Streamlining As-Built Surveys for Electric Cable Joint Duct Construction with Smartphone AR: Instant Verification Using Point Cloud Data

The need to advance as-built management in electric cable joint duct construction

Electric cable joint duct construction involves installing a shared duct (common conduit) under roads to house power and communication cables. With the nationwide push to remove utility poles, these joint duct installations are being carried out across many locations. In joint duct work, multiple pipes and cables must be accurately accommodated within a limited underground space, requiring high construction quality and rigorous as-built management. Because buried installations cannot be directly inspected from the surface after backfilling, it is extremely important to perform reliable as-built surveying during construction and to record the final positions and dimensions.

Moreover, clients (government agencies and road managers) have recently been strongly demanding more advanced and efficient as-built management. As part of ICT construction and i-Construction, the Ministry of Land, Infrastructure, Transport and Tourism expanded the application of 3D measurement technologies to electric cable joint duct construction from fiscal 2024. This has led to recommendations to use digital measurements such as point cloud data and CIM models for as-built management, which was traditionally based on drawings and tape measures. Enhancing as-built management for electric cable joint duct construction is therefore both a major challenge and an opportunity for ensuring quality and shortening construction periods.

Time, manpower, and accuracy issues in traditional surveying workflows

At present, many electric cable joint duct projects use conventional methods for as-built surveying. However, these methods present the following on-site problems.

• Time loss due to work stoppages: Work is temporarily halted at each process step to measure dimensions manually. For example, when measuring trench width or pipe depth after pipe installation, workers use tape measures or leveling staffs and take photos, which takes about 10–15 minutes per measurement including preparation. Other work must stop during that time. Because joint duct work often takes place at night, these time losses are a significant burden.

• Manpower burden from multi-person tasks: Traditional as-built surveys typically require around 2–4 people. Survey staff hold scales, another person reads measurements, and a recorder takes photos and notes—many tasks rely on manpower. When staff are limited, allocating this many people to surveying is itself difficult.

• Accuracy and omission risks: Human error inherent in manual work cannot be ignored. Tape measure tilt, reading mistakes, recording errors, or forgetting to take photos can occur. Heights (depths) and slopes of pipes are particularly difficult to grasp accurately because measurement points are limited. Also, photos alone make it hard to check details later, causing re-measurements or, in the worst case, rework (re-excavation after backfilling).

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

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

Recent leaps in smartphone camera and sensor technology have begun to be applied on survey sites. Many recent high-performance smartphones include infrared sensors known as LiDAR, enabling scanning of surrounding structures as 3D point clouds. Also, by connecting a compact high-precision GNSS (RTK-GNSS) receiver to a smartphone, positioning accuracy can be improved from the meter-level typical of GPS to the centimeter-level.

The smartphone + GNSS combination enables on-site application of AR and point cloud measurement. For example, waving a smartphone to scan the area around the worksite generates a 3D point cloud model of the piping 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 paper drawings are becoming understandable intuitively through a smartphone screen.

For site supervisors and construction managers, this innovation has the potential to greatly change how surveying is done. Without hauling heavy surveying equipment or employing large teams, as-built surveys can be completed with a single smartphone, and results can be checked and shared on the spot. The next sections examine how smartphone AR surveying can specifically assist in electric cable joint duct construction along the workflow.

Immediate as-built capture with smartphone point clouds right after pipe installation

In joint duct construction, pipes and boxes (e.g., concrete CC boxes) are set in the ground after excavation. At this stage, before backfilling, it is usually required to measure and photograph the installation positions and depths of the piping. Introducing smartphone-based point cloud measurement enables immediate capture and verification of as-built conditions right after pipe installation.

A construction manager equipped with a LiDAR-capable smartphone walks around the installed pipes and trench to scan. Just a few minutes of moving the smartphone records the trench interior in detail as 3D point cloud data. The point cloud realistically reflects pipe diameters and layout, depths, slopes, and surrounding terrain, allowing dimensions that formerly had to be measured individually to be comprehensively captured in a single scan.

After scanning, the point cloud data can be checked on-site immediately. For example, slicing the point cloud in a cross-section makes it obvious at a glance whether the buried depth (distance from ground surface to pipe crown) meets the specified design value. If any deviation from the design or abnormal pipe inclination is found, corrective action can be taken immediately before backfilling. The immediacy of as-built verification prevents missed errors and later rework, which is a major advantage.

