipelines on the spot as if seeing through the ground. If workers can intuitively grasp the state of buried pipes on site, safety measures will improve dramatically, and unnecessary trial excavations and rework can be reduced, improving construction efficiency.

This article explains the basic technologies and utilization methods of AR display of buried pipes at infrastructure sites. It also introduces how construction efficiency can be increased with up-to-date field cases and expected effects, and finally presents a simple surveying solution using LRTK.

The problem of underground buried pipes being "invisible"

The thing to avoid most in roadwork and excavation is accidentally damaging existing underground infrastructure such as water pipes and cables. Damaging an aging water main can lead to a large-scale leak, gas pipes can pose an explosion risk, and cutting power lines can cause blackouts and communication failures in the surrounding area, causing serious social disruption. In fact, many incidents of buried utility damage are reported domestically every year, and many of these are caused by not having an accurate understanding of what is buried there.

Therefore, great care has traditionally been taken in managing buried pipes. For new piping works, the pipe positions and depths are surveyed and recorded before backfilling, and information is preserved through photographs and drawings. On site, markings are made on the ground based on those drawings, and experienced workers carefully excavate while guessing “there should be a ○○ pipe around here.” Where necessary, ground-penetrating radar is used to confirm the locations of buried items, or trial excavations (actually digging to check directly) are performed. However, methods that rely on paper drawings and craftsmen’s intuition have limits, and especially in urban areas that have been repeatedly renovated, it is not uncommon for drawing information to differ from the actual site. There are frequent near-miss incidents where an unexpected pipe is found in a place thought to be clear.

Ultimately, the fundamental problem in infrastructure construction and maintenance is how to make invisible things visible. If underground piping structures could be intuitively understood on the spot, not only could excavation trouble be avoided, but inspection and replacement planning for aging pipes could also be dramatically streamlined. AR technology to visualize buried pipes is now expected as a solution.

Technology to visualize buried pipes with AR

AR (Augmented Reality) is a technology that overlays digital information such as CG onto real images captured by a camera. This makes it possible to display underground pipes and cables in a visible form on site. For example, if you point a smartphone or tablet camera at the ground, underground gas and water pipes can be rendered on the screen as if you were seeing through the surface, allowing workers to intuitively understand “what is buried directly under these feet and how.” No longer relying on paper drawings or guesswork, you can confirm underground structures on site as if you were looking at the real thing.

However, advanced alignment techniques are essential to display buried items in AR at the correct positions. If you simply rely on a smartphone’s built-in GPS or compass, horizontal position errors of several meters can occur, causing virtual pipe models to be displayed far from their actual buried positions. This is far from the precision required for what could be called “seeing through” the ground and could instead cause dangerous misrecognition. Moreover, conventional AR systems often require placing markers (image markers or QR codes) at each site or manual calibration of the model position initially. For managing roads and buried pipes over wide areas, it is unrealistic to place markers at every location or to manually calibrate each site.

The solution to these issues is markerless high-precision AR using the latest technologies: smartphone + LiDAR + RTK-GNSS. Modern smartphones come with advanced AR platforms that can track the device’s movement in space from camera images and IMU (inertial measurement unit) data. Higher-end phones also include a LiDAR (laser scanner) that can capture the surrounding environment as 3D point cloud data in real time. Because LiDAR can capture the shape and distance of the ground and structures with high accuracy, virtual objects (for example, a 3D model of an underground pipe) can be stably overlaid on the real world, and occlusion effects where objects hide behind others can be naturally represented. Since the smartphone itself can immediately build a three-dimensional map of the surroundings in addition to the camera image, the foundation for AR display has been dramatically strengthened.

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) proves powerful. As noted, ordinary smartphone GPS can have errors of several meters, but by using the RTK method (applying real-time corrections from a base station) those errors can be reduced to a few centimeters. RTK-GNSS has long been used in surveying, and recently GNSS receivers have become smaller and lighter, allowing the appearance of ultra-compact RTK-capable GNSS receivers that can be attached to smartphones. For example, a startup developed the “LRTK Phone” device that weighs about 165 g and is about 13 mm thick (0.51 in), and by attaching it to the back of a smartphone it enables positioning with centimeter-level accuracy. It runs for about 6 hours on its internal battery and can be attached to a phone case with one touch. It also supports the CLAS centimeter-level augmentation service provided by Japan’s Quasi-Zenith Satellite System “Michibiki,” so it can maintain centimeter accuracy using only augmentation signals from satellites even in mountainous areas without communication coverage. In urban areas, using RTK correction information via the Internet allows positioning errors to be kept within a few centimeters in real time anywhere in Japan. With such high-precision GNSS devices combined with smartphones, the era in which anyone can carry a high-precision positioning tool in their pocket is becoming a reality.

By combining the terrain point cloud data obtained with a phone’s LiDAR and the absolute position information provided by RTK-GNSS, “AR see-through of buried pipes” has finally become achievable on site with practical accuracy. If a 3D model of the buried pipes (or mesh data generated from point clouds) is preloaded on the smartphone, simply pointing the camera at the site on a later visit will display the underground pipe model perfectly aligned under the real ground. Because the ground itself is recognized by the device as a mesh model measured by LiDAR, virtual pipes appear properly buried in the soil (partially visible through the surface) and depth relationships can be intuitively understood. This AR see-through technology, which does not drift even when walking around freely without special markers, is transforming previously black-box underground infrastructure into “visible information” on site.

