Achieve pile-driving guidance with a smartphone! Zero construction errors with centimeter-level positioning (half-inch accuracy)

Table of Contents

• Traditional pile-driving work and challenges

• What is centimeter-level positioning with RTK-GNSS (centimeter-level accuracy, half-inch accuracy)?

• Mechanism for implementing pile-driving guidance using smartphones

• Advantages of smartphone-based pile-driving guidance

• On-site implementation procedures and accuracy management

• Benefits of LRTK implementation and use cases

• Frequently Asked Questions (FAQ)

Conventional Piling Work and Challenges

Piling work in civil engineering and construction projects is a critically important process that supports the foundations of structures. By driving piles into the positions and depths specified on the design drawings, the safety and stability of structures are ensured. However, conventional piling has had several challenges.

First, it is the labor involved in surveying and staking out pile positions. The positions where piles are to be driven are specified by coordinates on the drawings, but accurately identifying those positions on site required skilled surveying techniques. Typically, a team including surveyors used total stations and measuring tapes to measure distances from known control points and mark the ground. They installed wooden stakes or batter boards (chōhari) as reference marks, and heavy equipment operators relied on those stakes to install the piles. This optical surveying-based staking out was labor- and time-consuming, and under certain weather or terrain conditions the surveying itself could become difficult. Also, because it was done by humans, there was inevitably a risk of surveying errors and positional offsets, and even slight deviations could lead to later construction mistakes. If communication between the staking-out personnel and the heavy equipment operator was insufficient, miscommunication could also result in piles being driven in the wrong locations.

Next, safety issues cannot be ignored. Because the work of marking stake positions is carried out within areas where heavy machinery is operating, survey workers who get too close to the machines face a risk of accidents. In particular, placing marks to indicate stake positions on steep slopes or on muddy, unstable footing is extremely dangerous, and there were cases where it was physically impossible to drive stake markers. Also, on large-scale sites, machine guidance technologies have emerged that equip the heavy equipment itself with GNSS (satellite positioning) to automatically guide stake-driving positions, but because they require costly investment in dedicated equipment and systems, they have not been widely adopted at small and medium sites. As a result, many construction sites still face the challenges of ensuring accuracy of stake placement and low work efficiency.

Against this background, a new method that enables pile-driving work to be carried out more accurately, quickly, and safely has been sought.

What is centimeter-level positioning with RTK-GNSS

In recent years, a key technology attracting attention for solving this issue is centimeter-level positioning using RTK-GNSS. RTK (Real Time Kinematic) is a method of improving the accuracy of satellite positioning (GNSS, commonly known as GPS) by correcting errors in real time; by using correction information from a base station, positioning errors can be kept within a few centimeters (a few in). Put simply, it is an “ultra-high-precision GPS usable on-site”. While the accuracy of the GPS built into a typical smartphone is on the order of several meters (several ft), using RTK makes centimeter-level positioning (inch-level / in) possible, allowing design coordinates and actual positions to match exactly even on construction sites.

RTK-GNSS has dramatically changed pile-driving operations. If you input the drawing-specified coordinates of the pile-driving positions into the device, the RTK-enabled equipment can guide you to the indicated location, minimizing pile position deviations. Traditionally, surveyors used tape measures and transits to mark positions on site, but with RTK you can navigate directly to the target point on the design coordinates, allowing intermediate layout-marking work to be omitted. Even in the Ministry of Land, Infrastructure, Transport and Tourism–promoted “ICT construction” and “i-Construction” initiatives, improving construction accuracy through the use of GNSS positioning technology is an important theme. By incorporating RTK into pile-driving guidance, an environment is being created in which anyone can place piles with the same accuracy without relying on the intuition and experience of veteran workers.

Furthermore, in Japan the Quasi-Zenith Satellite System "Michibiki" has begun providing a centimeter-class augmentation service (CLAS), making RTK positioning easier to use even without installing dedicated base stations. By receiving correction data from the Geospatial Information Authority of Japan’s network of continuously operating reference stations via a communications line, or by receiving augmentation signals from the Michibiki satellites, stable cm-level positioning (half-inch accuracy) is possible anywhere in the country. With these systems in place, efforts to utilize RTK-GNSS’s high-precision positioning for pile-driving work have become practical at job sites.

