Table of Contents

• The problem of buried utilities being "invisible"

• Technology to visualize buried pipes with AR

• Workflow for using buried-pipe AR visualization

• Benefits of improved construction efficiency using buried-pipe AR

• Field case studies and future developments

• Conclusion: Simple surveying and AR visualization enabled by LRTK

• FAQ

Buried utilities that support social infrastructure—such as potable water pipes, gas mains, and power cables—are hidden underground and are not normally visible, so their presence is a major challenge at construction sites. Accidentally damaging a pipe can lead to serious incidents like water leaks, gas leaks, or power outages. Traditionally, buried utilities have been managed using as-built 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 unexpected excavation accidents continue to occur.

Recently, however, AR (augmented reality)—a technology that makes the invisible visible—has attracted attention. In particular, “buried-pipe AR visualization” combined with high-precision positioning technology RTK-GNSS now makes it possible to visualize deep underground pipelines on-site as if looking through the ground. If workers can intuitively grasp the status of buried pipes on-site, safety measures will improve dramatically, and unnecessary test excavations and rework can be reduced, leading to improved construction efficiency.

This article explains the basic technologies and practical uses of buried-pipe AR visualization at infrastructure sites. It also presents how construction efficiency can be improved with the latest field cases and expected effects, and finally introduces a simple surveying solution using LRTK.

The problem of buried utilities being "invisible"

The thing to avoid most in roadworks and excavation is accidentally damaging existing underground infrastructure such as water pipes and cables. Damaging aging potable water pipes can lead to large-scale water leaks; damaging gas mains can create an explosion risk. Cutting a power line can plunge surrounding areas into blackout and cause communication failures, with enormous impacts on social life. In fact, many incidents of buried-utility damage are reported domestically every year, and in many cases the cause is that people did not have an accurate understanding of what was buried where.

For this reason, extreme care has long been taken in managing buried utilities. In new pipe installation work, the position and depth of the pipes are surveyed and recorded before backfilling, and information is retained with photographs and drawings. On site, workers mark the ground based on those drawings, and experienced workers cautiously excavate while guessing “the XX pipe should be around here.” As needed, ground-penetrating radar is used to confirm the positions of buried objects, and test digs (actually digging a hole to confirm directly) are also performed. However, there are limits to methods that rely on paper drawings and craftsmen’s intuition, and in urban areas with repeated renovations it is not uncommon for the information on the drawings to differ from the on-site reality. There are frequent near-miss cases where an unexpected pipe appears from a place thought to be empty.

Ultimately, the fundamental problem in infrastructure construction and maintenance is how to make the invisible visible. If the underground piping structure could be intuitively understood on-site, excavation trouble could be avoided and inspection and replacement planning for aging pipes could be made dramatically more efficient. AR technology that visualizes buried pipes is now being looked to as a solution.

Technology to visualize buried pipes with AR

AR (Augmented Reality) overlays digital information such as CG onto real-world camera images. This makes it possible to display buried pipes and cables as visible on-site. For example, if you point a smartphone or tablet camera at the ground, the screen can render underground gas or water pipes as if you were seeing through the surface, allowing workers to intuitively understand “what is buried directly under this spot and how it is laid out.” No longer relying solely on paper drawings or guesswork, workers can check underground structures on-site as if viewing the actual objects.

However, accurate AR display of buried objects requires advanced alignment techniques. If you rely solely on a smartphone’s built-in GPS or compass, horizontal position errors of several meters can occur, causing the virtual pipe model to be displayed far from the actual buried location. This is far from the “see-through” precision required and could actually cause dangerous misidentification. Traditional AR systems also required placing markers (image markers or QR codes, etc.) on site or manually calibrating the model position at the start. For managing large areas of roads and buried utilities, placing markers or manually calibrating at every location is unrealistic.

