New Standard for 3D Surveying: Digital Construction Anyone Can Do with LRTK

Introduction

Digital transformation (DX) aimed at improving productivity and efficiency is rapidly advancing in the construction and civil engineering industries. There are also challenges such as a shortage of skilled surveyors and an aging workforce, so labor-saving through digital technologies is in demand. Among these, 3D surveying, which acquires and utilizes on-site information in three dimensions, is attracting attention as the core of digital construction. Precision surveying that used to require specialized surveyors and expensive equipment is also being transformed by technological innovation into something anyone can handle. This article explores the latest trends in 3D surveying and, through the surveying technology becoming the new standard—LRTK—examines how anyone can practice digital construction.

Evolution of Digital Construction Brought by 3D Surveying

In recent years, opportunities to handle survey data in 3D at construction sites have increased dramatically. By acquiring and utilizing terrain and structures as point clouds or 3D models, it has become possible to visualize gaps between design and construction and to streamline verification of as-built conditions. Data utilization via 3D surveying is also a key pillar of ICT construction promoted by the Ministry of Land, Infrastructure, Transport and Tourism (the so-called *i-Construction*). For example, it is becoming common to obtain detailed point cloud data of existing terrain with drone photogrammetry or laser scanners and use it for earthwork volume calculations and construction planning. With the introduction of 3D surveying, stakeholders can intuitively grasp site conditions that were not visible from drawings or numbers alone, making it easier to share understanding among parties, which leads to improved quality, safety, and shortened construction periods. Furthermore, 3D surveying data has begun to be used in technologies such as machine guidance (MG) and machine control (MC) for heavy equipment, creating a flow in which as-built data and design models obtained by surveying are directly reflected in construction.

Traditional Surveying Methods and Challenges

However, while the value of 3D surveying is being recognized, traditional methods had several hurdles. Performing high-accuracy surveys required specialized equipment such as total stations and GPS surveying instruments, and work was typically done by two-person teams including a surveyor. In addition, detailed point cloud measurement by laser scanners and photogrammetry via drone aerial photography have high equipment introduction costs and require advanced skills and dedicated software to handle. For these reasons, there were cases where small to medium-sized sites or sites with labor shortages could not fully introduce 3D surveying even if they wanted to. In particular, with the aging and shortage of surveying personnel, there are criticisms that the traditional “person-dependent surveying” has its limits.

Moreover, utilizing acquired 3D data on site required specialized knowledge such as coordinate transformation and data processing, making real-time sharing and utilization difficult. For example, even if point cloud data were obtained, it could only be used after processing on a high-performance PC, or on-site teams were limited to projecting the data onto 2D drawings. In other words, to fully enjoy the benefits of 3D surveying, substantial investment and expertise were traditionally indispensable.

New 3D Surveying Opened by LRTK

Amid these circumstances, LRTK has emerged as a solution that overturns conventional wisdom. LRTK is a next-generation positioning system that makes RTK-GNSS (real-time kinematic positioning) technology easily available on smartphones. By simply attaching a dedicated ultra-compact GNSS receiver to an iPhone or iPad, the positioning accuracy of a smartphone—which normally has errors of several meters—can be improved to the centimeter-level (half-inch level). In general GNSS positioning there are errors of several meters, but RTK corrects the position of the rover (the receiver at the point to be measured) to centimeter accuracy by simultaneously observing satellite signals at both a base station (a receiver with a known position) and the rover, and canceling out common error factors. By performing this processing in real time, the coordinates of the point to be measured can be calculated instantly with high accuracy. Traditionally, it was necessary to set up your own base station or transmit correction information via radio, but in recent years network RTK using the Geospatial Information Authority of Japan’s continuous reference station network and the spread of augmentation signals (CLAS) from Japan’s satellite system “Michibiki” have made centimeter-class positioning possible without a dedicated base station.

