Surveying Innovation in Railway Construction:
High-Precision Positioning and AR Guidance with Compact RTK Surveying Devices

In railway construction sites, surveying tasks have always been time-consuming and labor-intensive, with constant challenges in ensuring accuracy. Traditional manual surveying led to cumulative errors in points and an increase in work time, placing a significant burden on construction management. Additionally, the growing shortage of workers on-site and the aging of skilled workers have also become serious problems.

Against this backdrop, there is a strong demand for innovation through the digital transformation (DX) of surveying technology.

In recent years, RTK (Real-Time Kinematic) positioning technology has gained attention as a solution to these challenges. The evolution of RTK technology has made it possible to achieve real-time, high-precision surveying, which was previously difficult. Traditionally, achieving millimeter-level precision required static measurements or long-duration averaging, but with the advent of RTK, centimeter-level accuracy can now be achieved even while moving. This technological breakthrough holds great value, especially in fields like railway construction, where high precision is critical.

Now, compact RTK surveying GPS devices, which condense RTK technology into a palm-sized unit, are revolutionizing surveying tasks on-site. These small and lightweight devices allow a single person to easily perform high-precision positioning, overcoming the limitations of traditional surveying methods. This article will review the challenges of surveying in railway construction, explore the technology and advantages of compact RTK surveying GPS devices, and provide practical examples of high-precision positioning (stake driving) and AR guidance.

​

What is a Compact RTK Surveying GPS Device?

RTK (Real-Time Kinematic) positioning is a technology that uses two GNSS (satellite positioning) receivers at a base station and a moving station to simultaneously observe satellite signals. By applying error correction data sent from the base station, it calculates highly accurate positions in real-time. While standard GPS positioning typically results in errors of several meters, RTK allows for positioning accuracy in both vertical and horizontal directions to the centimeter level. Typically, the accuracy of RTK positioning is said to be around 2-3 cm horizontally and 3-4 cm vertically, which is particularly effective in precision-demanding construction surveying, such as in railway projects.

A compact RTK surveying GPS device is a cutting-edge piece of equipment that integrates this RTK-GNSS receiver into a compact form. In the past, achieving centimeter-level positioning required large and complex surveying equipment or systems. However, with the miniaturization and cost reduction of modules in recent years, devices that provide high-precision positioning in a portable size have emerged.

For example, as shown in the picture, there are devices where the receiver and controller are combined into a unit that can be held with one hand, greatly improving mobility. On railway construction sites, a compact RTK device makes surveying in narrow areas and quick setup and breakdown during nighttime work much easier, offering benefits in both safety and operational efficiency.

Compared to traditional surveying equipment (such as total stations or levels), compact RTK devices offer several distinct advantages. The first is the ability to complete surveying with just one person. A total station required two people: a surveyor and a prism holder, but with the spread of auto-tracking total stations (TS) and GNSS surveying, one-person surveying has become possible.

With a compact RTK device, it can be carried and operated by a single person from the start, making it highly effective in sites with manpower shortages. Additionally, the lack of need for line-of-sight is a significant advantage. Optical TS surveying requires line-of-sight between points, but RTK-GNSS only requires satellite reception, allowing for measurements that are less susceptible to obstacles. Furthermore, with devices that support network-based RTK (such as VRS systems), correction data can be obtained from surrounding electronic reference points without the need to place a base station on-site, unlike traditional RTK, which requires one. Thanks to these technological advancements, compact RTK surveying GPS devices have emerged as a new tool that enables "anywhere, anytime, accurate" surveying.

​

Achieving High-Precision Positioning and Layout

In railway construction, positioning tasks (such as layout marking and stake driving) are essential processes for determining the accurate alignment of tracks and the installation positions of structures. There are many situations where even millimeter-level deviations are not allowed, and traditionally, surveying teams have carefully repositioned and measured multiple times to ensure accuracy. By utilizing compact RTK surveying GPS devices, these positioning tasks can be drastically more efficient and precise.

RTK real-time positioning allows for quick offset calculations from known points and the precise placement of design coordinates on-site (staking out). For example, if the coordinates of the track center or the foundation of a structure, obtained from the design drawings, are entered into the device in advance, the device can guide you to that position and display it on the screen. Since RTK positioning errors are within just a few centimeters, it enables pinpoint accuracy in identifying critical points, such as the location of rail track installation or the position of anchor bolts for bridge piers. With traditional GPS, errors of several meters were common, requiring adjustments at the measurement points. However, with RTK, the initial setup is extremely accurate, reducing the need for rework.

​

The benefits brought by high-precision positioning are improvements in both quality and efficiency. As surveying accuracy increases, the risks of error correction and rework during the construction phase are reduced. In the case of railways, track irregularities and misalignment of structures directly impact operational safety, making accuracy in initial surveying essential for ensuring quality. The reliable data obtained through RTK surveying becomes the benchmark for subsequent construction management and inspection (as-built measurements), leading to overall improvements in project precision. Additionally, the ability to position a wide range of points at once reduces work time and contributes to project schedule compression. In one railway construction site, after setting up the main reference points with RTK, surveying time was significantly reduced compared to traditional methods, resulting in less burden on nighttime work and cost savings.

