Streamlining Surveying in Railway DX: Achieving Single-Person Surveying with LRTK

The wave of DX (digital transformation) is sweeping the railway industry, making operational efficiency and labor reduction urgent priorities. Among these, railway surveying is essential for safe, high-quality infrastructure, yet traditionally it has required night work and multiple personnel, placing a heavy burden on sites. This article explains efforts to streamline surveying operations in the context of railway DX. Using RTK-GNSS technology and smartphones, the new solution “LRTK” realizes high-precision surveying by a single person; here we detail how this is achieved and its effects.

Current State and Challenges of Surveying in Railways

Surveying for railway construction and maintenance plays a crucial role in determining the precise positions of track and structures. However, common surveying methods today present multiple on-site challenges. Typically, railway surveying is performed at night when train operations stop, using instruments such as total stations and requiring two or more people. The main issues with conventional methods can be summarized as follows.

• Burden of night work: Surveys must be conducted in limited hours after the last train, often in the dark, imposing a heavy burden on workers. The short available time creates pressure that makes it difficult to ensure sufficient surveying accuracy.

• Need for multiple personnel: Operating surveying equipment and holding a staff require at least two people, and often additional personnel such as safety monitors, resulting in multi-person teams. With labor shortages worsening, securing staff is not only difficult but also a significant burden in terms of labor costs and coordination.

• Variability in accuracy and reproducibility: Parts of the work depend on manual angle readings and sighting alignment, so measurement results can vary depending on the surveyor's experience and procedures. Reproducibility is an issue—different personnel can produce slight differences—and transferring data to paper drawings carried a risk of human error.

Thus, railway surveying, despite demanding high accuracy, has been plagued by the inefficiencies and errors inherent in night work, multi-person operations, and manual procedures.

The Context of Railway DX and the Need to Reduce Surveying Labor

Railway DX refers to the movement to revamp design, construction, and maintenance processes in railways using digital technology. With the Ministry of Land, Infrastructure, Transport and Tourism’s push for [i-Construction](https://www.mlit.go.jp/i-construction/), rail companies are also adopting advanced technologies such as BIM, point cloud data, and remote monitoring. For example, attempts are underway to simulate visibility checks for signaling equipment—previously done on-site at night—on 3D models of scanned track spaces. By using scanned site data and digital models, design reviews and clash checks can be done at a desk, greatly reducing night work.

In this DX context, reducing the labor of surveying is particularly important. Night surveying performed in short windows to avoid disrupting train operations has long been a bottleneck. Moreover, with overtime restrictions introduced under work-style reform laws applied to the construction industry from 2024, reducing the burden of night work has become urgent. As labor shortages and an aging workforce progress, new methods leveraging digital technology are essential to maintain high-precision surveying with limited personnel. If surveying DX enables site information to be acquired and shared efficiently with fewer personnel and based on data, it will have a significant impact on both maintaining railway infrastructure safety and improving productivity.

How RTK-GNSS and LRTK Work: High-Precision Positioning Features and Smartphone Integration

RTK-GNSS (real-time kinematic) is a positioning technique that achieves centimeter-level accuracy by correcting satellite positioning errors in real time. Standalone GPS typically has errors of several meters, but RTK uses observation data from a base station (a receiver installed at a known coordinate) and a rover (the measurement receiver). Error information computed at the base station is sent to the rover to correct its measurements. As a result, errors are greatly reduced and real-time positioning within a few centimeters can be obtained. In Japan, the start of operations of the quasi-zenith satellite “Michibiki” has improved positioning by smartphone-built-in GPS to roughly 5–10 cm (2.0–3.9 in) errors, but combining with RTK can further raise accuracy to a few centimeters. Using network RTK (Ntrip method), correction data can be obtained via the internet from nearby electronic reference points, allowing high-precision positioning without deploying your own base station on site.

LRTK is a compact GNSS receiver that makes RTK technology easy to use. LRTK is an external RTK-GNSS antenna/receiver attached to a smartphone; by linking with the smartphone it enables instantaneous centimeter-level positioning. Previously, high-precision GNSS equipment cost millions of yen, but LRTK is palm-sized (weighing approximately 125 g) and very compact, allowing low-cost deployment by leveraging existing smartphones. Coordinates of the current position are displayed in real time on the smartphone screen, and measured points can be saved with a single tap and shared to the cloud. In other words, the work of carrying heavy tripods and surveying instruments back and forth along the track can be completed with just a smartphone and a small device. In addition, by utilizing the smartphone’s camera and sensors, extended functions such as AR-assisted visualization and photogrammetry can be used. LRTK turns the smartphone into a “pocket-sized all-purpose surveying tool,” and the way field surveying is done is beginning to change significantly.

How to Achieve Single-Person Surveying (RTK + AR Navigation + Point Cloud Measurement)

By leveraging the aforementioned smartphone + RTK positioning technology, single-person surveying on site becomes a reality. The key technical elements are (1) high-precision positioning via RTK, (2) navigation and visualization via AR (augmented reality), and (3) point cloud measurement (3D scanning) using a smartphone. Combining these allows measurement, layout marking, and recording tasks—previously divided among multiple people—to be efficiently handled by one person.

