Innovating Rail Deformation Measurement with High-Precision Positioning! LRTK Makes Simple Surveying Accessible to Anyone

To ensure the safe operation of railways, it is crucial to detect even slight deformations of the tracks (rails) and perform appropriate repairs. Each time a train passes, large loads are applied to rails, sleepers, and the trackbed, and over time subtle changes (displacements) in rail position and elevation accumulate. Rails can also bend due to extreme summer heat as they expand, or track distortion can occur from ground subsidence and vibration. Accurately measuring such rail “deformations” (track distortions) and understanding deviations from standards is indispensable for railway infrastructure maintenance. Although periodic inspections using dedicated inspection vehicles called track inspection cars are performed, manual on-site measurements by personnel remain indispensable for detailed condition assessment and verification during repairs.

However, conventional deformation measurement has relied mainly on analog, labor-intensive manual work, requiring considerable effort and time. Now, a new approach leveraging high-precision positioning technology is attracting attention. With the latest solutions that utilize satellite positioning and smartphones, an era is approaching in which anyone can easily measure track deformations. This article explains why measuring rail deformation is important, the challenges and limitations of conventional methods, the revolutionary measurement mechanisms using high-precision GNSS and smartphones, and the future of labor-saving, fast, and high-precision maintenance inspections enabled by LRTK, from both field and management perspectives.

Why rail deformation measurement determines maintenance safety

Track deformation (track irregularities) is a critical factor that affects both railway safety and ride comfort. Various directional deviations—lateral displacement of rails (line deviation), vertical irregularities (level deviation), differences in height between the left and right rails (cross level or “twist”), and changes in gauge—can adversely affect train operation if they exceed allowable limits. Therefore, strict management standards are set for track irregularities, and if deformation exceeds allowable ranges (on the order of a few millimeters to several tens of millimeters), prompt repairs are carried out. For example, even a few millimeters of irregularity on a high-speed train can cause vibration and noise, and if left unaddressed, may lead to deterioration of track structures or, in the worst case, derailment. In fact, there have been reports of trains being forced to operate at reduced speeds or services being suspended when rails buckled from extreme summer heat. Regular inspection and measurement of track deformation to detect deviations from standards early and correct them is essential to maintain safe and comfortable transportation services for passengers.

Challenges of conventional deformation checks that rely on manual surveying and straightedges

Many conventional methods for checking rail deformation have relied on artisanal “manual surveying” and simple jigs. For example, to check line deviation (straightness), a roughly 10 m (32.8 ft) thread or wire is commonly stretched along the rail side, and the gap at the center is measured with a ruler to determine the amount of bend. To measure level irregularities, a straight board with a spirit level placed on the rail is used, and gaps at depressed points are measured with feeler gauges. Gauge is measured one by one with a dedicated gauge tool, and twist is checked by placing spirit levels on both rails and comparing height differences—careful manual measurement by personnel is indispensable.

However, these methods have several issues.

• Large labor burden: Stretching a long wire requires multiple workers, and carrying and repeatedly setting up heavy jigs during limited nighttime maintenance windows is physically demanding.

• Measurement variability: Manual work can produce measurement errors depending on skill level, and the same location may yield slightly different readings depending on the operator.

• Inefficient record management: On-site records are handwritten on paper forms and later digitized, which is time-consuming. Because measurement results are not retained as digital data, tracking long-term changes or correlating with other data is not easy.

Given these challenges, there are limits to obtaining high-precision deformation assessments and records within the limited overnight maintenance time, and improving efficiency has long been an issue. As a result, detailed deformation measurements could not be performed frequently, creating a gap between periodic inspections by track inspection cars and routine visual checks.

How deformation measurement is achieved with high-precision GNSS and smartphones

Recent technology is set to transform track deformation measurement. The key is the combination of high-precision GNSS (Global Navigation Satellite System) and smartphones. In RTK GNSS positioning, satellite data observed simultaneously by a base station receiver and a rover (measurement unit) are compared, and correction information is transmitted to the rover, dramatically improving GPS positioning from several meters of error to on the order of a few centimeters or better. In Japan, correction services such as the Quasi-Zenith Satellite System Michibiki (CLAS) and internet-based reference station networks (VRS, etc.) have been established, and leveraging this infrastructure enables centimeter-class real-time positioning in the field.

