AR construction support makes reverse staking easy! Site DX expands with LRTK introduction

Introduction: “Site DX (digital transformation)” aimed at improving productivity and reducing mistakes on construction sites has attracted attention in recent years. Among these, AR (augmented reality) construction support is a cutting-edge technology with great potential. For example, the traditional task of “reverse staking” (laying out the positions of structures on site based on survey data), which used to rely on manpower and experience, becomes much easier when AR is combined with high-precision positioning technology. Moreover, high-precision AR can now be achieved using just a smartphone and a small device instead of expensive specialized equipment. With chronic labor shortages and aging veteran technicians, there is increasing demand to streamline tasks such as surveying and staking using digital technology. This article explains how introducing the AR construction support tool “LRTK” makes reverse staking easier and how it helps spread site DX.

What is reverse staking? Challenges in conventional construction

“Reverse staking” is the process of accurately placing coordinates from design drawings or survey data onto the actual site. It is a critical step that determines building layouts and the positions of structures, and a single mistake can lead to irreparable errors. As a result, reverse staking has historically required advanced surveying skills and considerable effort. Whether reverse staking is performed accurately and quickly can directly affect the success of the entire subsequent construction process.

However, traditional reverse staking has had the following challenges.

• Requires skilled technicians and equipment: Reverse staking using surveying equipment such as total stations depended on the skills of surveyors or other specialists. It required setting up and operating expensive equipment, so it wasn’t something site personnel could easily do on their own.

• Time-consuming and manpower-intensive: Reverse staking usually requires two or more workers (for example, one person operating the survey instrument and another holding a prism or staff to mark positions). Staking using tape or chain measurements from reference points takes time for long-distance measurements and angle checks, and is susceptible to weather and site conditions.

• Complex calculations and risk of errors: Accurate positioning requires detailed calculations such as coordinate computations and traverse calculations. In the past, manual calculations were common, and calculation errors could lead to positional offsets. Although CAD and software now automate many calculations, the risk of human error or misreading instruments cannot be completely eliminated.

• Difficulties under special site conditions: It can be hard to mark positions on steep slopes, unstable footing, or areas with hard concrete where piles cannot be driven. Using traditional methods, accurate positioning in such places was difficult, and compromises on approximate positions were sometimes unavoidable.

As described above, reverse staking traditionally involved significant effort and risk.

How AR construction support revolutionizes reverse staking

AR construction support is expected to be the trump card that solves these challenges. By using AR technology, digital design information can be superimposed on the real-world view through a tablet or smartphone, visualizing design points on site.

Specifically, AR-capable construction support apps can display virtual markers and models on the camera view of the site. For reverse staking, the position layout that used to be done with paper drawings and surveying instruments can be performed by following AR guidance. For example, the app can project virtual piles or markings on the smartphone screen at design pile positions or foundation locations and guide the worker to those spots. A worker need only walk toward the arrows or target markers shown on the screen to reach the intended point. In other words, even without an experienced surveyor, a junior worker can go to the site with a smartphone and mark the correct location by following on-screen instructions.

The advantage of AR construction support lies in its intuitive understanding and simplification of tasks. Instead of chasing numbers and coordinates on drawings, the instructions “drive a pile here” or “excavate along this line” are displayed directly on the site view, allowing inexperienced staff to work without hesitation. Additionally, AR can display virtual piles (AR piles) where real piles cannot be driven, enabling positioning on steep slopes or paved surfaces where marking was difficult before. In practice, there are cases in which LRTK’s AR pile function was used in steep slope reinforcement work to project virtual piles from a safe location and mark the designated points. Even in environments where physical piles cannot be driven, AR enables reverse staking through unique methods, dramatically improving the flexibility and accuracy of reverse staking work.

However, high-precision positioning is essential to perform AR construction support accurately. Ordinary GPS can have errors of several meters, which would cause virtual piles to be far off and unusable. The key technology here is RTK (real-time kinematic) positioning. RTK corrects GNSS positioning errors in real time between a base station and a rover, reducing errors to within a few centimeters or less. RTK has been used in drone surveying and machine guidance, but recent miniaturization has made it possible for workers to carry it directly. Combining AR and RTK makes it possible to align digital information precisely with the real world, enabling true DX of reverse staking. AR is also being applied to other construction tasks such as rebar placement checks and visualization of underground utilities.

What is LRTK? An RTK×AR tool that works with your smartphone

A practical solution that makes RTK×AR construction DX easy to implement on site is LRTK. LRTK consists of an ultra-compact RTK-GNSS receiver, a dedicated app, and cloud services, and is used in combination with smartphones or tablets. Specifically, it includes a palm-sized GNSS antenna device that snaps onto the back of an iPhone or iPad and an intuitive smartphone app. Attaching this single device to a smartphone enables centimeter-level positioning and AR display that would normally require surveying equipment costing millions of yen.

With LRTK, high-precision positioning and measurement can be performed with one smartphone per person, from foremen to craftsmen. There is no complicated initial setup or cable connections: attach the device and launch the app, and high-precision positioning starts automatically. To support high-precision satellite positioning, LRTK is compatible with Japan’s Quasi-Zenith Satellite System (Michibiki) correction signals and network RTK via internet-based base station networks, enabling stable centimeter-level positioning even in mountainous areas or sites outside communication coverage. The built-in battery allows long operating times, making it a pocketable all-purpose surveying tool. LRTK also offers 3D point-cloud scanning using cameras and sensors, enabling advanced uses such as calculating embankment volumes or obtaining three-dimensional as-built records. The LRTK series includes the smartphone-mounted “Phone” model as well as pro models for helmet mounting and fixed-site use, selectable according to application. Many construction companies have already introduced LRTK, and it is becoming an essential tool on site.