First, RTK enables the surveyor to obtain absolute coordinates of measurement points on the spot with high precision, removing the need for another person to look through the equipment or to direct where to place the point. The surveyor can move around with a smartphone in hand, grasp their real-time coordinates, and record points as needed.

Next, with AR navigation, virtual guides and markers can be overlaid on the actual site view through the smartphone screen. For example, if the coordinates of target points from the design drawings are entered into an app, markers or arrows appear in the real scene viewed through the smartphone, and the worker simply walks in the indicated direction to reach the precise location. This eliminates the need to use a total station to read angles and distances while radioing instructions to an assistant, enabling fast single-person layout marking. AR can also overlay design lines or structural models on the real landscape so that one can intuitively check whether foundation heights and positions are appropriate.

Then there is point cloud measurement. A person can capture surrounding 3D point cloud data using the smartphone camera or LiDAR sensor. When combined with the high-precision self-positioning information from LRTK, photos and scans obtain accurate coordinates. High-precision 3D surveying used to require tripod-mounted laser scanners, but now a smartphone alone can quickly record detailed 3D models of the site. By fusing RTK accuracy, AR visual assistance, and the information-richness of point cloud measurement, the entire sequence of tasks—“accurately marking points,” “measuring wide areas,” and “visualizing results”—can be completed by a single person.

Workflow from Measurement to As-Built/Drawing Comparison and Ledger Integration

With digital surveying technologies, survey data captured on site can be used directly for construction management and record updates. Previously, creating drawings from handwritten notes and confirming as-built conditions took time, but smartphone + RTK surveying enables seamless linkage from measurement to drawing comparison and ledger reflection. A typical workflow example is shown below.

• High-precision data acquisition on site: The surveyor uses a smartphone + LRTK to capture coordinates of points and shape data of structures on site. The data obtained are tagged with centimeter-level accuracy (half-inch accuracy) and saved in real time on the smartphone. Photos can be taken at each survey point as needed, and a LiDAR scan can be performed by walking around to record detailed site conditions.

• Data sharing to the cloud: Data are uploaded to the cloud simultaneously with measurement and stored on a shared platform connecting the site and the office. Coordinates, photos, and point clouds sent from the site smartphone can be shared in real time with office staff. This enables other personnel to check data and immediately request additional measurements before the surveyor returns. Remote experts can also view the data and provide advice, facilitating collaboration.

• Comparison of as-built data and design drawings: On the cloud or in dedicated software, the captured as-built data can be overlaid with design drawings or 3D design models for comparison. By comparing coordinate values of each survey point with design values or calculating differences between point clouds and the BIM model, one can verify whether the finished work conforms to the design. The differences can be visualized as a color-coded heat map (elevation difference map), making it easy to identify areas that are higher or lower than specified.

• Feedback and on-site correction: If discrepancies with the design are found, the information can be fed back to the site immediately. If the generated heat map or difference data are displayed in AR on the site smartphone, workers can identify misaligned locations on the spot and quickly perform corrective work. This prevents rework discovered later and realizes a PDCA cycle that ensures quality on site in real time.

• Deliverables creation and ledger integration: Survey data can be used directly as digital deliverables. The cloud system can automatically generate as-built drawings and reports, or data can be imported into CAD software for drafting. Final as-built data are reflected in the maintenance ledger database, keeping asset information up to date. Because information previously managed on paper forms or Excel is centralized digitally, accurate information is immediately available for future refurbishment planning or periodic inspections.

By connecting the entire workflow digitally, information loss between the site and the office is reduced, enabling surveying that looks beyond mere measurement to its downstream use.

On-Site Use Cases: Structure Layout, Piling, As-Built Heat Maps, and History Management

When single-person high-precision surveying becomes possible, new applications emerge across railway construction and maintenance. Below are representative use cases.

• Structure layout (marking): Single-person surveying shines when marking the positions for structures such as bridge piers and signal foundations. Conventionally, a surveyor would use a transit to check angles and radio an assistant to place stakes or chalk marks. With an RTK-capable smartphone and AR, the worker can mark the exact position by following on-screen guides. For example, the edge of a platform or the position for an overhead line pole can be marked precisely by one person at the AR marker shown on the screen. Because positioning accuracy is high, downstream fine adjustments are reduced and the reliability of structure placement improves.

• Accuracy control in piling: In foundation works for tunnels and viaducts, LRTK-enabled single-person surveying is effective for piling. If planned coordinates for each pile are pre-registered, pile-driving machine operators can check positions on their smartphone before work. After installation, the operator can independently measure the coordinates of each pile head and instantly check deviations from design positions. Measuring multiple piles in a short time and displaying a heat map lets one view overall variability. This allows positional errors to be corrected the same day, contributing to structural quality assurance.

