Ensure pile driving layout accuracy with your smartphone! The capabilities of LRTK coordinate guidance

When performing pile layout staking (setting out) on site, nothing is more important than the accuracy of placing points exactly where the design specifies. Even a deviation of just a few centimeters (a few in) can affect the position or elevation of structures and lead to rework or serious problems. However, achieving such high-precision pile layout (marking out) with conventional methods is not easy.

What is attracting attention now is LRTK coordinate guidance, which combines a smartphone with the latest GNSS technology. This makes it possible for even non-expert surveyors to secure centimeter-level positioning with a smartphone in hand. In this article, we explain the challenges of layout staking and how LRTK addresses them, and introduce the capabilities of coordinate guidance, AR display, and cloud synchronization that anyone can use with a smartphone.

Required accuracy for layout staking and traditional challenges

In construction site pile layout staking (marking out), it is necessary to mark positions and elevations exactly as shown on the design drawings to determine the positions for piles and structures. This work, known as “reverse staking,” often requires millimeter-level accuracy. If the foundation pile position is off by even a few centimeters (a few in), mismatches with the superstructure can occur, and in the worst case this may lead to insufficient bearing capacity or the need to redo construction. In other words, securing layout staking accuracy is essential for quality control and safe construction.

However, achieving centimeter accuracy in layout staking with conventional techniques involved significant burden. For example, when using optical surveying instruments such as total stations, a two-person team including a skilled operator is required for setup and backsighting. The equipment is large and heavy and cumbersome to carry, requiring repeated setup on each site, which is inefficient. Also, general-purpose handheld GPS receivers have positioning errors of around 5–10 m, far from the few-centimeter accuracy required for pile layout. Therefore, when high accuracy was required, it was necessary to prepare expensive RTK-GNSS receivers and base stations and have surveyors with specialized knowledge use real-time correction information for positioning.

As labor shortages and aging of skilled workers progress in the construction industry, maintaining such time- and cost-consuming surveying methods has become difficult. To perform pile layout without compromising accuracy with limited personnel and budget, more accessible and high-precision new technologies were needed.

RTK-class positioning accuracy realized by LRTK

LRTK has emerged as a solution to these challenges. LRTK is a system consisting of a small high-precision GNSS receiver device and a smartphone app, which is attached to a smartphone for use. Developed by a startup originating from Tokyo Institute of Technology, attaching this LRTK device to an iPhone or iPad instantly turns a pocket-sized smartphone into a surveying instrument capable of centimeter-level positioning (half-inch-level).

Compared with procuring conventional optical instruments or survey GNSS equipment, LRTK drastically reduces the required hardware because only a smartphone and a small device are needed, thereby significantly lowering introduction costs. The burden of purchasing expensive dedicated equipment for multiple personnel is reduced, making it easier to incorporate into routine construction management tasks.

LRTK supports the RTK-GNSS (real-time kinematic) method and achieves positioning accuracy comparable to dedicated instruments. By using a high-performance multi-frequency antenna and Japan’s quasi-zenith satellite “Michibiki” distribution of the centimeter-level augmentation service (CLAS signal; half-inch-level), or network RTK via the internet (Ntrip), it is possible to obtain position coordinates with errors within a few centimeters (a few in) anywhere. In open areas, turning on the power and waiting tens of seconds typically brings the fix solution to convergence, enabling outstanding on-site accuracy of about ±2 cm (±0.8 in) horizontally and within ±4 cm (±1.6 in) vertically. This accuracy rivals that of conventional optical surveying and expensive GNSS equipment and fully meets the accuracy requirements for pile staking surveys. LRTK also natively supports Japan’s plane rectangular coordinate system and automatically calculates geoid height (height correction) simultaneously with measurement. The acquired coordinate values can be used directly in design drawings and CAD software, eliminating the need to worry about cumbersome coordinate transformations.