The solution to these issues is markerless high-precision AR using the combination of smartphone + LiDAR + RTK-GNSS. Modern smartphones include advanced AR platforms that track the device’s motion in space using camera imagery and IMU (inertial measurement unit) data. Higher-end models also include LiDAR, a laser scanner that acquires the surrounding environment as real-time 3D point-cloud data. Because LiDAR can capture the shape and distances of the ground and structures with high precision, virtual objects (for example, a 3D model of an underground pipe) can be stably overlaid on the real world and occlusion—where virtual objects are naturally hidden behind real ones—can be expressed naturally. The smartphone itself can instantly construct a 3D map of the surroundings in addition to the camera image, greatly strengthening the foundation for AR display.

The final piece remaining is knowing exactly “where the device itself is.” This is where high-precision positioning technology RTK-GNSS (Real-Time Kinematic satellite positioning) excels. As noted, ordinary smartphone GPS can have meter-level errors, but using RTK (applying real-time error corrections from a base station) can reduce those errors to a few centimeters. RTK-GNSS has long been used in surveying, and recent miniaturization and weight reduction of receivers have produced ultra-compact RTK-capable GNSS receivers that can be attached to smartphones. For example, a startup developed a device called the “LRTK Phone” that weighs about 165 g and is about 13 mm (0.51 in) thick; attaching it to the back of a smartphone enables centimeter-level positioning. It runs for about 6 hours on its internal battery and can be attached to a phone case with one touch. It also supports Japan’s Quasi-Zenith Satellite System (QZSS) centimeter-class augmentation service (CLAS) and can maintain centimeter-level accuracy (half-inch accuracy) using only augmentation signals from satellites even in mountainous areas outside communications coverage. In urban areas, using conventional Internet-based RTK correction information enables real-time positioning errors to be kept within a few centimeters anywhere in Japan. With these high-precision GNSS devices paired with smartphones, the era in which “anyone can carry a high-precision positioning tool in their pocket” is becoming a reality.

By combining LiDAR point-cloud data of terrain captured by a smartphone with absolute positioning information obtained from RTK-GNSS, “AR see-through” of buried pipes on-site has finally become practically realizable at usable accuracy. If a 3D model of buried pipes (or mesh data generated from point clouds) acquired beforehand is loaded into the smartphone, visiting the same site later and pointing the camera at the ground will cause the underground pipe model to align and be displayed exactly under the real ground. Because the device recognizes the ground itself as a mesh model measured by LiDAR, virtual pipes can be appropriately occluded so they appear buried under the ground (partly visible through the surface), and the depth relationships are intuitively understandable. This AR see-through technology, which does not require special markers and remains accurate even when freely walking around, is turning underground infrastructure—previously a black box—into visible on-site information.

Workflow for using buried-pipe AR visualization

• 3D recording of buried pipes (at time of construction): For example, when installing new pipes under a road, scan the pipes and excavation area with a LiDAR-equipped smartphone before backfilling. If an RTK-GNSS receiver is attached to the smartphone, the acquired point-cloud data will automatically have high-precision position coordinates (public coordinates) attached and can be uploaded to the cloud as-is. On a dedicated system, a 3D mesh model of the piping is automatically generated from the point cloud, creating a digital record of the exact route, depth, and shape of the buried pipe. Previously, measuring dimensions after burial to create drawings or spraying the temporarily restored road surface to mark pipe routes was necessary, but with this workflow a detailed 3D record is completed simply by scanning.

• Data sharing and management: Point-cloud and model data acquired on site can be shared via the cloud immediately and viewed and used from office PCs or other devices. If incorporated into asset management ledgers or GIS, the data can be accumulated for future inspection planning and coordination with other construction. Using cloud-based analysis tools, you can, with one click, measure pipe diameters or burial depths from arbitrary cross-sections of the point cloud, or automatically calculate the volume of soil used for excavation/backfilling. Site supervisors and construction managers can grasp the necessary numeric information instantly without manually creating CAD drawings from field notes or performing hand calculations. Because site and office data can be shared in real time, supervisors do not need to be physically present to issue precise instructions while viewing the point-cloud model, and they can advance arrangements such as spoil disposal or equipment procurement in advance.

