Guide stakeout coordinates accurately with cm level accuracy (half-inch accuracy): The new standard in construction surveying

Table of Contents

• Challenges of Conventional Pile-driving Operations

• Centimeter-level Positioning Achieved with RTK-GNSS

• Realizing Pile-driving Coordinate Guidance with Smartphones

• Implementation Steps for the Pile-driving Coordinate Guidance System

• Benefits of cm level accuracy (half-inch accuracy) in Pile-driving Guidance

• Simplified Surveying with LRTK

• Frequently Asked Questions (FAQ)

Challenges of Conventional Pile Driving Work

In civil and construction projects, pile driving — installing piles that serve as the foundation of structures at the exact positions specified in the design drawings — is critically important. Because even slight misalignments can affect the safety and quality of a building, it is necessary on-site to lay out pile positions based on the coordinates specified in the drawings with not even a few centimeters (a few inches) of deviation. However, conventional methods for determining pile driving positions were by no means easy.

Usually a team of several people, including experienced surveyors, used total stations (optical surveying instruments) and tape measures to measure distances and angles from known reference points, marking the ground and determining each pile location one by one. They installed stake markers such as wooden stakes and batter boards (chōhari), and heavy equipment operators relied on those markers to drive the piles. This kind of positioning work using optical surveying required a great deal of manpower and time, and on large sites, when installing dozens of piles, the surveying and layout (positioning) work alone could often take a full day or more.

Furthermore, manual surveying and layout work carries the risk of human error. A slight misreading or recording mistake can lead to a shift in pile positions, and if it is discovered after construction that the positions do not match, re-driving piles or repairing structures may be necessary, resulting in rework. Poor communication between the surveyor and the heavy equipment operator can also lead to cases where, due to incorrect instructions, piles are driven in the wrong locations.

Additionally, because marking pile locations is carried out within areas where heavy machinery is operating, safety concerns cannot be ignored. If surveyors try to force markings on steep slopes with poor footing, they risk falling or sliding, and at sites with many obstructions that block the line of sight there were also physical constraints: surveying instruments could not secure a clear line of sight and therefore could not achieve the required accuracy.

In recent years, "machine guidance" technology that equips heavy machinery with GNSS to automatically guide pile-driving positions has emerged, but because it requires expensive investment in dedicated equipment and systems, the reality is that the barrier to adoption is high at small- and medium-sized sites. As a result, many construction sites still face the challenges of ensuring pile-driving accuracy and low work efficiency.

Moreover, the construction industry as a whole is experiencing a worsening labor shortage and an aging of skilled technicians, making it increasingly difficult to sustain traditional methods that rely on experienced personnel. Against this backdrop, there has been a strong demand for new methods to carry out pile-driving surveying more accurately, quickly, and safely.

Centimeter-level positioning realized by RTK-GNSS

One of the key technologies attracting attention to solve this issue is RTK-GNSS, which enables centimeter-level (half-inch-level) high-precision positioning. RTK (Real Time Kinematic, real-time kinematic) is a method that dramatically improves the accuracy of satellite-based positioning (GNSS) by correcting errors in real time, and by using correction data from base stations and augmentation signals from satellites it can reduce positioning errors to within a few centimeters (within a few in). Simply put, it's like "ultra-high-precision GPS" that can be used on-site.

The accuracy of the GPS built into a typical smartphone is on the order of several meters (several ft), but using RTK methods you can match the coordinates on the design drawings exactly to the actual position. If centimeter-level positioning (cm level accuracy (half-inch accuracy)) becomes possible, it will be possible to place stakes on construction sites at the positions shown on the drawings.

If you utilize RTK-GNSS for pile positioning guidance, you only need to enter the coordinates of the pile positions specified on the drawings into the device, and the device will navigate to those points to minimize deviations in pile location. Traditionally, surveyors set out stakes on site using tape measures and transits, but by using RTK you can omit the intermediate layout-marking work and be guided directly to the target design coordinates.

Indeed, even in the Ministry of Land, Infrastructure, Transport and Tourism's "ICT construction" and "i-Construction" initiatives, improving construction accuracy through the use of GNSS positioning technology has become an important theme. By incorporating RTK into pile-driving guidance, an environment is being established in which anyone can position piles with the same accuracy without relying on the intuition and experience of veteran workers.

