Dramatic Reduction of Pile-Driving Errors with RTK AR! A New Method for High-Precision Guidance

In civil engineering and construction sites, even a slight deviation in pile-driving position directly affects the overall quality and safety of a structure. Installing the pile center with an accuracy of a few millimeters is required, but in complex site environments errors in pile positions and coordinate layout mistakes continue to occur. Attracting attention as a new method that drastically reduces these pile-driving mistakes and enables anyone to be guided to high-precision positions is “RTK AR.” This article explains in detail the mechanism of pile-driving guidance using the latest technology that combines RTK (high-precision GNSS positioning) and AR (augmented reality), as well as its implementation effects, operational points, and future possibilities.

Site challenges: impacts of pile-driving mistakes and precision requirements

In pile-driving work at construction sites, ensuring pile center accuracy (the accuracy of the pile’s center position) is extremely important. A single pile’s position shift can lead to distortion of the superstructure or defects in the frame. Especially in foundation work for high-rise buildings and bridge construction, strict standards set the allowable pile center deviation at a few millimeters. On site, survey technicians repeatedly verify positions before pile-driving and strive to reduce coordinate-guidance mistakes to nearly zero.

However, in practice, in narrow sites or environments with poor visibility, the disappearance of pile position markings and survey point errors tend to occur. For example, markings on the ground can be erased by heavy equipment traffic, or surveying lines of sight can be blocked by temporary enclosures or existing structures, requiring rework to re-establish positions. A single erroneous pile position can cause delays to the entire subsequent process or lead to rework, placing significant pressure on site managers to prevent pile-driving mistakes. Large effort is expended to eliminate human error, such as implementing a double-check system with multiple survey teams or having construction managers patrol sites to reconfirm markings. Even so, completely eliminating human error is difficult, and on site there is a growing concern: “How can we make pile-driving guidance more accurate and efficient?”

Conventional pile-guidance methods and their limits

Conventional pile-coordinate layout (stakeout) largely relied on the craftsmanship of experienced survey technicians. The general method first calculates pile positions from design drawing coordinates, then determines them from site control points using tape measures or optical surveying instruments (total stations, etc.), and marks them on the ground or structures. On wide, open sites, reference lines called cho-hari—strings and stakes—may be set around the perimeter, and offsets measured from their intersections to determine positions. However, in tight urban lots or projects including basement levels, it is difficult to deploy large-scale cho-hari due to space constraints, and positions must be remeasured frequently using known points or temporary columns as references.

High-precision pile position layout requires total stations (TS) and prisms, but this method also has time and manpower constraints. Setting up a TS requires ensuring sufficient lines of sight within the site and aligning instrument and back-sight points. As underground structures increase, the instrument must be repositioned and recalculated from known points. TS surveying usually requires a two-person team (one operating the instrument and one holding the prism at the survey point). Placing personnel in narrow excavation pits or at high elevations poses safety burdens, and surveying cannot be performed efficiently with too few people.

Also, in conventional methods, the reliability of the markings themselves is limited. Paint marks or wooden stakes tend to fade or shift as construction progresses, leading to frequent re-marking. Manual work inevitably entails human errors. For example, slack or misreading of measuring tapes, transcription errors in coordinate calculations, and other small oversights can cause significant position deviations. In short, conventional pile-guidance methods face threefold limitations—time-consuming, labor-intensive, and prone to error—which become bottlenecks on sites demanding strict precision.

A new high-precision guidance method using RTK AR

As a trump card to solve these challenges, pile-guidance using RTK AR has emerged. RTK AR is a new method that combines RTK, a high-precision positioning technology using GNSS (Global Navigation Satellite Systems), with AR display on smart devices to provide on-site position guidance.

RTK positioning improvement: RTK (Real Time Kinematic) is a technology that obtains centimeter-level positioning accuracy by receiving satellite signals simultaneously at a base station (reference point) and a rover (the worker’s device) and correcting errors from the observation differences between them in real time. Traditionally, RTK required dedicated large GNSS receivers and radio equipment, but recently compact high-performance GNSS antennas have enabled RTK positioning on smartphones and tablets. Even without installing a base station, using network RTK correction information over the internet (for example, a network of electronic reference stations) or Japan’s Quasi-Zenith Satellite System “Michibiki” high-precision augmentation service (CLAS) allows a rover device alone to achieve positioning accuracy from several centimeters to several millimeters. This era allows a worker’s smartphone to function as a high-precision surveying instrument.

