Table of contents

• What is CLAS? Differences from RTK and benefits

• Accuracy required for piling and conventional challenges (TS, tape measure, optical limits)

• Basic configuration and workflow of coordinate guidance using CLAS‑compatible receivers

• Pile positioning coordinate guidance steps with LRTK (equipment setup, calling survey points, AR guidance)

• Using public coordinates vs. local coordinates and points to watch

• Field case studies and results (accuracy, time savings, personnel reduction, etc.)

• Site management linked with point clouds and photogrammetry (pile position verification, as‑built management)

• Natural introduction of smartphone surveying with LRTK (on‑site and cloud use)

• FAQ: Questions about CLAS, LRTK, and coordinate guidance

What is CLAS? Differences from RTK and benefits

First, CLAS stands for the “centimeter‑level augmentation service,” a high‑precision positioning service provided by Japan’s Quasi‑Zenith Satellite System (QZSS, “Michibiki”). It generates correction data based on error information derived from the Geospatial Information Authority of Japan’s network of reference stations, and delivers these corrections directly via satellites to improve GNSS positioning accuracy to the centimeter level. With a dedicated CLAS‑compatible receiver, you can receive the correction data via satellite without a communications line or a local base station, enabling high‑precision positioning anywhere in Japan. A major appeal of CLAS is that this correction signal is free to use and that it is reliable even in mountainous areas outside mobile coverage or at disaster sites where communications may be disrupted.

On the other hand, conventional RTK positioning (Real Time Kinematic) uses two GNSS receivers—a base station and a rover—and computes positions by real‑time correction of the difference in satellite signals received by both. Traditionally, this required setting up your own base station on site or receiving base station data through a communications network (VRS, etc.). In other words, high‑precision positioning required radio equipment, internet connections, and sometimes paid correction service subscriptions. The key difference between CLAS and RTK is how correction information is obtained. CLAS‑compatible equipment receives corrections directly from satellites, so it can operate independently, with no distance limitation to a base station. RTK accuracy is more stable when close to the base station, whereas CLAS provides nearly uniform accuracy nationwide. Also, because CLAS does not rely on communications infrastructure, it can be used in places where network connectivity is difficult and is effective at disaster sites where communications have failed. Overall, CLAS can be described as a “wide‑area, easy RTK,” a cutting‑edge technology that delivers centimeter‑level accuracy while greatly reducing expensive equipment and complex setup.

Accuracy required for piling and conventional challenges (TS, tape measure, optical limits)

Pile work on civil engineering and construction sites (such as setting survey stakes or locating foundation piles) is a critical process that affects the entire structure. If piles are not placed at the exact coordinates specified in the design drawings, downstream work can deviate, leading to quality defects or construction errors. Therefore, piling requires high accuracy where even errors of a few centimeters are unacceptable. However, until now, pile positioning has relied heavily on manual work by surveyors.

Conventionally, surveying staff would use the coordinates from the drawings and lay out positions on site using tape measures and total stations (TS), marking the ground with stakes or paint. This method has several challenges. First, it is labor‑ and time‑intensive. Tasks such as assembling batter boards in pairs and repeating measurements require careful preparation. There is also a high potential for human error; incorrect point layout or marking mistakes can force re‑piling. Optical TS surveying requires line‑of‑sight, so work becomes difficult on complex terrain or at sites with obstructions. For example, in mountainous areas or in poor visibility conditions such as at night or in fog, maintaining accuracy is difficult due to the limitations of visual guidance. Additionally, many sites depend on specialized surveying teams, which raises labor costs, and work efficiency is affected by weather and time of day. In short, conventional pile layout surveying is effortful and inefficient in order to achieve required accuracy.

Basic configuration and workflow of coordinate guidance using CLAS‑compatible receivers

One solution to these challenges is GNSS coordinate guidance for pile work. By combining a CLAS‑compatible high‑precision GNSS receiver (for example, the LRTK series) with a smartphone, anyone can easily guide piles to the target coordinates. The basic configuration is a compact CLAS‑compatible RTK‑GNSS receiver and a smartphone or tablet with a dedicated app installed. The receiver picks up multiple satellite signals, including the millimeter‑wave augmentation signal (L6 band), and computes a high‑precision current position. This receiver pairs with the smartphone via Bluetooth or cable and streams real‑time positioning results (current coordinates) to the app.

On site, you first power on the receiver and acquire satellites in an open sky area. If the CLAS satellite augmentation signal is received, centimeter‑level positioning is achievable within a few minutes. Next, load the design coordinate data for construction onto the smartphone and select the stake position (survey point) you want to guide to in the app. The app screen displays the “current position” and the “target stake position,” and directional arrows and distance are updated in real time. The operator follows the guidance on the smartphone and moves to the spot where the receiver carried matches the target coordinates. In AR mode, holding up the smartphone overlays a marker for the target on the camera image, allowing intuitive recognition of “this is where the pile should be driven.”

