The 3D Surveying Revolution at Construction Sites: Achieving Labor Savings and DX at Once with LRTK

Basics and Current State of 3D Surveying

In recent years, surveying technology has advanced significantly in the construction industry, and "3D surveying" has attracted attention. 3D surveying is a method of measuring terrain and structures in three dimensions to obtain each point's X, Y, Z coordinates (horizontal position and elevation). It is characterized by its ability to record detailed shape data that could not be obtained by conventional planar surveying, and it can output this data as point cloud data (a collection of countless survey points) useful for as-built control and design. Various 3D measurement technologies, such as drone photogrammetry and terrestrial laser scanners, have also emerged, enabling efficient surveying of wide areas. The Ministry of Land, Infrastructure, Transport and Tourism's i-Construction recommends the use of 3D models in construction processes, and in response, the adoption of 3D surveying technologies at sites is rapidly progressing.

However, even cutting-edge 3D surveying technologies have challenges. High-performance 3D laser scanners are very expensive and require specialized operators, making them difficult for small and medium-sized construction companies to adopt. Drone photogrammetry is also effective but is not a panacea, as it is affected by weather and may require aviation law applications. In many sites, traditional surveying instruments such as total stations and levels remain the mainstay, and point measurements by manpower are central. In this context, "3D surveying by RTK positioning" is attracting attention as a method that can achieve both digitization and high efficiency while extending conventional techniques. In particular, recently an RTK technology that can be used inexpensively and easily, called LRTK (low-cost RTK: Low-cost Real Time Kinematic), has emerged and is poised to bring a new revolution to surveying at construction sites.

Challenges of Surveying Tasks at Construction Sites

Surveying tasks at civil engineering and construction sites have long had several pointed-out issues. The first is the problem of manpower and time. Conventional surveying with a total station generally requires a two-person team: a surveyor operating the instrument and another person holding a prism at the target point. On large sites, the instrument must be set up multiple times, and angle and distance are read for each survey point. Therefore, the more survey points there are, the more time and effort are required, and a large number of work hours must be allocated to surveying planning. In addition, experienced surveyors are limited in number, and labor shortages and aging are problems.

Second is the issue of accuracy and rework. For example, when setting out batter boards (establishing reference positions for construction), even a slight surveying error can lead to construction mistakes and rework costs. To reduce height errors, experienced personnel must perform careful leveling with a level instrument, so ensuring accuracy takes effort. Furthermore, environmental factors such as poor line-of-sight in mountainous areas or near tall buildings in urban areas—where a total station's beam may not reach or GNSS cannot be received—are also problematic. Traditionally, surveying methods were selected according to the situation and additional control points or night work were used as countermeasures, but these also added burdens to the site.

Third is the delay in data utilization and DX (digital transformation). Survey results are organized as drawings and numeric tables, but conventional approaches often rely on paper drawings or PDFs for delivery, and the valuable survey data obtained is frequently not fully utilized. Since site information is managed with photos and notes, information sharing takes time, and integration with construction management systems or BIM/CIM (3D models) is not smooth. Promoting DX at sites requires digitization of the entire process from surveying through design and construction, but conventional surveying methods alone make real-time data reflection and centralized management difficult.

Overview of LRTK Technology and Its Benefits

LRTK (low-cost RTK) positioning technology is expected to be a trump card to solve these issues. First, RTK (Real Time Kinematic) refers to a centimeter-level high-precision positioning method using satellite positioning (GNSS). Both a base station (fixed receiver) and a rover (mobile receiver) simultaneously receive signals from GNSS satellites, and by transmitting error information obtained at the base station to the rover in real time for correction, errors that would be several meters with standalone positioning can be reduced to a few centimeters or less. In Japan, networked RTK that uses Geospatial Information Authority of Japan's CORS and the Quasi-Zenith Satellite System Michibiki (CLAS augmentation signals) has become widespread, making it possible to achieve high-precision real-time positioning without installing a local base station.

LRTK (Low-cost RTK) is a technical concept for realizing RTK positioning more cheaply and easily. Specifically, instead of expensive survey-grade GNSS receivers, it combines small high-precision GNSS modules with general-purpose devices such as smartphones and tablets for positioning. This dramatically reduces equipment costs while maintaining centimeter-class accuracy comparable to conventional instruments. For example, using an LRTK-compatible receiver that can be attached to a smartphone allows it to function as a pocket-sized surveying instrument, enabling on-site surveying without carrying dedicated equipment. Because it supports receiving correction data via Michibiki's CLAS signal and mobile communications, it can continue positioning even in areas without cellular coverage, which is another advantage.

