Confirm buried pipes with AR: Safe excavation before digging with AR heatmaps

Table of contents

• Conventional buried pipe management and excavation accident risks

• Technology to透視 and visualize underground buried objects with AR

• RTK-GNSS that enables centimeter-level accuracy (cm level accuracy (half-inch accuracy))

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

• Safe excavation planning enabled by AR heatmaps

• Main benefits of buried pipe AR display and AR heatmaps

• Field case studies and future prospects

• Conclusion: Simple surveying and high-precision AR display realized by LRTK

• FAQ

Conventional buried pipe management and excavation accident risks

In roadworks and on-site excavation tasks, the greatest concern is accidentally damaging underground lifelines such as water pipes, gas pipes, and power cables. Damaging an old water main can lead to a large-scale leak, while a gas pipe can cause leaks or explosions. Cutting power lines or communication cables can cause blackouts or communication outages in surrounding areas, severely disrupting social life. In fact, damage incidents to underground utilities are reported nationwide almost every year, and many are caused by not having an accurate understanding of what is buried there.

To prevent such accidents, meticulous care has long been taken in the construction and maintenance of buried pipes. In piping work, before backfilling, survey measurements are taken to record the position and depth of pipes, and photos and drawings are kept. On site, workers rely on those drawings and markings on the ground, and experienced personnel cautiously excavate while estimating, “there should be a pipe around here.” As needed, ground-penetrating radar (GPR) is used to detect buried objects, or trial excavations are conducted for direct confirmation. However, management that relies on paper drawings and veterans’ intuition has limits, and it is not easy to mentally grasp the precise spatial relationships of complex piping networks underground. Especially in urban areas that have undergone repeated renovations, there are many cases where the drawing information and the actual buried conditions disagree, and incidents where an unexpected pipe appears from a place thought to be clear are not uncommon.

In short, the fundamental challenge in infrastructure management is how to make the invisible visible. If buried structures could be intuitively visualized, not only could excavation troubles be avoided, but inspections and replacement planning of aging pipes could also be dramatically streamlined. That is why AR (Augmented Reality) technology for visualizing buried pipes is attracting attention now.

Technology to透視 and visualize underground buried objects with AR

AR (Augmented Reality) is a technology that overlays digital information onto real-world images seen through a camera. By using this, pipes and cables buried underground can be virtually displayed on-site in a way that appears to be “visible.” For example, if a worker points a smartphone or tablet camera at the ground, underground water pipes or gas pipes can be rendered on the screen as if seen through the surface, allowing the worker to intuitively understand “what is buried directly beneath this spot and how.” Without relying on drawings or guesses, underground structures can be checked on-site as if visually inspecting the actual objects.

However, to accurately “see through” buried objects with AR, advanced alignment technology is essential. If relying on consumer smartphone GPS or electronic compasses, planar position errors of several meters can occur, causing virtual pipe models to be displayed far offset from their actual buried positions. This is far from the precision required to call it “透視” (seeing-through), and could even introduce danger through misidentification. Also, conventional outdoor AR systems typically required placing markers (alignment references) at each site or manually adjusting the model position (calibration) during initialization. For managing entire roadways or long-distance buried pipes, placing markers or repeatedly performing manual alignment is impractical.

To solve these issues, a markerless high-precision AR technology combining smartphone + LiDAR + RTK-GNSS has emerged in recent years. Modern smartphones come with advanced AR platforms that track device movement within space using camera footage and IMU (inertial measurement unit) data. Higher-end models even have built-in small LiDAR (light detection and ranging) sensors that can acquire the surrounding environment as 3D point cloud data in real time. Because LiDAR can accurately capture the shape and distance of the ground and structures, virtual objects (such as 3D models of underground pipes) can be stably overlaid on the real world, and occlusion effects where virtual objects are hidden behind real objects can be naturally represented. In other words, smartphones can now instantly build a three-dimensional spatial map of their surroundings in addition to the camera image, greatly strengthening the foundation for AR display.

The remaining final piece is for the device itself to know its exact location. This is where the powerful high-precision positioning technology RTK-GNSS (Real-Time Kinematic Global Navigation Satellite System) comes into play.

RTK-GNSS that enables centimeter-level accuracy (cm level accuracy (half-inch accuracy))

RTK (Real-Time Kinematic) GNSS positioning is a technique that dramatically improves GNSS positioning accuracy by using real-time correction information from a reference station. Through relative positioning with a fixed reference point, it can reduce the usual meter-level errors to within a few centimeters. Since centimeter-class accuracy (cm level accuracy (half-inch accuracy)) can be obtained both horizontally and vertically, RTK has long been used in civil engineering surveying.

