Drive stakes immediately from drawing coordinates! Streamline reverse-staking operations with smartphone high-precision coordinate guidance

Pile-driving work at construction sites (setting pile positions and reverse-driving) is an important process that requires accuracy and efficiency. In particular, deviations in pile centers directly affect the overall quality and safety of structures, and strict standards for high-rise buildings and bridges do not allow even deviations of a few millimeters (a few tenths of an inch). However, conventional methods have required time and manpower for setting pile centers and reverse-driving, with survey specialists repeatedly checking positions as a matter of course. In this article, we introduce high-precision coordinate guidance using smartphones and LRTK that overturns this conventional on-site practice. It reproduces the coordinates on drawings directly in the field, and provides a detailed explanation of the new system that enables anyone to accurately indicate pile-driving positions and its effects.

On-site Challenges: Issues with Conventional Pile Driving Operations

Traditional pile-driving (surveying and marking-out) work has been accompanied by numerous challenges. The main issues are as follows:

• Requires manpower: High-precision pile positioning requires surveying using a total station (TS) and a prism, and the work was typically performed by two-person teams (instrument operator + prism holder). Placing two people in narrow excavation pits or at heights is a significant safety burden, and at sites with labor shortages it became difficult in itself to secure a surveying crew.

• Reliance on experience and intuition: In confined urban sites and environments with poor visibility, dimensions often had to be remeasured from control points multiple times, and ultimately one had to rely on the instincts and experience of veteran surveyors. The work tended to become person-dependent, creating a risk of variation in accuracy and efficiency depending on the skill of the person in charge.

• Time-consuming and laborious: Each time a TS was set up, time was required for instrument installation, leveling, and aligning to benchmarks, and reconfiguration and recalculation were necessary whenever basements or floors changed. Even when stretching chōhari (chōhari: the reference alignment string), space constraints prevented large-scale installation and caused frequent fine remeasurements. Inefficient procedures accumulated even for positioning a single pile, tending to put pressure on the overall construction schedule.

• Risk of human error: Slack in measuring tapes, misreadings, and transcription errors of coordinate values cannot be eliminated entirely. Marks on the ground can be erased or shifted by the passage of heavy machinery, leading to re-surveying and re-marking each time. In pile-driving work that requires precision, such minor mistakes can lead to significant rework.

As described above, the triple constraints of time-consuming, labor-intensive, and prone to errors have long plagued conventional pile-driving surveying, hindering productivity improvements at construction sites. In addition, the aging of surveying technicians and a shortage of personnel have become serious issues, and construction being halted while "waiting for surveying" was not uncommon.

Staking work anyone can do with a smartphone and high-precision coordinate guidance

So how can we solve these issues? One answer is stake-out coordinate guidance that combines smartphones and high-precision GNSS positioning technology. Today, by attaching an ultra-compact RTK-GNSS receiver to a smartphone such as an iPhone, it has become possible to measure positions with centimeter-level accuracy (half-inch accuracy). This technological innovation is making a world where stake-out positioning that used to require multiple people can be completed by a single person a reality.

*The compact RTK-GNSS receiver "LRTK Phone" mounted on a smartphone. Pocket-sized, a single unit can handle everything from surveying to stakeout guidance. On-site, when set on a dedicated pole (monopod) and used, it provides stable positioning like conventional surveying equipment.*

LRTK Phone is a pocket-sized, all-purpose surveying device developed by a startup from Tokyo Institute of Technology. A receiver weighing only approximately 165 g and about 1 cm (0.4 in) thick attaches to a smartphone, and using a dedicated app, surveying that previously required several kilograms of equipment can now be completed with just a single smartphone + a small device. Using satellite positioning with the RTK (real-time kinematic) method, high-precision global coordinates can be obtained in real time, with horizontal positions accurate to within a few centimeters (within a few inches). The app automatically handles complex setup and calculations, so you can start using it immediately without specialized knowledge.

Using this smartphone surveying tool, you can transfer coordinates from drawings directly to the field. For example, if you upload the coordinate data for stake positions shown on the design drawings to the cloud in advance, on site you can reach the target position simply by following the guidance on the smartphone screen. There is no longer a need for experienced surveyors to measure positions with tape measures in hand. Because anyone can intuitively determine stake-driving positions, even sites suffering from labor shortages can drastically reduce wasted time waiting for surveying.