Furthermore, point cloud data can be given absolute coordinates (public coordinates). If you establish reference points with GNSS, the acquired point cloud can be aligned to the survey coordinate system. This enables direct comparison of measurement results with design coordinates or direct use of the data for as-built drawings submitted to authorities. Smartphone point cloud measurement offers a new possibility for rapidly and accurately acquiring as-built data in the limited time available immediately after pipe installation.

AR overlay and visual confirmation of buried positions

Once point cloud data are acquired, the next step is visual confirmation using AR overlays. AR technology that overlays virtual objects on the scene via a smartphone or tablet screen is extremely effective for “seeing” buried objects.

Specifically, load the point cloud model of the pipeline acquired before backfilling or the design pipe line into the smartphone and display it in AR on site. The underground piping, which should be invisible on the ground, is visualized on the smartphone screen as if seen through the surface. Site supervisors and inspectors can hold up the smartphone and directly see the pipe positions, depths, and routes from the surface. Where previously one had to compare drawings and the site and imagine the buried positions, AR makes it intuitive.

This AR overlay confirmation is also powerful during as-built inspections. Showing the screen to clients or inspectors with remarks like “the pipe is installed to this depth here” is more convincing than showing paper drawings or photos alone. If you display both the point cloud model and the design model in AR, you can visually demonstrate construction accuracy: when a pipe is laid according to the design, the two models overlap; if misaligned, the AR view shows the displacement. This allows you to visually present evidence of as-built management on the spot and share construction quality with all stakeholders.

Moreover, stored data of the acquired buried pipes will be useful for future maintenance or excavation work. By keeping point cloud data that record buried positions, you can display them in AR during later nearby excavations to accurately avoid existing underground pipes. Visualizing buried positions with smartphone AR thus contributes not only to on-site as-built confirmation but also to future safe 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 by a small team or even a single person. As noted above, traditional as-built surveying required multiple people, but with just a smartphone and necessary equipment, a site supervisor can carry out the whole process alone. In some advanced sites, construction managers themselves perform point cloud scans and photo documentation with a smartphone and share the measurement results to the cloud immediately.

Enabling one-person operations makes it easier to cope with staff-short sites and night or short-duration work. For example, if an unexpected additional measurement is needed late at night, the responsible person on site can handle it without summoning a separate survey team. This allows for rapid decision-making and flexible progress of the schedule.

Also, if each worker carries a smartphone, everyone can capture as-built data when needed, reducing waiting times and improving efficiency. With real-time data sharing, a supervisor waiting in the office can immediately check back. Introducing smartphone AR surveying becomes a new option for teams running sites with few staff and enhances operational flexibility.

Document preparation changes too: integrated management of point cloud data and photos

Smartphone point cloud measurement and AR use bring transformation not only to on-site measurement but also to the preparation of as-built management documents. Traditionally, as-built management involved recording measurement results in field notebooks, later redrafting drawings, and creating reports by pasting photos onto sheets—work that consumed a lot of time. Introducing smartphone AR surveying greatly streamlines this process.

First, point cloud data themselves serve as detailed 3D records that can complement or replace paper sketches and numerous photos. For example, where previously one took photos with a tape measure to indicate pipe depth, a point cloud allows depth measurements on arbitrary cross sections. Extracting that cross-sectional image produces record material that is as reliable as, or more reliable than, a photo.

Also, smartphone apps and compatible software can automatically extract dimensional values and perform pass/fail checks from acquired point cloud data. Tools that overlay the design CIM model and the as-built point cloud to generate an as-built heat map color-coded for compliance have started to appear. Using such functions reduces the need for manual calculations and drawings when creating as-built documents, enabling automatic output and judgment based on digital data.

Photo management also changes. Photos taken with a smartphone that include high-precision position information can be placed and managed on a map along with point clouds and drawings. Each photo’s location is obvious, making it easy to describe report items like “near the intersection approx. X m.” Cloud services that handle point clouds, photos, and drawings integratively are beginning to emerge, shifting as-built record keeping from paper and file-based approaches to centralized data management.

Thus, introducing smartphone AR surveying paves the way to digitize the entire workflow from measurement to documentation and reporting. This reduces burdens for both field and office staff and can significantly shorten the time spent on as-built management.

Reported on-site benefits: shortened schedules, stable accuracy, and improved collaboration with subcontractors

Sites that have actually introduced smartphone AR as-built surveying have reported various positive effects. Particularly notable are three benefits: shortened schedules, stabilized surveying accuracy, and improved collaboration with subcontractors.