How smartphones enable stake-driving guidance

A technology that has made RTK-GNSS even easier to use is smartphone-based stake-driving guidance. In recent years, compact RTK-GNSS receivers that pair with smartphones have appeared, enabling centimeter-level positioning that previously required dedicated equipment on smartphones. For example, simply attaching a dedicated small receiver to a smartphone or tablet instantly transforms it into a pocket-sized portable surveying instrument. With a device called "LRTK Phone" developed by a startup, simply attaching an approximately 125 g receiver to an iPhone enables centimeter-accuracy surveying, ushering in an era in which anyone on site can carry one high-precision GNSS terminal per person.

In a smartphone-based pile-driving guidance system, your current position and the target pile location are clearly displayed on a dedicated app. Even workers without surveying expertise can operate it intuitively, and by simply following the instructions on the smartphone screen they can reach the target point. For example, if you preload the installation coordinate data for the piles to be constructed into the app via the cloud, then on site you only need to select the scheduled pile number or point and navigation to that location will begin. The screen displays a real-time arrow indicating the direction to the destination and the distance, and the person in charge only needs to walk the site holding the smartphone and follow the guidance.

When you approach the target point, the display becomes more detailed, showing the remaining distance such as "○ cm (○ in)" and finally presenting a message like "Here it is!" to indicate the exact spot, so you can identify the precise pile-driving location without hesitation. It's like a car navigation system for construction sites. Even inexperienced newcomers can find the pile position without confusion, enabling highly repeatable construction that doesn't rely on experienced workers' intuition.

Also, AR (Augmented Reality) technology combined with a smartphone camera can strongly support pile-driving guidance. AR is a technology that overlays digital information onto real-world images. Familiar examples include smartphone-camera games that project characters onto the camera view, and map apps that display arrows over the camera feed to provide directions. In construction, this AR can be applied to overlay pile position data from design drawings onto actual site footage, visualizing on the screen instructions such as "Drive the pile here". For example, if you select the coordinates of a pile position specified on the drawings in an app, a virtual pile (AR pile) indicating that point will appear standing in the smartphone camera view. This makes it immediately obvious where to drive the pile even in dark areas or on wide vacant lots with no markers, simply by looking at the smartphone screen, so the exact point where the pile should be driven is clear at a glance.

Thus, the combination of RTK positioning × smartphones × AR is evolving guidance for pile placement into a new phase that could be called "pile-placement navigation." With high-precision positioning and AR guidance, the way it guides pile locations in real time on-site is truly a construction style of the future. It also supports cloud integration, allowing positioning results and construction data to be saved to and shared in the cloud on-site. This simplifies reporting back at the office and enables seamless data connections between the field and the office. The introduction of smartphone pile-placement guidance is expected to allow anyone to immediately set accurate pile positions and to dramatically improve productivity and accuracy on construction sites.

Benefits of Smartphone-Guided Piling

Piling guidance using a smartphone and RTK-GNSS offers many advantages compared with conventional methods. What is especially emphasized are four points: reduced manpower, speed, accuracy, and error prevention. Let's look at each in detail.

• Improved positioning accuracy and prevention of construction errors: By using RTK to provide centimeter-level accuracy (cm level accuracy (half-inch accuracy)), pile position deviations are almost eliminated. Because piles can be driven into the exact positions specified in the design drawings, performance degradation of structures and rework caused by misalignment can be prevented. It is especially effective for projects that require strict positional accuracy, such as high-rise buildings and bridges. Previously there was a risk that pile positions would shift due to human error, but digital guidance can significantly reduce construction errors.

• Improved work efficiency and faster construction: Compared with setting out by a surveying crew, work time is drastically reduced. For example, stake-positioning work that used to take half a day with conventional optical surveying instruments has been reported to be completed in about 1 hour with digital guidance using a smartphone and RTK. In one comparative experiment, stake setting with GNSS+AR was verified to take about 1/6 of the time of conventional optical surveying. Surveying tasks that previously required multiple people can now be carried out quickly with a minimal number of personnel, directly shortening overall construction schedules and improving productivity.

• Labor reduction and personnel cost savings: Because high-precision stake positioning can be performed without relying on experienced surveying technicians, it is easy to introduce even on sites with labor shortages. A single worker can carry a smartphone and perform stake-outs, allowing the reduction of multi-person teams that were previously required (a surveyor plus an assistant). As a result, this helps compress personnel costs, and the staff freed up can be redirected to other important tasks. Also, compared with high-precision surveying equipment that used to cost on the order of several million yen, smartphone-based GNSS receivers are beginning to be offered very inexpensively. Because initial investment costs can be kept down, small and medium-sized enterprises and small-scale construction projects can adopt them easily, and one-device-per-person deployment is realistic.