In summary, the coordinate guidance workflow is “high‑precision measurement of current position” → “comparison with the target coordinate” → “guided movement.” What used to be a manual transfer of drawing coordinates to the field is digitized and automated by the GNSS receiver and app. This allows even inexperienced workers to accurately place piles without pre‑marking by a surveyor. Because CLAS‑compatible receivers simply require setting up the device and selecting survey point data, they are an accessible basic configuration that can be used immediately on site, even by those without surveying expertise.

Pile positioning coordinate guidance steps with LRTK (equipment setup, calling survey points, AR guidance)

Now let’s look step by step at how to perform pile coordinate guidance using an LRTK device and a smartphone.

• Equipment preparation and setup: On arrival at the site, attach the LRTK receiver to the designated mount (for example: the top of a dedicated pole or the top of the smartphone). Power on the receiver and establish a Bluetooth connection with the smartphone or tablet. Launch the LRTK app and confirm that GNSS positioning data is being received from the receiver (check satellite acquisition status and accuracy display, and confirm that a Fix solution is obtained).

• Loading and calling survey point data: Import the design coordinate data prepared in the app. This is typically a list of stake positions (coordinate table) exported from construction drawings as CSV, etc. Select the survey point number of the stake you want to guide to, and that point’s coordinates become the target. If needed, confirm the site coordinate system settings here (public coordinate zone or local coordinate offsets).

• Position alignment using AR guidance: Once a survey point is selected, the screen shows the “bearing to the target” and “distance,” so carry the smartphone and move in the indicated direction. While moving, the on‑screen arrows and distance update in real time; the closer you get, the smaller the distance. If AR mode is enabled, a marker or flag indicating the target will be projected on the smartphone’s camera view. For example, it can appear as if a red pin is standing on the ground, making the pile position visually intuitive. Because GNSS tracks the user’s position with high precision, the AR marker aligns precisely with the actual point and does not drift as the user moves.

• Marking and installing the pile: When the displayed distance is nearly zero and the AR marker appears at your feet, that is the design coordinate for driving the pile. Confirm there is no positional error and mark the ground (temporarily place the pile or spray paint). Then drive the pile with machinery or a hammer. If the LRTK receiver is attached during driving, you can immediately measure the pile head coordinates after installation to verify there was no misalignment during driving.

• Recording and moving to the next point: After installing a pile, mark the survey point as completed in the app. If necessary, measure and save the installed pile’s coordinates and take photographic records. These data can be automatically uploaded to the cloud, enabling immediate sharing without returning to the office. After finishing one pile, select the next survey point and repeat the same procedure. Repeating this workflow allows a single person to complete pile work sequentially—one of the major advantages of LRTK coordinate guidance.

*(※Fix solution: a GNSS state in which the solution achieves centimeter‑level error. Standalone positioning or a Float solution (accuracy on the order of tens of centimeters) does not provide sufficient accuracy for pile guidance, so you must wait until a Fix solution is obtained.)*

Using public coordinates vs. local coordinates and points to watch

When using GNSS, it is important to be aware of the site’s coordinate system. In Japan, surveying and design typically use public coordinate systems (such as the plane rectangular coordinate system based on JGD2011), but some sites adopt a proprietary local coordinate system (a coordinate system with an arbitrary origin or orientation). CLAS‑compatible receivers generally provide positions in global references such as WGS84 or JGD2011, which may not directly match the coordinates on the site drawings. In such cases, you need to align them via a process called localization (site calibration).

Specifically, measure known points on site (points with accurately known coordinates) with GNSS and compare the measured results with the design coordinates to calculate the translation and rotation needed. Applying this correction in the app or receiver converts all subsequent GNSS points into the local coordinate system. For example, if you use a control point given in a public coordinate system (e.g., a Geospatial Information Authority benchmark), you can align to the public coordinate zone; if you use known points defined in a previous project’s local coordinates, you can conform to that local system.

A key rule is to follow the coordinate system specified in the design drawings or by the client. On sites using public coordinates, set the LRTK app to the appropriate plane rectangular coordinate zone or output latitude/longitude and convert later. For local coordinate systems, perform localization using at least one known point (preferably multiple points), otherwise coordinates will be offset. Also note that GNSS provides ellipsoidal height, which differs from the site’s TBM (benchmark) elevation reference. Apply geoid height conversion or adjust using known site elevations as required to manage vertical errors. By handling coordinate systems correctly, CLAS‑compatible GNSS positioning can be directly used in the site’s coordinate system, ensuring smooth data consistency with downstream processes.

