Streamline As-Built Surveying for Utility Conduit Construction with Smartphone AR: Immediate Verification via Point Cloud Data

The increasing demand for advanced as-built management in utility conduit construction

Utility conduit construction for electric and communication lines involves installing shared ducts (common conduits) beneath roads to house power and communication cables. With the nationwide push for pole removal, these shared utility conduit projects are being carried out across many locations. In conduit work, multiple pipes and cables must be accurately accommodated within constrained underground spaces, demanding high construction quality and rigorous as-built management. Because buried installations cannot be directly inspected from the surface after backfilling, it is critically important to perform reliable as-built surveying during construction and to record the final positions and dimensions of completed works.

Moreover, clients (such as government agencies and road administrators) have recently been strongly pushing for more advanced and efficient as-built management. As part of ICT construction and i-Construction initiatives, the Ministry of Land, Infrastructure, Transport and Tourism expanded the application of 3D measurement technologies to utility conduit construction starting in fiscal 2024. As a result, digital measurement using point cloud data and CIM models is increasingly recommended for as-built management, which had traditionally relied mainly on drawings and tape measures. Enhancing as-built management for utility conduit construction represents both a major challenge and an opportunity for ensuring quality and shortening construction schedules.

Time, labor, and accuracy issues in conventional surveying workflows

Many current utility conduit projects still use traditional methods for as-built surveying. However, these methods present the following on-site issues:

• Time loss from stopping work: Work is temporarily halted at each process checkpoint for manual measurements. For example, after installing the conduit, workers use tape measures or staffs to measure trench width or pipe depth and take photos, which typically takes about 10–15 minutes per measurement including preparation. Other tasks must pause during that time. For conduit construction, which often occurs at night, this time loss is a significant burden.

• Labor burden from multi-person operations: Conventional as-built surveying usually requires around 2–4 personnel. A surveyor holds the scale, another person reads measurements, and a recorder takes photos and notes—many tasks rely on manpower. When staffing is limited, allocating this many people to surveying itself is difficult.

• Risk of inaccuracies and omissions: Human error inherent in manual work cannot be ignored. Tape angle, reading mistakes, recording errors, or forgotten photos can occur. Especially for pipe elevation (depth) and slope—where measurement points are limited—it can be hard to grasp the whole picture accurately. Photos alone may not allow later detailed verification, leading to re-measurement or, in the worst case, rework such as re-excavation after backfilling.

To address these time, labor, and accuracy challenges in as-built surveying, new technologies are being sought. A promising solution is the use of AR (augmented reality) on smartphones combined with GNSS and point cloud data.

How smartphones and GNSS are changing the field: AR and point cloud surveying applications

Recent advances in smartphone cameras and sensors have enabled their use in surveying. Many modern high-performance smartphones are equipped with infrared sensors called LiDAR, allowing surroundings to be scanned as 3D point clouds. By pairing a smartphone with a compact high-precision GNSS (RTK-GNSS) receiver, positioning accuracy can be improved from meter-level GPS down to centimeter-level.

This smartphone+GNSS combination allows on-site surveying to adopt AR and point cloud measurement. For example, scanning a construction area with a smartphone can generate a 3D point cloud model of pipes and structures on the spot. On the smartphone screen, the point cloud or design model can be overlaid on the real-world view (AR display). Tasks that previously relied on craftsmen’s intuition or checking drawings can now be understood intuitively through the phone’s screen.

For site supervisors and construction managers, this technological innovation has the potential to significantly change how surveying is done. Without hauling heavy survey equipment or deploying many people, as-built surveying can be completed with a single smartphone, and results can be checked and shared immediately. The following sections examine how smartphone AR surveying specifically benefits utility conduit construction along the workflow.

Capture as-built data immediately after pipe installation with smartphone point clouds

In utility conduit work, pipes and boxes (e.g., concrete CC boxes) are placed in the excavated trench. At this stage, before backfilling, it is usually required to measure the installation position and depth of the pipes and to take photos. Introducing smartphone point cloud measurement enables instant as-built capture and verification immediately after pipe installation.

A construction manager with a LiDAR-equipped smartphone walks around and scans the placed pipes and trench surroundings. Just a few minutes of moving the smartphone records the entire trench as 3D point cloud data. Because the point cloud realistically reflects pipe diameters and layouts, depths, slopes, and surrounding terrain, dimensions that used to be measured individually can be comprehensively captured in a single scan.

