Surveying Innovation for Railway Infrastructure Works: Achieving Labor Savings and Improved Accuracy with Smartphone RTK

The Reality and Challenges of Surveying in Railway Infrastructure Works

Surveying is indispensable at railway construction sites for accurately locating all structures such as tracks, signals, and platforms. Railways are infrastructure that supports safe and comfortable transportation, and even slight positional deviations can affect running stability and equipment functionality, so construction requires high accuracy. Particularly, laying and adjusting track requires millimeter-level precision; on high-speed rail, even errors of a few millimeters can affect ride comfort and safety. For this reason, rigorous surveying work—from establishing control points to measuring the positions of each piece of equipment—is routinely performed in railway construction.

However, surveying for railway infrastructure works poses several unique challenges. First, because train services usually continue to operate, construction and surveying must be carried out during the brief periods when services stop at night (from after the last train until before the first train). This night work has an extremely limited working window, requiring surveys to be conducted quickly and accurately in the dark. The pressure to measure many points within a short work window, combined with worker fatigue, raises the risk of human error.

Second, railway works tend to proceed on a short construction schedule. To minimize impacts on train operations, overall schedules are often compressed, and surveying must be made more efficient. A large number of survey points must be processed within limited days and nighttime hours, and conventional methods often leave both manpower and time stretched to the limit. Furthermore, railway facilities are frequently located in narrow spaces along tracks, making it difficult to set up tripods or large equipment.

Third is the high-precision requirement specific to railways. For example, when extending a station platform, heights and positions must be aligned to millimeter tolerance so there is no step or lateral misalignment with existing sections. Also, when installing signals or catenary poles, the installed position and height must precisely match the design to ensure proper clearance from trains. In railways, many cases tolerate “no deviation at all,” so minimizing surveying errors is critical. Even skilled technicians face limits when relying on manual methods for precise work during short nighttime shifts, making it difficult to achieve both efficiency and accuracy.

Limitations of Conventional Survey Methods (Total Stations, Tape Measures, etc.)

Long-used surveying methods in railway works include total stations (TS), levels, and tape measurements. A total station is a high-precision optical surveying instrument that measures distance and angle to a prism-mounted staff to compute three-dimensional coordinates. For short distances it can achieve millimeter-order accuracy, enabling precise stakeout. However, a critical weakness of TS surveying is that it requires a clear line of sight. Measurement cannot be performed unless there is an unobstructed view between the instrument and the target point, and on long railway sections or at sites with many obstacles, frequent instrument relocations or the placement of intermediate relay points (temporary control points) becomes necessary. In long-route surveys, repeated TS repositioning can allow cumulative errors to build up, and correcting these requires additional effort. Also, TS work typically requires two people (instrument operator + staff holding the prism), so it cannot be done alone; although robotic TS units are making single-person surveys more feasible, they remain extremely expensive and still require repeated moves to cover wide areas.

On the other hand, analog measurements such as tape measures and levels have also been used at railway sites. For example, directly measuring track gauge or offsets to structures with a tape is simple, but as manual work it is susceptible to reading and recording errors. In dark conditions or on unstable footing at night, simply stretching a tape correctly can be difficult, introducing centimeter-level errors. Maintaining accuracy without relying on experienced personnel is especially challenging, making human error and dependence on skill level persistent issues.

Conventional surveying often manages construction using local coordinates (site-specific reference coordinate systems), causing problems when reconciling data between adjacent work sections. For continuous infrastructure like railways, unified coordinate management across the entire line is desirable, but traditionally survey results have had to be adjusted per site to fit together, adding work.

Overall, conventional methods centered on total stations and tape measures can achieve high accuracy but suffer from low work efficiency, placing a heavy staffing burden on night-time, short-schedule railway projects. Field surveyors have asked, “Can we survey more easily while maintaining accuracy?” and the arrival of new technologies has been eagerly awaited.