Furthermore, in Japan the Quasi-Zenith Satellite System “Michibiki” began providing a centimeter-class positioning 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 Continuously Operating Reference Station network via communication lines, or by receiving augmentation signals directly from the Michibiki satellites, stable cm level accuracy (half-inch accuracy) positioning is possible anywhere in the country. With this infrastructure in place, efforts to apply high-precision RTK-GNSS positioning to pile-driving operations have become realistic at worksites.

Realizing stakeout coordinate guidance with smartphones

The technology that has made it easier to enjoy the benefits of RTK-GNSS is stakeout coordinate guidance using smartphones. In recent years, compact RTK-capable GNSS receivers that connect with smartphones have appeared, making centimeter-level positioning (cm level, half-inch accuracy), which previously required dedicated equipment, possible on smartphones as well. By attaching a dedicated high-precision GNSS unit to a smartphone and receiving correction information (network RTK or satellite CLAS signals) via mobile communications, the smartphone at hand can measure its current position in real time with an accuracy of several centimeters (several in).

If you then link this high-precision current position information with the coordinate data of pile positions obtained from the design drawings, digital navigation to pile-driving points becomes possible. Load the pile coordinate data from the construction plan into a surveying app for smartphones, and when you select the point you want to be guided to, the direction and distance to the target point are displayed on the screen. For example, if you are prompted "Target point is 6.3 m (20.7 ft) to the northeast," just hold your smartphone in one hand and proceed 6.3 m (20.7 ft) to the northeast as directed. An on-screen arrow indicates the direction to go, and the distance readout decreases as you approach, showing "50 cm (19.7 in) remaining" and "10 cm (3.9 in) remaining." Eventually, when you overlap the target coordinates, the distance display becomes 0, and that is the exact position where the pile should be driven.

Furthermore, by displaying virtual stake markers (AR stakes) on the smartphone’s camera feed, you can intuitively confirm the position where the stake should be driven. When an AR marker that fits the ground perfectly appears on the screen, that exact spot is the staking point. Like a construction-site version of a car navigation system, anyone can pinpoint the precise location simply by following the digital arrows and markers.

This smart stake layout guidance allows stake positioning work that traditionally required two or more people pulling a tape measure to be completed by 1 person with just a smartphone in hand. Because no advanced surveying knowledge is required and you simply follow the on‑screen prompts to move and mark, even inexperienced workers can perform the stake layout tasks.

Reports from sites that have actually implemented GNSS×AR-based pile-driving guidance indicate that “the time required for marking pile positions has been dramatically reduced, and pile re-drives and corrections in later processes have almost ceased to occur.” In one validation, pile-position marking that previously took half a day with several people, including surveyors, was completed in just a few tens of minutes by utilizing digital guidance. Results that greatly exceed conventional methods in both accuracy and efficiency have been confirmed, and pile-driving surveying can be said to be entering an innovative stage in which efficiency and labor-saving and higher accuracy are advancing simultaneously.

Implementation steps for the pile-driving coordinate guidance system

Now, let's look at the basic steps to perform pile-driving coordinate guidance on-site using a high-precision GNSS combined with a smartphone.

• Preparation of design data: First, prepare the coordinate data for the pile locations determined during the construction planning stage. If you import a list of pile coordinates obtained from design drawings or CAD drawings (latitude and longitude or planar coordinates) into a surveying app on your smartphone, you can quickly call up the points you want to guide to on site. If the system is cloud-enabled, you can also sync the design data uploaded from a PC in advance with the smartphones on site.

• GNSS Device Setup: Once on site, attach an RTK-capable compact GNSS receiver (high-precision GNSS unit) to your smartphone and power it on. The phone and receiver connect wirelessly via Bluetooth or similar, and satellite acquisition and RTK positioning initialization complete within tens of seconds. If you use a network-based RTK service, receive correction information on the smartphone and confirm that positioning has reached cm level accuracy (half-inch accuracy). Once ready, with the smartphone in the palm of your hand you will have accuracy comparable to conventional surveying equipment.

• Guidance to the stake location: When you select the stake number or point you want to be guided to in the surveying app, the direction and distance to the destination are displayed on the screen. Follow the instructions and move; the location where the distance display reaches 0 is the staking position. The worker marks that indicated spot and installs the stake at the planned location. If you use the smartphone’s AR display function, a virtual stake marker will appear on the camera view, so there’s no risk of missing the intended point even on large sites.

