The 3D Surveying Revolution on 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 X, Y, Z coordinates (horizontal position and elevation) for each point. It can record detailed shape data that conventional planar surveying could not capture and can output results as point cloud data (a collection of countless measurement points) useful for construction quality control and design. Various 3D measurement technologies such as drone photogrammetry and terrestrial laser scanners have emerged, enabling efficient surveying over wide areas. The Ministry of Land, Infrastructure, Transport and Tourism’s *i-Construction* initiative recommends the use of 3D models in construction processes, and in response, the adoption of 3D surveying technologies on sites is rapidly progressing.

However, cutting-edge 3D surveying technologies also face 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 effective but can be affected by weather and requires airspace permission, so it is not a universal solution. Many sites still rely primarily on conventional surveying instruments such as total stations (electro-optical distance meters) and levels, with point measurements conducted manually. In this context, "3D surveying using RTK positioning" is gaining attention as a method that can achieve both digitization and higher efficiency while staying on the trajectory of conventional techniques. In particular, the recent appearance of LRTK (low-cost RTK: *Low-cost Real Time Kinematic*)—which makes RTK technology affordable and easy to use—is poised to bring a new revolution to surveying on construction sites.

Challenges in Surveying Work on Construction Sites

Several longstanding challenges have been pointed out in surveying work at civil engineering and construction sites. The first is the manpower and time issue. With conventional total station surveying, a two-person team is standard: a surveyor operates the instrument while another person holds a prism at the target point. On large sites the instrument must be re-set many times, and angle and distance readings are taken for each survey point. As the number of points increases, time and effort increase, requiring significant labor in the surveying plan. Moreover, highly experienced surveyors are limited in number, and labor shortages and an aging workforce are also issues.

The second issue is accuracy and rework. For example, when setting out batter boards (reference positions for construction), even small surveying errors can lead to construction mistakes and rework costs. Ensuring elevation accuracy requires skilled personnel to perform careful leveling with a level, which is time-consuming. Environmental constraints such as poor lines of sight in mountainous areas or near high-rise buildings—where total station beams cannot reach or GNSS signals cannot be received—also pose problems. Traditionally, survey methods were switched according to conditions, with additional control points or night work used as countermeasures, but this added burden to site operations.

The third issue is the delay in data utilization and DX (digital transformation). Surveying results are organized as drawings and numerical tables, but conventional methods rely on paper drawings or PDFs for handover, and the valuable surveying data obtained is often underutilized. Managing site information with photos and notes makes information sharing time-consuming, and integration with construction management systems or BIM/CIM (3D models) is not always smooth. Promoting DX on sites requires digitizing the entire process from surveying through design and construction, but conventional surveying methods alone make real-time data reflection and centralized management difficult.

LRTK Technology Overview and Benefits

A key solution expected to address these challenges is LRTK (Low-cost RTK) positioning technology. First, RTK (Real-Time Kinematic) is a satellite positioning (GNSS) method that achieves centimeter-level accuracy. Both a base station (static receiver) and a rover (mobile receiver) simultaneously receive signals from GNSS satellites; the base station sends real-time correction data to the rover to reduce errors that would otherwise be several meters with standalone positioning down to a few centimeters or less. In Japan, network RTK that uses GNSS reference stations from the Geospatial Information Authority of Japan and the Quasi-Zenith Satellite System Michibiki (CLAS augmentation signals) is widespread, allowing high-precision real-time positioning without installing a private base station.

LRTK (Low-cost RTK) is a technical concept that makes RTK positioning more affordable and accessible. Specifically, instead of expensive survey-grade GNSS receivers, LRTK combines small, high-precision GNSS modules with consumer devices like smartphones and tablets for positioning. This significantly reduces equipment costs while maintaining centimeter-level accuracy comparable to conventional instruments. For example, using an LRTK-compatible receiver that attaches to a smartphone enables a pocket-sized surveying instrument that can perform on-site surveys without carrying dedicated equipment. Because it supports Michibiki CLAS signals and correction data reception via mobile communications, it can continue positioning even in areas without regular communication coverage, which is another advantage.