Principles and Accuracy of RTK-GNSS Positioning (Real-Time Centimeter-Level Positioning)

One technology attracting attention recently is RTK-GNSS positioning. RTK (Real Time Kinematic) is a method that achieves centimeter-level accuracy by correcting GNSS positioning errors in real time. Standalone GNSS positioning, used by smartphones or car navigation systems, typically has errors of several to tens of meters due to factors such as signal delay through the atmosphere and clock errors in receivers and satellites. RTK installs a receiver with known precise coordinates called a base station, which sends the error information it receives to a mobile receiver (rover). The rover applies corrections to its GNSS data to cancel errors and compute a high-precision position in real time. Simply put, it’s a system that “uses information from a point with a known position to correct the deviation of the point you want to know now.”

With this RTK method, real-time positioning with horizontal accuracy of about 1–2 cm (0.4–0.8 in) and vertical accuracy of about 3–5 cm (1.2–2.0 in) becomes possible. In Japan, network RTK systems (such as VRS) that utilize the Geospatial Information Authority of Japan’s reference station network and private GNSS station networks are widespread, allowing users to obtain correction information without setting up their own base station. Satellite-based correction services such as the Japanese quasi-zenith satellite system “Michibiki” also provide centimeter-level augmentation services (CLAS), enabling reception of correction signals directly from satellites. These developments mean that RTK positioning can increasingly be used in urban and mountainous areas depending on communication conditions and circumstances.

The positioning accuracy of RTK-GNSS is defined in public surveying standards as “within 15 mm horizontally and within 50 mm vertically.” In actual field measurements, network RTK has been confirmed to fall within an error range of about 3–4 cm (1.2–1.6 in). This is generally sufficient accuracy for as-built management and stakeout in railway works. Of course, extremely demanding millimeter-level precision situations still require precise optical surveys (for example, leveling with 1 mm height accuracy), but in most cases RTK provides practical accuracy comparable to TS surveying.

RTK’s advantages are not limited to accuracy. Because results are available in real time, coordinates can be checked on site and immediately applied to construction. Data that previously had to be processed and drawn in the office before use can now be used instantly on site. For example, during track laying, workers carrying an RTK receiver can immediately measure and confirm any displacement of the newly laid track center. This improves on-site responsiveness, prevents rework, and enhances quality control.

Mobile Surveying with Smartphones + Small GNSS Receivers (LRTK)

While the usefulness of RTK-GNSS is clear, conventional systems required specialized, high-performance GNSS receivers and controllers that were extremely expensive and bulky. Recently, however, an innovative solution has emerged: mobile RTK surveying using a smartphone combined with a compact GNSS receiver. This system is called “LRTK.” By using a palm-sized GNSS receiver that attaches to a smartphone, a consumer smartphone can be transformed into a centimeter-precision surveying instrument.

These small GNSS units weigh only a few hundred grams—for example, an LRTK device weighs about 125 g—and are about 1 cm thick. They can be mounted on the back of a phone or attached to a pole (monopod) and include an internal battery that allows about 6 hours of continuous measurement and supports USB charging, so they can be powered by mobile batteries in the field. They also support Michibiki’s CLAS signal, meaning correction information can be obtained via satellites even outside cellular coverage; CLAS-enabled smartphone RTK can continue positioning in mountainous or no-cell-signal areas.

Connection to the smartphone is wireless and operated via a dedicated surveying app. On the LRTK app, starting positioning and recording points can be performed with a single tap, and acquired coordinate data are uploaded to the cloud in real time. Field data can be immediately checked by the office or collaborators, making reporting and sharing of survey results smooth. Data management that used to involve field notebooks or carrying USB sticks is automated through cloud synchronization, eliminating paper notes and preventing transcription errors.

In terms of usability, the smartphone plus compact GNSS combo incorporates features tailored to field needs. For example, by mounting the device on an optional surveying pole, a single operator can stably and accurately observe points. Even if the pole is not perfectly vertical, built-in sensors can perform tilt compensation to compute correct position coordinates (for compatible models). The phone’s camera can be linked to capture photos with high-precision coordinates or to perform simple on-site 3D scanning (point cloud capture). It becomes an all-in-one surveying tool capable of annotating measured points with photos and overlaying acquired point clouds with design 3D data on the phone screen.