• On-site use via AR display (during maintenance and management): The accumulated 3D data of buried pipes can be displayed on-site with AR for future inspections or renovation work. Even if the same road is excavated years later for another project, there is no need to dig out old drawings and confirm buried objects by test digs. Simply launching an AR app on a smartphone and pointing the camera at the ground displays the positions and routes of pipes beneath the road surface as visual overlays on site. For example, information such as “there is one water pipe with a diameter of ○○ mm directly below here” or “a gas pipe runs in parallel further in” is shown as color-coded virtual pipe models overlaid on the real scene, making them immediately apparent to anyone. Depth information can also be displayed via labels, allowing sharing of vertical position relationships on-site—such as “this water pipe is buried 1.2 m (3.9 ft) below the surface.” Searching for buried objects, which used to rely on the intuition of experienced workers and historical documents, becomes a visible process based on digital data that anyone can perform.

Benefits of improved construction efficiency using buried-pipe AR

• Preventing excavation accidents: Because AR lets you accurately understand burial position and depth in advance, the risk of pipe damage from erroneous excavation by heavy machinery is greatly reduced. Visualizing invisible hazards like gas mains and power lines before excavation significantly strengthens safety measures.

• Streamlining and labor savings: The need to compare drawings and the ground and infer positions is eliminated, allowing excavation and investigation only where necessary, which shortens work time. Multiple processes such as surveying, stake setting, and pipe recordkeeping can be completed with a single smartphone, leading to expected reductions in personnel, shorter construction periods, and cost savings.

• Improved record accuracy: Digital records from LiDAR scans can preserve the position and shape of buried objects to millimeter-level precision. These far more accurate data form a reliable information base for future management ledgers compared with paper drawings or oral transmission. Data stored in the cloud are not susceptible to loss or degradation.

• Advanced inspection planning: AR enables innovation in replacement planning and periodic inspections of aging pipes. Overlaying current 3D data with past repair histories on-site allows rapid and accurate identification of sections that should be replaced and consideration of reinforcement measures. For example, in investigations of road subsidence risk, displaying ground-penetrating-radar-detected cavities and degraded sewer data in AR while marking on-site ensures no risk areas are overlooked. Data-driven inspection planning greatly enhances preventive maintenance efficiency.

• Smoother information sharing and consensus building: AR-visualized information functions as a common language on-site. In roadworks, multiple utilities such as water, gas, and communications are involved; by integrating each utility’s pipe data and displaying them together in AR, everyone can share the same “underground visualized” information during joint on-site meetings. This reduces the need to reconcile paper drawings and prevents misunderstandings and communication errors. When explaining to clients or nearby residents, AR allows intuitive demonstrations like “these are the pipes beneath this road” via a smartphone, smoothing understanding and consensus building.

• Promoting on-site DX: Introducing RTK×AR strongly accelerates digital transformation (DX) of construction sites. This approach aligns with the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiative, and the use of ICT and 3D data contributes to productivity improvements and advanced safety management. Work that used to rely on experience and intuition becomes data-driven, and “visualization” enables anyone to make accurate judgments and perform tasks on site. As a result, quality defects and rework are reduced, contributing to lower life-cycle costs for infrastructure maintenance.

Field case studies and future developments

High-precision AR visualization of buried pipes using RTK×AR is already being used at actual construction sites. Domestically, a startup combined a tablet terminal with an RTK positioning unit to develop a system that displays underground buried pipes on-site in AR. Without spreading drawings or performing test digs, the positions of buried objects can be understood three-dimensionally on the spot, contributing to improved safety and work efficiency. Trials at actual sites reported significant effects such as completing buried-pipe documentation without photography or CAD drawing creation and quickly identifying pipe locations later with AR during re-excavation. Field workers also reported positive feedback such as “searching for buried objects that used to rely on intuition can now be done by anyone” and “operations were intuitive and usable without training,” indicating promising adoption on sites.

Looking overseas, outdoor high-precision AR systems are beginning to attract attention as world-first technologies in the construction industry. Systems that combine high-performance GNSS receivers and AR allow designers’ 3D models and real-world scenery to be overlaid on a smartphone with centimeter-level precision, enabling 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 spreading across a wide range of projects—from bridge construction to water and sewer maintenance.