Workflow for using AR display of buried pipes

• 3D recording of buried pipes (during construction): For example, when burying new pipes under a road, scan the pipes and 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 will automatically be tagged with high-precision position coordinates (public coordinates) and uploaded to the cloud as is. A dedicated system automatically generates a 3D mesh model of the pipe portion from the point cloud, digitally recording the exact route, depth, and shape of the buried pipe. Traditionally, it was necessary to measure dimensions after burial to create drawings or to spray-mark the pipe route on a temporarily restored road surface, but with this workflow a detailed 3D record is completed simply by scanning.

• Data sharing and management: Point cloud and model data of buried pipes acquired on site can be shared immediately via the cloud and viewed and used from office PCs or other devices. If integrated into asset ledgers or GIS, the data can be accumulated as asset information and used for future inspection planning and coordination with other works. Cloud-based analysis tools can also perform one-click operations such as measuring pipe diameter or burial depth from point clouds on arbitrary cross-sections, or automatically calculating the volume of soil required for excavation and backfilling. Site supervisors and construction managers can immediately obtain the necessary numerical information without creating CAD drawings from field notebooks or doing manual calculations. Because data can be shared in real time between the site and the office, managers not present at the site can give accurate instructions while viewing the point cloud model, and arrangements such as spoil disposal or equipment procurement can be advanced in advance.

• On-site use with AR display (during maintenance and management): The accumulated 3D data of buried pipes can be displayed on site with AR for future inspections or repair work. Even if the same road is excavated years later for another project, there is no need to pull out old drawings and guess locations or confirm them by trial excavation. By launching an AR app on a smartphone and pointing the camera, the positions and routes of pipes buried under the road are visually displayed on the spot. For example, information such as “a single water pipe with a diameter of ○○ mm (○○ in) runs directly below here” or “a gas pipe runs parallel on the far side” is displayed as colored virtual pipe models overlaid on the real scene and can be immediately understood by anyone. Depth information can also be confirmed with label displays, so vertical position relationships such as “this water pipe is buried 1.2 m (3.9 ft) below the ground surface” can be shared on site. The search for buried items that once relied on the intuition of experienced veterans and past records is transformed into a visible process that anyone can perform based on digital data.

Benefits of improved construction efficiency through AR use for buried pipes

• Preventing excavation accidents: By accurately understanding the buried positions and depths in advance with AR, the risk of pipe damage due to accidental excavation by heavy machinery is greatly reduced. Visualizing hidden hazards such as gas pipes and power lines before excavation significantly enhances safety measures.

• Streamlining and labor-saving: The time spent comparing drawings with on-site conditions and guessing positions is eliminated, allowing excavation and investigation only where necessary, thereby shortening work time. Multiple processes such as surveying, staking-out, and pipe recording can be completed with a single smartphone, leading to reductions in personnel, shorter construction periods, and cost savings.

• Improved recording accuracy: Digital records obtained by LiDAR scanning can store the position and shape of buried items to the millimeter. This data is far more accurate than relying on paper drawings or oral tradition and provides a highly reliable information base for future asset ledgers. Since the data is stored in the cloud, there is no worry about loss or degradation.

• Advanced inspection planning: AR brings innovation to renewal planning and periodic inspections of aging pipes. By overlaying current 3D data with past repair histories on site, you can quickly and accurately identify sections that need replacement and consider reinforcement measures. For example, in investigating areas at risk of road collapse, AR display can be used to show void locations detected by ground-penetrating radar or deterioration data of sewer pipes while marking the site, ensuring no risk areas are missed. Such data-driven inspection planning greatly improves preventive maintenance efficiency.

• Smooth information sharing and consensus building: Visualized information via AR functions as a common language on site. In roadworks where multiple operators such as water, gas, and communications companies are involved, consolidating each party’s pipe data and displaying them together in AR allows all parties at joint on-site meetings to share the same “visible underground” information. This reduces the time spent comparing paper drawings and prevents misunderstandings and communication errors. It also facilitates smooth understanding and consensus-building when explaining to clients or nearby residents, since you can intuitively show “these are the pipes under this road” through a smartphone.

• Promoting on-site DX: Introducing RTK×AR strongly supports digital transformation (DX) at construction sites. It aligns with the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiatives, and the use of ICT and three-dimensional data contributes to productivity improvements and advanced safety management. Tasks that formerly relied on experience and intuition become data-driven, and visualization enables anyone to make accurate decisions and perform tasks on site. As a result, quality defects and rework are reduced, which is expected to lead to lower life-cycle costs for infrastructure maintenance.

