Evolving Pile-Driving Guidance Without Benchmarks: Dramatic On-site Efficiency and Accuracy Improvements Using AR×GNSS

Table of Contents

• Required high accuracy and on-site challenges for pile-driving guidance

• Limits of conventional pile-driving guidance methods (temporary benchmark construction)

• Innovation of “benchmark-less” pile-driving guidance using AR×GNSS

• Main benefits of introducing AR×GNSS

• Use of simple surveying “LRTK” with smartphone GNSS

• Frequently Asked Questions (FAQ)

Required high accuracy and on-site challenges for pile-driving guidance

In pile-driving operations in construction, it is required to place pile centers (pile cores) at the design locations with extremely high accuracy. Especially in foundation work for high-rise buildings and pier work for bridges, tolerance for pile-center deviation can be as strict as a few millimeters. A positional error in even a single pile can cause distortion or quality defects in the entire superstructure, so it is necessary to reduce mistakes in pile-driving guidance during the pre-construction surveying stage to as close to zero as possible.

However, on actual sites, marking mistakes or incorrect point setting for pile positions cannot be entirely avoided, and preventing pile-driving errors has long been a major concern for site managers. For example, markings sprayed on the ground can be erased by the movement of heavy machinery, or surveying sightlines can be blocked by temporary enclosures or existing structures, forcing position setting to be redone. If one pile position is incorrect, it can lead to delays or rework across subsequent processes, so sites often assign multiple surveying teams for double checks or have construction managers repeatedly patrol to confirm markings. Even so, completely eliminating human error is difficult, and calls for “a more accurate and efficient way to guide pile positions” are growing louder.

Limits of conventional pile-driving guidance methods (temporary benchmark construction)

Conventionally, pile positioning (layout) has relied heavily on artisanal techniques performed by skilled surveyors. In common practice, surveyors first calculate pile positions from site reference points using measuring tapes, total stations (TS), and other optical surveying instruments based on coordinates shown on design drawings, and then mark those positions on the ground or on structures. In wide open sites, a temporary reference frame called a 丁張 (chouhari)—constructed from stakes and boards with string lines—may be erected, and positions can be determined by measuring offset distances from the intersections of those strings. However, in narrow urban sites or works including underground floors, space constraints often prevent installation of large chouhari, requiring frequent re-measurement from known points or temporary posts.

High-precision pile-center setting also requires TS and prism surveying, but this method has time and manpower constraints. Setting a TS requires sufficient line-of-sight, and as underground structures or obstructions increase, the instrument point must be relocated and re-measured and re-calculated from known points, creating extra work. Moreover, TS surveying typically requires two people (an operator and a prism staff), so deploying personnel in narrow excavation pits or at height poses safety burdens, and with small crews surveying can become infeasible.

Traditional manual methods also limit the reliability of markings themselves. Spray marks on the ground or wooden stakes tend to be erased or shifted as work progresses, causing frequent re-marking calls. As long as humans handle tapes and surveying instruments, human error is unavoidable. Slack or misreading of tapes, copy errors while transcribing calculated values, and other small oversights can cause significant positional deviations. In short, conventional pile-guidance methods face threefold limitations—“time-consuming,” “labor-intensive,” and “prone to mistakes”—which become major bottlenecks on sites with strict accuracy requirements.

Innovation of “benchmark-less” pile-driving guidance using AR×GNSS

A trump card that has emerged to solve the above issues is the “benchmark-less” construction that combines AR technology with high-precision GNSS. Among these, pile-driving guidance that fuses RTK GNSS positioning (Real-Time Kinematic) and AR visualization on smart devices—RTK×AR—is gaining attention as a revolutionary method that allows anyone on-site to guide positions accurately.

First is the high-precision positioning enabled by RTK-GNSS. RTK is a technology that simultaneously receives satellite signals at a base station (reference point) and a rover (worker’s device) and corrects errors between the two to achieve centimeter-level real-time positioning. Traditionally, RTK positioning required dedicated large GNSS receivers and radio equipment, but with the advent of high-performance compact GNSS antennas, precise RTK positioning is now achievable with smartphones and tablets. Furthermore, network RTK, which uses correction information provided over the internet by infrastructure such as the Geospatial Information Authority’s reference station network and the quasi-zenith satellite system “Michibiki” (CLAS, etc.), is spreading, enabling rover-only setups to obtain accuracies from several centimeters down to several millimeters. The era has arrived in which a smartphone in the hands of a site worker can function as a high-precision surveying instrument.