• Recording and Sharing: After finishing driving a pile, take a photo on site with your smartphone camera to create a record. The photo is automatically tagged with coordinates determined by GNSS positioning and uploaded to the cloud. There is no need to manually recompile the data after returning to the office; you can instantly share from the field which pile was installed where. As geotagged photo data accumulates, later inspections and the preparation of reporting materials are also streamlined.

As described above, by using a pile-staking guidance system that combines a smartphone and GNSS, even people without surveying expertise can achieve accurate pile positioning simply by following the on-screen guidance. There is no need to pull out a tape measure or compare drawings for each task, and the fact that the on-site processes of surveying, position guidance, and recording can be completed with a single smartphone is a major innovation.

Benefits of cm level accuracy (half-inch accuracy) pile-driving guidance

When pile-driving coordinate guidance using smartphones and GNSS is introduced on-site, various advantages compared with conventional methods can be achieved in terms of accuracy, efficiency, and safety. The main effects are summarized as follows.

• Precision improvement: Centimeter-level (cm level; half-inch accuracy) coordinate guidance using RTK-GNSS almost eliminates pile positional deviations. It enables precise construction according to design drawings, preventing assembly defects and repair work caused by pile center misalignment. In particular, even for projects that require high accuracy, such as high-rise buildings and bridges, pile-driving work can be entrusted with confidence.

• Significant improvement in work efficiency: The time spent on surveying and staking out positions is greatly reduced. Because position measurements that previously required multiple people can now be completed by a single person, the effort involved in coordinating personnel is also reduced. For example, there are cases where staking that used to take half a day can be completed in a matter of tens of minutes, resulting in a dramatic increase in productivity. The accompanying reduction in labor costs due to labor-saving measures should not be overlooked.

• Labor-saving and skill standardization: Because workers only need to follow on-screen guidance on a smartphone, even those who are not experienced surveyors can carry out stakeout work. Processes that previously relied on specialist technicians can be handled mainly by general workers, so it can be readily adopted at sites facing labor shortages. Also, since the equipment consists only of a smartphone and a compact receiver, initial deployment costs can be kept down, and operations such as deploying one device per person on site are realistic. It also leads to skill standardization across the entire site and contributes to eliminating dependence on specific individuals.

• Improved safety: You no longer need to manually set stake positions in hazardous locations. By using AR displays, you can place virtual markers on-site and confirm positions from a safe location, even on unstable steep slopes or in areas that are difficult to access. Because this reduces surveying work around heavy machinery, it also lowers the risk of contact accidents. It also reduces workers' physical burden, allowing them to carry out tasks more safely and with greater ease.

• Quality Control and Data Utilization: Digital positioning data and photographic records are automatically retained, making post-construction as-built inspections and reporting work easier. Keeping a history of which pile was installed at which coordinates is useful for later position verification and for additional work. Because objective evidence can be presented as explanatory materials to clients and supervisory authorities, highly reliable quality control can be achieved.

• Promoting versatile on-site DX: Once this smartphone surveying system is introduced, it can be widely used for purposes beyond pile driving. In addition to application to layout marking (positioning) work, it can of course be used for marking foundation and anchor positions, and for accuracy verification through as-built measurements after construction. It can also visualize the location information of pipes and cables buried underground with AR displays, aiding safety checks during excavation work. Furthermore, it is possible to overlay 3D models and drawing data from the design stage onto on-site video to intuitively share the completed image. In short, in any situation where “indicating accurate positions on site” is necessary, intuitive guidance using GNSS×AR demonstrates its strengths and accelerates on-site digital transformation (DX).

Simple surveying with LRTK

As an example of a solution that allows you to immediately practice stake-driving guidance using high-precision GNSS and a smartphone, we introduce LRTK. LRTK is an all-in-one field surveying tool composed of a compact RTK-GNSS receiver, a dedicated smartphone app, and a cloud service. By attaching a receiver weighing about 150 g to a smartphone, a palm-sized smartphone instantly transforms into a surveying instrument capable of centimeter-level positioning. The acquired current position data are synchronized with the design coordinates on the cloud and displayed in real time on the onsite smartphone screen, so surveying, layout, and recording can all be completed with a single smartphone, which is its key feature: completed with a single smartphone.