Making this RTK positioning technology easy for anyone to use on-site are the ultracompact RTK-compatible GNSS receivers that have appeared in recent years. For example, a device called the LRTK Phone developed by a startup from Tokyo Institute of Technology enables RTK positioning simply by attaching a receiver weighing about 165g and about 13 mm (0.51 in) thick to the back of a smartphone. It runs on a built-in battery for about 6 hours and can be attached with a single touch like a phone case. It also supports the centimeter-level positioning augmentation service provided by Japan’s Quasi-Zenith Satellite System “Michibiki” (CLAS) (cm level accuracy (half-inch accuracy)), so it can maintain stable centimeter accuracy from satellite augmentation signals alone even in mountainous areas without mobile coverage. In urban areas, using conventional internet-based RTK correction services allows real-time correction of positioning errors to within a few centimeters nationwide. In other words, the integration of such high-precision GNSS devices with smartphones is making the era of “everyone carrying a high-precision positioning tool in their pocket” a reality.

A future in which each field engineer carries a smartphone with a high-precision GNSS receiver and can quickly take it out for surveying or AR display is already becoming realistic. In fact, the latest solutions present positioning results and navigation information on the smartphone screen with intuitive Japanese UIs, so they are designed to be easy to use without special expertise. For example, staking out (marking positions) that used to be done by two-person teams can now be done by one person holding a lightweight pole with an RTK receiver attached to a smartphone, and placing stakes accurately by following on-screen guidance. With easy-to-use high-precision GNSS, productivity and accuracy in surveying and construction management are expected to improve dramatically.

Workflow for 3D recording of buried pipes and AR visualization

• 3D recording of buried pipes (during construction): When new piping is installed, the pipes and excavation area are scanned with a smartphone (with LiDAR) and recorded before backfilling. If the smartphone has an RTK-compatible GNSS receiver attached, the acquired point cloud data is immediately georeferenced with high-precision world coordinates (geodetic or planar coordinates), and the data is automatically saved to the cloud. A dedicated system automatically generates 3D mesh models of the pipe sections from the point cloud data, creating accurate digital records of the routes, depths, and shapes of the buried pipes. Previously, people measured with tapes after burial to create drawings or spray-marked pipe routes on temporarily restored road surfaces, but with this workflow, detailed 3D records are completed simply by scanning.

• Data sharing and management: The 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 imported into maintenance ledgers or GIS as asset information, they help with future inspection planning and coordination with other works. Using cloud-based analysis functions, advanced processing such as measuring pipe diameters or burial depths on arbitrary cross-sections or automatically calculating excavation and backfill volumes can be done with a single button. Site supervisors and construction managers can grasp necessary numerical information immediately without drawing CAD diagrams or doing manual calculations. Because data can be shared in real time between the field and the office, office staff can give instructions while viewing the 3D model, accelerate soil disposal or material arrangements, and so on, even without being on site.

• On-site use through AR visualization (for maintenance and management): Accumulated 3D data of buried pipes can be used for AR display during future inspections or renovation work. Even if the same road is excavated in a later project, there is no need to rely on old drawings or perform trial excavations. With 3D record data, simply launching an AR app on a smartphone and pointing the camera at the site displays the types and routes of pipes buried beneath the road surface in 3D on-site. Information such as “a single water pipe of diameter ○○ mm (○○ in) runs directly beneath this spot” or “a gas pipe runs parallel further in” is shown as colored models overlaid on the real scene, making it obvious to anyone at a glance. Depth information is also labeled, so vertical relationships can be intuitively understood.

Safe excavation planning enabled by AR heatmaps

An AR heatmap visualizes deviations and differences on 3D measured data or design data as color distributions (heatmaps) and overlays them onto the real world. Traditionally, heatmaps have been used mainly for as-built management (verifying post-construction shapes against design) to show whether the finished terrain matches the design in colored distributions, but this technology is also powerful in the excavation planning stage.

For example, by comparing on-site terrain data with the design excavation model in advance for a planned excavation area, a heatmap can show “where and how much to excavate.” If overlaid on the ground via AR on a smartphone or tablet, site workers can intuitively grasp elevation differences and excavation surpluses/deficits. Areas that need deep excavation can be shown in red or orange, while areas that require little to no removal can be blue or green, enabling one-look judgment of which parts to prioritize. This prevents over-excavation or under-excavation and allows work to proceed safely and efficiently to the planned shape.