Smartphone RTK is also attractive cost-wise. Traditional fixed RTK equipment required initial investments in the hundreds of thousands of dollars (or millions of yen), but using only a smartphone and an add-on device greatly lowers the initial barrier. Small and medium-sized contractors and in-house surveying teams can more readily adopt the technology, making surveying internal and routine—a democratizing tool. In practice, early adopters report that “once we used smartphone RTK, we couldn’t go back to conventional surveying equipment,” indicating its potential to change field norms.

Specific Surveying Use Cases in Railway Infrastructure

High-precision positioning via smartphone RTK is expected to be useful in many aspects of railway infrastructure work. Below are specific applications in the railway field.

• Surveying and staking out track centerline: It can be used for positioning the centerline when constructing new track or for measuring displacement of existing track. RTK allows accurate coordinate acquisition over long stretches without worrying about errors between control points, making it suitable for surveying wide areas of track. Even during limited night-time windows, workers can walk along tracks with an RTK receiver on a pole and continuously measure the track centerline, efficiently verifying and setting track alignment.

• Measuring positions for platform fences and platform screen doors: When installing platform fences or movable platform gates, it is necessary to precisely determine distances from the platform edge and the positions of support posts. Smartphone RTK allows rapid measurement and staking of mounting coordinates on the platform, enabling consistent positioning along long platforms. During night-time station work, necessary points can be measured without installing heavy equipment, allowing safe work in a short time.

• Locating structures such as signal poles and signposts: When installing signals, catenary poles, or speed limit signs along the track, the offset distance and height from the track center specified in the design must be accurately set. By marking the installation coordinates on site using RTK positioning beforehand, there is no confusion when foundations are placed with heavy equipment. Tasks that used to require measuring offsets with tapes or setting batter boards can now be completed quickly with a smartphone, and RTK’s high-precision data are also useful for post-installation as-built verification and as-built management to check for deviations from drawings.

• Surveying and recording cable routes: Smartphone RTK is useful when laying signal or communication cables. For example, when burying conduit for cables, the route can be surveyed with point clouds beforehand to consider the optimal path, and the final buried positions can be recorded with high precision. A single worker carrying smartphone RTK can walk the cable route and acquire continuous route coordinate data, facilitating drawing generation and registration in asset management ledgers.

• Confirming foundation heights and positions: When installing foundation concrete for substations or signal controllers, smartphone RTK can immediately confirm both position and elevation. It can measure absolute elevation on site as well as relative positions from existing tracks or platforms, which is useful for ensuring drainage slopes and checking interference with other equipment. When multiple foundations are installed, the relative positions can be checked on site to prevent re-excavation due to construction errors.

Construction Support by Linking AR Navigation and 3D Point Cloud Acquisition

The advantages of smartphone RTK surveying go beyond merely measuring point coordinates. Combining AR (augmented reality) features and camera-based 3D scanning functions of smartphones makes it a powerful tool for supporting on-site construction.

The AR navigation function displays the direction and distance to set target points in real time on the phone screen. For instance, for specified stakeout positions or equipment installation points in the design, pointing the phone shows arrows or target markers so workers can intuitively locate precise positions on site. This revolutionary method allows operators to understand “where to install” without traditional survey stakes or chalk marks. In narrow station interiors, AR guidance enables quick staking without the need for line-of-sight.

AR can also overlay 3D models from design data onto real-world views. For example, superimposing a model of an extended platform on site images lets stakeholders preview the finished appearance and detect design-site interferences (such as insufficient clearance). Sharing AR visualizations with clients and stakeholders helps build consensus by showing results that are difficult to convey by drawings alone, reducing misalignments in understanding during construction.