LRTK's main features include the ability to position pile driving and layout markings to within a few centimeters (a few in) thanks to high-precision positioning, the ability to place virtual stake markers at specified coordinates and visualize them in AR, and a coordinate navigation function that provides real-time guidance of remaining distance and direction simply by calling up stake data registered in the cloud. It also supports remote guidance, allowing positions to be checked from a safe, remote location even at hazardous sites where physical stakes cannot be placed. Tasks that traditionally required heavy, expensive equipment and skilled operators can be easily performed with a familiar smartphone using LRTK. The device itself is dustproof and waterproof and is an integrated unit with a built-in antenna and battery, so it can be used reliably even in harsh outdoor conditions. Bluetooth connectivity enables cable-free operation, so it won't get in the way even when walking around the site.

By utilizing LRTK, you can digitize the traditional pile-driving work that relied on paper drawings and craftsmen's skills, creating sites where anyone can perform accurate positioning. This is truly an innovative solution that makes "pile-driving guidance anyone can do" possible. The LRTK series reduces work time and improves productivity through high-precision positioning, contributing to the digital transformation (DX) of the construction industry.

If you are currently experiencing issues with stakeout accuracy or work efficiency, introducing smart surveying technologies like LRTK can be an opportunity to greatly reduce the burden on site. For more details, please also visit the [LRTK official site](https://www.lrtk.lefixea.com/) and check the latest information and case studies.

Frequently Asked Questions (FAQ)

Q. What equipment and preparations are needed to use smart pile-driving guidance? A. Basically, a GNSS receiver capable of centimeter-level positioning accuracy (half-inch accuracy) and a smartphone (or tablet) connected to it are required. Specifically, attach a high-precision GNSS unit that supports the RTK method to the smartphone and provide a communication environment (such as a mobile network) to receive correction information. If you are outdoors in an open area with a clear view of the sky, combining these will allow you to perform pile-driving guidance on-site immediately.

Q. Can accurate stake placement be done using only a smartphone's built-in GPS? A. Unfortunately, standalone positioning with the GPS built into a typical smartphone can have errors on the order of several meters, making it unsuitable for precise stake placement. To achieve centimeter-level accuracy (cm level accuracy, half-inch accuracy), corrections via RTK-GNSS are essential; only with dedicated high-precision GNSS devices or augmentation services from satellites or networks does it realize its full potential. For example, using a solution like LRTK can enable high-precision positioning even with an ordinary smartphone, so you can rest assured.

Q. Can inexperienced workers handle it? A. Yes. It is designed for intuitive operation, so even those without specialized surveying knowledge can use it. You simply follow the guides displayed on the smartphone screen to move and confirm positions, so no difficult calculations or settings are required. As long as they learn the basic operations, even non-veterans should be able to use it effectively on site. In fact, there have been reports of cases where stake-setting work that previously relied on surveyors was carried out without problems by only junior staff.

Q. Does weather or the surrounding environment affect accuracy or operations? A. Basically, as long as you are outdoors with an open sky, it can be used stably regardless of the weather. However, because GNSS positioning needs to receive satellite signals from the sky, accuracy will be poor in places surrounded by tall buildings, inside tunnels, or indoors. Also, when using network-type RTK corrections, you need to be within a communication coverage area. In mountainous areas where radio signals are unstable, it is possible to cope by using the Quasi-Zenith Satellite System Michibiki services (such as CLAS), which can receive augmentation signals directly from satellites. Note that AR display itself is possible at night, but a minimum amount of light is required for the smartphone camera to capture the real scene.

Q. Can this technology be used for applications other than pile driving? A. Yes, its application range extends beyond pile driving. On building and civil engineering sites, AR coordinate navigation can also be applied to setting out foundations and anchor positions, marking equipment installation positions, and accuracy verification through as-built measurements after construction. It can also visualize the location information of buried pipes and cables with AR displays to assist safety checks during excavation work. Furthermore, it is possible to overlay 3D models and drawing data from the design phase onto site footage to intuitively share the completed image. In short, in any situation that requires "showing accurate positions on site," intuitive guidance technology using GNSS and AR will prove effective.