The LRTK device itself is pocket-sized and lightweight, and designed to be easy to carry on site (about 130 g). It has an internal battery and a high-performance antenna. Using a dedicated smartphone app, you can obtain positioning data at the tap of a button at the point to be measured and immediately record and share it. No complicated operations are required, and attaching the device is a one-touch action. A user interface that can be used intuitively even by people who have not received special training is provided. In short, LRTK transforms a smartphone into a “pocket-sized all-purpose surveying instrument,” lowering precision surveying—which previously relied on specialists—down to a level that anyone can perform routinely.

Digitization of the Field Realized by LRTK

By utilizing LRTK, the following types of digital construction can be practiced by anyone at the site:

• High-accuracy surveying (acquisition of positional coordinates): Simply point a smartphone at the point to be surveyed and press a button to record latitude, longitude, and elevation coordinates with centimeter-level (half-inch-level) accuracy. Tasks that used to require surveying stakes or the work of skilled staff can be performed quickly by one person with LRTK. Acquired coordinate data are automatically converted into the prescribed coordinate system (such as the plane rectangular coordinate system), so they can be immediately used for design verification and as-built management.

• 3D point cloud measurement and earthwork calculation: By combining a smartphone camera or LiDAR function with LRTK’s high-accuracy positioning, you can acquire the site’s terrain and structures as 3D point cloud data. The acquired point cloud can be visualized as a 3D model in the cloud, and excavation and embankment volume calculations (earthwork calculations) can be performed automatically at the touch of a button. This enables site personnel themselves to easily perform 3D as-built measurement, which used to be left to specialized contractors.

• AR-based construction support: You can overlay a design-stage 3D model onto the site view through a smartphone and intuitively share the completed image. Thanks to LRTK’s high-accuracy position and orientation tracking, there is almost no misalignment between the model and reality, so the model remains correctly positioned even when you walk around and view it from different angles. Using this, you can easily discover and correct discrepancies between the design model and site conditions on the spot, or share the completed form with clients and workers to align construction imagery. In practice, applications have begun such as AR display of embankment models over actual terrain for preliminary confirmation in levee construction.

• Instant sharing and utilization of survey data: Positioning data, point clouds, and images obtained with the LRTK app can be uploaded to the cloud on the spot and shared internally and externally. You can immediately check survey results from the office or compare data between remote sites. With cloud-based maps and CAD integration functions, you can immediately cross-reference coordinates acquired on site with drawings and BIM/CIM models. Real-time data sharing reduces reporting and review time lags and is expected to accelerate the PDCA cycle of construction management.

In this way, LRTK not only enables measuring and recording, but also realizes end-to-end workflows on site up to “showing,” “comparing,” and “utilizing” the measured data. It is truly a tool that strongly supports field digitization.

For example, at a certain road construction site, LRTK was used to 3D-scan the existing terrain before construction and overlay it with the design model to verify there were no issues during the construction planning stage. During construction, excavation depths were measured as needed with LRTK, and cloud-based automatically calculated earthwork data were shared immediately, preventing over- or under-excavation. Processes that would have previously required separate specialist teams or later analysis were completed by a single technician in hand, improving the overall efficiency and accuracy of the work.

Furthermore, during the 2023 Noto Peninsula earthquake, LRTK was used for rapid 3D recording of affected sites. High-precision data collected on site were shared immediately and contributed to damage assessment and recovery planning. Combined with such achievements, mobile surveying technologies like LRTK are steadily increasing their presence in the civil engineering and construction sectors.

Comparison with Other Surveying Technologies

• Total station (electro-optical surveying): Total stations, which provide millimeter-level high accuracy, determine positions by measuring straight-line distances and angles from control points to prisms. However, measurements require line-of-sight and are typically performed by two people. Points can only be acquired one at a time, so surveying large areas is time-consuming and labor-intensive. Also, to obtain accurate coordinates with a total station you need to set up the instrument relative to known points in advance. By contrast, LRTK can obtain global coordinates directly through satellite positioning without initial setup. Because LRTK uses satellite positioning, it has fewer line-of-sight constraints and allows one person to survey wide areas in a short time.