The main advantages of LRTK technology are summarized as follows.

• Mobility and simplicity: The equipment is compact and lightweight, easy to carry and set up. Intuitive operation linked to smartphone apps makes it easy for technicians without specialized training to use. Tasks that previously required two or more people can increasingly be handled solo with LRTK.

• Real-time capability: As the name RTK implies, corrections are applied simultaneously with observations, so coordinates are determined on site instantly. There is no time lag of returning to the office for analysis and computation, and results can be confirmed on the spot. If comparison with design values or additional measurements are needed, they can be handled immediately, speeding decision-making.

• High accuracy: Because centimeter-level positioning accuracy can be obtained, it can be used reliably for staking out structures and as-built verification. For example, typical LRTK receivers have horizontal position errors of ±2-3 cm (±0.8-1.2 in) and vertical errors of ±3-5 cm (±1.2-2.0 in). If millimeter-level accuracy is required, it can be adequately supplemented by spot checks using conventional optical surveying.

• Low cost: Initial investment is lower compared to conventional surveying equipment. There is no need to procure expensive GNSS receivers and dedicated data loggers, and commercially available tablets and smartphones can be used. In addition, public subsidies for ICT adoption may apply in some cases, steadily lowering economic barriers.

• Data integration: A benefit of using smart devices is the ease of digital integration—uploading positioning data directly to the cloud, linking photos and notes with location information, and so on. Photos and notes taken on site are tagged with accurate coordinates, making it smooth to import them into CAD drawings or BIM models in later stages. Immediate data sharing enables remote inspections and rapid decision-making.

Comparison with Conventional Methods (GNSS Surveying, Total Stations, etc.)

GNSS surveying using LRTK differs noticeably from conventional surveying methods. Below is a comparison with representative methods.

• Total station surveying: Optical total stations (TS) can acquire survey points with millimeter-level precision and remain indispensable for tasks such as installing structures and displacement measurement. However, TS surveying requires an operator and an assistant, and can measure only one point within line-of-sight at a time. On rugged sites, repeated re-setting is required to secure survey lines, reducing efficiency for large-scale surveys. Nighttime or rainy work is also difficult. In contrast, GNSS surveying using LRTK can quickly measure a wide range of points regardless of line-of-sight as long as satellites can be observed. For typical terrain surveys on flat open land, carrying one LRTK unit and walking can observe many points in a short time, significantly reducing work time compared to a TS.

• Conventional GNSS surveying: Before RTK, GNSS surveying often relied on static positioning methods that required long observation times and post-processing. Moreover, achieving high precision in real time required large, expensive survey-grade equipment, making operation difficult except for major companies with dedicated technicians. Even after the spread of networked RTK, license fees per receiver and communication costs remained barriers for small sites. LRTK lowers those barriers by enabling similar effects with small, inexpensive equipment and existing communication infrastructure. However, like any GNSS method, LRTK has limitations in areas where the sky is obstructed (between tall buildings, inside forests, tunnels, etc.), where positioning is difficult. In such cases, continued use of TS, terrestrial laser scanners, or post-processed PPK methods may be effective.

• Photogrammetry (UAV, etc.): Drone photogrammetry can acquire terrain in a short time over areas where people cannot enter or that are vast. However, obtaining positional information from aerial photos requires coordinates of ground control points visible in the photos. RTK or LRTK is useful for measuring those control points. Also, if a drone is equipped with an RTK receiver, RTK-enabled UAVs can perform high-precision mapping without ground control points. Photogrammetry is affected by weather and shooting conditions, but used together with LRTK it can enhance data accuracy and reliability. Conversely, LRTK alone cannot capture detailed surface "area" information like point cloud data representing the ground surface. Ideally, photogrammetry or laser scanning should be used to obtain surface data and combined with point data from LRTK as needed.

As described above, GNSS surveying with LRTK complements the strengths and offsets the weaknesses of conventional methods. It does not entirely replace existing technologies but offers a new option that shifts from "measuring points manually" to "measuring areas and points with digital technology," bringing major changes to on-site surveying workflows.

