Learning from LRTK Use Cases: The Effects and Benefits of 3D Construction

What is 3D Construction

In recent years, the method known as 3D construction has been attracting attention at construction and civil engineering sites. 3D construction refers to an approach that captures site topography and structures three-dimensionally as point cloud data or 3D models and uses that data for construction planning and management. Site conditions that were difficult to grasp with conventional two-dimensional drawings and numerical data can be intuitively visualized using 3D data. As a result, many benefits can be obtained, such as early detection of gaps between design drawings and the construction site, more efficient post-construction as-built management, and easier sharing of understanding among stakeholders. The utilization of 3D data is also a key pillar of ICT construction (*i-Construction*) promoted by the Ministry of Land, Infrastructure, Transport and Tourism, and it is becoming common to use detailed point clouds obtained by drone photogrammetry and laser scanner surveying for earthwork quantity calculation (volume calculation) and quantity/progress management. 3D design data are also used in machine control (MC) and machine guidance (MG) for heavy equipment, and the trend of consistently using three-dimensional information from surveying through design and construction is accelerating across the industry.

Why 3D Construction Is Gaining Attention

So why is 3D construction attracting so much attention now? Behind this trend are challenges facing the construction industry, such as labor shortages and an aging workforce of skilled technicians. As veteran surveyors and construction managers retire, a lack of younger personnel has revealed the limits of traditional labor-intensive construction management. At the same time, there is an increasing demand for more advanced quality control and as-built management, making it necessary to perform accurate surveying and construction efficiently with limited staff. In response to these circumstances, the government has been promoting productivity improvements through ICT construction under the banner of *i-Construction*. Among these, digital technologies such as 3D surveying and AR are expected to be solutions that allow measurement and management of large areas in a short time with a small crew, contributing to reduced human error and improved safety. For example, by leveraging the latest RTK-GNSS technology, even inexperienced workers can use a smartphone to achieve centimeter-level positioning (half-inch accuracy) and point cloud measurements, making it possible for a single person to produce results equal to or better than traditional methods. In other words, 3D construction is seen as a trump card against the worsening onsite labor shortage and, at the same time, as the key to dramatically improving site efficiency and construction quality.

Features of LRTK

One of the new technologies supporting 3D construction as described above is LRTK. LRTK (pronounced "el-are-tee-kay") is an ultra-compact GNSS receiver for performing high-precision surveying using a smartphone, attached to and used with an iPhone or iPad. Precise positioning that traditionally required specialized GPS surveying equipment and skilled operators can, with this device, be performed easily by anyone, enabling centimeter-level (half-inch-level) positioning and 3D measurement. The main features of LRTK can be summarized as follows:

• Ease of use (smartphone-integrated): By simply attaching the compact device weighing approximately 150 g (5.3 oz) to the back of your smartphone, you’re ready to go. After connecting via Bluetooth or Lightning, surveying can begin with the press of a button in the dedicated app. There is no need to carry tripods or heavy equipment, and the convenience of handling everything with just a smartphone—from as-built measurement to staking out coordinates—is a major advantage.

• High-precision positioning: Supports the RTK-GNSS method, improving traditional smartphone GPS errors of several meters to approximately horizontal ±2–3 cm (±0.8–1.2 in) and vertical ±3–4 cm (±1.2–1.6 in) accuracy. It is compatible with the Geospatial Information Authority of Japan’s Continuously Operating Reference Station network (Ntrip) and correction signals from Japan’s Quasi-Zenith Satellite System Michibiki (CLAS), enabling stable centimeter-level positioning (cm level accuracy, half-inch accuracy) depending on the site’s communication environment. Even in locations without cellular reception, positioning can be continued using CLAS, making it effective in mountainous areas and disaster sites.

• Cloud-linked data sharing: Measured coordinate data, point cloud models, photos, and more are uploaded to the cloud in real time. Colleagues in the office and clients can instantly share the latest information acquired on site. Measurement results are plotted on maps and can be viewed by anyone from a web browser, smoothing reporting and quantity management. Output to CSV and drawing data is also supported, greatly reducing the time previously required to organize and distribute surveying results.

• Versatile functions: LRTK is not just for measuring positions; it offers a rich set of features to support on-site DX. For example, there is a point cloud measurement function that combines iPhone LiDAR to scan the surroundings while walking and acquire high-density point cloud data, and a photo positioning function that automatically records the shooting location (coordinates) and orientation simply by taking a photo with your smartphone. It also includes a coordinate navigation (coordinate guidance) function that guides you on the screen when the smartphone approaches a pre-registered coordinate, and an AR function that overlays design 3D models and underground utility locations onto the camera image. By leveraging these features, it can be used as an “all-purpose surveying instrument” that enables a single person to intuitively handle everything from surveying to construction verification.