Recently introduced are compact RTK-GNSS receivers that attach to smartphones. By attaching a dedicated device to a smartphone and launching an app, anyone can easily use high-precision positioning. Coordinates obtained from positioning are instantly displayed in Japanese plane coordinate systems or global geodetic systems (latitude/longitude), and apps automate coordinate transformations and height corrections that previously required expertise, allowing operation without specialized surveying knowledge. Even novice technicians who are familiar with smartphone operation can immediately use the system in the field, enabling stable measurements that do not depend on experience. By checking current position and measurements on the smartphone screen and recording the position and elevation of points along the rail, continuous measurement of track deformation is possible. For example, simply touching the device lightly to a point on the rail and tapping a button on the smartphone instantly records latitude, longitude, and height for that point. There is no longer a need to stretch long threads or set up spirit levels. Simple surveying with GNSS and a smartphone is enabling a new style of deformation measurement that anyone in the field can handle. Moreover, unlike optical distance measurement, GNSS surveying does not require line-of-sight between instruments, so measurements can be taken in mountainous or obstructed sections without installing relay points. The ability to quickly assess track condition over long sections with consistent accuracy is a major advantage.

LRTK positioning accuracy and centerline evaluation at the centimeter level

A concrete solution that operationalizes smartphone RTK positioning is LRTK. LRTK is a pocket-sized compact device (weighing approximately 125g) that, when combined with a smartphone, achieves accuracy comparable to conventional surveying instruments. Its positioning accuracy is remarkable: even standalone positioning yields planar errors of a few centimeters and elevation errors of a few centimeters. By averaging measurements over a certain period, planar accuracy can approach less than 1 cm (0.39 in). In actual maintenance sites, coordinates obtained with LRTK have shown accuracy comparable to optical surveying results from instruments such as total stations.

With centimeter-class precision, the track “line” (straightness) can be quantitatively evaluated. For example, on a straight section, a measured sequence of centerline coordinates obtained with LRTK can be used to draw the actual alignment and calculate, in millimeters, how far the shape deviates from an ideal straight line. For vertical irregularities (rail height unevenness), acquired elevation data can be used to compute deviation values using a 10 m (32.8 ft) chord or to plot cross sections showing displacements, allowing detailed analysis of track heave or settlement. On curves, comparing measured coordinates with design curve (radius) data enables assessment of local over- or under-bending. While conventional methods could only grasp deformation via center deviations of 10 m chords, LRTK provides continuous coordinate data for detailed analysis. Of course, elevation displacements and gauge changes can similarly be obtained as accurate point-by-point values. For example, gauge can be calculated on-site by measuring the inner positions of the left and right rails and computing their difference. Because LRTK offers centimeter-level precision, even tiny deformations can be detected and quantified, enabling more reliable maintenance decision-making.

Visualizing alignment with point cloud records and comparing with design

Using LRTK, many points along the track can be measured quickly to obtain what is effectively a “point cloud” of the track. Plotting a dense sequence of measured points along the rail intuitively visualizes the actual alignment (track centerline or rail positions). In the past, field workers judged deformation-prone locations from individual measurement values, but point cloud data enables a one-glance understanding of overall alignment distortion through graphs or diagrams. Moreover, overlaying the ideal alignment data from design (for example, route plans or reference coordinates) allows quantitative comparison with the current condition. Visualizing “which point deviates by how many millimeters from the design” makes it significantly easier to identify repair locations and prioritize actions.

LRTK also enables scanning of 3D point clouds around the track using the smartphone camera or built-in LiDAR, allowing three-dimensional recording of site conditions. Sharing point cloud models of the track and surrounding structures and terrain in the cloud allows office staff to grasp deformation points and the surrounding environment in detail without visiting the site. Archiving inspection scenes digitally as a whole is another advantage not available with conventional methods.

Linking deformation measurement with AR for “visible” inspections

Measurement data from LRTK combined with AR (augmented reality) technology is changing the nature of field inspections. When looking at the track through a smartphone camera, virtual reference lines and measurement results are overlaid on the screen, enabling immediate recognition of deformation conditions. High-precision positioning accurately determines current position and orientation, so AR-displayed reference lines correspond correctly to real-world locations. For example, an AR display can show the ideal rail extension on a straight section and visualize which side and by how much the actual rail is displaced. For vertical irregularities, annotations such as “this point is settled by ◯ mm compared to the reference” can be displayed in AR, allowing intuitive understanding of required correction amounts while viewing the actual object. The visual inspection that once relied on craftsmen’s intuition and experience is evolving into an accessible, accurate “visualized inspection” through AR. Simply pointing a smartphone at the site makes rail deviations visually apparent—this is revolutionary for maintenance inspections.