The main benefits of LRTK technology are summarized as follows:

• Mobility and simplicity: Devices are compact and lightweight, making them easy to carry and set up. Intuitive operation via smartphone apps allows technicians without specialized training to use them. Tasks that used to require two or more people can increasingly be handled by a single person with LRTK.

• Real-time capability: As RTK implies, corrections are applied during observation, and coordinates are fixed on-site immediately. There is no time lag from measuring to returning to the office for processing, so results can be confirmed on the spot. When additional measurements or comparisons with design values are needed, they can be handled immediately, speeding up decision-making.

• High accuracy: Centimeter-level positioning accuracy is achievable, making LRTK reliable for setting out structures and confirming as-built shapes. Typical LRTK receivers achieve horizontal accuracy of about ±2–3 cm and vertical accuracy of about ±3–5 cm. For applications requiring millimeter-level accuracy, selective verification with conventional optical surveying can sufficiently complement LRTK.

• Low cost: Initial investment is lower than for traditional survey instruments. There is no need to purchase expensive GNSS receivers or dedicated data loggers, and commercial tablets or smartphones can be used. Additionally, national or municipal subsidies for ICT adoption may apply, steadily lowering economic barriers.

• Data integration: Using smart devices makes it easy to upload positioning data to the cloud and link photos and notes with location information for digital management. Photos and notes taken on site can be tagged with precise coordinates, facilitating smooth incorporation into CAD drawings or BIM models. Instant sharing of survey data enables remote inspections and faster decision-making.

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

GNSS surveying using LRTK differs in several notable ways from conventional surveying methods. Below is a comparison with representative techniques.

• Total station surveying: Optical total stations (TS) can acquire points with millimeter-level precision and remain indispensable for tasks like setting and displacement measurement of structures. However, TS surveying requires two people (operator and assistant) and measures only one point within the line of sight at a time. On rugged sites repeated re-setting is needed to maintain survey lines, reducing efficiency for large-scale surveys, and working at night or in rain is challenging. In contrast, GNSS surveying with LRTK can rapidly measure many points over a wide area regardless of line-of-sight, as long as satellites can be captured. On flat open sites, a single LRTK unit carried while walking can observe numerous points in a short time, significantly reducing work time compared to TS.

• Conventional GNSS surveying: Before RTK, GNSS surveying typically relied on static methods requiring long observation times and post-processing. Achieving real-time high precision formerly required large and expensive survey-grade equipment, making operation difficult for companies without dedicated staff. Even after network RTK spread, license fees per receiver and communication costs remained barriers for small sites. LRTK lowers these hurdles by offering compact, inexpensive devices that achieve similar effects using existing communication infrastructure. However, GNSS-specific limitations remain: places with obstructed sky view (between tall buildings, inside woods, tunnels) still pose challenges for LRTK. In such cases, it remains effective to combine LRTK with TS, terrestrial laser scanners, or post-processed PPK (Post-Processed Kinematic) techniques.

• Photogrammetry (UAV, etc.): Drone photogrammetry can capture terrain over large or inaccessible areas in a short time, but deriving absolute positions from aerial photos requires ground control points with known coordinates. RTK or LRTK can be used for those ground control surveys. Also, drones equipped with RTK receivers can perform high-accuracy mapping without ground control as RTK-capable UAVs. While photogrammetry is affected by weather and shooting conditions, using it together with LRTK can improve data accuracy and reliability. Conversely, LRTK alone cannot capture detailed surface "area" information like point clouds of the ground surface; when such surface data are needed, combining photogrammetry or laser scanning for surface data with LRTK point data is ideal.

As described above, GNSS surveying using LRTK integrates the advantages of conventional methods while compensating for their shortcomings. It does not entirely replace existing technologies but provides a new option of measuring both areas and points digitally, bringing major changes to on-site surveying workflows.