• Improved safety: Digital guidance reduces the need for people to work in hazardous locations. Using AR technology, locations that were previously dangerous to enter, such as steep slopes, high places, and waterfronts, can be checked from safe locations. Because guide personnel no longer need to give close-range directions around heavy machinery, safety for both heavy equipment operators and workers is enhanced. The physical burden on workers is also reduced, allowing them to carry out construction with greater peace of mind. As a result, this leads to reduced accident risk and strengthened safety management.

• Improved quality control and simplified recordkeeping: With smartphone guidance, location data and construction results are automatically recorded digitally. The exact coordinates and timestamps of each pile installation are stored in the cloud and can later be viewed in a list. Geolocation coordinates are also automatically attached to photos taken on site, providing evidence of which piles were installed at their designed positions. This makes post-construction quality inspections and report preparation easier, and allows objective data to be presented as supporting materials for clients and regulatory authorities. Because the data are digitized, omissions and entry errors are prevented, improving the reliability of quality management.

• Multi-purpose use (versatility): The introduced smartphone + RTK system is useful in situations beyond pile driving. For example, not only for pile position stakeout (layout marking), but when combined with the LiDAR capabilities of iPhone or iPad and photogrammetry, it can perform measurement of point cloud data for as-built management, locate buried structures (structures buried underground), and display overlays of 3D design models on site, making it applicable to a wide range of uses. Once this system is implemented, it will serve multifacetedly as an all-in-one tool for on-site DX (digital transformation). It contributes to site efficiency and visualization by, for example, scanning surrounding terrain between pile-driving guidance tasks to perform instantaneous volume calculations, or displaying AR renderings of the expected finished view to share with stakeholders.

As described above, the new technology that leverages smartphones and RTK brings together the advantages needed to achieve the ideal construction of "high accuracy, speed, and safety". Because it can collectively resolve issues that have traditionally been problematic—securing positioning accuracy, long work times, labor shortages, and safety concerns—expectations among on-site stakeholders are rising.

Procedures for On-site Deployment and Accuracy Management

Now, we will present the procedures for actually using this smartphone-based pile-driving guidance technology on site, and the key points to ensure accuracy.

1. Preparation of design data (preliminary stage): At the construction planning stage, prepare the design coordinate data for the piles to be installed. For example, compile a coordinate list of all pile centers in Excel or a similar format and upload it to a cloud system. This enables on-site personnel to immediately reference the construction location data in the app without having to spread paper drawings.

2. Equipment and app setup: When you arrive on site, attach a small RTK-GNSS receiver to your smartphone or tablet and launch the dedicated app. When you power on the receiver it begins receiving positioning signals from satellites and simultaneously acquires base station data and satellite augmentation signals to enable centimeter-level positioning (cm level accuracy (half-inch accuracy)). Typically, within tens of seconds after power-up RTK will be ready for high-precision positioning. The app screen displays the current coordinates and the RTK FIX state (an indication that the solution is stable), so confirm that positioning has stabilized before starting work.

3. Guidance to the stake location: If you select the number or name of the stake you want to be guided to within the app, navigation to that target point will start automatically. The screen displays the direction and distance to proceed, for example, "5 m (16.4 ft) to the northeast," so follow those instructions to move. When heading to a distant location, a large arrow indicates the general direction, and as you get closer it shows in detail how many centimeters (cm) remain. Just before the target point messages like "2 cm (0.8 in) to go" and "Here it is!" appear, and you finally arrive at the point that matches the design coordinates.

4. Position verification and marking: When you reach the indicated point, activate your smartphone camera and check the surrounding view on the screen. If you can see on the screen that a virtual stake (AR stake) is standing at the design-specified position, that is proof you are standing on the exact point; if the virtual stake appears misaligned with the real scene, the position is not yet correct, so make small adjustments. Once in the correct position, mark the ground or use spray paint for marking. If necessary, you can drive small marker stakes or pins into the ground to indicate the spot physically, but because AR stakes can substitute as markers you can keep this to a minimum. Also, when driving piles directly with heavy equipment, signal the operator “this is the position” and guide the pile driver to the correct location.

5. Accuracy verification and recording: After the piles have been driven into their designated positions, finish by taking photographs with a smartphone to record them. If you take the photos with an app, the exact coordinates and orientation information of the location will be automatically tagged to the photos and saved. Furthermore, that data is uploaded to the cloud in real time and can be immediately checked from an office PC. This allows you to later check how many centimeters (inches) each pile deviated from its design position. For example, if a supervisor later looks at the data in the cloud, they can objectively confirm that “all piles have been driven within ±3 cm (±1.2 in) of the design coordinates,” and this can be used directly as reporting material for the client.