After scanning, the point cloud can be reviewed on-site immediately. For example, by taking a cross-section of the point cloud, you can instantly see whether the pipe burial depth (from the ground surface to the top of the pipe) meets the design values. If discrepancies or abnormal pipe inclinations are detected on the spot, corrective action can be taken before backfilling. The immediacy of as-built verification helps prevent missed errors and later rework.

Additionally, point cloud data can be georeferenced with absolute coordinates (public coordinate systems). By establishing reference points with GNSS, the captured point cloud can be aligned to surveying coordinates. This allows direct comparison of measurement results with design coordinates and can be used directly for as-built drawings submitted to authorities. Smartphone point cloud measurement offers a new capability to quickly and accurately obtain as-built data in the limited time window immediately after pipe installation.

AR overlay for visual confirmation of buried positions

Once point cloud data is captured, the next step is visual confirmation via AR display. AR technology that overlays virtual objects on the smartphone or tablet screen is highly effective for “seeing the unseen” underground elements.

Specifically, load the pre-backfill point cloud model of the pipe run or the design pipe line into the smartphone and display it in AR on site. Underground pipes that should not be visible on the ground will appear on the smartphone screen as if seen through the surface. Site supervisors and inspectors can point the phone at the ground to directly confirm the pipe locations, depths, and routes. Where previously one had to compare drawings with the site and imagine the underground layout, AR makes it easy to intuitively understand those buried positions.

This AR overlay is also powerful during as-built inspections. When showing a client or inspector the screen that says "this pipe is installed at this depth here," it is more persuasive than paper drawings or photos alone. If point cloud and design models are displayed together in AR, construction accuracy can be visually demonstrated: when installed correctly, the models align; when offset, the discrepancy is visible in AR. This allows visual on-site presentation of as-built evidence, enabling all stakeholders to share construction quality understanding.

Moreover, the captured buried pipe data is useful for future maintenance and excavation work. Storing the point cloud that records buried locations means that when digging nearby later for other works, AR display can help accurately avoid existing underground pipes. Visualizing buried positions with smartphone AR thus contributes not only to on-site as-built confirmation but also to safer future construction.

Complete measurement, recording, and reporting by one person: a new option for small crews

One of the biggest strengths of smartphone AR surveying is that measurement through recording can be completed with few personnel. As noted above, tasks that previously required multiple people can be conducted by a single site supervisor equipped with a smartphone and necessary peripherals. Advanced sites have begun operations where a construction manager scans point clouds and records photos with a phone, then instantly shares the results to the cloud.

Enabling one-person operations makes it easier to cope with labor-shortage sites and nighttime or short-duration work. For example, if an unexpected additional measurement is needed late at night, the on-site responsible person can handle it immediately without calling in a survey team from another department. This enables faster decisions and more flexible scheduling.

Also, if each worker has a smartphone, they can capture as-built data whenever needed, reducing waiting times and improving efficiency. With an environment that shares data in real time, a supervisor waiting in the office can immediately check back. Introducing smartphone AR surveying provides a new option for operating sites with small crews and enhances operational flexibility.

Documentation changes too: integrated management of point clouds and photos

Point cloud measurement and AR use via smartphones transform not only on-site surveying but also the creation of as-built management documents. Traditionally, as-built management required recording measurements in field notebooks, later drafting drawings, and pasting photos onto report sheets. Smartphone AR surveying significantly streamlines this process.

First, point cloud data itself is a detailed 3D record that can complement or replace paper sketches and multiple photos. For example, instead of taking photos with a tape measure to show pipe depth, point clouds allow depth measurements from any section. Extracting such sectional images provides record material that is as reliable as, or more reliable than, conventional photos.

In addition, smartphone apps and compatible software can automatically extract dimensional values from captured point clouds and perform pass/fail judgments. Tools that overlay design CIM models and as-built point clouds to generate a as-built heat map with color-coded compliance indicators are emerging. Using these functions reduces manual calculations and drawing, enabling automatic reporting and judgment based on digital data when preparing as-built management documents.

Photo management also changes. Photos taken with a smartphone that include high-precision location information can be placed on a map alongside point clouds and drawings for integrated management. It becomes immediately clear where each photo was taken, making it easy to describe locations in reports (e.g., "near XX intersection, about X meters"). Cloud services that manage point clouds, photos, and drawings together are emerging, shifting as-built recordkeeping from paper and file-based methods to centralized data management.

Thus, adopting smartphone AR surveying opens the way to digitize the entire process from measuring to documentation and reporting. This reduces burdens both on-site and in the office and can greatly shorten the time spent on as-built management.

Reported on-site benefits: schedule reduction, stable accuracy, and improved collaboration with subcontractors

Sites that have adopted smartphone AR as-built surveying report various positive effects. The most notable are shorter schedules, stabilized surveying accuracy, and improved coordination with subcontractors.