Also, because this system uses GNSS satellite signals, ensuring line-of-sight (visibility) like with a total station is not required. Positioning is possible anywhere the sky is open, unaffected by obstacles or the presence of nighttime lighting (even outside of communication coverage, positioning can continue by using correction information from Japan's Quasi-Zenith Satellite "Michibiki"). In other words, from large development sites to mountainous areas, stake positioning work can be carried out with high mobility.

High-precision coordinate guidance using smartphones and LRTK is precisely realizing a world of "instant staking from drawing coordinates." Even without relying on the skills of veteran craftsmen, a single worker with a smartphone can complete the staking work—such a new construction style is beginning to spread at worksites.

Features and Strengths of LRTK Coordinate Guidance

Using a smartphone plus LRTK for stake-driving coordinate guidance offers various advantages not found in conventional methods. Here, we introduce three main strengths.

Apply drawing coordinates directly to pile positions

Using LRTK coordinate guidance, you can directly reflect the coordinate values from the design drawings to the stake positions on site. Traditionally, manual work such as calculating offsets from control points or measuring from the intersection of batter boards with a tape measure was required, but with LRTK the system automatically navigates to pre-registered numeric coordinates, eliminating the need for complicated on-site calculations and measurements. This prevents human misreading and calculation errors, allowing stakes to be driven exactly where the design specifies. Because all you need are the XY coordinates on the drawings, a major advantage is that there is no loss of information in the handover from design to construction. The data synchronizes to a smartphone app via the cloud, so even if there are design changes, you can be immediately guided to the new coordinates.

Intuitive Positioning Guidance Using AR Display

The LRTK app includes an AR (augmented reality) feature that can overlay stake position markers and models onto the camera view. This makes it easy for people without surveying expertise to visually recognize the exact points where stakes should be driven. For example, virtual stakes and arrows appear on the smartphone screen, allowing workers to identify points without hesitation by comparing them with the real scene. Even when changing viewpoints and walking around, the AR markers remain fixed at their designated positions on the ground, so there is no worry about them shifting or being lost. Furthermore, even in locations where physical stakes cannot be driven (concrete pavement or off-site points), it is possible to place virtual stakes in AR and continue to indicate the positions. This high visibility makes on-site sharing and verification significantly smoother.

Pile-driving work that can be completed by one person

The biggest advantage is that the pile-driving positioning work can be completed by a single person: pile-driving positioning work can be completed by a single person. By introducing LRTK, surveying work that used to require 2–3 people can be handled solo, greatly contributing to labor reduction on site. If you mount a smartphone and receiver on a dedicated monopod (pole), the user themselves becomes the prism and, by following the guidance on the smartphone screen to stand at the survey point, both surveying and pile-driving guidance are completed. Flexibility in personnel allocation increases, allowing manpower to be redirected to other tasks, and there are also safety benefits because it eliminates the need to squeeze multiple people into confined spaces. Also, because results can be obtained with simple operations, dependence on specific workers is easily eliminated, allowing stable quality to be maintained even in the absence of veterans. By using a smartphone app that anyone can operate, the situation of “only that person can do this task” is removed, and it is expected to bridge the skills transfer gap.

Procedure for guiding stakeout coordinates using the LRTK app

Now, let's look at the basic workflow for guiding and marking stake positions using a smartphone and LRTK. The operation is intuitive, and almost no special equipment preparation is required.

• Preparation of design coordinate data: Register in advance the coordinate values of the points where piles are to be driven (reference points and the position coordinates of structures) in the cloud-based LRTK system. You can simply upload a coordinate list from CAD data (such as CSV or GeoJSON formats).

• On-site setup: Upon arrival, attach the LRTK receiver to the smartphone and turn it on. If necessary, fix the phone to a monopod (pole), hold it vertically, and use it like a surveying rod. Launch the LRTK app to begin positioning your current location, and by receiving correction information make the device capable of positioning with cm level accuracy (half-inch accuracy).

• Select the point to guide to: Select the target coordinate point in the app. Specify the desired point from the map or coordinate list, and tap the "Navigate to this coordinate" button to start navigation.

• Start of coarse guidance: Move according to the guidance displayed on the smartphone screen. The screen displays the direction and approximate distance to the target point, and a compass or arrows will guide you with prompts like "xx m (yy ft) ahead". The worker holds the smartphone and follows the instructions to approach the destination.