Use case at a land development site

On earthwork sites involving land development, embankment, and excavation, accurately grasping soil volumes and verifying as-built conditions has traditionally been time-consuming. At one residential land development site, this process was greatly streamlined by mobile scanning using LRTK. A staff member attached an LRTK to an iPhone and scanned the ground surface while walking the development area; even within an area of roughly 50 m by 50 m (164.0 ft by 164.0 ft), they were able to acquire high-density point cloud data amounting to hundreds of thousands of points in about five minutes. Because the obtained point clouds already have coordinate information attached from the start, there is no need to align them with control points after measurement. By comparing consecutive point clouds on the spot, excavation and fill volumes can be calculated immediately and used for daily as-built management and volume tracking. This method dramatically shortened the traditional as-built measurements that had been taken point by point manually. In fact, at this site, soil volume calculations that used to take several days were completed the same day, and there were surprised comments such as “it’s as if one person’s work became twice as productive.” By utilizing LRTK, even a limited workforce can grasp site progress in real time, making this a good example of improved construction management efficiency and shortened schedules.

Application examples in road construction

The benefits of 3D construction are also evident in projects that build new or improve existing roads and bridges. At one road site, the existing terrain was 3D-scanned with LRTK before work began, and the design's 3D model was overlaid on the point cloud data for pre-construction review. By using AR functions to visualize the completed appearance of embankments and structures on site, they were able to detect discrepancies between the design and the actual conditions early—discrepancies that would not have been noticed from drawings alone—and this helped to revise the construction plan.

During construction, the responsible engineer measured the depth and shape of excavation points as needed with LRTK and immediately shared the earth volume data automatically calculated in the cloud. As a result, over-excavation and under-excavation were prevented on the spot, leading to high-quality construction with reduced variability in as-built results. Processes that previously required separate inspections by a specialist surveying team or later data analysis can be completed immediately by a single person on site using LRTK. This case shows that real-time measurement and data sharing reduced unnecessary rework and improved overall site efficiency and accuracy. In addition, sharing the AR completed model displayed on a tablet with clients and heavy equipment operators aligned everyone’s understanding and helped smooth communication.

Applications in the Water and Sewerage Sector

In infrastructure fields such as water supply and sewerage, 3D construction technology is also contributing to solving on-site challenges. Knowing the exact locations of buried water and sewer pipes is directly linked to maintenance management and construction safety. In one municipality, an initiative was undertaken to comprehensively organize location data for the city's water and sewer facilities using LRTK. Staff patrolled points such as valves and manhole tops of pipes buried under roads, measured and recorded the coordinates of each point with LRTK, and consolidated them in the cloud. As a result, the locations of all buried facilities were digitized with centimeter-level accuracy (half-inch accuracy), which is being used for new construction projects and plans to replace aging pipes.

Also, LRTK’s AR functionality is highly effective for visualizing buried utilities. For example, before excavation work, if the routes of underground water and gas pipes are displayed as AR overlays through a smartphone camera, workers can intuitively understand what lies beneath the ground. Compared with relying only on drawings, being able to determine the exact locations of buried assets in advance greatly reduces the risk of accidental pipe damage. Moreover, by using LRTK’s coordinate navigation feature, personnel can reach managed buried valve points on site without getting lost. In this way, if infrastructure assets are gradually measured digitally with a one-smartphone-per-person surveying tool, building a “digital twin” that reproduces a city’s underground buried utilities and structures in the future is not out of reach. The use of LRTK is a good example of achieving safe and efficient water and sewer infrastructure management.

Use cases in disaster response

LRTK has also proven powerful in situations requiring emergency response, such as earthquakes and landslides. In the Noto Peninsula earthquake that occurred in 2023, while communications infrastructure was cut off immediately after the disaster, municipal staff walked through the rubble with smartphones mounted on their helmets and rapidly surveyed damage using LRTK. By receiving augmentation signals (CLAS) from the Michibiki satellite, centimeter-level positioning (cm level accuracy (half-inch accuracy)) became possible even outside network coverage, allowing damage locations in areas isolated by road disruptions to be recorded with precise coordinates. Because individuals could move lightly and perform surveys on their own, investigations could be completed with the minimum necessary personnel even in dangerous areas where aftershocks continued. The acquired data were mapped at the field base and the extent of the damage was shared instantly. As a result, the lead time to drafting recovery plans was greatly shortened, leading to earlier commencement of restoration work. In addition, enabling staff to perform measurements of disaster conditions themselves—work that had previously been outsourced to external surveying companies—also contributed to reduced emergency response costs and the internalization of technical skills.

The advantages of single-person surveying are also being demonstrated at landslide sites caused by torrential rains. In one heavy rain disaster, the person in charge performed LRTK measurements alone from a safe position on the hillside where collapsed debris had accumulated. By using continuous positioning mode, they simply walked around the perimeter of the hazardous area and recorded coordinate points in succession, accurately grasping the extent of the collapsed debris in a short time. Because the volume of the displaced soil could be calculated immediately from the data obtained on site, they were able to accurately determine the necessary heavy machinery and number of dump trucks to arrange, which smoothed the planning of recovery work. Compared with conventional methods in which multiple people risked surveying the site and then calculated earth volumes after returning, LRTK — which allows “measure and compute immediately” on site — dramatically increases the speed of initial response. Since one person can perform the measurements, no time is needed to arrange personnel and unnecessary entries are avoided, greatly enhancing safety. These disaster response cases also demonstrate that mobile 3D surveying technology is a valuable tool in crisis management.