• Shorter schedules and increased productivity: Surveying time has been drastically reduced compared to traditional methods. At one site, a measurement and photo task that took 15 minutes with 2–4 people was completed in about 3 minutes by a single smartphone scan. Over multiple tasks this yields substantial time savings, enabling earlier completion of night work and shortening overall schedules. Reduced rework from missed measurements or deficiencies also eliminates needless extra work and improves overall productivity.

• Stable quality and accuracy: Point cloud measurement eliminates human omissions and reduces variability in as-built data. Because all locations can be digitally recorded, there is no worry about "burying something that wasn’t measured." Regarding measurement accuracy, smartphone LiDAR point clouds have proven sufficiently practical compared to specialized equipment. Consistently following the same data acquisition and analysis procedures stabilizes surveying accuracy regardless of the experience level of on-site staff.

• Improved coordination with subcontractors and stakeholders: Visualizing and sharing construction data in 3D improves communication with subcontractors and supervisors. For example, earthwork and pipe contractors can review the AR screen together on site to confirm "we will backfill to this level" or "the installation is at this height," reducing misunderstandings. There have also been cases of sharing as-built data via the cloud with remote designers and clients in real time. This enables the whole team to grasp site conditions in real time and quickly consult and respond when issues arise.

These benefits are often best appreciated through actual use on site. Staff who were initially skeptical have come to trust the data accuracy and convenience after experiencing the system and some now say they would be uneasy without it. In complex utility conduit works, smartphone AR surveying is already delivering tangible results.

What is LRTK: how smartphone RTK enables high-precision AR surveying

Here we touch on a key technology supporting smartphone AR surveying: RTK-GNSS. RTK (Real Time Kinematic) is a real-time correction technique in satellite positioning that uses correction data from a base station to achieve centimeter-level positioning. RTK positioning, which traditionally required survey-grade GNSS equipment, has recently become available for smartphones. One such smartphone RTK solution is called LRTK.

[LRTK](https://www.lrtk.lefixea.com/) is the name of a compact RTK-GNSS receiver and dedicated app used with smartphones. For example, attaching a device such as the LRTK Phone to a smartphone enables reception of centimeter-level correction services provided by Japan’s QZSS (Michibiki) and correction information from various reference stations, allowing the smartphone to obtain highly accurate position coordinates. This enables photographs and scanned point clouds taken with the phone to be tagged with extremely accurate location information within a few centimeters of error.

With high-precision positioning, AR accuracy also improves dramatically. Conventional smartphone AR has been mainly for indoor use because outdoor GPS errors often cause misalignment between virtual objects and real positions. But with RTK-enabled LRTK, satellite positioning aligns the site coordinates and 3D models accurately, enabling AR that doesn’t drift while walking even on large outdoor sites. Time-consuming initial alignment is unnecessary; once the smartphone is turned on, models can be correctly placed in real-world coordinates immediately.

LRTK’s app also integrates useful on-site functions such as point cloud scanning, geotagged photo capture, and cloud data sharing. Captured point clouds can be managed in the cloud, shared with team members, or overlaid with design drawings and national 3D urban models (e.g., PLATEAU). In effect, the smartphone evolves into a "universal surveying instrument," making high-precision surveying and AR visualization—previously possible only with expensive dedicated equipment—easily accessible.

Start with a single pipe: recommendations for introducing LRTK and AR surveying

Having understood the benefits of smartphone AR surveying, the next step is considering how to introduce it practically. Adopting new technology often raises the question, "Will it really work?" For this reason, we recommend piloting the technology on a single pipe section first.

For example, on a 15 m span of a utility conduit project, try running smartphone point cloud scans in parallel with conventional measurements during pipe installation. You may be surprised by the ease and the volume of information obtained. Using the scan data to create as-built drawings or to verify buried positions in AR may reveal insights that paper records alone cannot provide. Sharing visualized data with site foremen and subcontractors can also demonstrate the value of "making things visible" and improve communication.

Smartphone RTK solutions like LRTK are relatively easy to introduce. All you need is a smartphone, the receiver, and the app. Even without special training, intuitive operation enables scanning and AR display. Start small so site members can get comfortable with the system and gradually move toward full-scale implementation.

As-built management for utility conduit construction is at a turning point. Shifting from paper and manual processes to digital methods and smart device use can realize both quality assurance and efficiency. Consider trying smartphone AR surveying with LRTK. A small step—starting with a single pipe—may lead to major improvements for future sites.