Additionally, smartphone + RTK 3D point cloud acquisition is a noteworthy feature. Using the phone camera or LiDAR (on compatible models), the site can be scanned to easily acquire point cloud data of surrounding structures and terrain. Traditionally, point clouds (laser scans) required expensive dedicated equipment, but smartphones can now perform 3D surveying by simply moving as if taking photos. Combining RTK accuracy means the entire acquired point cloud can be tagged with absolute coordinates (map coordinates), which is a major advantage. With a defined positional reference, point clouds captured on different days can be accurately aligned, and comparison with design models becomes straightforward.

For example, to measure the volume of collapsed material on a long slope, walking the slope and scanning with smartphone RTK can produce wide-area terrain point clouds in minutes. Processing these in the cloud can enable on-site volume calculations. In railway civil works, point clouds are increasingly used for disaster recovery planning and pre/post-construction shape comparisons; smartphone RTK makes it possible to quickly and easily acquire as-built 3D data, enabling in-house surveying that was previously outsourced.

By combining smartphone RTK with AR and point cloud technologies, surveying and construction management are integrating at the field level. Data are no longer collected and left unused; they can be immediately used for construction decisions and record-keeping, making smartphone RTK a strong driver of DX (digital transformation) in railway construction.

Effects on Reducing Labor Burden, Improving Safety, and Refining Construction Records

Below is a summary of the effects achieved by introducing smartphone RTK surveying from the perspectives of labor, safety, and record accuracy.

First, reduction of labor burden. RTK surveying can generally be completed by a single worker, which is a significant advantage on labor-short sites. In track maintenance, tasks that previously required multiple night-shift personnel are now sometimes completed by one person carrying a smartphone RTK device. Reducing survey team size allows reallocating personnel to other tasks, reducing the need for standby staff and helping correct long working hours. Single-person mobility also increases planning flexibility and eliminates inefficiencies where other processes are held up waiting for surveying.

Next, improved safety. Night work at railway sites involves risks and poor footing, but smartphone RTK reduces the amount of equipment to carry and enables rapid surveying, shortening on-site time. Being able to finish the tension of monitoring approaching trains and avoiding heavy equipment in a shorter timeframe contributes to worker safety and health. Measurements at hazardous locations can also be performed remotely; for example, surveying cliffs beside tracks or high bridge structures can be done without approaching by using extension poles with RTK or combining with drones. Labor-saving and reduction of personnel go hand in hand with safety improvements, and smartphone RTK realizes both.

Finally, refinement of construction records. All survey data acquired with smartphone RTK are coordinate-tagged within a few centimeters and stored in the cloud. This allows construction records that previously relied on paper drawings and photographs to be kept as spatially referenced digital data. If the as-built positions of equipment are stored as high-precision data after completion, future maintenance can precisely track degradation or displacement, and it aids verification when problems occur. As reporting materials to clients, three-dimensional models based on point clouds and coordinate data are more persuasive and make it easier to objectively demonstrate construction quality. Infrastructure managers, including railway operators and government agencies, emphasize the development of digital records, and smartphone RTK enables easy acquisition of the accurate on-site information that underpins digital construction and maintenance DX.

Innovate Your Site by Introducing Smartphone RTK “LRTK”

The LRTK system introduced here as a solution for smartphone RTK surveying has the potential to bring unprecedented innovation to railway infrastructure sites. With a compact, lightweight LRTK unit and a smartphone, anyone can quickly start centimeter-level positioning. Designed to be easy to use even for non-specialist surveyors, it enables intuitive workflows from positioning to data utilization, making on-site surveying dramatically simpler.

LRTK is already being used in the railway field, with reports such as “We were able to efficiently complete stakeout of platform extensions and track centerline checks during a short period after the last train” and “Smartphone RTK gave us breathing room during limited night work, allowing time for safety checks and quality inspections.” Field staff express surprise at its mobility and accuracy, and once they experience its convenience it becomes indispensable.

Construction managers and survey teams involved in railway infrastructure works should consider adopting smartphone RTK surveying solutions. By leveraging LRTK, you can realize labor savings and advanced capabilities that overturn conventional practices. Reducing survey burden and improving accuracy directly contribute to shortened construction schedules, cost savings, and enhanced safety. Embrace the latest smartphone RTK technology and take railway infrastructure construction to the next level.