Field case studies and results (accuracy, time savings, personnel reduction, etc.)

Sites that have implemented high‑precision LRTK coordinate guidance systems report not only improved accuracy but also significant gains in operational efficiency and cost reductions. Below are typical effects and case examples.

• Dramatic improvement in construction accuracy: GNSS guidance drastically reduces human error, allowing piles to be driven within a few centimeters of the target coordinates. Even in situations where machinery operators previously relied on marks set by surveying teams and intuition, following the device guidance enables precise placement. This reduces scatter in pile positions and has led to reports of zero rework in quality control. High‑precision pile installation prevents foundation misalignment and contributes to improved overall structural quality.

• Substantial time savings: Introducing GNSS coordinate guidance has dramatically reduced the time required for stakeout in many cases. For example, there are reports where using GNSS + AR stakeout reduced the time to about one‑sixth of that required by conventional optical surveying methods. Simplified point selection and improved movement efficiency enable many more piles to be processed per day. In one road project, stakeout that used to take half a day was completed in under an hour, directly shortening the construction schedule. Time savings translate to reduced construction costs and more schedule margin, contributing to overall site productivity.

• Personnel reduction, labor savings, and safety improvements: Tasks that previously required two to three people can be completed by one person using LRTK. Eliminating the need for survey assistants or verifiers yields significant personnel cost reductions and allows redeployment of staff to other tasks. Fewer personnel on site also reduces the number of people entering areas where heavy machinery operates, improving safety management. For example, on a bridge project, surveying personnel used to enter narrow scaffolding to mark positions; replacing that with GNSS guidance enabled safe, speedy pile foundation positioning. Site feedback includes phrases like “freed from laborious batter board setup and tape measurements” and “short duration work in extreme heat or cold reduces operator burden,” indicating improved labor conditions through automation.

• Wider applicability (useful across many site types): Pile coordinate guidance has been adopted in a wide variety of projects, from roads and bridges to water/sewer works and land development. For instance, in road work it enabled accurate placement of stakes along the road centerline and boundary marking while eliminating conventional batter boards. In bridge projects, GNSS guidance was used for pier layout in mountainous areas with poor sightlines, achieving improved placement accuracy for all piles. Long pipeline installations benefited from efficient single‑operator marking at regular intervals, completing large‑area surveys in short periods. Thus, accuracy and efficiency are achieved across many site types, and with support from the Ministry of Land, Infrastructure, Transport and Tourism’s push for *i‑Construction (ICT construction)*, adoption is expanding from major contractors to small and medium construction firms.

Site management linked with point clouds and photogrammetry (pile position verification, as‑built management)

LRTK‑based pile guidance offers added value beyond simply driving piles: it enables immediate utilization of survey data. Position information obtained with a GNSS receiver and smartphone can be directly linked with photos and point cloud data to support site management.

For example, immediately after installing a pile, take a photo of the pile with your smartphone to tag the image with high‑precision coordinates and timestamps. Plotting these photos on a cloud map later makes it simple to see “which pile was installed at which location.” This is powerful when verifying pile locations and creating as‑built documentation. Compared to handwritten field notes, digital photos with coordinates eliminate mistakes and are easier to share, providing strong evidentiary support during inspections.

Modern smartphones and tablets also include simple photogrammetry functions and, in some models, LiDAR sensors for 3D point cloud scanning. When combined with LRTK, point cloud data obtained this way can be immediately assigned absolute coordinates (public coordinates). For example, scanning terrain or structures with an iPad LiDAR fused with high‑precision position and attitude information from LRTK yields a site‑wide point cloud model in an accurate coordinate system. These 3D point clouds are directly usable for as‑built management. Capturing the surrounding ground and structures after pile installation allows digital verification of pile positions and elevations against design. You can measure distances, tilt, and positional relationships in the point cloud and check deviations from design values, enabling advanced quality control right on site.

Furthermore, uploading point clouds and photo data to the cloud allows real‑time sharing with the office and partner companies. This makes it possible for site managers to drive piles while office staff concurrently prepare as‑built inspections. A smartphone‑centered LRTK workflow integrates positioning and measurement to streamline site management and seamlessly connects the formerly separate tasks of “construction” and “as‑built verification.”

Natural introduction of smartphone surveying with LRTK (on‑site and cloud use)

Sites introducing ICT devices for the first time may worry, “Can we master this?” However, smartphone‑paired GNSS receivers like LRTK offer the ease of use and familiarity needed to dispel such concerns. Because a commonly used smartphone is the platform, site staff can operate the system intuitively and start without specialized knowledge. In LRTK deployments, users have reported that “surveying felt like using a smartphone app” and “coordinate matching worked like a game, so even new staff didn’t get confused.”