Labor Savings, Cost Reduction, and DX Effects from LRTK Adoption

Next, let’s look concretely at the effects when LRTK is introduced on site. The key words are labor savings, cost reduction, and DX promotion.

Labor savings (efficiency improvement): The biggest advantage of using LRTK is a dramatic increase in surveying efficiency. For example, at one site, terrain surveying that took two days with a total station was completed in half a day after introducing LRTK. The ease of observing by carrying a single device means that tasks such as control point surveying and batter board setting, which previously required several people, can often be handled by one person. This allows personnel to be allocated to other core tasks, improving overall site productivity. Real-time positioning results also help capture all necessary data on-site, reducing missed measurements and subsequent rework or site revisits.

Cost reduction: The labor-saving effects directly reduce personnel and outsourcing costs. If a company can perform simple as-built surveys or batter board setting in-house instead of outsourcing, outsourcing expenses can be cut. In fact, some small and medium-sized contractors that introduced LRTK reported significant annual reductions in outsourced surveying costs. Shorter workdays also reduce machine and labor standby time, producing cost advantages from shorter schedules. Although an initial investment in LRTK equipment is required, it is cheaper than dedicated instruments and has lower operating costs, resulting in a high cost-effectiveness. Furthermore, subsidies for introducing high-precision GNSS surveying equipment as part of i-Construction may be available, and national policy is supporting site DX cost-wise.

DX promotion: LRTK adoption not only improves operational efficiency but also strongly advances site digitization (DX). Survey information that previously relied on paper drawings and verbal communication can be shared as electronic data immediately with LRTK. For example, coordinates obtained with LRTK can be shared with the office via the cloud and directly reflected in CAD drawings or CIM models, enabling seamless workflows. This allows real-time verification of survey results and makes it realistic for remote engineers to check and give instructions without visiting the site. Because photos and comments can be linked to location data, creating an on-site information database becomes easier. Accumulated data can be analyzed by AI to optimize construction planning or predict risks, offering advanced DX applications. The digital transformation of surveying through LRTK will contribute to making construction sites smarter overall.

Main Use Cases and Deployment Patterns for LRTK

LRTK and high-precision GNSS surveying are already being used in various sites. Here are some principal use cases and deployment patterns in construction.

• Pre-construction terrain surveying and site assessment: Using LRTK for surveying existing terrain before construction allows rapid acquisition of wide-area terrain data. In mountainous slope stabilization projects, steep slopes inaccessible to workers can be measured safely as long as satellites are visible. Derived point clouds and contour data speed up planning and earthwork volume calculations, shortening the project timeline.

• Batter board setting and position staking: LRTK is powerful for setting out structures. Traditionally, batter boards were set using angles and distances from control points measured by TS, but with an LRTK rover, you can go to the stake location and mark it while confirming coordinates on-site. Obstacles or buildings that block line-of-sight are not a problem, and large-scale stake-outs across wide sites are much more efficient. Because even novice technicians can set out positions to within a few centimeters, LRTK is also a useful training tool for younger engineers.

• Integration 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 aerial photography to align aerial images. Alternatively, using RTK-capable drones enables capture without ground control for high-accuracy as-built point clouds. This combination is particularly effective in places like logged forests or large earthwork sites where detailed manual measurement is difficult.

• ICT construction equipment and machine guidance: GNSS-based machine guidance is gaining ground in earthworks. Bulldozers and excavators equipped with GNSS antennas and communication devices can automatically control blade elevation based on real-time position. LRTK serves as foundational technology for such ICT-equipped machines. Operators can shape the ground to design surfaces without relying on visual references or batter boards, contributing to labor savings and quality improvement. Operating with stable accuracy at night or in rain is another major advantage.

• Infrastructure maintenance and disaster response: High-precision positioning is also being used for road and railway maintenance. LRTK enables quick acquisition of multi-point elevation and position data for subsidence monitoring or track distortion measurements, aiding anomaly detection and repair planning. It is also useful for rapid post-disaster damage assessment. Using RTK drones and LRTK for 3D surveying of collapsed sites or breached levees allows quick modeling of damage to plan recovery work.