By following the above procedure, even those who are not surveying professionals can accurately mark pile-driving positions on site. What matters is confirming at the outset that the instrument's positioning accuracy is stable. RTK-GNSS performs best in open-sky environments, so be mindful of satellite reception when there are tall buildings or trees nearby. Check the number of satellites captured and the FIX/Float status displayed on the app, and it is important to determine positions only after it has firmly reached a FIX solution (a state in which centimeter-level accuracy (cm level accuracy, half-inch accuracy) is secured). Also, if possible, it is reassuring to perform positioning on a known point (a point whose coordinates are known) before work to confirm that the instrument is correctly reflecting correction information. By keeping these points in mind, you should be able to proceed with pile-driving guidance on site using stable, high-precision positioning.

Implementation Effects and Use Cases of LRTK

At actual construction sites, the benefits of introducing smartphone + RTK–based high-precision pile-driving guidance have been reported one after another. Here, using the smartphone guidance system LRTK as an example, we introduce field use cases and the results achieved.

● Productivity improvement in foundation work: In the foundation pile installation of a certain building, the traditional method involved a team including a surveyor indicating pile positions with batter boards and pile markers, while the heavy equipment operator confirmed them visually during pile driving. After introducing LRTK, the workflow changed so that the site supervisor, smartphone in hand, could check and mark pile positions one by one alone and then instruct the heavy equipment operator by radio based on that data. As a result, the time required to set out pile positions at each location was drastically reduced, and the overall progress of the foundation work improved dramatically. The layout of all piles, which used to take half a day, was completed in a few hours, producing labor-cost reductions through reduced personnel. In addition, digital positioning records made it possible to show later as evidence (proof) that "each pile was constructed within a few centimeters (a few in) of the design position," which has smoothed explanations to the client. In terms of quality control as well, a high level of data-driven reliability has been ensured.

● Safe construction at hazardous locations: LRTK is being used at sites where anchor piles or civil engineering piles are installed on slopes, such as steep slope works and river levee reinforcement. Traditionally, to survey and mark pile positions on dangerous slopes, workers had to descend onto the slope wearing safety harnesses, which imposed a large burden and risk. Using LRTK's AR stake display feature, virtual stakes can be projected so their positions can be confirmed from below the slope or from a safe distance, allowing workers to avoid entering hazardous areas unnecessarily. At an actual site, an advanced method was also trialed in which a drone performed spraying paint from a drone to mark locations using the AR stake points displayed on a smartphone as a reference. As a result, they succeeded in drastically reducing manual surveying work on slopes, ensuring safety while significantly cutting work time and labor.

● Use in disaster recovery sites: At infrastructure disaster recovery sites, smartphone RTK has contributed to rapid surveying and stake-out guidance. In large-scale disasters, communication infrastructure and survey control points may be damaged, but LRTK can continue high-precision positioning even in areas outside communication coverage by receiving augmentation signals directly from Japan's satellite "Michibiki." In fact, there are cases where, when base stations and mobile networks were severed, LRTK devices performed positioning using only satellite augmentation and helped identify survey and stake-out locations at disaster sites. Because smartphone RTK equipment is small and easy to carry, it can be deployed immediately to sites where heavy machinery or large surveying instruments cannot be brought in, and its mobility and accuracy are highly valued in disaster response.

The implementation benefits derived from the above cases are summarized as follows.

• Significant improvement in accuracy: The guidance accuracy for driving piles to their designed positions has dramatically increased, making rework and repairs due to pile misalignment almost zero. Even projects that require strict precision can be reliably handled with digital guidance.

• Time savings: Surveying and positioning work has become overwhelmingly faster, contributing to a shortening of the overall construction schedule. Remarkable efficiencies have been demonstrated on site, such as reducing pile-marking work to one-sixth.

• Reduced manpower and cost savings: Survey staffing can be greatly reduced, helping to alleviate chronic shortages of skilled personnel and lower labor costs. Equipment costs are also low, so the initial investment burden is small, and the fact that it is easy to implement even on small-scale sites is highly valued.

• Dramatic improvement in safety: It eliminates the need to perform risky surveying in hazardous areas and reduces the risk of guidance personnel coming into contact with heavy equipment. Because work can always be done from safe zones, it reduces accident risk and offers major benefits for occupational safety and health.

• Enhanced quality control: Data-driven construction management becomes possible, allowing suppression of variability in as-built results. With construction records stored digitally, later inspections and reporting are faster and more accurate. Being able to demonstrate quality based on objective data also increases client trust.