Although small and lightweight enough to integrate with a smartphone, LRTK can perform continuous positioning for about 6 hours on its internal battery. You can use it on site for more than half a day without worrying about battery depletion, and it can be operated while charging from a mobile battery if necessary. This portability and endurance make it realistic for workers to keep an LRTK in their tool pouch and take it out for immediate positioning and staking when needed, realizing the concept of “one device per person” as a surveying tool.

Furthermore, it is notable that LRTK is an integrated system in which device, app, and cloud cooperate. The small device handles high-precision positioning, the smartphone app provides an intuitive UI and camera/LiDAR sensor integration, and cloud services support data management and sharing. For example, acquired positioning results and point cloud data can be saved and synchronized to the cloud from the app on the spot, allowing progress to be checked from the office. With LRTK’s integrated hardware, software, and cloud, on-site surveying tasks can be handled all-in-one.

Coordinate guidance on a smartphone: pile layout without getting lost

One of the strengths of the LRTK system is its intuitive coordinate guidance (navigation) function on the smartphone. If you enter reference points or the target coordinates for pile positions into the app in advance, when you approach those locations on site the smartphone screen displays an arrow and distance to guide the user. It’s essentially a car-navigation system for surveying: simply follow the instructions to arrive precisely at the point without getting lost. This allows construction managers without surveying expertise to reach the instructed coordinates on their own and perform tasks such as driving piles or marking out single-handedly.

Traditionally, a surveyor would use a total station to indicate direction and distance while an assistant followed those instructions to drive piles, a two-person operation. With LRTK coordinate guidance, pile layout staking can be completed with a single tap on a smartphone. Attach the device to a monopod or pole and level it with a bubble level, and you can achieve centimeter-level placement simply by moving while holding the smartphone. Because the operator can work while looking at the smartphone screen, deviations from the target are immediately correctable, reducing unnecessary rework. As a result, not only does work efficiency improve, but labor reduction and decreased human error due to fewer personnel are significant benefits.

Intuitive confirmation of target positions with AR display

A notable smartphone-specific feature is visualization via AR (augmented reality) display that works with the camera. The LRTK app can import coordinate data and 3D models from design drawings and overlay them on the real-world site view. For example, projecting pile positions or finished-line outlines onto the actual ground or buildings via AR makes it immediately obvious where to set piles. With virtual markers appearing at layout points, the task that previously required cross-referencing drawings and estimating positions becomes much easier.

Applying AR further allows instant verification on site of whether a completed structure matches the design position and elevation. By overlaying the pre-registered design model with point cloud data or positioning results obtained by LRTK, any deviations become visible immediately. For example, after concrete placement, color-coding the error from the design elevation makes it possible to instantly identify areas that are “○ cm higher/lower than specified” (a few centimeters (a few in)). Using AR visualization in this way contributes to accuracy verification of layout staking and prevents rework. Visualizing underground buried pipe routes and site boundary lines from drawings on the ground via AR can also help prevent damage during excavation and assist in boundary confirmation.

Cloud synchronization connects site and office for information sharing

LRTK’s power extends beyond hardware and app to integration with cloud services, making on-site information sharing highly effective. Data obtained through positioning and pile layout work can be uploaded to the cloud with a single tap. Uploaded location information and photos are automatically plotted on a map and stored in the cloud project. With an Internet connection, office staff and clients can view the latest site survey data from a browser, enabling real-time information sharing.

Cloud synchronization streamlines communication between the site and remote locations. For example, if you mark the pile location on site and immediately send the coordinates and photos to headquarters via the cloud, the responsible person can promptly check the as-built condition. There is no need to later re-enter hand-recorded numbers from paper drawings or carry data back on a USB stick. Because the most up-to-date data is centrally managed and always shared, this leads to error-free construction management and faster decision-making.

Labor savings and improved safety with one device per person

By introducing LRTK, on-site work efficiency and safety significantly improve. Pile staking surveying that used to require two people can now be completed by one, making it possible to handle sites with personnel shortages. The burden of carrying heavy equipment between measurement points is eliminated, reducing physical strain and near-miss incidents for workers. With a smartphone-based surveying tool always at hand, you can measure whenever needed, reducing waiting times and setup losses.