Labor Savings, Cost Reduction, and DX Effects Brought by LRTK Adoption

Next, let's look concretely at the effects obtained when LRTK is actually introduced on site. The keywords are labor savings, cost reduction, and DX promotion.

Labor savings (efficiency improvement): The greatest advantage of using LRTK is the dramatic improvement in surveying efficiency. For example, at one site, a terrain survey that previously took two days with a total station was completed in half a day after adopting LRTK. The ease of carrying and observing with a single operator increases the number of instances where tasks that previously required multiple people—such as control point surveys and batter board setting—can be handled by one person. Personnel can be allocated to other core tasks, improving overall site productivity. Real-time positioning results also contribute to efficiency by allowing necessary data to be fully captured on the spot. Fewer omissions mean fewer re-measurements and fewer site revisits.

Cost reduction: The labor-saving effects described above directly reduce labor and outsourcing costs. If simple on-site surveys and setting out, previously outsourced to surveying firms, can be handled in-house, outsourcing costs can be reduced. In fact, some small and medium construction companies that introduced LRTK equipment and started in-house construction surveying estimate substantial annual reductions in outsourced surveying expenses. Shorter workdays also reduce idle time for machines and personnel, producing cost advantages from shorter schedules. Although initial investment in LRTK equipment is required, it is cheaper than dedicated instruments and has lower operating costs, so cost-effectiveness is high. Moreover, subsidies for introducing high-precision GNSS surveying equipment as i-Construction-compatible devices are available in some cases, and national policy supports DX-related cost assistance.

DX promotion: LRTK adoption not only improves operational efficiency but strongly promotes site digitization (DX). Surveying information that previously relied on paper drawings and verbal communication can be shared immediately as electronic data via LRTK. For example, coordinate data obtained by LRTK can be shared with the office via cloud and reflected directly in CAD drawings or CIM models in a seamless workflow. This enables real-time verification of survey results and makes it realistic for remote technicians to check and give instructions without visiting the site. Linking photos and comments with location information also advances the creation of a site information database. Accumulated data can be analyzed by AI to optimize construction plans and predict risks, enabling advanced DX utilization. The digital transformation of surveying through LRTK leads to smarter construction sites overall.

Main Use Cases and Adoption Patterns for LRTK

LRTK and high-precision GNSS surveying are already being used in various sites. Below are some main use cases and adoption patterns in construction.

• Pre-construction terrain surveying and as-built assessment: Using LRTK for surveying existing terrain before work begins allows rapid acquisition of wide-area terrain data. In mountainous earthworks, steep slopes inaccessible to workers can be safely surveyed as long as satellites are visible. The obtained point clouds and contour data enable quick planning and earthwork volume calculations, shortening schedules.

• Batter board setting and staking out: LRTK is powerful for staking out structure positions. Traditionally, batter boards were set by measuring angles and distances from control points with a TS, but with an LRTK rover brought to the stake location, coordinates can be confirmed and marked on the spot. Obstacles or buildings that obstruct line-of-sight are not a problem, and large numbers of stakes over wide areas can be handled efficiently. Because positioning can be done to within a few centimeters without requiring experienced personnel, LRTK is also useful as a training tool for younger technicians.

• Coordination with UAV photogrammetry: As noted earlier, drone photogrammetry and LRTK complement each other. Specifically, LRTK can be used to measure coordinates of ground control points before drone flights for image georeferencing. Alternatively, using RTK-enabled drones allows high-precision point cloud data for as-built measurements without ground control points. The combination is especially effective in places difficult to measure by hand, such as areas of forest clearing or large earthworks.

• ICT construction machinery and machine guidance: GNSS-based machine guidance technology is starting to spread in earthworks. By installing GNSS antennas and communications on bulldozers and excavators, their position is tracked in real time and blade height is automatically controlled. LRTK serves as the foundational technology for such ICT machinery. Operators can shape the ground according to design surfaces without relying on sight or batter boards, contributing to labor savings and quality improvement. The ability to work with stable accuracy at night or in rain is another major advantage.

• Infrastructure maintenance and disaster response: High-precision positioning is increasingly used in road and railway maintenance. LRTK allows rapid collection of multi-point elevation and position data for tasks such as road subsidence monitoring and track deformation measurement, aiding anomaly detection and repair planning. It is also effective for disaster response: deploying RTK drones and LRTK for 3D surveying of collapsed areas or breached embankments allows rapid modeling of damage for restoration planning.