Intuitive coordinate guidance via AR display: Even if RTK provides high-precision current position information, an easy-to-understand presentation method is necessary to utilize it for on-site guidance. The device’s AR navigation function is useful here. Using a dedicated app, target points from the design drawings and arrow markers for guidance are overlaid on the real-site view seen through the camera. For example, selecting the pile coordinate data registered in the cloud and starting navigation causes the smartphone screen to display the direction arrow and distance to the target in real time. The worker simply walks in the direction indicated by the on-screen arrow, and as the distance approaches zero it becomes intuitive that they are approaching the target coordinate. Near the target, the arrow rotates subtly to prompt fine adjustments, and by moving the device as instructed the worker can reach the target position with an error of a few centimeters or less. Without conscious awareness of complex survey calculations, simply “following the on-screen guidance” allows accurate placement at the pile center—this is a revolutionary system that differs markedly from traditional pile-guidance that relied on the intuition and experience of skilled workers.

With AR, positions can also be indicated where physical marking is impossible. For example, on floors covered with concrete or in hazardous areas that are difficult to enter, a virtual pile (AR pile) can be placed on the smartphone screen to indicate the location, enabling identification of points away from safe areas. In some cases, for remote or steep locations that surveyors cannot physically enter, coordinates can be obtained from photos and a virtual pile projected later for on-site confirmation. RTK AR technology is an innovative solution that opens the way for pile-guidance under difficult conditions previously impossible to handle.

Main effects of introducing RTK AR

Introducing RTK AR for pile-guidance on site yields the following notable advantages compared to conventional methods.

• Dramatic improvement in work efficiency: RTK AR navigation significantly shortens the time required for pile stakeout. For example, one comparison reported that using a GNSS-based AR pile system reduced the time required for survey point guidance to about 1/6 of that for conventional optical surveying stakeout. Where stakeout once required a two-person team and half a day, RTK AR can allow a single person to complete the task within a few hours in many cases. Because many points can be guided continuously while moving, the number of points processed per day increases, directly contributing to shorter construction periods and acceleration of schedules.

• Improved pile center accuracy and reduced errors: RTK positioning itself delivers high accuracy—often below several centimeters—so pile center deviations can be minimized. In addition, the visual guidance from AR greatly reduces the room for human error. Previously, operators and workers determined construction positions based on marks made by surveyors, but with RTK AR users are directly navigated to digital target coordinates, eliminating transmission losses and reading errors. If the pile-driving machine is guided to the specified position according to the on-screen instructions, pile installation can match the design coordinates. Human errors that frequently occurred on site—such as missed or mistaken markings—are dramatically reduced because the same AR guide is shown to everyone.

• Labor savings and improved safety: RTK AR enables surveying and guidance tasks that once required multiple people to be completed by a single person, saving substantial human resources. In the construction industry, which suffers from severe labor shortages, labor savings directly improve productivity. A further benefit from single-person surveying is that fewer workers need to enter areas where heavy machinery is operating, reducing safety risks. Stakeout work at heights or deep excavations is minimized, and AR guidance from a safe, distant area reduces fall-risk and lessens workers’ physical burdens.

• Enhanced data recording and quality control: RTK AR systems automatically record guidance results and error information for each survey point as digital records. For example, logs can store coordinate errors at reached pile positions and the time taken for guidance, allowing construction managers to verify workmanship later or save it as a quality record. There is no need for the traditional manual process of writing notes in paper fieldbooks and later cross-checking. If a mistake occurs, data history makes it easier to trace the cause and use findings to prevent recurrence. Thus RTK AR contributes not only to surveying efficiency but also to improved management through visualization of construction quality.

Application of AR to as-built management and as-built comparisons

RTK AR technology is powerful not only during pile-driving but also for as-built management and inspection of finished work. Traditionally, inspecting as-built conditions (the shape and dimensions of completed structures) required comparing as-built drawings with the site and marking nonconforming areas for rework. If as-built measurements are taken with RTK-capable devices, the acquired point cloud and coordinate data inherently have centimeter-level accuracy (half-inch accuracy), enabling automatic comparison without having to align the measured points to the design 3D model. For example, on the cloud you can compare the design model with the measured point cloud to create a heatmap that color-codes deviations, download that to a tablet, and overlay it on the site view in AR. Simply pointing a smartphone or tablet at the site lets you immediately see which parts of the construction match the design and where there are excesses or shortfalls, enabling you to identify spots requiring repair or additional work on the spot.