• Conventional RTK-GNSS survey instruments: High-accuracy GNSS survey instruments have existed for some time, but they required large, stationary receivers and dedicated controllers and were expensive. LRTK achieves equivalent positioning accuracy with a pocket-sized device and dramatically improved usability by leveraging smartphones. In addition, functions such as point cloud measurement and AR display give LRTK an overall capability that conventional GNSS instruments do not offer.

• 3D laser scanners: Three-dimensional laser scanners can rapidly acquire vast point clouds and are suitable for millimeter-level detailed shape measurement. However, the equipment is expensive and cumbersome to transport, and aligning acquired data with map coordinates may require placing targets and post-processing. Also, scanning large areas in detail often requires multiple setups of the scanner, whereas LRTK allows an operator to walk around and continuously acquire data from various angles. For applications that do not demand ultra-high-density measurements, LRTK’s easy 3D measurement—where an operator can measure sufficient point cloud density while moving around the site and use the data in a known coordinate system—is often sufficient.

• Drone photogrammetry: Photogrammetry using unmanned aerial vehicles can create 3D models of wide areas in a short time, but it involves flight permissions, is affected by weather, and data processing can take time. Generating point clouds and models from aerial images requires processing in specialized software, whereas LRTK’s immediacy—allowing data to be used right after measurement—is attractive. Site personnel can start surveying from the ground immediately, and LRTK flexibly handles measurements in narrow areas, indoors, or in shadowed regions of structures where drones are difficult. LRTK is agile for routine progress measurements and detailed local surveys, and when combined with drone surveying, the two approaches can complement each other’s weaknesses.

Benefits of Introducing LRTK

Introducing LRTK to the site yields many benefits:

• Simplicity: As a smartphone-based tool, operation is intuitive, and staff without specialized training can quickly become proficient. Site workers can acquire necessary data themselves without requesting the surveying department, reducing waiting times. The familiar smartphone operation makes it easy to introduce to younger staff.

• Labor saving and efficiency improvement: Enabling one-person surveying allows efficient progress of surveying tasks even at sites suffering labor shortages. Layout work and as-built measurements that used to require two or more people can be completed by one person in a short time. Data processing and transcription to drawings are automated, greatly shortening the time from measurement to reporting.

• Low cost: With an LRTK device and a smartphone, there is no need to purchase expensive dedicated surveying instruments, reducing initial investment. Maintenance and outsourcing costs can be lowered, and it is feasible to deploy multiple units as needed. Because it is inexpensive and easy to deploy, it is possible to equip many site staff and promote the democratization of measurement.

• Improved accuracy and reliability: Centimeter-level positioning dramatically increases the accuracy of as-built construction and the reliability of surveying results. Compared to general GPS positioning with errors of several meters, the improvement is orders of magnitude, reducing rework and mistakes caused by positional errors and directly enhancing quality control. Measurement data automatically record timestamps and positioning status, ensuring reliability as evidence.

• Real-time decision making: Because measurement data are shared to the cloud instantly, relevant parties can grasp the situation and make decisions on the spot. Remote supervisors can check the latest information and issue instructions without visiting the site. This shortens the time lag from “measure and report to seek instructions,” enabling rapid on-site decision making. Construction management based on real-time 3D information is likely to become the standard for future project management.

• Adaptation for the future: Precise 3D data obtained with LRTK directly support increasing use of BIM/CIM and digital twins. It becomes easier to comply with new standards and guidelines such as the Ministry of Land, Infrastructure, Transport and Tourism’s 3D as-built management procedures, enabling smooth implementation of construction that follows the times.

Conclusion: Toward Digital Construction Anyone Can Do

3D surveying is no longer a special technology reserved for a few experts; it is becoming the new standard that anyone on site can utilize. LRTK, the driving force behind this change, dramatically lowers the barriers to digital construction and transforms the site beyond mere measurement to include post-measurement utilization. Even inexperienced workers can perform high-accuracy surveys and intuitive AR visualization with a smartphone in hand, immediately share data, and link to the next action. The day when such scenes become commonplace is not far off.

Experience this revolutionary technology that overturns conventional wisdom at your site. By leveraging LRTK, “3D surveying anyone can do” becomes a reality, and your site will step into a new stage of digital construction.