LRTK streamlines rail distance measurement – improved efficiency with automatic cloud recording

In railway fieldwork, rail distance measurement plays an important role in daily maintenance and construction. Measuring distances with millimeter-level precision helps ensure safety and construction quality, from track lengths to equipment installation locations. However, current measurement tasks require manpower and time, and nighttime work is particularly burdensome. This article organizes the purposes and challenges of rail distance measurement and introduces a labor-saving solution using the latest RTK (Real Time Kinematic) technology combined with a smartphone. From the efficiency gains of automatic cloud recording of photos and point clouds to improved visibility with AR (augmented reality), we explain the details from a field perspective.

Purposes and challenges of rail distance measurement

Accurately measuring rail distances is indispensable for railway maintenance and construction. For example, when placing equipment or positioning structures based on track kilometer posts, it is necessary to confirm that installations are positioned according to the drawings. It is also important to measure track gauge (the width between the left and right rails) and straightness in straight sections to monitor deviations from standards. If the gauge widens or narrows, the risk of derailment increases, and deviations in straightness affect ride comfort and safety. Properly measuring and managing various dimensions around the rail thus forms the foundation for the safety and comfort of railway infrastructure.

However, there are several challenges in rail distance measurement in the field. First is that the measurement targets are very long and environmental conditions are severe. Tracks laid outdoors extend over tens of kilometers and are affected by weather and terrain. Because trains run during the day, it is difficult to secure sufficient working time, and maintenance staff often perform measurements in the limited time after nighttime train service stops. Working in darkness reduces visibility and increases physical burden. Second are human errors and variability. Conventional manual measurement can produce reading mistakes or omissions in records. Some processes rely on the intuition and experience of veterans, and individual technicians’ skill levels can affect accuracy and efficiency. These challenges have driven the demand for a more labor-saving, reliable, and efficient rail distance measurement method.

Current methods and their problems (total station, tape measure, distance meter, etc.)

There are several distance measurement methods used at railway sites today, each with weaknesses.

• Total station (TS) surveying: A high-precision optical surveying instrument that uses prism reflection to measure distances and angles. It can ensure millimeter-level accuracy, but it requires a line of sight between the surveying instrument and the prism. Therefore, on tracks with many curves or significant elevation differences, it is necessary to repeatedly reposition tripods or set intermediate survey points, which is time-consuming. Measuring long sections can take multiple days. The equipment also requires skilled operation and usually needs two or more staff (one to operate the instrument and one to hold the prism). For wide-area surveys, manpower and time burdens are large, making it difficult to complete sufficient surveying within short nighttime work windows.

• Tape measures or survey chains: As a simple distance measurement method, tape measures are sometimes used to directly measure distances on the rail. They are useful for short sections or measurements between points, but are unsuitable for long distances because the tape must be manually extended and read. When using 50 m (164.0 ft) or 100 m (328.1 ft) tapes joined together, errors accumulate due to tape sag, thermal expansion, and misreading. Two or more people are required to pull the tape taut, and on windy days or on uneven ballast it can be difficult to keep the tape perfectly straight. Especially during nighttime work with limited lighting, reading the gradations is burdensome and the risk of measurement mistakes increases.

• Laser distance meters and measuring wheels: Recently, handheld laser distance meters (laser rangefinders) are sometimes used. These devices measure distance by pointing a laser at a wall or target, but in railway contexts they may require a reflective target and cannot directly measure distances along curved rails. Alternatively, a measuring wheel can be rolled along the track while an operator counts to measure the extension. This is convenient for measuring continuous distances, but slight slippage or bumps over long distances can cause errors, and they are difficult to use on sloped track. Both methods ultimately often rely on a person visually reading numbers and recording them by hand, making data transcription and organization laborious.

As described above, conventional methods require manpower and time and suffer from delayed digitization and sharing of measurement results. Field notes with measured values are often taken back to the office and manually entered into Excel or CAD, a process that invites errors and delays result reflection. Additionally, surveyors are often too occupied with measurement itself to take photos or create detailed records. Solving these issues requires fundamentally streamlining the measurement process and introducing new approaches that enable seamless data collection through to recording.

How RTK + smartphone delivers high-precision distance measurement

A notable recent solution combines RTK (real-time kinematic) positioning with a smartphone for high-precision surveying. RTK is a technique that corrects satellite positioning (GPS, etc.) errors in real time to determine positions with centimeter-level precision. Standard smartphone GPS has errors of several meters, but in Japan, the use of the Quasi-Zenith Satellite System “Michibiki” can improve accuracy to several tens of centimeters. For railway surveying, that is still insufficient, so RTK using correction information from a base station has started to be adopted.

Specifically, a small external RTK-GNSS receiver (for example, the LRTK device from Refikia) is attached to a smartphone. On a dedicated app linked to the phone, raw satellite data and correction data from a reference station are combined in real time to calculate a highly accurate self-position. As a result, the smartphone becomes a position-measuring device with centimeter-level precision (cm level accuracy (half-inch accuracy)).