AR heatmaps can also be applied to raise awareness of underground hazards. For example, if locations where buried pipes are particularly shallow or where multiple conduits cross and create high-risk areas are emphasized in red on the heatmap, heavy equipment operators and workers can remain constantly aware of danger zones through the AR display. Visualizing invisible risks in advance is expected to prevent excavation accidents caused by human error during work.

In practice, the effectiveness of AR heatmaps has been confirmed in field demonstrations by the Ministry of Land, Infrastructure, Transport and Tourism. When as-built data was projected as heatmaps on tablets at sites, defect locations that were difficult to notice on flat reports were easily identified on the spot, and information sharing among responsible parties became smoother. Because the actual finished work and the AR heatmap information can be compared on the screen at the same time, pinpointing the locations to check takes little time, allowing real-time judgment of as-built quality — a point that was evaluated positively. In this way, intuitive visualization via AR heatmaps is bringing new value to safety and quality management on site.

Main benefits of buried pipe AR display and AR heatmaps

• Prevention of accidents involving underground utilities: By understanding the precise position and depth of buried objects via AR before excavation, the risk of damaging pipes with heavy machinery due to mistaken digging can be greatly reduced. Making invisible hazards such as gas pipes or high-voltage lines visible in advance significantly strengthens safety measures.

• Improved efficiency and labor savings: Eliminating the need to compare drawings and the site to estimate buried positions saves time and allows excavation and inspection work to be carried out efficiently and only where necessary, shortening work time. Because multiple processes such as surveying, staking, and as-built recording can be completed with a single smartphone, reductions in personnel, shorter construction periods, and cost savings can be expected.

• Improved recording accuracy: Accurate digital records from point cloud scans can store the positions and shapes of buried objects down to millimeter resolution. This leaves far more accurate data than relying on paper drawings or verbal handovers, providing a reliable information base for future works.

• Advanced maintenance and inspection planning: Using AR enables innovative methods for planning replacement of aging pipes and regular inspections. By overlaying current 3D data with past repair histories on site, sections to be replaced and reinforcement measures can be identified and considered quickly and appropriately. For example, in investigations of potential road sinkhole locations, AR can display underground cavity positions identified by GPR and deterioration data of sewer pipes while marking the site, ensuring risk areas are exhaustively identified. Such data-driven inspection planning will dramatically improve preventive maintenance efficiency.

• Smoother information sharing and consensus building: Visual AR information serves as a common language among site stakeholders. For instance, roadworks often involve multiple buried-utility operators (water, gas, communication), but integrating each pipe’s data and displaying them together in AR enables all parties to share the same “visualized underground” information during joint site meetings. This reduces the effort of comparing paper conduit diagrams and prevents misunderstandings or transmission errors that cause trouble. When explaining to clients or nearby residents, AR allows one to intuitively show, through a smartphone, “how many conduits run under this road,” facilitating understanding and consensus-building.

• Promotion of on-site DX: The introduction of RTK×AR strongly promotes digitalization (DX) at construction sites. It aligns with the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiative and is attracting attention as part of smart construction and infrastructure maintenance DX. Consistent data-driven operation from surveying to construction and maintenance enables overall process efficiency and sophistication. Active adoption of digital technologies also helps address industry challenges such as labor shortages and knowledge transfer, and is expected to contribute to reduced lifecycle costs in the long term.

Field case studies and future prospects

Visualization of buried pipes using RTK×AR is already being utilized at actual construction sites. Domestically, a startup developed a system that combines an RTK positioning unit with a tablet to display underground buried pipes in AR on-site. Without spreading drawings or performing trial excavations, workers can grasp the positions of buried objects in 3D on the spot, contributing to improved safety and work efficiency. Field trials reported that records of pipe installation were completed without photo shooting or CAD drawing creation and that later excavation operations could immediately locate pipes using AR display, yielding significant benefits. Workers also reported, “Searching for buried objects that used to rely on intuition is now possible for anyone,” and “the operation was intuitive and usable without training,” indicating promising uptake on site.

Looking overseas, high-precision outdoor AR systems are beginning to attract attention in the construction industry as world-first technologies. Systems that combine high-performance GNSS receivers and AR can overlay 3D design models and real-world scenes with centimeter-level precision through a smartphone, enabling intuitive on-site sharing and verification of complex BIM models and underground utility information. In both 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 sewage maintenance.