Moreover, the smartphone’s intuitive UI and guidance functions enable accurate staking work even without specialized skills. In situations that previously relied heavily on veteran technicians, younger staff can achieve equivalent results simply by following the app’s instructions, helping to close the skills-transfer gap. The Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiative emphasizes ICT utilization and labor-saving, and LRTK is an encouraging tool that supports such site digital transformation.

How to use LRTK coordinate guidance

Finally, let’s review the general steps for performing smartphone-based pile staking surveying with LRTK. The steps are simple, and even without surveying experience you can reproduce design coordinates on site using the following procedure.

• Device attachment: Attach the LRTK device to an iPhone or other smartphone with a single touch and turn on the power.

• Positioning preparation: Launch the dedicated LRTK app and receive satellite position information, waiting until high-precision positioning reaches the fix state (typically a few tens of seconds).

• Set target coordinates: Enter the coordinates of reference points or planned pile positions you want to guide on the app. You can also import design data (coordinate lists or CAD drawings) in advance.

• Start guidance: Activate coordinate guidance mode and move according to the direction and distance information displayed on the smartphone screen. Switch to AR mode as needed to verify the target position through the camera while approaching. (When using a pole with the LRTK attached, leveling with a bubble will stabilize accuracy.)

• Set out and record: When the arrow indicates the target and the distance approaches zero, drive the pile or mark the spot to complete the staking. The coordinates and site photos of the staked points can be uploaded to the cloud on the spot and shared with the entire team.

Conclusion: Dramatically improving layout staking accuracy with smartphone × LRTK

The new surveying method combining a smartphone and LRTK dramatically improves pile layout staking accuracy. With centimeter-level RTK positioning for precise coordinate placement, smartphone-based coordinate navigation anyone can use, AR-based spatial visualization, and cloud-based information sharing, a groundbreaking workflow that overturns conventional norms has been realized.

By utilizing LRTK coordinate guidance, the following effects on pile staking surveying can be expected:

• High-precision placement: RTK-GNSS enables positioning within a few centimeters (a few in). Reference point setting and marking out are reliable. Elevation can also be measured precisely, allowing confident installation of critical structures.

• Simple smartphone operation: An intuitive app UI makes it easy for anyone to use, and accurate guidance is possible without specialized knowledge. Complex formulas and technical jargon need not be considered, enabling younger staff to become immediately effective.

• AR visualization of the site: Design data overlaid on camera imagery lets you grasp target positions and elevations at a glance, preventing construction mistakes and oversights. Overlaying drawings and the site helps prevent construction errors and oversights.

• Real-time information sharing: Survey data and photos sync to the cloud instantly. Latest information is shareable between site and office so remote clients or supervisors can immediately understand site conditions and issue additional instructions or confirmations online.

• Labor savings and improved safety: Surveys are completed with fewer personnel and in less time. Heavy equipment transport is reduced, lowering workload and accident risk. Operations no longer need to rely entirely on experienced personnel, helping to address labor shortages.

• Versatile uses: High-precision 3D point cloud scanning and geotagged photo capture enable tasks beyond pile staking with a single smartphone. Digital measurement of various site scenes becomes possible, accelerating DX across construction management.

Truly, the era when an iPhone becomes a surveying instrument has arrived. The smartphone × LRTK combination enables anyone to easily perform reverse staking surveys without relying on master craftsman skills or expensive dedicated equipment, and its adoption is expected to grow. If you are a construction manager struggling to ensure pile staking accuracy, consider adopting this new approach on site. LRTK coordinate guidance will markedly improve the accuracy and efficiency of pile staking work and contribute greatly to safe and secure construction management. Why not take this opportunity to realize on-site DX and quality improvement with smartphone-based reverse staking surveying? The new era of staking accuracy has already begun.