LRTK thus plays a wide role across the construction lifecycle, from surveying and construction to maintenance. Its flexible operation makes it suitable for projects of various scales, from small civil works to national-level infrastructure.

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, following these steps can enable a smooth rollout.

• Formulate an implementation plan: Clarify site needs and challenges and determine which tasks LRTK will be applied to. Consider required accuracy, coverage, and compatibility with existing surveying systems (for example, links to existing control points and coordinate systems). Decide at this stage whether to install your own base station or use network RTK (VRS, etc.).

• Select equipment and services: Choose and procure LRTK-compatible devices (rover receivers) and base station equipment if needed. Connection methods vary by smartphone/tablet model, so check supported OS and app environments. If using network RTK, arrange NTRIP service contracts and SIM cards. To start cheaply, consider receivers that attach to existing tablets.

• Initial setup and trial operation: After setup, validate accuracy by surveying known points. Confirm the geodetic datum (e.g., JGD2011 in Japan) is set correctly and that coordinate transformations from latitude/longitude to plane coordinates match site references. Initially compare results with values obtained 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 sufficient testing, start using LRTK for surveying in real projects. During operation, continuously monitor GNSS satellite reception and correction data communications, and immediately re-measure or use backup methods if abnormalities occur. Perform check surveys on control points before and after daily work to verify system accuracy. Share equipment handling procedures and precautions among site staff, and decide backup strategies (for example, selective use of TS) for contingencies.

• Evaluate results and expand: After introduction, evaluate how much efficiency and accuracy improved across surveying tasks. Quantitatively compare reduced labor, costs, and achieved data accuracy, and share success cases internally. If benefits are substantial, expand use to other sites and projects and aim to establish LRTK as a company standard surveying method. Actively adopt software updates and new services from manufacturers and providers to continuously broaden applications.

Notes and cautions at implementation:

• Ensure sky visibility: LRTK relies on GNSS satellite signals, so an open sky above the antenna is ideal. In high-rise urban areas or forests, satellites may not be adequately visible, causing accuracy degradation or loss of positioning. In such environments, move the measurement location slightly, take brief readings through canopy gaps, or supplement with TS surveying.

• Check communication environment: Network RTK requires internet connectivity at the rover. In mountainous or underground locations where mobile signals are weak, consider setting up relays or using offline modes (data logging for later PPK processing). Michibiki’s CLAS can provide augmentation information even where mobile coverage is absent, but satellite visibility must still be ensured.

• Initial investment: LRTK adoption requires some initial cost, but as noted, the reduction in personnel costs and productivity gains often justify the investment. Make use of government support programs (e.g., subsidies for ICT construction equipment) to maximize cost-effectiveness.

• Accuracy management: Especially at the start, continuously verify that positioning results meet required accuracy. Perform confirmation surveys on known points at the start and end of each day or around critical measurements, and conduct cross-checks. If large errors are detected, immediately investigate the cause and reconfigure equipment or check correction data. Establishing accuracy management practices will maximize LRTK reliability.

Conclusion: Accelerate On-Site DX with Simple Surveying Using LRTK

The introduction of 3D surveying is a major trend that can dramatically improve productivity and safety on construction sites. Among these developments, the emergence of LRTK marks the start of a new era where anyone can easily use high-precision positioning. Tasks that were previously outsourced for simple on-site surveys and as-built checks can potentially be completed in-house by staff in a short time using LRTK. Labor saved through surveying can be redirected to tasks that add value, contributing to work-style reform. Also, as site data is digitally collected and accumulated, construction sophistication and faster decision-making become possible.

Faced with labor shortages and the need to improve productivity, leveraging simple surveying with LRTK can be a highly effective solution for the construction industry. Start by applying this new surveying style to small projects and see how it performs on site. LRTK, which achieves labor savings and DX at once, can change conventional practices on site and strongly drive the first steps toward construction DX.