It is likely that these high-precision AR technologies will become more generalized and simplified and eventually establish themselves as the industry’s new normal. A future in which every worker instinctively points a smartphone to check design drawings and underground conditions in AR while working is just ahead. By allowing anyone to handle accurate, real-time information based on spatial coordinates without relying on expensive surveying equipment or specialized skills, a productivity revolution in the construction and infrastructure sectors is expected to accelerate.

Conclusion: Simple surveying and high-precision AR display realized by LRTK

Visualizing buried pipes with RTK×AR has the potential to bring major transformation to infrastructure maintenance and civil construction sites. Overlaying digital data onto the real world with centimeter-level position accuracy (cm level accuracy (half-inch accuracy)) is shifting work that used to rely on skilled workers’ intuition toward data-driven smart construction. One solution gaining attention for making this cutting-edge technology easy to use on site is LRTK.

LRTK is an integrated system that enables anyone to achieve centimeter-level positioning and AR visualization easily through a small RTK-GNSS receiver attached to a smartphone and a dedicated app. Many AR surveying tools require pre-placement of markers or complicated initial calibration, but with LRTK, RTK can fix within tens of seconds from power-on and high-precision AR can be started immediately. No special calibration work is required, and the convenience of being ready to use upon arrival on site is a major feature. Cloud integration also allows seamless operations such as downloading design data and point clouds to display in AR on site, or immediately sharing data measured on-site to the cloud. The UI is designed so that workers without specialized knowledge can use it intuitively, and there are reports that “one smartphone per person covered surveying, staking, inspection, photo recording, and AR simulation.”

By using LRTK, sites can dramatically improve productivity and safety without expensive surveying instruments or large teams. Beyond透視 display of buried pipes, it can be applied to a wide range of uses such as as-built verification of structures and construction navigation, serving as a true “universal surveying instrument” and a trump card for on-site DX. Surveying firms, municipal civil departments, and construction contractors are encouraged to adopt this state-of-the-art RTK×AR technology and step into a new stage of smart infrastructure management. For more details, product information and case studies are available on the [LRTK official website](https://www.lrtk.lefixea.com/). If interested, please take a look. With LRTK, evolve your sites to the next stage.

FAQ

Q: What equipment and preparations are needed to display buried pipes in AR on site? A: A smartphone or tablet and a compatible AR app are required. The latest iPhones and iPads have AR functionality (ARKit) built in, so they can be used without additional equipment, 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 ahead of time for a smooth start.

Q: Can AR display be done with only 2D drawing data? Is a 3D model essential? A: AR display is possible even with only 2D drawing data such as plan views. Even without a 3D model, you can project pipeline route lines from the drawing onto the ground or display virtual markers and symbols at key points. For example, you can place a 2D CAD drawing (DXF) or an image plan as a background on the AR and check for discrepancies with the site. However, a 3D model allows height information to be included for three-dimensional interference checks, so it is preferable to prepare one if possible.

Q: How accurate is buried pipe AR display? Is smartphone GPS alone sufficient? A: Typical smartphone GPS and standard AR features may result in offsets on the order of tens of centimeters to meters. For rough confirmation purposes that may be acceptable, but they are unreliable for pinpointing exact excavation locations. On the other hand, combining high-precision positioning such as LRTK can reduce horizontal and vertical errors to within a few centimeters, enabling AR displays that essentially match the buried pipe positions. The ability to secure centimeter-level accuracy suitable for actual construction is a major difference.

Q: Is special knowledge or training required? Can site staff use it proficiently? A: Advanced skills like CG software operation are unnecessary; generally anyone can use it by following the dedicated app’s guidance. LRTK’s UI is designed to be usable even by those with limited surveying experience, allowing positioning and AR display by button operations. With a short training session for site staff, it can quickly be applied to daily construction management.

Q: Is it necessary to install markers or reference points in advance for AR display? A: When using LRTK, special marker installation is generally unnecessary. GNSS positioning allows the device itself to serve as a reference point and automatically display models at designated coordinates. However, indoors or in places without GPS signals, you may need to rely on ARKit’s plane detection or visual markers. In such cases, using clear reference points such as room corners or floor patterns to place models improves accuracy. For wide outdoor work areas, coordinate alignment via LRTK remains the most efficient approach.