• Fine guidance and positioning: When you approach the target coordinate, the app switches to a more detailed guidance mode. When the remaining distance is on the order of several tens of centimeters (several tens of inches), the display zooms in and arrows and guide circles allow for centimeter-level alignment (half-inch accuracy). If necessary, switch to AR camera mode and project a virtual pile marker onto the ground through the smartphone screen for final confirmation.

• Installing/marking the pile: When the phone's instruction reaches around "±0 cm (±0 in)" and you've reached the designated position, drive the pile into that spot (or mark it with paint, etc.). Thanks to LRTK's high-precision positioning, the pile will be positioned exactly as shown on the design drawings. Finally, record the point in the app as "Installation complete" and the pile-driving guidance task is finished.

*Example coordinate-guidance screens of the LRTK app. The left image shows how it navigates the worker by displaying the direction and distance to the target point, and the right image shows the screen when it switches to precision-guidance mode near the target point, performing alignment to centimeter-level accuracy (cm level accuracy, half-inch accuracy). Its intuitive UI lets even beginners reach the point without getting lost.*

The workflow is very simple: 'select the data and start guidance → move as instructed → place the stake at that location'. The app displays the error between the current position and the target coordinates in real time, making fine adjustments easy. If necessary, you can save the coordinates measured at each point and later perform a comparison of measured coordinates and design values in the cloud. It eliminates the hassle of taking notes in a paper field book, and the ability to record and share with a single button is another attractive efficiency.

Benefits of Implementation: Improved Accuracy and Labor Savings Transform the Workplace

Introducing smartphone high-precision positioning for pile-driving coordinate guidance brings the following effects to the site.

• Labor savings: Since one person can carry out everything from surveying to staking out, this directly leads to substantial reductions in manpower and shortened work times. Waiting for surveying crews is reduced, and pile-driving preparations can proceed in parallel with other construction work, contributing to overall productivity gains. The burden of transporting and setting up heavy equipment is also eliminated, achieving physical labor savings.

• Eliminating dependence on individuals: Because anyone can perform high-precision pile-driving by following the smartphone app’s guidance, it breaks the situation of relying entirely on specific veteran workers. By enabling standardization of work without depending on experience or intuition, quality variability between personnel is reduced, making it easier to address shortages of skilled workers and generational transitions.

• Improved accuracy: Positioning accuracy with RTK is dramatically higher than conventional manual methods, minimizing errors between survey points and cumulative drift. Because management is always in global coordinates, unification of surveying standards is also easy, making inconsistencies unlikely even when multiple teams work concurrently. As a result, deviations in pile positions and construction defects are prevented in advance, reducing rework in later stages and ensuring the quality of structures.

Another benefit not to be overlooked is the ease of recording and sharing through digitization. Survey data and stake positions acquired with LRTK can be synchronized to the cloud instantly, allowing you to monitor on-site progress in real time from the office and share as-built data with stakeholders. Secondary effects such as improved efficiency in report preparation and inspections can also be expected.

Summary: Revolutionizing pile-driving work with simplified surveying enabled by LRTK

The pile position layout work that traditionally required manpower and time is being dramatically transformed by the introduction of simplified surveying using smartphones and LRTK. By reproducing the drawing coordinates directly on site and intuitively checking them with AR, a single person can accurately install piles — this new method directly addresses the shortage of survey personnel and leads to a dramatic improvement in construction efficiency. On sites that have actually adopted the LRTK Phone, comments such as “There is less waiting for surveying, giving us more leeway in the schedule” and “Even non-veterans can be trusted to handle pile setting with confidence” are beginning to emerge.

The key point is that advanced surveying becomes possible with the convenience of only a smartphone being needed. Pocket-sized devices and apps have ushered in an era in which each field worker can immediately assume the role of a surveyor. If you are pursuing improvements in the accuracy, speed, and labor savings of stakeout work, the option of high-precision smartphone coordinate guidance is now indispensable.

If your site is feeling the limitations of conventional methods, why not revolutionize pile-driving work by introducing simple surveying with LRTK? This solution, which combines state-of-the-art RTK technology with the convenience of a smartphone, should greatly contribute to improving productivity and ensuring quality at your site. Experience the new pile-driving style and let’s realize a future where anyone can perform pile driving.