This AR-enabled immediate as-built comparison drastically speeds up inspection and rework. Previously, measurement data had to be brought back to the office for analysis, problematic areas marked on drawings, and then re-located on site in an inefficient cycle. Being able to directly confirm “design vs. site differences” in AR makes it possible to complete corrective work on the same day. There is also expanding use of projecting 3D design data (BIM/CIM) at full scale on site and conducting as-built inspections with the client present. Displaying a model of the planned finished structure on a tablet and comparing it to the actual object makes it intuitive for the client to understand construction accuracy, smoothing consensus building and handover inspections. RTK AR as-built management strongly supports site DX by enhancing both quality assurance and consensus building.

Operational notes and troubleshooting for RTK AR

Although RTK AR is innovative, several points should be noted to ensure stable on-site use.

• Ensuring satellite reception environment: RTK GNSS depends on satellite signals. In areas where satellite sky view is limited, such as streets of tall buildings or mountain valleys, choose as open-to-the-sky positions as possible for positioning, or increase reception by using Michibiki in Japan and multi-GNSS support (GPS, GLONASS, Galileo, etc.). Because RTK AR is difficult to use indoors or underground when satellites cannot be captured, it is important to identify in advance the areas where positioning is possible.

• Maintaining communication and coordinate corrections: When using network RTK, stable reception of correction information via mobile data is essential. In tunnels or mountainous areas where mobile coverage is lost, consider temporarily installing a base station or switching surveying methods. Also regularly confirm that the device’s GNSS reception mode maintains an RTK fixed solution (Fix), and when accuracy degrades decide whether to reinitialize positioning.

• Confirming coordinate systems and AR calibration: Verify in advance that the GNSS-derived coordinate system matches the coordinate system used in the design drawings (such as a plane rectangular coordinate system). It is recommended to set the device at a known site point and check whether the AR-displayed position matches the actual location. Proper initial calibration minimizes accumulated discrepancies from positioning and AR display errors. Because a device’s electronic compass (heading) can be disturbed by nearby metal objects, calibrate it as needed and confirm that the AR-indicated direction is accurate.

• Equipment and power management: Prolonged on-site use of smartphones or tablets consumes batteries quickly. High-precision positioning and real-time AR place heavy loads on devices, so prepare spare batteries or charging options. Also consider measures against overheating and water ingress when using devices in direct sunlight or rain. Protect devices with rugged cases and straps to avoid troubles from drops or water exposure.

• Prior practice and manual preparation: Although operation is simple, training and information sharing are essential to embed new technology on site. Before deploying RTK AR in actual pile-driving, perform demonstrations at vacant lots and share usage procedures with all personnel. Decide backup procedures in case of system malfunction (alternative surveying methods and contact protocols for responsible personnel). Use manufacturer manuals and support desks to ensure site staff can use RTK AR without confusion.

Future prospects: RTK AR changing construction of the future

High-precision guidance using RTK AR is expected to expand into various applications in the future. Currently AR use focuses on tablets and smartphones, but attempts to display navigation directly in workers’ fields of view using AR glasses (smart glasses) are likely to advance. Hands-free, continuous AR information during work could further improve efficiency. RTK AR technology can also be applied beyond pile-driving—to machine operation support, buried utility detection, as-built inspection, infrastructure inspection, and more. For example, displaying underground utility locations in AR before excavation could prevent digging accidents, and integrating with systems mounted on heavy equipment could enable high-precision machine-guided construction.

Advances in satellite positioning and AR technologies will also fuel growth. With more GNSS satellites and enhanced augmentation signals, stable centimeter-level positioning will become possible even in poor reception areas. Improvements in device performance and spatial recognition will make precise outdoor AR overlays that do not drift increasingly feasible. With initiatives like the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction and construction DX promotion, the trend of using digital technologies to improve productivity and quality will accelerate. The dramatic reduction of pile-driving mistakes and efficient construction enabled by RTK AR will likely become the new standard on future construction sites.

Introducing RTK AR on site: start simple surveying with LRTK

Although RTK AR may sound like an advanced system, tools that can be used on site are already available. One such tool is the compact RTK-GNSS system for smartphones called “LRTK.” Attaching LRTK to a smartphone makes centimeter-class simple surveying and AR-based pile position guidance readily achievable. Without dedicated equipment or large surveying instruments, your handheld device becomes a high-precision GNSS receiver and navigates you to target coordinates with intuitive AR displays.

Tasks that previously required specialized surveying skills and multiple people can now be performed accurately by a single person by introducing systems like LRTK. RTK AR’s new method is a weapon for surveying companies to improve efficiency and service value, contributes to quality assurance and labor savings for municipal civil engineering departments, and is a trump card for contractors to shorten schedules and reduce costs. Consider introducing RTK AR technology to experience on-site reductions in pile-driving mistakes and productivity improvements. Make high-precision construction—soon to be the new normal—a competitive advantage for your company.