• Shortened schedules and increased productivity: Survey times have been greatly reduced compared with traditional methods. At one site, measurements and photo work that previously took 2–4 people 15 minutes were completed by a single smartphone scan in about 3 minutes. Accumulated time savings led to earlier completion of night work and overall schedule shortening. Also, fewer reworks due to missed measurements or defects increased productivity.

• Stable quality and accuracy: Point cloud measurement eliminated human omissions and reduced variation in as-built data. Because all locations are digitally recorded, the risk of “measuring after backfilling” is eliminated. Regarding measurement accuracy, smartphone LiDAR point clouds have proven sufficiently practical compared with specialized equipment. By following consistent procedures for data acquisition and analysis, surveying accuracy became stable and less dependent on the experience of site personnel.

• Improved collaboration with subcontractors and stakeholders: Visualizing and sharing construction data in 3D improved communication with subcontractors and supervisors. For example, earthwork and piping contractors can view the AR screen together and confirm “we will backfill up to here” or “this is installed at this elevation,” reducing misunderstandings. Cases where as-built data were shared in the cloud allowed remote designers and clients to access information immediately. This enabled the whole team to understand the site in real time and to quickly discuss and respond when issues arose.

These benefits are best appreciated by actually using smartphone AR surveying on site. Staff who were initially skeptical often came to trust the method after experiencing the data accuracy and ease of use, sometimes saying they would be uneasy without it. In complex jobs like electric cable joint duct construction, smartphone AR surveying is producing solid results.

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

Here we touch on RTK-GNSS, the key technology supporting smartphone AR surveying. RTK (Real Time Kinematic) is a real-time correction technique in satellite positioning that enables centimeter-level positioning by using correction information from a base station. Historically, RTK positioning required survey-grade GNSS instruments, but recently RTK has become available for smartphones. Enter the smartphone RTK solution called LRTK.

[LRTK](https://www.lrtk.lefixea.com/) is the name of a small RTK-GNSS receiver and dedicated app that attach to or connect with a smartphone. For example, by simply attaching a device such as the LRTK Phone to a smartphone, you can receive centimeter-level augmentation services provided by QZSS (Michibiki) and correction information from reference stations, obtaining high-precision coordinates on the smartphone. This allows photos and scanned point clouds taken with the smartphone to be tagged with extremely accurate position information within a few centimeters of error.

With accurate position information, AR precision also improves dramatically. Traditional smartphone AR was mainly for indoor use and suffered from alignment errors outdoors due to GPS inaccuracies. But with RTK-capable LRTK, you can align site coordinates and 3D models accurately by satellite positioning, achieving AR that “doesn’t drift while walking” even on large outdoor sites. Initial cumbersome alignment steps are unnecessary; start the smartphone and models are placed correctly in the real space immediately.

The LRTK app also integrates useful on-site functions such as point cloud scanning, geotagged photo capture, and cloud data sharing. You can manage acquired point clouds on the cloud, share them with other team members, or visualize them overlaid with design drawings or national 3D city models (such as PLATEAU). In short, the smartphone evolves into an “all-purpose surveying device,” making high-precision surveying and AR visualization—previously only possible with expensive dedicated equipment—easily achievable with LRTK.

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

Having explained the merits of smartphone AR surveying, the next consideration is how to actually introduce it. Understandably, there may be doubts about whether the new technology really works. We therefore recommend trying it experimentally on a single pipe section first.

For example, in one span of an electric cable joint duct project (about 15 m (49.2 ft)), try performing smartphone point cloud scans in parallel with conventional methods during pipe installation. When you actually scan, you may be surprised by the ease of use and the amount of information obtained. Using the scan data to draft as-built drawings or confirm buried positions in AR may reveal insights that paper materials alone cannot provide. Sharing the visualized data with site foremen and subcontractors will likely improve communication and provide an immediate sense of value.

Smartphone RTK solutions like LRTK are relatively easy to introduce. All you need are a smartphone, the receiver, and an app. Without special training, intuitive operations let you perform scans and AR displays. Start small and let site members become familiar with the workflow, then gradually move to full-scale adoption.

As-built management for electric cable joint duct construction is at a turning point. Shifting from paper- and manual-centered work to digital and smart device utilization can achieve both quality assurance and efficiency. Please consider trying smartphone AR surveying with LRTK. A small first step starting with a single pipe may lead to major future improvements on site.