• Quality control with as-built heat maps: Digital surveying is powerful for as-built measurements after civil works completion. Using LRTK to capture point clouds of roadbeds and concrete structures and comparing them to the 3D design model, automated heat maps showing elevation differences can be generated. For example, one can visualize whether an embankment surface is several centimeters higher or lower than designed with gradient coloration across the surface. Staff can check the heat map on a tablet on site and immediately repair areas outside tolerance. Heat maps can also be overlaid in AR on the real world, enabling intuitive identification of correction locations without driving survey points—so you can instantly grasp where to correct. Faster as-built management and visible quality improvements streamline inspection and correction tasks.

• History management of survey data and use in maintenance: Single-person surveying also helps track long-term changes in track and structures. Periodically measuring and storing coordinates of the same locations with LRTK allows quantitative recording of settlement and displacement. Previously, track displacement was managed by measuring lengths or visual checks, but keeping absolute-coordinate histories makes it possible to detect millimeter-level changes. Accumulated data can be time-series analyzed in ledgers or GIS, enabling early detection of trends such as “the entrance area of XX tunnel is settling by a few mm per year” and supporting planned repairs and preventive maintenance. Digital centralization of data ensures accurate history reference even when personnel change, facilitating smooth knowledge transfer.

Implementation Effects: What Labor Reduction, Time Savings, and Accuracy Improvements Bring

Introducing the latest surveying DX solutions yields a wide range of benefits on site. Below are the main implementation effects of achieving single-person surveying.

• Labor reduction (fewer personnel): The most direct effect is a significant reduction in the personnel required for surveying. With LRTK, tasks that traditionally required two people can be completed by one, making it easier to carry out surveying even on crews short of staff. This frees up personnel for other tasks and improves organizational productivity. It also mitigates constraints caused by shortages of skilled surveyors.

• Shorter working time (time-saving): Single-person surveying shortens the time required for surveying itself. There is no need to repeatedly set up heavy equipment or spend time walking back and forth between points; necessary data can be collected in a short time. For example, simply walking along the track with an LRTK-equipped smartphone can continuously capture coordinates, avoiding stops at each survey point and the need for communication between people. This prevents long night shifts and allows more survey locations to be covered within limited work windows. Effects include shorter construction periods and cost savings from reduced overtime.

• Improved surveying accuracy and reproducibility: RTK-GNSS dramatically improves positioning accuracy, and digital measurement increases reproducibility so that anyone achieves the same results. Human reading errors and recording mistakes are reduced, and all acquired data are automatically saved to the cloud, preventing omissions and transmission errors. There is no need to later transcribe values written on paper. Improved surveying accuracy directly enhances construction precision and safety, underpinning reliable infrastructure work.

• Skills transfer and human resource development: Digitizing parts of the veteran surveyor’s intuition and experience contributes to skills transfer. Easy-to-use smartphone apps enable young or novice staff to perform advanced surveying, achieving “surveying not reliant on individuals.” This alleviates skill gaps caused by retirements and helps maintain stable surveying capabilities into the future. Accumulated digital survey data become shared assets within the company and can be used for knowledge visualization and training materials. Shifting to data-driven construction management yields both reduced reliance on individuals and quality improvements.

• Work-style reform and improved safety: Introducing single-person surveying contributes to work-style reform and safety enhancements on site. Reducing the frequency and duration of night work by streamlining surveying directly reduces worker burden and working hours. Fewer large-team, overnight tasks reduce risks from physical fatigue and sleep deprivation. Lightweight equipment enabling small teams to work nimbly also reduces the time exposed to danger when working near tracks or at heights, shortening the time workers are at risk from passing trains. There are reports that reduced workload in high-summer sites is appreciated, showing benefits in extreme heat or cold. Consequently, secondary benefits such as lower accident risk and improved safety awareness lead to better site conditions.

Conclusion: LRTK Applications and Prospects in the Railway Sector

In practice, LRTK has been used in urban station improvement projects to efficiently complete platform reference setting and track centerline layout by a single person within the limited post-last-train work window. Surveys that once took multiple people over several nights were completed quickly, minimizing impacts on train operations while progressing construction. For maintenance of railway equipment, combining LRTK and smartphone LiDAR has enabled coordinate-tagged point cloud capture of the entire asset set, including tracks and overhead line poles, and obtaining detailed 3D as-built models in a short time—something previously difficult to achieve. Such high-resolution data are expected to be used as digital twins for remote monitoring of equipment displacement and as an innovative approach to reduce the number of nighttime site inspections.

Digitalizing and reducing the labor of surveying is an unavoidable theme in promoting railway DX. Solutions like LRTK overturn the conventional wisdom that “surveying requires veterans and overnight work,” ushering in a new era where “anyone can safely and efficiently survey with a smartphone in hand.” As field DX accelerates, smart surveying with LRTK will likely become a new standard in the railway industry. Actively adopting digital technologies in future railway maintenance and construction will be key to enhancing safety and sustainability. Please take this opportunity to experience on site the potential of single-person surveying, the trump card of railway DX.