• Promotion of on-site DX: High-precision pile-driving guidance serves as a foothold for digitizing other surveying, measurement, and construction management tasks. Once smartphone RTK is introduced, not only pile driving but various on-site measurements and AR applications become possible, greatly contributing to the digital transformation of the site.

Thus, smartphone-linked pile-driving guidance technologies represented by LRTK can be said to be a solution that brings to the worksite "accurate, fast, and safe construction." If you currently feel challenges in ensuring the accuracy of pile-driving work, labor shortages, operational inefficiency, or safety management, it is well worth considering the introduction of such cutting-edge technologies. Although they are advanced tools, they are simple to operate, and even first-time users will quickly find them to be reliable allies on site. By harnessing the power of cm-class positioning realized on smartphones (cm level accuracy (half-inch accuracy)), why not aim for "a worksite where anyone can drive piles accurately without mistakes"? With unmatched pile-driving accuracy and speedy construction, LRTK — a powerful partner that leads projects to success — will surely help pioneer the future of the worksite.

Frequently Asked Questions (FAQ)

Q1. Is centimeter-level (cm-level accuracy; half-inch accuracy) positioning really possible with a smartphone? A. Yes, it is possible. The accuracy of typical smartphone built-in GPS is several meters (several ft), but by attaching a dedicated RTK-GNSS receiver and using correction information, positioning with errors of a few centimeters (a few in) can be achieved. In practice, by utilizing Japan's public geodetic services (the Continuously Operating Reference Station network) and augmentation signals from quasi-zenith satellites, smartphones can achieve accuracy comparable to conventional surveying equipment. However, to obtain high accuracy, a good environment for receiving satellite signals and stable reception of correction data are necessary.

Q2. Can it be used without specialized knowledge or qualifications? A. No problem. The smartphone guidance system is designed to be intuitive and can be used without specialized surveying knowledge. The app displays an arrow and the distance to the destination, so you can identify the stake location simply by following the on-screen directions. The AR display also makes the spot to "place the stake" obvious at a glance, so beginners won't get confused. As long as you know the procedure for preparing coordinate data in advance, it is designed so that anyone can use it.

Q3. Can it be used in mountainous areas outside of cellular coverage? A. Yes, it is possible depending on the conditions. At sites without internet connectivity, RTK positioning is achieved by directly receiving wireless communication–based correction services provided by the country or region or augmentation signals from satellites. In Japan, even in mountainous areas or remote islands where mobile signals do not reach, if the QZSS Michibiki "CLAS" signal can be received, correction information can be obtained, enabling standalone centimeter-level positioning (half-inch accuracy). There have been cases where, even at disaster sites where communications infrastructure was unusable, smartphone RTK devices were able to continue high-precision positioning using satellite augmentation. However, positioning is difficult inside tunnels or building interiors where satellites cannot be received at all, so in those cases it is necessary to temporarily supplement with conventional methods.

Q4. How should positioning accuracy be verified on site? A. You can check it on the app. Many RTK-capable apps display indicators of current accuracy and satellite reception status (e.g., whether it is FIX, estimated error values, number of satellites). First, those should be in a good state (for example, displayed as FIX or RTK FIX). If you want extra assurance, before work you can try positioning at a known point and compare the obtained coordinates with the known values. After driving a stake, you can also measure the stake head again with the receiver and display the difference from the design value. LRTK apps also have functions to observe a point multiple times and calculate the average; for example, by positioning one point 60 times and averaging you can narrow the error down to less than 1 cm (<0.4 in), which is a useful tool for accuracy verification. In short, always check the app’s accuracy display and, if in doubt, double-check so you can be confident of the accuracy on site.

Q5. What equipment and preparations are required for implementation? A. Essentially, a smartphone (or tablet), an RTK-GNSS receiver, and the dedicated app and correction data are required. The smartphone does not need to be high-end, but it must be a model that can connect to the GNSS receiver. The RTK-GNSS receiver uses compact devices sold by manufacturers. As for obtaining correction data, you either access a regional reference-station network via the internet or receive satellite augmentation signals directly. Products like LRTK provide the receiver unit and a smartphone app as a set, and have a system that lets you log in to a cloud service to automatically retrieve correction data. Before implementation, the main thing to prepare is prior coordinate data (design values), and after acquiring the equipment you can start field use after a short initial setup. The ease of introducing and operating it in-house without hiring a specialist contractor is also an attractive feature of smartphone-based stake guidance technology.