The basic workflow for distance measurement using RTK + smartphone is as follows:

• Measurement start and reference alignment: When RTK positioning is started in the smartphone app, your current position is determined to centimeter precision. Stand at the starting point of the section to be measured and register it as a reference point (for example, naming it “xx km point”).

• Continuous positioning while moving: If staff carry the smartphone and walk along the rail, the trajectory is recorded in real time. RTK acquires continuous coordinates along the walked path, and the exact distance of a particular section is automatically calculated from this sequence of coordinates. Because the distance follows the actual traveled trajectory, including curves and gradients, errors that accumulate when measuring sequentially with a tape are eliminated.

• Recording required points: Tapping the screen at key points captures the coordinates of that location and saves them to the cloud. For example, you can measure and record on the spot the cumulative distance from the start or absolute coordinates for locations such as bridge joints or signal post installation points.

• Immediate result display: Measured distances are displayed instantly on the smartphone screen, and distances between distant points can be calculated easily within the app. For short distances like track gauge, it is also possible to measure the distance between two points by holding the smartphone over the top of each rail. While gauge measurements traditionally used dedicated gauges, the device can digitally obtain numeric values (for locations requiring very high precision, traditional methods may be used in combination, but overall values can be grasped immediately).

With RTK + smartphone surveying, many measurement tasks previously requiring multiple people can be completed by a single person. There is no need to carry heavy tripods and surveying equipment along the track; a smartphone and a small device that fit in a pocket are sufficient for wide-area distance measurement. As long as satellites can be received, accuracy remains stable even in locations with poor sight lines (for example, CLAS-compatible Michibiki devices can position even outside mobile coverage), enabling reliable data acquisition in mountainous areas and at night.

Automatic saving of measurement data and benefits of photo and point-cloud recording

One major advantage of RTK-enabled smartphone measurement is that measurement and recording proceed concurrently. Traditionally, measured values were written into a notebook at the site and later re-entered into a PC. With smartphone surveying, digital data are generated and saved at the same time as measurement. In systems like LRTK, not only positioning data but also site photos, point-cloud data, and timestamps are automatically linked and saved.

For example, if you take a photo with the smartphone when measuring a point, the site photo is uploaded to the cloud along with the high-precision coordinates of that location. Photos are tagged with shooting time, orientation, and positioning data, so it is immediately clear later “when, where, and in which direction the photo was taken.” This avoids confusion when reviewing data later about which measurement corresponds to which location. Because the site situation (surrounding structures and terrain) is also saved in photos, the office can understand the on-site context remotely.

Furthermore, using a smartphone’s built-in LiDAR scanner or multi-photo 3D reconstruction, you can obtain point-cloud data (3D surveying data) and save it simultaneously with distance measurements. Even non-experts can obtain point-cloud models of rails, sleepers, and nearby equipment in a short time simply by holding up the smartphone and walking. Since acquired point clouds have geographic coordinates, later analyses such as measuring the distance between any two points on the point cloud or calculating area and volume are easy. For example, if you scan around a turnout, you can later remeasure gauge or frog spacing in detail from the office. If there are locations you wished you had measured on site, the point cloud can eliminate the need to return for additional measurements.

Such automatic recording also greatly reduces human error. The risk of illegible handwritten notes or lost paper forms is eliminated, enabling reliable data accumulation. Photos and point clouds recorded simultaneously with measurements become highly evidentiary, smoothing later verification and report creation. Because a cloud-based, photo-attached measurement result list is ready immediately after measurement, reports can be compiled as soon as staff return from the site, eliminating the need to match photos with measurement notebooks as before.

History management, drawing comparison via cloud sharing, and reduced nighttime work

Measurement data obtained by smartphone are uploaded to the cloud directly from the site. On the cloud, measured points’ coordinates and distances are plotted on a map, with photos and point clouds linked and stored. This cloud sharing dramatically improves information transfer and history management within railway operators.

First, accumulating data in the cloud makes history management easy. You can track, in time series, when and what measurements were taken for a given track section and what the results were. For example, by comparing annual track inspection data in the cloud, you can identify long-term changes such as “the gauge has widened by ○ mm (○ in) compared to last year” or “gradual settlement is progressing in a particular section.” While searching paper records is a chore, cloud data can be searched and viewed by stakeholders as needed, aiding long-term maintenance planning.

Second, it is easy to perform comparisons with design drawings and other data. Cloud surveying data are already in a public coordinate system, so you can directly compare planned positions on CAD drawings or BIM models with measured positions. For example, the LRTK cloud allows uploading design alignment data (track centerlines and structure layouts) and overlaying them with measured point clouds and positioning points. This lets you visually confirm whether the actual track alignment matches the design. Straightness deviations, which were traditionally checked with string lines and offset distance calculations, can now be evaluated objectively on digital data. By comparing with drawings, you can identify spots that require on-site correction before nighttime work.