Effects and Benefits of 3D Construction

Summarizing the main effects that 3D construction and the introduction of LRTK bring to the construction site, the following points can be noted.

• Greatly improved work efficiency: The man-hours and time required for surveying and as-built measurement are dramatically reduced. Surveying work that used to take 2–3 people a full day has, in some cases, been completed by one person within a few hours. By utilizing point cloud data to reduce manual work, there have been reports of small- to medium-sized sites achieving reduced labor by 50–60%.

• Shortened construction schedule and real-time management: Because data measured on site can be shared to the cloud immediately and as-built confirmations and earthwork quantity calculations can be done on the spot, decision-making speed improves markedly. With daily progress management carried out in a timely manner, reviews of construction plans and changes to arrangements can be handled quickly. In fact, some sites have been able to shorten the overall construction period compared to the original plan by introducing 3D construction.

• Improved quality and accuracy: Centimeter-level surveying data (cm level accuracy (half-inch accuracy)) combined with AR visualization raises the level of construction accuracy and quality control. Deviations between the design model and the site can be detected and corrected in advance, reducing variability in as-built conditions and construction mistakes. Using 3D data for as-built inspections enables objective evaluations rather than subjective judgment, increasing the reliability of quality certification.

• Improved safety: Enabling single-person surveying minimizes the number of people who need to enter hazardous slopes or disaster sites. Pile-driving work in areas with poor footing can be completed quickly and safely with AR guidance, and surveying at heights and in confined spaces can be carried out with reduced risk. Accurately locating buried utilities helps prevent excavation accidents and contributes to lowering the risk of occupational and construction incidents.

• Cost reduction: The synergistic effects of increased efficiency and fewer mistakes also bring cost benefits. Reducing the frequency of outsourcing surveying compresses labor costs, and preventing excessive excavation and material waste curbs unnecessary expenditures. In addition, cloud-based information sharing reduces rework and the extra costs associated with redo construction. 3D construction, which enables labor reduction while maintaining quality, can be considered an excellent initiative in terms of cost performance.

Tips and Considerations When Implementing LRTK

LRTK is convenient, but to make the most of it on site, there are some tips and points to be aware of.

Alignment with existing data coordinates: When matching surveyed points with drawings or design data, it is important to confirm the coordinate system. LRTK supports plane rectangular coordinate systems and performs automatic conversion, but it is reassuring to verify accuracy at known control points on site beforehand. If necessary, set up conversion to local coordinates and ensure the acquired data precisely matches existing drawings without displacement.

Check communication environment and correction mode: Within smartphone coverage, using network RTK provides stable high accuracy, but in areas without radio reception such as mountainous regions or inside tunnels, switching to Michibiki (CLAS) corrections is essential depending on conditions. Know the positioning modes in advance and, if necessary, take measures appropriate to the environment, such as attaching an external antenna.

Handling equipment and battery management: The LRTK device has an internal battery that lasts about 6 hours. This is sufficient for typical working periods, but for long continuous surveys it's wise to prepare spare batteries or charging options. Also, using a monopod or tripod to secure the smartphone reduces camera shake, enabling more stable positioning and photography. For high-elevation measurements, extend the monopod to bring the sensor closer; make effective use of accessory equipment.

Points when using AR features: For AR guidance of stake positions or visualization of the finished form, you need to register design data accurately to the LRTK Cloud beforehand. LRTK automatically aligns model positions, but pay attention to calibrating the smartphone's orientation sensor and to awareness of the surroundings, and check each time that markers are displayed without offset. Since screen visibility changes with weather and brightness, consider site-environment measures such as using a sunshade as needed.

Safety considerations: Just because tasks can be done alone doesn't mean safety management at hazardous locations can be neglected. Continue to enforce basic safety measures such as monitoring the surroundings and verbal communication, and assign assistants when necessary. Especially when working while focused on the smartphone screen, take care to check your footing and prevent contact with heavy machinery. While leveraging the latest technology, it is important to operate with the unchanged principle that site safety comes first.

Summary

The era in which anyone can practice high-precision 3D construction without relying on skilled personnel is becoming a reality. By utilizing smartphone surveying devices like LRTK, even a limited workforce can promote on-site DX and achieve both productivity and quality improvements. LRTK incorporates various innovations to support simple surveying on site, such as photo positioning, which records location just by taking a picture; coordinate recording, which logs coordinates with a single button press; a mechanism to cloud-sync data on the spot; stable measurement using a monopod measurement method; and a volume calculation function that automatically computes fill and excavation volumes from the acquired point cloud.

By leveraging these features, even staff without surveying expertise can smoothly handle everything from necessary data acquisition to sharing, which in turn will lead to increased efficiency in overall construction management. It is a solution that truly embodies the concept of “iPhone surveying,” enabling high‑precision surveys to be completed with nothing more than a handheld iPhone, and LRTK’s simplified surveying functions are sure to become a reliable ally at many sites going forward.