Intuitive surveying with GNSS devices and AR display! Position guidance that anyone can do

Intuitive Surveying Revolution Brought by GNSS Devices and AR

In the construction and surveying industries, the combination of GNSS (Global Navigation Satellite System) devices and AR (augmented reality) technology has recently brought revolutionary changes to the field. A GNSS device receives radio signals from multiple positioning satellites—including GPS and Japan’s quasi-zenith satellite “Michibiki”—and computes a highly accurate current position. AR technology overlays digital information such as 3D models and annotations onto the camera view of a smartphone or tablet and displays it in real time.

Traditionally, surveying tasks such as stake setting and as-built verification required expensive, heavy specialized equipment and skilled surveyors, and even a single positioning operation involved complicated procedures requiring multiple people. However, now by utilizing small, high-precision GNSS devices that attach to smartphones (supporting centimeter-level RTK (real-time kinematic) positioning; cm level accuracy (half-inch accuracy)) and AR displays, a new workflow—often called “smartphone surveying”—is becoming a reality. By attaching a palm-sized GNSS device to a smartphone and overlaying digital design data onto real space for visualization, position guidance and design verification at the site can be performed intuitively and in real time. Because workers can perform tasks while viewing 3D models and reference lines on the spot, even those without specialized knowledge can carry out accurate surveying and construction support, enabling efficient work progress even on sites suffering from labor shortages.

The fusion of GNSS devices and AR, enabling intuitive surveying, is attracting significant attention as a groundbreaking technology that supports DX (digital transformation) at construction sites. This aligns with the Ministry of Land, Infrastructure, Transport and Tourism’s promotion of the i-Construction initiative, and the use of 3D data and on-site DX is accelerating across the industry. The era of “one-person-one-device surveying”, in which surveying through construction management can be completed with a single smartphone, is finally becoming realistic.

Piling work: Accurate positioning with AR guidance even by one person

Stake setting (positioning) is the work of installing stakes or markers at locations specified on design drawings, but traditional methods involved a lot of labor. Optical surveying instruments such as a total station are mounted on a tripod, a surveyor operates the instrument, and an assistant holds a staff rod on site to align the position—work that is commonly done by a two-person team. Even to mark a single point, workers must measure distance from a reference point with a tape measure and make a mark, or the assistant must adjust the stake position in response to the surveyor’s signals, so these cumbersome procedures take time. If there are many stake locations on a large development site, this alone can take a whole day, which is not uncommon. Furthermore, because the work is done by hand, human error cannot be avoided; if a stake is driven in the wrong place due to misreading the drawings or recording mistakes, it can lead to later rework or construction errors. There were also major accuracy challenges: inexpensive handheld GPS units can have errors of several meters (several ft), making them unusable for precise positioning, and high-precision surveying had to rely on GNSS equipment costing on the order of several million yen and the experience of skilled personnel.

Overturning the conventional practices of such stake-driving work is GNSS devices and AR-based automatic guidance. If you preload the coordinate data of stake locations from the construction drawings into a GNSS-enabled smartphone app, the direction and remaining distance to each point from your current position are displayed in real time. For example, the screen might display guidance like “Target point: 5 cm (2.0 in) east, 10 cm (3.9 in) north,” so a worker can follow those instructions and reach the target location precisely by taking only a few steps. The positioning work that previously required several people can now be completed by a single person holding a smartphone. Switching to AR mode displays virtual stakes and arrows over the smartphone’s camera image, allowing users to intuitively identify the points where a stake should be driven. Even without seasoned intuition or complex surveying knowledge, simply following the on-screen instructions makes accurate stake-driving possible, greatly reducing survey-point errors and the need to re-drive stakes. Work times are dramatically shortened; there are reports of positioning work that used to take half a day being completed in just a few tens of minutes. Also, with GNSS surveying there is the advantage that, unlike optical instruments, you don’t need to worry about maintaining line-of-sight or re-setting equipment, and you can continue measuring efficiently even on sites with elevation differences or obstacles. Of course, there’s no need to pull out a tape measure or shout signals to each other. Thanks to GNSS centimeter positioning (half-inch positioning) and AR-based visual guidance, stake-driving work has become dramatically more efficient and higher-precision, and workers’ burden has been greatly reduced.

Design Verification: Overlay 3D Models on Site for Intuitive Confirmation

Design images that were hard to grasp from paper drawings or 3D models on a computer screen can be visualized over the actual site scene using AR. If you project models of the planned structure or design lines created with BIM/CIM directly onto the real view through a smartphone or tablet camera, workers standing on site can intuitively grasp the finished form. For example, in earthwork projects, AR can display the designed embankment heights and shapes on site, allowing you to immediately find areas that are lacking by comparing them with the current terrain. Slopes and positional relationships that used to require interpreting drawings and checking survey points can now be understood at a glance, directly contributing to the prevention of construction errors. Also, because the expected completion can be shown on the spot, it is powerful in situations of consensus building, such as explanations to clients and nearby residents. Construction details that are difficult to imagine on paper can be intuitively accepted by anyone when projected full-size with AR.