Furthermore, the compact RTK devices facilitate the digital integration of data. The obtained coordinate data can be instantly uploaded to the cloud, where it can be cross-referenced with design data or BIM/CIM models for verification. This allows for a seamless connection between the surveying, design, and construction cycles, enabling real-time feedback as part of the broader trend of construction DX. The use of high-precision positioning technology in railway construction is simultaneously improving both accuracy and productivity, changing the way the industry works.

​

Innovation in Surveying Tasks through AR Guidance

When combined with RTK technology, a new and increasingly recognized approach in recent years is the use of AR (Augmented Reality) guidance for surveying support. By using AR technology, surveying data and design information are overlaid onto real-world visuals, allowing workers to intuitively check positions and heights. Especially in surveying and construction management, the combination of high-precision positioning technology (RTK-GNSS) and AR has led to initiatives where 3D design models are overlaid onto the actual site in real-time.

In the AR guidance system, the current position, obtained through RTK, is used as the basis for projecting the positions of target objects on design drawings or BIM models onto the device screen. For example, when viewing the site through a tablet or AR glasses, 3D models of tracks or structures based on the design are displayed, aligning perfectly with the real-world scene. This allows workers to immediately determine whether the surveyed points are in the correct position according to the design, and any discrepancies can be instantly detected and corrected.

In practice, visualizing the positions of rebar and formwork in AR during construction has been proven to prevent mistakes in real-time due to discrepancies between the drawings and the actual site.

Since it provides visual information that anyone can intuitively understand, sharing information with workers who have no surveying expertise or other stakeholders is also much smoother. In the past, it was difficult for less experienced workers to visualize the on-site position from the numerical values on the drawings, but AR guidance bridges that gap, reducing the burden on field workers and simultaneously improving construction accuracy.

In railway construction, using AR guidance, for example, the centerline of a curved track can be visualized on the ground, ensuring safe track laying. Additionally, for complex structures like station platforms, the completed design can be projected onto the site for verification, preventing mistakes in installation position and height in advance. Furthermore, AR guidance also has high educational benefits, as it allows younger engineers to visually learn the "critical points" from experienced professionals. By combining the expertise of seasoned workers with digital technology, we are moving away from subjective tasks and approaching an era where anyone can perform accurate surveying and construction.

​

Introduction to LRTK Products

Here, we introduce the LRTK product, which has gained attention as the latest compact RTK surveying GPS device. LRTK integrates the RTK positioning technology mentioned above with AR guidance functionality, making it an all-in-one device designed for use in railway construction and civil surveying projects. Let’s highlight some of its features:

• Compact and Lightweight Design: The LRTK device is compact enough to be held with one hand, making it easy to carry all the necessary equipment. It is equipped with dustproof and waterproof performance (IP-rated), ensuring reliable use even in rainy or dusty environments such as railway construction sites. Unlike traditional stationary equipment or tripods, it is easy to maneuver even in narrow areas beside the tracks.

• Centimeter-Level High Precision Positioning: By collaborating with the electronic reference point network of the Geospatial Information Authority of Japan and its own base station, LRTK ensures positioning accuracy within just a few centimeters. Combining RTK-GNSS with an IMU (Inertial Measurement Unit) enables stable positioning even in areas with poor satellite signal reception, such as under elevated tracks or near tunnel entrances. The high surveying accuracy complies with public surveying standards and meets the quality requirements for railway construction.

• AR Guidance and Navigation Functionality: The dedicated tablet app displays 3D design models and survey points in AR, supporting layout marking and as-built checks on-site. Compared to competing products, LRTK has a more advanced AR functionality, allowing seamless integration of design data and on-site projections. For example, the device can guide the user to a designated point according to the survey plan and display a clear message like “This is the installation point” once the user reaches the designated location.

• User-Friendly Workflow: LRTK significantly simplifies the surveying workflow on-site. With its intuitive user interface, it can be operated by even non-experts with minimal training. Complex processes such as setting up the base station or adjusting wireless frequencies are automated, allowing surveying to begin within minutes of powering on. Surveying data is shared in real-time through cloud integration, eliminating the need for data organization once back at the office.

 

As described above, LRTK is a product that combines high precision and ease of use, bringing innovation to surveying in railway construction. While other traditional products are high-precision but large and require specialized knowledge, LRTK differentiates itself by being compact and easy for anyone to use. This makes it easy for small to medium-sized civil contractors and surveying companies to adopt, contributing to the promotion of digital transformation (DX) across the entire site.

The impact of improving surveying workflows with LRTK is significant. For example, in the past, separate equipment and personnel were needed for each step: surveying → layout marking → construction → as-built measurement. However, with LRTK, one device can handle everything from surveying to as-built verification, enabling a consistent digital workflow. Any discrepancies between surveying results and construction can be immediately corrected through AR verification on-site, transforming the workflow from "measure and finish" to "measure and immediately apply to construction." This will not only revolutionize railway construction but also dramatically improve productivity in all infrastructure construction sites.