Coordinate Navigation Dramatically Reduces Piling Errors! LRTK at the Forefront of Jobsite Use

Have you ever been unsure about where to place a pile on site, or felt uneasy about surveying results and had a close call? A reliable technology has emerged to solve such on-site problems. That is the coordinate navigation (coordinate guidance) technology using LRTK. When performing tasks such as piling at construction sites, the indispensable process is the reverse setting-out, in which design data coordinates are transferred to the field in advance. However, conventional reverse setting-out work was time-consuming and prone to human error. Errors in pile position or elevation directly affect structural safety, so piling mistakes are a critical issue that must never occur. Background factors such as the aging of experienced survey technicians, labor shortages, and responding to aging infrastructure mean that improving construction accuracy and efficiency is strongly demanded. As a trump card to solve these challenges and drastically reduce piling errors, coordinate navigation technology utilizing LRTK has attracted attention.

Coordinate navigation with LRTK is an innovative system that combines a smartphone with an ultra-compact high-precision GNSS receiver to navigate workers to the target pile locations. Traditionally, surveyors set up reference marks on site using batter boards or string lines and workers relied on those markings to drive piles. But this method required experience and effort, and often caused positional drift and rework. With the advent of LRTK, anyone can follow guidance on a smartphone screen to reach the intended point, dramatically improving construction accuracy and efficiency.

Challenges of Reverse Setting-out (Surveying) Work

First, reverse setting-out (surveying) work means determining the site coordinates of structures listed on the design drawings and driving piles accordingly. Typically, surveyors install reference lines and points using surveying instruments such as total stations or batter boards for marking, and workers drive piles following those reference marks. This conventional method requires skilled techniques and multiple personnel, takes time for preparation and measurement, and is prone to errors in position setting due to human mistakes. In practice, even slight measurement errors can deviate pile positions by several centimeters, leading to rework or reconstruction in subsequent processes. If pile position errors cause major structural defects, it could result in enormous rework costs such as foundation demolition and reconstruction and schedule delays. In addition, the recent aging of skilled workers and worsening labor shortages have made it difficult to maintain a structure that can perform reverse setting-out efficiently. With conventional methods, laying out positions for large structures often takes more than half a day, placing a burden on site operations.

What is LRTK? Coordinate Navigation Achieved with a Smartphone

LRTK (L-R-T-K) is a system composed of a compact high-precision GNSS positioning device that attaches to a smartphone, a dedicated app, and cloud services. Standard GPS built into smartphones has errors on the order of meters, but LRTK achieves centimeter-level RTK positioning accuracy (RTK positioning accuracy) using the RTK (Real Time Kinematic) method. By simply attaching a compact receiver weighing about 125 g and about 13 mm (0.51 in) thick to a smartphone with one touch, you can obtain centimeter-level current position in real time.

By receiving correction data from reference stations (such as network RTK or the QZSS “Michibiki” CLAS signal) via the dedicated app, LRTK can stably maintain cm level accuracy (half-inch accuracy) even in environments that were previously difficult without installing a local base station, such as under trees or under elevated structures. The obtained positioning results and photo data can be synchronized to the cloud immediately, and design coordinate data can be downloaded from the cloud in advance. This allows workers to accurately know their position in global coordinates on site and, with the coordinate navigation function described below, be guided to designated coordinate points without specialized surveying knowledge. The fact that anyone can perform highly accurate reverse setting-out with just a smartphone—without relying on expensive surveying equipment or advanced skills—is revolutionary.

Features of LRTK and Its Use in Reverse Setting-out

Centimeter-level Accuracy with RTK Positioning

The greatest feature of LRTK is centimeter-class positioning accuracy via RTK-GNSS. With high precision—about ±2 cm (±0.8 in) in horizontal position and about ±3 cm (±1.2 in) in elevation—you can grasp your current position and virtually eliminate pile position drift. Conventional smartphone GPS has errors of several meters and could not be used for direct reverse setting-out, but with LRTK the error is contained to a few centimeters, allowing you to accurately mark planned points. RTK positioning using correction signals is also highly stable, and because it maintains accuracy even in poor line-of-sight site environments, its reliability on site is excellent. This high precision greatly reduces surveying errors that cause piling mistakes.