Streamlining asset management through cloud management and ledger integration

Deformation measurement data collected with LRTK can be uploaded and shared to the cloud immediately. Each time a measurement button is pressed in the field, the obtained coordinates and values are sent to the cloud in real time via smartphone communication, allowing managers in the office to check results instantly. This enables timely communication between field workers and managers based on the same data, speeding up deformation assessment and countermeasure planning. Remote support is also possible, with experienced engineers in remote locations viewing data in real time and providing advice, breaking down barriers between field and office. Accumulated cloud data also makes it easy to compare with past measurements and perform trend analysis. You can graph the progression of deformation between periodic inspections, detect gradual settlement trends, or verify whether alignment stabilizes after repair.

Cloud data can also integrate with railway asset management ledgers. By exporting measured deformation amounts and coordinate data in prescribed formats and importing them into maintenance ledgers for each route, field inspection results automatically reflect in the asset database. Previously, field records had to be organized on paper or spreadsheets and later transcribed into ledgers, but using LRTK’s cloud enables one-click recording and reporting. Managers can review data on maps or drawings and link photos or point cloud models as needed. Immediate accumulation of deformation measurement results into ledgers creates valuable data resources for future preventive maintenance planning. If accumulated data are incorporated into BIM/CIM models or digital twins of track facilities, advanced uses such as checking differences between current conditions and design in 3D become possible.

LRTK delivers the threefold benefits of labor-saving, speed, and high precision

By utilizing LRTK, rail deformation inspections are transformed into an ideal form that combines “labor-saving, speed, and high precision.”

• Labor-saving: Track measurements previously conducted by multiple personnel can be completed by a single person with LRTK. There is no need for complicated instrument setup or post-processing, greatly reducing physical burden and staffing arrangements.

• Speed: Measurement time is drastically shortened. For instance, measuring alignment over a 100 m (328.1 ft) section that previously took tens of minutes to an hour for thread setup and recording can be completed in a few minutes while walking with LRTK. Constraints on train operations are reduced, enabling efficient inspections within short available work windows. Faster measurements also allow more frequent patrol inspections, contributing to earlier detection of abnormalities.

• High precision: Deformations so small that they might be missed by visual or manual measurement can be captured in data. Results are obtained in centimeter units, enabling reliable repair decisions. High-precision measurement directly improves the quality of track maintenance.

Enjoying these three benefits simultaneously opens a major breakthrough for maintenance teams facing the challenge of keeping safe track with limited personnel and time.

Case studies: the reality of smartphone surveying that can be introduced from a single span

In practice, some railway operators have begun adopting LRTK in the field. Its appeal is that it can be introduced easily even on a small scale. The dedicated equipment is compact and easy to handle, and no special installation work is required, so small lines and sites can try it out easily. For example, at one maintenance district, a trial smartphone survey was conducted on a single span (several tens of meters) and results were compared with conventional methods. The trial accurately detected even slight settlement, and the results essentially matched those from manual records. Yet the required time was less than half and only one person was needed, prompting field staff to say, “We’d like to measure other sections like this.” In another case, measurement data shared to the cloud after a night shift was immediately reviewed by headquarters engineers and reflected in the following day’s repair plan. Lead time from field work completion to repair planning was greatly reduced, enabling prompt responses. Thus, LRTK is a solution that can demonstrate benefits from small-scale trials and expand to broader rail inspections. Smartphone surveying for deformation inspection is reaching practical stages even for smaller railway lines such as light rail transit (LRT) and regional private railways. LRTK, which enables labor and efficiency improvements, is poised to become a strong ally for maintenance sites regardless of railway size.

The first step to rail deformation inspection with LRTK

We have reviewed the importance of rail deformation measurement and the innovations brought by the latest technology. By leveraging the high-precision positioning device LRTK, track deformation inspections that once required many personnel and time can now be performed quickly and reliably by a single person. No complex operations or specialized knowledge are necessary—if you have a smartphone, you can perform measurement, recording, sharing, and reporting on-site immediately. As a first small step toward DX (digital transformation) in maintenance operations, consider introducing smartphone surveying with LRTK.

Digitizing deformation inspections that once relied on paper and artisan skills can achieve both improved safety and operational efficiency. The new era of maintenance inspections opened by LRTK will elevate railway infrastructure management to even greater heights.

As a new standard for rail deformation measurement, it may not be long before LRTK is active at railway sites across the country. Field feedback already expresses high expectations for its effects.