Starting with the concrete task of pile guidance makes on‑site acceptance easier and often leads to a natural expansion into smartphone surveying overall. After using LRTK for pile layout, teams often try surveying existing terrain and photo documentation with the same equipment. Once accustomed, they use the system as an electronic field book for point surveys, for simple depth or elevation checks, or for placing control markers for drone photogrammetry—realizing that the smartphone + GNSS combo is a versatile surveying tool for many site tasks.

LRTK also integrates with cloud services (LRTK Cloud), allowing immediate upload of survey data, photos, and point clouds from the field. Team members can share data on the cloud or view maps in a browser, improving data management efficiency and speeding up reporting tasks. The former hassle of carrying data on USB drives and importing it to a PC is eliminated; cloud use centralizes survey information in real time. As a result, the barrier to “site DX” is lowered and paper‑based, manual workflows are replaced by digital processes.

The benefits of introducing smartphone surveying with LRTK go beyond a single productivity gain. It acts as a catalyst for site‑wide digitalization and labor saving, contributing to productivity improvements and workstyle reform. A small initial success—“we could drive piles with a smartphone”—builds confidence and interest that lead to “we can do surveying with a smartphone” and “we can visualize the site on the cloud,” accelerating ICT adoption. Because LRTK lowers the adoption barrier, it is truly a strategic tool to naturally promote on‑site DX (digital transformation).

FAQ: Questions about CLAS, LRTK, and coordinate guidance

Q: What is required to use CLAS? How is it different from conventional RTK? A: To use CLAS you need a CLAS‑compatible GNSS receiver (for example, an LRTK or other CLAS‑capable device) and an environment where satellite signals can be received. No internet connection or base station is required; a dedicated device can receive correction signals directly from the satellites. Unlike conventional RTK, which requires base station data, CLAS can achieve centimeter‑level positioning standalone anywhere in Japan, which is the major difference.

Q: How accurate is an LRTK receiver? Is it reliable? A: High‑precision GNSS receivers like LRTK typically achieve horizontal positions within a few centimeters and vertical errors within a few centimeters to a few tens of centimeters (under good conditions, horizontal accuracy can be around 2–3 cm). When a CLAS or RTK Fix solution is obtained, positioning is very stable and is sufficiently accurate for civil engineering pile work and as‑built measurements. However, accuracy can temporarily degrade in environments where satellites are obstructed, so maintaining a good sky view is desirable. Periodic checks against known points help ensure reliability.

Q: Can beginners use GNSS guidance? Is specialized knowledge required? A: Yes. Smartphone apps are designed to be intuitive, so users without specialized surveying experience can operate them. Operators simply follow on‑screen arrows and distance indicators, so beginners generally have little trouble. With a short introductory training, staff from junior to senior levels can use the system. Complex coordinate calculations and settings are handled automatically by the system, so even those who “don’t understand surveying” can start confidently.

Q: How do I use it in a local coordinate system? A: The LRTK app supports public coordinate systems (plane rectangular coordinate zones, etc.) and WGS84 latitude/longitude outputs. If the site uses a proprietary local coordinate system, you must observe at least one known point on site with a known local coordinate value and perform localization in the app to apply the correction. The procedure involves inputting the difference between the measured value and the theoretical value to correct subsequent positioning. Detailed steps are in the manual, but the operation is generally as simple as entering a few numbers in the app.

Q: Is CLAS satellite augmentation available outside Japan? A: CLAS is targeted at Japan and surrounding regions and is available almost nationwide within Japan, but it is not usable overseas. For high‑precision positioning abroad, use local satellite augmentation services (SBAS or other PPP services) or internet‑based RTK services. The LRTK receiver itself supports multi‑frequency, multi‑GNSS, so with an NTRIP connection it can perform RTK positioning overseas.

Q: Can it be used in harsh conditions like rain or cold regions? A: LRTK receivers are dust‑ and water‑resistant and can operate in light rain (many models have IP65–IP67 protection). They also have wide operating temperature ranges, with performance reported from snowy mountains in winter to hot summers. Batteries are tested for cold environments, with operations reported around −20°C in some cases. However, electronic devices still require protection in prolonged heavy rain, and extreme conditions can degrade satellite reception, so operate with caution and appropriate protection.

Q: What other uses are there besides piling? A: LRTK is useful for many positioning and surveying tasks beyond pile guidance. Examples include surface elevation checks (roadbed as‑built checks), recording positions of buried utilities, setting aerial targets for drone photogrammetry, guiding earthmoving machinery, point surveying for as‑built drawings, and even agricultural field partitioning or tree planting guidance in forestry. Because high‑precision positions can be obtained with just a smartphone, many sites are beginning to perform surveys themselves that previously required specialized contractors. In short, any task that requires position layout or measurement can be adapted.