Thus, LRTK is active across the entire construction lifecycle from surveying and construction to maintenance. Its flexible applicability to site needs makes it worth considering for projects of various scales, from small civil works to national infrastructure projects.

Steps and Points to Note for Implementation

Finally, let's cover general steps and points to keep in mind when introducing LRTK on site. Even for first-time users of high-precision GNSS positioning, a smooth rollout is possible by following these steps.

• Implementation planning: Identify site needs and challenges and decide which tasks will use LRTK. Consider required accuracy, coverage area, and compatibility with existing surveying systems (e.g., connection to existing control points and coordinate systems). Also decide whether to install your own base station or use networked RTK (VRS, etc.) at this stage.

• Equipment and service selection: Select and procure LRTK-compatible devices (rover receivers) and base station equipment if needed. Since connection methods vary by smartphone/tablet model, check supported OS and app environments. If using networked RTK, arrange NTRIP service contracts and prepare SIM cards. For a low-cost start, consider receivers that attach to existing tablets as a trial.

• Initial setup and trial operation: After setup, first verify accuracy by positioning at known points. Confirm the geodetic datum (e.g., JGD2011 in Japan) and that conversions from latitude/longitude to plane coordinates match site standards. Initially, compare results with values measured by conventional methods to understand differences. If unfamiliar with operation, trial LRTK on a small site to experience the workflow before full deployment.

• Full-scale on-site operation: After adequate testing, start using LRTK for surveying on real projects. During operations, constantly monitor GNSS satellite reception and correction-data communications, and promptly remeasure or supplement with backup methods if abnormalities occur. Make it routine to perform check surveys at control points before and after daily work to ensure system accuracy. Share equipment handling procedures and precautions among site staff and establish backup methods (e.g., combining TS measurements at key points).

• Evaluate effects and expand: After implementation, evaluate how much efficiency and accuracy improved across surveying tasks. Quantitatively compare saved work hours, costs, and achieved data accuracy, and share success stories internally. If effects are large, horizontally expand to other sites and projects and aim to establish LRTK as a company-standard surveying method. Actively adopt software updates and new services announced by manufacturers or providers to continuously broaden application scope.

Points to note at introduction:

• Ensure open sky above the antenna: LRTK depends on GNSS satellite signals, so an open sky above the antenna is ideal. In high-rise urban areas or forests, satellites may not be sufficiently captured, causing degraded accuracy or loss of positioning. In such environments, consider moving the positioning location slightly, taking quick measurements in gaps between trees, or supplementing with TS surveys.

• Check communication environment: For networked RTK, the rover needs internet connectivity. In mountainous areas or underground, mobile signals may be unavailable, so consider setting up repeaters or using offline modes (saving data logs for later PPK processing). Using Michibiki's CLAS can provide augmentation information even outside cellular coverage, but satellite visibility must still be ensured.

• Initial investment: Introducing LRTK involves some initial cost. However, as mentioned earlier, many cases can achieve payback through labor-cost reductions and productivity gains. Make active use of support systems such as the MLIT subsidies for ICT construction equipment to maximize cost-effectiveness.

• Accuracy management: Especially during the initial phase, continuously verify that obtained positioning results meet required accuracies. Perform verification and cross-checks at known points at the beginning and end of each day and before and after critical measurements. If large errors are detected, immediately investigate causes and reconfigure equipment or verify correction data. Establishing habits of accuracy management will maximize LRTK reliability.

Conclusion: Accelerate Site DX with Simple LRTK Surveying

The introduction of 3D surveying is a major trend that can dramatically improve productivity and safety at construction sites. Among these, the emergence of LRTK marks the beginning of a new era in which anyone can easily utilize high-precision positioning. Simple on-site surveys and as-built verification that were previously outsourced can potentially be completed quickly by in-house staff using LRTK. By reallocating resources saved from surveying to other value-added tasks, it can also contribute to work-style reform. In addition, the digital collection and accumulation of site data enable advanced construction methods and faster decision-making.

Against the backdrop of labor shortages and the need to improve productivity in the construction industry, using LRTK for simple surveying can be an extremely effective solution. Why not start by introducing this new surveying style on small-scale projects? LRTK, which simultaneously achieves labor savings and DX, will reshape site conventions and powerfully drive the first steps toward construction DX.