Because data are shared in the cloud, headquarters or office staff can monitor the site situation in real time and provide support. Since data are viewable immediately after measurement, you can contact design staff on the spot and ask, for example, “There is a 5 mm (0.20 in) deviation in alignment near the XX bridge — is that within tolerance?” This speeds feedback between site and office and reduces downtime waiting for decisions.

As a result, these efficiencies lead to reduced nighttime work. In addition to faster measurement itself (one person can complete it in a short time), preparation and post-processing times are reduced. For example, a track positioning and recording task that previously took four hours after the last train has been reported to be completed in about two hours after introducing LRTK, allowing the remaining time to be used for repairs or for earlier withdrawal. Shorter work times reduce worker burden and improve safety during late-night periods (providing more margin before train service resumes). Moreover, because efficiencies enable work to be performed with the minimum necessary personnel, it becomes easier to secure nighttime staff and is expected to help address labor shortages.

Improved visibility with AR technology and support for younger staff

On RTK + smartphone platforms, the high-precision positioning information obtained can be used for AR (augmented reality) displays. AR technology overlays digital design information and measurement results on real-world images, greatly improving on-site visibility.

For example, consider a track relocation project where the design centerline must be aligned with the actual installed position. Through a smartphone or tablet screen, a virtual track (a 3D model or guideline that should be in the design position) is displayed over the real rails. If the actual rail is offset from that virtual line, you can immediately see in which direction and by how many centimeters to move it. This greatly simplifies tasks that veterans used to perform by measuring with string or rulers and instructing “move it X millimeters to the right.” With AR, visual instructions can be given, so even young workers can easily understand and carry out correction work accurately.

AR is also useful for positioning posts such as catenary poles and signals. By displaying virtual markings or arrows on the ground based on design coordinates, you can avoid the hassle of measuring with a tape and driving stakes. Using LRTK’s “coordinate navigation” function, the smartphone screen can guide users as if it were a car navigation system, e.g., “2.3 m (7.5 ft) to the northeast to the target point,” enabling less experienced staff to reach the prescribed position without confusion. As an “AR piling aid,” a marker can appear when you approach an installation site, enabling precise placement and height for staking (layout) work.

AR-enhanced visibility also facilitates on-site communication. For example, during a pre-nightwork briefing, showing the actual track image with planned lines overlaid on a tablet makes adjustments that are hard to convey on paper drawings immediately clear. Differences in mental images between veterans and younger staff can be reconciled using AR, allowing confirmation of work procedures with a shared understanding. Thus, AR is more than just a visual convenience; it can be a tool that supports skill transfer and team information sharing.

LRTK case studies: efficiency gains in distance measurement and effects of automatic recording

Finally, let us confirm the effects through actual LRTK deployment examples. In one railway maintenance district, LRTK-based rail distance measurement and cloud recording were trialed. Tasks that previously used total stations and levels for alignment and elevation checks, requiring 2–3 people and a half-night of work, were made possible with a single smartphone equipped with LRTK.

In the first nighttime inspection after introduction, veteran maintenance staff reported astonishing results: “It’s simply easier and faster. The previous surveying seems like a lie.” Site staff were greatly surprised that the amount of work could be drastically reduced even in intense heat. In practice, point-cloud data and measurement results obtained by walking approximately 500 m (1,640.4 ft) along the track were shared to the cloud on the spot and plotted in real time on the site office PC. Managers could immediately instruct necessary repairs based on that data, and report creation that used to be done the next day was completed the same day. Eliminating entry into paper ledgers and transcription into Excel dramatically shortened lead time from measurement to reporting.

In another example, LRTK is used for equipment inspections. Because photos taken with a smartphone are automatically tagged with position coordinates, it is immediately clear which location each photo corresponds to. Railway company staff reported that time to compile inspection reports was reduced to less than half of previous times, and work accuracy improved. LRTK series products are beginning to be introduced in power, railway, and other infrastructure sectors, producing significant efficiency and accuracy gains in inspection work and report preparation.

Thus, smartphone surveying with LRTK is expected to be a trump card for field DX (digital transformation), bringing new life to railway infrastructure maintenance. The era in which “anyone can survey with a smartphone in one hand” is becoming realistic. Work that used to rely on veteran technicians’ experience and intuition is shifting toward objective data-driven management. The smartphone + RTK approach, which achieves both labor-saving/efficiency and precision, is a solution that also addresses serious labor shortages and skill-transfer challenges.

Going forward, high-precision smartphone surveying tools such as LRTK will likely spread across civil engineering and construction as well as the railway industry. With cloud integration and AR features added, on-site productivity and safety should improve dramatically. Even the painstaking work of rail distance measurement has evolved smartly with the latest technologies. Please consider implementing LRTK-enabled “easy and reliable distance measurement” at your workplace to achieve efficiency gains and quality improvements in maintenance work.