Easy for Anyone with Smartphone Operation

LRTK runs on a smartphone app, so there is no need to learn the complicated operations unique to dedicated instruments. When you select a target coordinate in the app and start the “Go to this coordinate” function, an arrow indicating direction and the distance to the target are displayed in real time on the screen, guiding the worker like an on-site car navigation system. As you approach, the guidance display becomes finer, and when you reach the target point you are notified by sound and screen display, so even people without surveying knowledge can place piles at the correct positions without hesitation. Because each person can set positions using their own smartphone, there is no need for multiple people to share surveying and piling tasks as in conventional methods. The simplicity of requiring only a pocketable device plus a smartphone increases site mobility and makes it easy for anyone to use. Since digital guidance can guarantee accuracy without relying on the intuition or experience of skilled workers, it is also beneficial for skill succession and human resource development. The training burden at introduction is small, and site staff can start using it after a short operation briefing.

Cloud Integration for Data Sharing

LRTK integrates with cloud services, making data management smooth. If you upload a coordinate list of pile positions extracted from design drawings to the cloud in advance, you can call it up instantly on the site smartphone and use it for navigation. Conversely, coordinates measured and recorded on site and geotagged photos are saved and shared in the cloud in real time, eliminating the need for post-return data organization or double entry. With the latest design information always synchronized with the site, you can prevent construction errors caused by miscommunication or overlooking paper drawings. For example, if a design change occurs midway, corrected coordinates can be shared instantly via the cloud, reducing the risk of constructing based on outdated drawings. Because stakeholders can share information on the cloud, immediate confirmation of completed pile positions and reflection in as-built management can also be done quickly.

Intuitive Guidance with AR Navigation

LRTK also features navigation using AR (augmented reality). By displaying the site through the smartphone camera and virtually overlaying design target points and structure lines on the real scene, workers can intuitively share recognition of “this is the specified location.” For example, you can project a design model or coordinate data uploaded to the cloud in AR on site and display virtual flags or marks at pile positions. Using the AR marking-out function, you can visualize design lines on the smartphone screen without drawing lines on the ground, allowing even inexperienced workers to proceed with construction at accurate positions and orientations. Visual guidance via AR also makes verification easier and contributes to further reduction of human error.

How to Use LRTK Coordinate Navigation

Below is a step-by-step explanation of the basic flow of reverse setting-out work using LRTK.

• Preparation of design data：Extract coordinate data for pile positions and other required points from the construction drawings in advance and upload them to the LRTK cloud (SIMA format or CSV format supported). By preparing the coordinate list needed on site in the cloud beforehand, you can call it up smoothly after starting work.

• Equipment setup：On site, power on the LRTK terminal, attach it to the smartphone, and launch the dedicated app. Wait several tens of seconds for the satellite to be acquired and the RTK status to become Fix; then centimeter-level positioning with cm level accuracy (half-inch accuracy) will begin. Once positioning accuracy stabilizes, navigation is ready. LRTK also offers a dedicated lightweight monopod pole, and in situations requiring more stable positioning the terminal can be attached to the end of the pole and placed on the ground.

• Start navigation：Select the coordinate of the target pile in the app and start the “Go to this coordinate” function. An arrow (direction) and a numeric value (distance) are displayed in real time on the smartphone screen, so follow those guides and move toward the target direction. For example, it may display “northeast by 2.35 m (7.71 ft),” and the number will get smaller as you approach. If needed, switch to AR mode to display the target point as a marker on the smartphone camera view.

• Piling / marking：When the screen display is nearly zero and you have arrived at the target point, mark that point and drive the pile. You can accurately determine the pile location alone without the conventional step where a surveyor aims and a worker sets the pile.

• Record results：After all piles are installed, measure the coordinates of each pile with LRTK and save them to the cloud. If you take site photos with your smartphone, they are automatically uploaded to the cloud as geotagged construction records. This enables immediate sharing of as-built information with the office after piling is completed, speeding up inspection and approval processes.