Going forward, this kind of high-precision AR technology is likely to become more generalized and simplified and become the industry norm. A future in which each worker routinely points a smartphone on-site to check design drawings and underground conditions in AR while working is approaching. By enabling anyone to handle accurate spatial-coordinate-based information in real time without expensive surveying equipment or special skills, a productivity revolution in the construction and infrastructure sectors is expected to accelerate.

Conclusion: Simple surveying and AR visualization enabled by LRTK

Buried-pipe visualization with RTK×AR has the potential to transform infrastructure maintenance and civil engineering construction sites. Overlaying digital data onto physical space with centimeter-level positional accuracy is shifting work that used to rely on specialists’ experience toward data-driven smart construction. One solution gaining attention for easy on-site use of this advanced technology is LRTK.

LRTK is an integrated system that combines a small RTK-GNSS receiver that attaches to a smartphone with a dedicated app to enable anyone to easily achieve centimeter-level positioning and AR visualization. Many conventional AR surveying tools require prior marker placement or complicated initial calibration, but with LRTK the RTK can Fix (satellite lock) in a few tens of seconds after powering the device on, allowing high-precision AR to start immediately. No special calibration work is required, and the system’s readiness for immediate on-site use is a major feature. Cloud integration also allows seamless operations such as downloading design data or point-cloud survey data to display in AR on-site, and uploading measured data from the field for immediate sharing. Designed to be intuitive even for workers without specialized knowledge, there are reports of single smartphones per person being sufficient to handle surveying, layout marking, inspection, photographic records, and AR simulation.

By using LRTK, it is possible to dramatically improve site productivity and safety without expensive equipment or large surveying teams. Beyond see-through display of buried pipes, LRTK can be applied to verifying as-built shapes of structures, construction navigation, and many other uses, making it a true “all-purpose surveying instrument” and a trump card for on-site DX. Surveying companies, municipal civil engineering departments, and construction firms should consider adopting this cutting-edge RTK×AR technology to take a step into a new stage of smart infrastructure management. For product information and case studies, please see the [LRTK official site](https://www.lrtk.lefixea.com/). Advance your sites to the next stage with LRTK.

FAQ

Q: What is needed to display buried pipes in AR? A: Basically, you need digital data that includes the position information of the buried pipes (e.g., 3D models or point-cloud data) and an AR-capable device to display it on-site. Specifically, prepare design drawings or scan data acquired at the time of construction, and use a system that combines a smartphone or tablet with a high-precision GNSS receiver (RTK-capable). This allows virtual pipe models to be accurately overlaid on camera imagery on-site.

Q: How accurate is buried-pipe AR visualization? A: Using RTK-GNSS, buried pipes can be displayed with an accuracy on the order of a few centimeters in both horizontal and vertical directions. Whereas GPS-only AR used to have errors of several meters, high-precision positioning reduces the discrepancy between virtual models and actual pipe positions to a level that is hardly perceptible to the human eye. Therefore, it is reasonable to consider the AR-displayed pipe positions as nearly matching the real objects.

Q: If AR visualization is available, are drawings and ground markings unnecessary? A: AR lets you confirm pipe positions directly on-site, so the need to compare paper drawings or spray-mark the road surface can be greatly reduced. In practice, there are cases where AR adoption eliminated the need for photographic records or CAD drawing creation for buried-pipe work. However, drawings and data themselves should still be retained as management records, and AR should be treated as a tool to support on-site work. For final construction confirmation, always cross-check with digital data and ensure safety thoroughly.

Q: Can workers who are not familiar with IT use this technology? A: Yes. Modern AR apps are designed for intuitive operation. With simple UIs that display buried pipes by merely pointing the smartphone camera, special skills are not required. Field feedback includes reports that “it was intuitive to use without training,” and workers who are comfortable with smartphones—even older workers—can use it without issue. Providing basic operation guidance at introduction will enable many people to adopt AR on-site without resistance.

Q: Can AR visualize things other than buried pipes? A: Of course. AR can be applied to many targets beyond underground pipes. For example, a 3D model of a completed concrete structure can be displayed on-site at full scale for construction checks or navigation, or during equipment maintenance target bolts can be highlighted in AR to prevent missing tightening. In short, as long as positional data are digitized, AR can turn “hard-to-see” things into visible forms on-site, not limited to underground utilities.