Next is intuitive navigation using AR (augmented reality). Even with highly accurate current-position data, an easy-to-understand presentation is essential to utilize it for on-site guidance. This is where AR navigation, which overlays digital information onto camera images on smartphones or tablets, excels. In a dedicated app, when design coordinate data for pile positions is pre-registered in the cloud and the user selects “start navigation,” directional arrows and distance to the target point are displayed in real time on the live image. The worker simply walks in the direction shown by the on-screen arrow, and as the distance reading approaches zero it becomes intuitively clear they have reached the target coordinates. Near the target, the arrow rotates finely to prompt micro-adjustments, and by adjusting the device’s orientation and position as instructed, the worker can ultimately position themselves within a few centimeters of the target. Without needing complex coordinate calculations or advanced surveying skills, the worker can align their standing position to the exact pile center by simply following the on-screen instructions—a revolutionary approach that departs from traditional artisanal pile-guidance methods.

With AR, positions can be set even where physical marking is difficult. For example, on concrete-covered floors or hazardous areas that are difficult to access, a virtual pile (AR pile) can be placed on the smartphone screen to indicate a position, enabling pinpoint guidance from a safe distance. In some cases, locations that workers cannot physically enter—remote sites or steep slopes—can be recorded by taking photographs to obtain coordinates, with virtual piles projected later to confirm positions. RTK×AR technology thus opens the door to pile-driving guidance under adverse conditions that were previously impractical, making it a groundbreaking solution.

Main benefits of introducing AR×GNSS

Introducing such “benchmark-less” pile-driving 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 positioning. In one comparative experiment, using an AR pile-driving system with GNSS reduced the time required for point guidance to approximately 1/6 compared with conventional optical surveying layout. Tasks that previously took a two-person team half a day for pile-center setting can be completed by one person within a few hours with RTK×AR. Because one person can continuously guide many points, the number of points processed per day increases dramatically, directly contributing to shorter construction periods and schedule advancement.

• Improved pile-center accuracy and reduced human error: RTK-GNSS yields positioning accuracy of a few centimeters horizontally and vertically, minimizing pile-center deviations. In addition, AR visual guidance greatly reduces the room for human misreading or communication errors. Traditionally, machine operators or workers judged positions based on marks set by surveyors, but with RTK×AR users are directly navigated to digital target coordinates, eliminating losses or misinterpretations in intermediate communication. If the piling machine is guided to the position indicated on the screen, piles can be installed precisely at the design coordinates. Because the same AR guide is shown to everyone, common site human errors such as missed markings or incorrect positioning are dramatically reduced.

• Labor savings and improved safety: RTK×AR allows surveying and guidance tasks that previously required multiple people to be completed by one person, greatly saving personnel resources. In the construction industry facing severe labor shortages, reducing personnel directly translates to increased productivity. A secondary benefit of one-person surveying is that fewer workers need to enter hazardous areas while heavy machinery is operating, reducing safety risks. Layout work in high places or deep excavations can be minimized, enabling AR guidance from a safe distance to help prevent falls and reduce physical strain on workers. Additionally, in narrow sites where stakes or ropes used to obstruct machinery, such obstacles are eliminated, and GNSS guidance on monitors allows consistent accuracy even at night or in rain, enabling work to proceed on schedule regardless of weather or time.

• Enhanced quality control through digital records: RTK×AR systems automatically record guidance results and error information for each survey point as digital records. For example, final errors at reached pile positions and time taken for guidance are logged in the cloud, allowing construction managers to verify as-built conditions later or use the records for quality control. The traditional effort of hand-recording in field notebooks and reconciling with drawings at the office is no longer necessary, and if mistakes occur, the data history can be used to trace causes and prevent recurrence. Because all points are managed and saved digitally in a unified coordinate system, a point can be accurately restored even after a benchmark is removed mid-construction. This visualization of construction processes and improved traceability help ensure the quality of the final deliverable.

Use of simple surveying “LRTK” with smartphone GNSS

High-end RTK×AR systems for pile-guidance might at first seem difficult to adopt. However, recently there have been solutions that make such high-precision positioning and AR guidance easily accessible. One such solution is the pocket-sized RTK-GNSS receiver system for use with smartphones and tablets called LRTK. LRTK (low-cost RTK) consists of a pocket-sized GNSS receiver attachable to a smartphone or tablet and a dedicated app, enabling surveying and layout at ± several centimeters accuracy without expensive dedicated surveying equipment. Developed by venture companies, this LRTK system is attracting attention as a revolutionary solution that turns a user’s smartphone into a versatile on-site surveying instrument.