On-site Case Studies: Dramatic Reduction in Piling Errors

Actual sites that introduced LRTK report remarkable effects in reverse setting-out work. At one mid-sized building construction, LRTK coordinate navigation was used to set out 50 foundation piles. Previously, a surveying team (2–3 people) took more than half a day to set up batter boards and mark pile centers, but at this site the site supervisor himself visited each point with a smartphone in hand and completed position setting for all piles in just a few hours. Moreover, deviations of each pile’s installed position averaged within 1–2 cm (0.4–0.8 in), and there was zero rework. Work time was reduced to less than half compared with conventional methods, and there were no problems caused by piling errors. Construction managers in charge said that uncertainty in position setting disappeared and gave them peace of mind, and that even sites without a resident experienced surveyor could proceed with piling confidently.

At another civil engineering site, coordinate guidance with LRTK greatly reduced the need to set up batter boards, dramatically improving the efficiency of surveying and marking-out processes. Reports indicate that using the coordinate navigation app increased position-setting speed by 1.5 to 2 times compared with conventional methods, contributing to reduced worker burden and shorter schedules. Some sites combine AR-based digital marking-out and perform construction line checks with almost no physical batter boards. For example, in roadworks, using LRTK’s AR function to display shoulder or structure completion positions on the smartphone screen can reduce the effort of setting batter boards while ensuring accurate shape checks. Additionally, LRTK coordinate navigation is powerful for restoring reference points or boundary piles that are hidden by vegetation and cannot be visually confirmed. By calling up known point coordinates saved in the cloud and projecting their positions with AR, markers buried in vegetation can be found efficiently. Surveyors no longer need to search through brush for long periods, and point restoration work has been greatly simplified.

Main benefits of introduction:

• Dramatic reduction in piling errors：Accurate position setting with coordinate navigation prevents construction errors and rework

• Increased work efficiency：Surveying that previously required multiple people becomes unnecessary, greatly shortening position-setting time

• Labor and effort savings：One person can perform piling work, alleviating shortages of skilled workers and labor cost issues

• Improved quality and management：Survey data centralized in the cloud enables immediate information sharing and ensures construction quality

• Improved safety：Reducing marking-out work in hazardous areas lowers workers’ safety risks

• Cost reduction：One device can be used for multiple purposes, making it more economical than acquiring multiple dedicated surveying instruments. Also, by internalizing surveying work that was previously outsourced, cost reductions can be expected

In fact, LRTK is beginning to be used across a wide range of sites, from major general contractors to small and medium-sized construction firms, surveyors, and infrastructure managers, regardless of scale. As a result, digitization of positioning and measurement work and labor-saving via digital technology are steadily progressing beyond just reverse setting-out. There is also a trend to combine machine guidance on excavators and other heavy equipment equipped with RTK-GNSS, using the high-precision coordinates obtained by LRTK for automatic control of machinery. This enables excavation and embankment work to proceed to the specified shape without installing batter boards, contributing to improved safety and productivity. The spread of these smart surveying technologies is expected to accelerate further.

Conclusion: The Future Opened by DX in Reverse Setting-out

Finally, coordinate navigation technology using LRTK can be said to be a solution that brings a revolution to reverse setting-out work at construction sites. It is a groundbreaking presence that rewrites the conventional wisdom of reverse setting-out that relied on manpower. High-precision positioning and intuitive navigation bring piling errors as close to zero as possible, enabling anyone to perform accurate position setting in a short time. With labor shortages worsening, the ability to perform surveying and piling efficiently by a single person is a major advantage and will be highly useful in construction management environments where DX (digital transformation) is required. This also aligns with the Ministry of Land, Infrastructure, Transport and Tourism’s promotion of ICT construction and i-Construction and strongly supports site DX. By embracing the latest LRTK technology rather than clinging to conventional methods, reverse setting-out DX that achieves both improved construction accuracy and operational efficiency is advancing at the front lines of sites. As LRTK evolves further, stronger integration with heavy equipment automatic control and BIM/CIM data is expected to accelerate construction DX even more. This new reverse setting-out method, combining accuracy, efficiency, and safety, is likely to become the standard. A future without reverse setting-out errors is already near. Let us actively utilize digital technologies like LRTK and further promote DX on site.