Field cases and future developments

The visualization technology for buried pipes using RTK×AR is already being used at actual construction sites. Domestically, a startup combined a tablet with an RTK positioning unit to develop a system that displays underground buried pipes in AR on site. Without spreading drawings or performing trial excavations, the system allows three-dimensional understanding of buried items on the spot, contributing to improved safety and work efficiency. Trials at actual construction sites reported that records of buried pipe works were completed without photo documentation or CAD drawing creation, and later re-excavation work successfully located pipes immediately using AR display, demonstrating significant effects. Workers also reported positively that “the hunt for buried items that used to depend on intuition can now be done by anyone” and “the operation was intuitive and usable without training,” indicating promising prospects for site adoption.

Looking overseas, outdoor high-precision AR systems are starting to attract attention as world-first technologies in the construction industry. Systems that combine high-performance GNSS receivers and AR to overlay 3D design models on real-world scenes through smartphones with centimeter-level accuracy are emerging, allowing complex BIM models and underground utility information to be intuitively shared and verified on site. Both in Japan and abroad, initiatives for construction DX and smart maintenance using RTK×AR are becoming active, and adoption is progressing across a wide range of projects from bridge construction to water and sewer maintenance.

In the future, such high-precision AR technologies are likely to become more generalized and simplified and may become the new norm across the industry. A future is imminent in which each worker routinely points a smartphone at the site to check design drawings and underground utilities in AR as they work. Without relying on expensive surveying equipment or specialized skills, everyone will be able to handle accurate information based on spatial coordinates in real time, further accelerating a productivity revolution in construction and infrastructure sectors.

Conclusion: Simple surveying and AR display made possible by LRTK

The visualization of buried pipes using RTK×AR has the potential to greatly transform infrastructure maintenance and civil engineering work sites. By overlaying digital data onto real space with centimeter-level positional accuracy, tasks that once relied on skilled workers’ experience are beginning to shift to data-driven smart construction. LRTK is attracting attention as a solution that allows this advanced technology to be easily used on site.

LRTK is an integrated system that enables anyone to achieve centimeter-level positioning and AR visualization easily with a small RTK-GNSS receiver attached to a smartphone and a dedicated app. Many common AR surveying tools require prior marker placement or complicated initial calibration, but with LRTK the RTK fixes within tens of seconds after powering on the device, allowing immediate start of high-precision AR. No special calibration work is required, and its ease of use on site is a major feature. Cloud integration also allows design data and point cloud survey data to be downloaded on site for AR display, and measured data to be uploaded and shared instantly. It is designed to be intuitive for non-experts, and there are reports that a single smartphone per person enabled surveying, staking-out, inspection, photo documentation, and AR simulation.

By using LRTK, high-cost equipment and large surveying teams are unnecessary, and site productivity and safety can be dramatically improved. In addition to see-through display of buried pipes, it can be applied to verifying as-built shapes of structures, construction navigation, and a wide range of other uses, making it a true “universal surveying tool” and a trump card for on-site DX. Surveying firms, municipal civil departments, and construction companies are encouraged to adopt this cutting-edge RTK×AR technology to step into a new stage of smart infrastructure management. For more information on products and case studies, please see the [LRTK official site](https://www.lrtk.lefixea.com/). Take your site to the next stage with LRTK.

FAQ

Q: What is required to display buried pipes in AR? A: Basically, you need digital data containing the position information of buried pipes (e.g., 3D models or point cloud data) and an AR-compatible device to display it on site. Specifically, prepare design drawings or scan data obtained during construction, and use a system that combines a smartphone or tablet with a high-precision GNSS receiver (RTK-capable). This enables accurate overlay of virtual pipe models onto the camera image on site.

Q: How accurate is AR display of buried pipes? A: Using RTK-GNSS, buried pipes can be displayed with errors on the order of a few centimeters in both horizontal and vertical directions. Conventional GPS-only AR could have deviations of several meters, but high-precision positioning reduces the offset between virtual models and actual pipe locations to a level that is barely discernible to the human eye. Therefore, it is reasonable to consider AR-displayed pipe positions as essentially matching the real objects.

Q: Does AR make drawings and ground markings unnecessary? A: Because AR allows direct confirmation of buried pipe locations on site, the time spent comparing paper drawings or spray-marking the road surface can be greatly reduced. There are cases where photo records and CAD drawing creation for buried pipe works were omitted after AR introduction. However, drawings and data should still be maintained as management records, and AR is a tool to support on-site work. For final construction verification, please cross-check with digital data and ensure safety thoroughly.

Q: Can workers who are not familiar with IT use it well? A: Yes. Recent AR apps are designed for intuitive operation. With a simple UI that displays buried pipes just by pointing the smartphone camera, no special skills are required. Feedback from the field indicates that “it was intuitive enough to use without training,” and even older workers who are familiar with smartphones can use it without problems. With basic operation guidance at introduction, most people can adopt AR on site without resistance.

Q: What else can be visualized with AR besides buried pipes? A: Of course. AR can be applied to many targets beyond underground pipes. For example, a 3D model of the expected shape of a concrete structure can be displayed at full scale on site for construction checks and navigation, or AR can highlight bolts to prevent missed tightening during machinery maintenance. In short, as long as positional information has been digitized, AR can make “hard-to-see things” visible on site, not limited to underground utilities.