Four strengths of LRTK that streamline reverse staking

Introducing LRTK brings the following strengths and benefits to site construction management, including reverse staking.

• Accuracy ensured by centimeter-level RTK positioning: LRTK achieves high-precision positioning with errors from several centimeters to several millimeters (several inches to several hundredths of an inch). In actual tests, single-point positioning errors of about 10–20 mm (0.39–0.79 in) have been reported, and by averaging positioning data errors can be reduced to 8 mm (0.31 in) or less in some cases. This prevents discrepancies between virtual piles or design models displayed in AR and the real world. Because points are shown with accurate global coordinates at all times, the accuracy of reverse staking and as-built management improves dramatically.

• Intuitive AR navigation support: The dedicated app’s AR functionality projects design points and lines onto the site view and guides workers to designated positions. Arrow and target displays direct workers to the next installation point, enabling accurate piling and staking even without specialists. Because a worker’s position is continuously corrected with GNSS as they move, AR displays remain stable and resistant to drift. It is also possible to overlay 3D models directly on site to share the finished image with stakeholders.

• Easy operation with a smartphone for anyone: Because LRTK runs on familiar smartphones, it can be used intuitively without special training. Using existing smartphones eliminates the need to procure dedicated devices, making it low-cost and easy to deploy across sites. Workers can record measurement points or take photos with a tap of a button, and download design data and display AR with simple taps. Site personnel can complete required positioning and verification tasks on the spot without relying on a specialized surveying team.

• Cloud integration to promote site DX: Coordinates, point clouds, and photos captured with LRTK are automatically uploaded to the cloud and shared immediately with office PCs and other devices. Points laid out on site are plotted on cloud maps as-is, allowing real-time progress monitoring from the office. Conversely, if designers place the latest BIM/CIM models in the cloud, site staff can download them immediately for AR display and implementation. With permission and history management functions, data tampering prevention and secure information sharing are assured. For example, photos automatically record the capture coordinates and camera orientation, enabling later comparative inspections from the same angle. Centralizing data via the cloud keeps the site and office synchronized, speeding decision making and reducing rework.

Effects of introducing LRTK and the spread of site DX

Introducing LRTK on site is expected to produce effects not only in streamlining and enhancing reverse staking itself but also across many surrounding operations. Sites that have adopted LRTK report feedback such as “survey waits were eliminated and schedules shortened,” “staking was completed by younger workers alone,” and “we could respond immediately to design changes.”

Key effects include:

• Greatly improved work efficiency: Because one person can perform surveying and positioning, waiting for personnel or setup time is reduced and construction cycles speed up. For example, staking that used to take half a day can be completed in about one hour. Freeing up skilled workers allows reallocation of resources to other critical tasks, helping mitigate labor shortages.

• Improved accuracy and quality: Construction based on consistently accurate position information drastically reduces rework and corrections. Variability in as-built results decreases, and quality inspections proceed smoothly. Being able to demonstrate that construction matches the design with data streamlines inspections and client approvals, enabling reliable quality management and confidence to proceed without worrying about accumulated errors.

• Enhanced safety: Shorter surveying times in hazardous locations reduce worker burden and risk. For example, staking along road edges or on slopes can be done quickly, lowering the risk of traffic accidents or falls.

• Promotion of data use and information sharing: Survey data and photos collected on site are stored as electronic data, simplifying report creation and as-built documentation. Comparing current data with past construction or inspection records on the cloud aids future maintenance planning. It also supports paperless forms. Immediate sharing of information between site, headquarters, and clients speeds decision making and accelerates site DX.

• Contribution to skills transfer and human resource development: Intuitive AR support enables young or inexperienced workers to understand key points while working, improving on-the-job training quality. Visualizing what used to rely on veterans’ “intuition and experience” using digital tools reduces dependence on individuals and helps standardize skills.

Conclusion: Site transformation through reverse staking DX

Digitizing reverse staking is an entry point for construction site DX. Introducing RTK-compatible AR construction support tools like LRTK dramatically simplifies previously complex positioning tasks so that anyone can perform them accurately. This not only streamlines a single process but also directly contributes to overall construction productivity and quality assurance, thereby strengthening a company’s competitiveness. It also aligns with the Ministry of Land, Infrastructure, Transport and Tourism’s push for i-Construction (ICT construction), so adoption is likely to grow.

The new style of “one smartphone per person for surveying” is already becoming a reality on many sites. Reports of solo surveying using LRTK are frequently seen on social media, with growing surprise at its accuracy and convenience. LRTK, which lets you “turn the site into a drawing and bring the drawing directly to the site” through AR and RTK, is a reliable partner for promoting site DX. While AR glasses–integrated solutions are expected in the future, at present the smartphone plus compact RTK device combination offers the most practical mix of ease and accuracy. The time saved by making reverse staking easier can be redirected to other value-added tasks, further expanding DX across the entire site.

Take a step toward digital construction management that breaks with conventional assumptions, and experience reverse staking DX through AR construction support. The future of your site will change dramatically.