If design coordinate data is pre-registered in the LRTK app via the cloud, site workers only need to start the smartphone plus GNSS receiver and select the target point to be ready. The screen displays guidance arrows and guides, providing coordinate navigation that leads anyone to the target position without confusion, and includes AR pile-driving that overlays design points on the camera image. Coordinates and site photos of surveyed points are automatically saved and shared in the cloud, so by the time workers return to the office the data needed to create as-built drawings and reports are already available, seamlessly connecting the field and office.

Introducing such a simple RTK surveying system allows anyone at sites suffering shortages of professional surveyors to act as a surveyor. Initial costs are also generally much lower than those for conventional GNSS surveying kits, and with the spread of network RTK services and government ICT support measures, the economic barriers are rapidly falling. The old assumptions that “surveying must be left to specialists” and “temporary benchmark work is inevitably time-consuming” are already beginning to change. Consider adopting the latest GNSS×AR technologies at your sites. Once you experience their combined labor savings and high accuracy, you may find it hard to return to traditional benchmark-centered surveying and pile-driving.

Frequently Asked Questions (FAQ)

Q: What is benchmark-less construction? A: “丁張り (chouhari)” refers to temporary markers assembled from stakes, boards, and string lines used on construction sites to indicate reference heights and positions. Benchmark-less construction refers to a method of guiding installation positions of structures without such conventional chouhari by using digital positioning data and guidance. By employing GNSS positioning and AR technology, piles and installed components can be accurately indicated without placing wooden stakes or string lines.

Q: Is the accuracy of GNSS-based pile-guidance sufficient? A: Using high-precision GNSS in RTK mode, self-positioning can generally be measured to about ±2–3 cm (±0.8–1.2 in) horizontally and ±3–5 cm (±1.2–2.0 in) vertically. This accuracy is acceptable for many civil engineering works and is adequate for pile-guidance. Moreover, because human errors in surveying tasks (misreading or marking mistakes) are greatly reduced, overall construction accuracy often improves. Another advantage of GNSS positioning is that all points are managed in a single coordinate reference system, so cumulative errors between points do not occur. If a reference stake placed earlier is removed during construction, the same coordinates can be re-measured to accurately restore the position. For critical structural elements that require millimeter-level accuracy, optical surveying can still be used selectively to verify key points.

Q: Can AR-based pile-guidance be used at night or in rain? A: Yes. Because benchmark-less construction uses digital guides instead of physical strings or chalk, work can continue even in low-light or adverse weather when physical marks are hard to see. As long as GNSS reception is available, guidance information can be displayed on tablets or machine monitors at night with maintained accuracy. However, in locations with poor satellite reception—such as between tall buildings or under dense tree cover—accuracy may degrade or positioning may become unstable. In such cases, consider measures such as pre-measuring reference points in open areas, using equipment capable of tracking multiple satellite constellations (GPS, GLONASS, Michibiki, etc.), or supplementing with conventional optical surveying during daylight as needed.

Q: I’m concerned about the cost of introducing a new system. Are expensive devices required? A: Recently, affordable small GNSS receivers like LRTK that pair with smartphones have appeared, creating an environment where benchmark-less construction can be started without purchasing expensive dedicated machinery. Initial costs are generally much lower than those of conventional optical surveying instruments or full-feature GNSS kits. In addition, government subsidies for ICT construction promotion and options like equipment rental help lower financial barriers. Consider starting at a scale that fits your company.

Q: I worry that site staff won’t be able to use it. Are special skills or training required? A: Operation is intuitive: users essentially follow arrows or AR markers displayed on the screen to move and guide pile-driving machines. Even those without specialized surveying knowledge can handle the system after learning the procedures. That said, disseminating knowledge and practice are important for embedding new technologies on-site. Prior to full operation, conduct demonstrations on vacant lots and share procedures with all staff. Also use manufacturer manuals and support services, and plan backup procedures (alternative surveying methods or contact arrangements) in case of system failures. Once users become familiar, a single person can perform high-accuracy point setting.

Q: Can AR×GNSS be used for applications other than pile-driving? A: Yes. RTK×AR technology has wide applications beyond pile-guidance. For example, combined with machine guidance for heavy equipment, operators can check design lines and heights on in-cabin monitors and perform automatic or semi-automatic excavation and grading. For as-built inspections, coordinate data can be compared to design 3D models to create deviation heat maps and display them in AR on tablets for quality control. Accurate coordinate information from GNSS surveying can also be used in infrastructure maintenance, such as road subsidence monitoring or periodic inspections of structures, enabling efficient measurement of many points to track long-term changes.