The key to realizing this high-accuracy AR construction simulation is combining it with high-precision GNSS positioning. Because ordinary smartphone GPS can have errors of several meters (several ft), accurately georeferencing large 3D models across expansive sites is difficult. However, by using RTK GNSS receivers, errors can be reduced to around several centimeters (several in), allowing model placement to be aligned with the coordinates specified in the design drawings. The positioning accuracy is on the order of horizontal ±1-2 cm (±0.4-0.8 in) and vertical ±3 cm (±1.2 in), comparable to conventional total stations (electro-optical distance measuring instruments) or expensive GNSS surveying equipment. Furthermore, by using the smartphone’s LiDAR scanner (light detection and ranging sensor), the surrounding terrain and structures can be scanned in three dimensions, so the system can automatically adjust heights so virtual models do not sink into or float above the ground and can render occlusion that accounts for overlaps with existing objects. Even positional information for underground buried structures can be visualized on the surface with AR, helping to prevent accidental damage during excavation. These technologies make models displayed in AR appear stable and aligned with reality, enabling accurate on-site design verification and construction planning.

Actual use cases have been widely reported, ranging from pre-construction simulation to verification of as-built (finished structures). Before construction, AR is used to confirm the finished image and optimize construction sequencing, and during construction there have been trials in which heavy-equipment operators perform work while visually identifying excavation limits with AR markers. After construction, the design model can be overlaid onto the completed structures or terrain for as-built verification, allowing discrepancies with the design values to be checked on the spot. The process that was traditionally carried out by surveying after completion and verifying on drawings can be done in real time on site with AR, helping to prevent rework and streamline quality control. Furthermore, the fact that 3D design data can be utilized with inexpensive equipment even on small sites, not just large projects, is significant for broadening the reach of construction DX. The on-site use of design data via such high-precision AR has attracted wide interest—from large general contractors promoting BIM/CIM to small and medium-sized contractors, clients, and local governments—and may become the new norm at construction sites in the future.

Inspection and Maintenance: Smart Recording with Geotagged Photos and AR

GNSS×AR is highly effective for routine inspections of infrastructure such as bridges and tunnels, as well as for as-built quality control during construction. In traditional inspections, when an inspector found an abnormality on site, it was common to record it with notes and photos and later mark the location on drawings. But with this method, photos do not retain precise location information or camera orientation, so when reviewed later others have difficulty determining "which location was photographed." Even if you want to track long-term changes over time, it is difficult to photograph the exact same location and angle each time, making quantitative comparisons challenging. Because the area that can be covered within limited time is also limited, there is a risk of oversights at some inspection locations. Furthermore, organizing accumulated photos and preparing reports was time-consuming and placed a heavy burden on field technicians.

To address these challenges, coordinate photos (positioning photos) integrated with GNSS information have emerged. When an inspection site is photographed with a smartphone connected to a GNSS device, the photo is automatically tagged with the latitude, longitude, height of the shooting location, and the camera orientation (azimuth). Because records that integrate photos and location data are stored in the cloud, it becomes possible to reliably identify "which place and which direction a photo depicts," and these are accumulated as a digital ledger. Furthermore, by using AR features, the positions of previously taken photos are displayed as icons in the real world, so on site it is easy to hold up the smartphone screen, stand at the same point as before, and take a new photo from the same angle. For example, in bridge inspections, photo markers of previous shots appear over parts of the bridge, allowing workers to retake photos in precisely the same composition and compare changes such as cracks at a glance. There is no need to worry about aligning positions or adjusting angles; consistent historical data from high-precision positioning is accumulated. Also, inspection data uploaded to the cloud on site can be shared and viewed immediately from office PCs or tablets, making report creation and information sharing with stakeholders smooth. If desired, scanning the structure's surface with the smartphone's LiDAR and saving it as point cloud data makes it possible to quantitatively compare deformations and damaged areas in three dimensions. Leveraging AR + coordinate photos (positioning photos) can fundamentally streamline infrastructure inspection and maintenance processes, contributing greatly to preventing oversights and improving the accuracy of records.

Recommendation for Simple Surveying Using the Smartphone-Connected GNSS Device "LRTK"

As described above, GNSS × AR technology delivers powerful capabilities across various surveying and construction support scenarios, and a concrete solution that makes this easy to realize is "LRTK". LRTK is an ultra-compact RTK-GNSS terminal used in conjunction with a smartphone; weighing only about 165 g and with a thickness of about 1 cm (0.4 in), simply attaching the device to the back of a smartphone allows centimeter-level accuracy (cm level accuracy (half-inch accuracy)) positioning anytime, anywhere. With its built-in antenna and battery, if you power on this terminal and launch the dedicated app, high-precision RTK positioning begins in just a few tens of seconds. No troublesome base station installation or specialized configuration is required, your position is plotted on the smartphone screen in real time, and you can intuitively use all functions such as the aforementioned AR guidance and coordinate photos.

The LRTK system supports network RTK using the Geospatial Information Authority of Japan’s electronic reference points and the quasi-zenith satellite Michibiki’s centimeter-level augmentation service (CLAS), enabling high-precision positioning even at sites such as mountainous areas where internet connectivity is difficult. In addition, by integrating with a smartphone’s built-in LiDAR and camera, it enables high-precision point cloud data acquisition with georeferenced position information and on-site 3D scanning, which can be used for as-built management and earthwork volume calculations. Positioning data, photos, and point clouds are immediately synchronized to the cloud, allowing field results to be shared instantly with the office and stakeholders to facilitate rapid decision-making. It also makes it possible to monitor site progress from a remote office and provide appropriate instructions in real time. Furthermore, the continuous operating time is approximately 6 hours, supporting long-duration work while powering from a mobile battery via USB. While it is possible to mount and stabilize the device on a monopod or pole when necessary, in principle high-precision positioning, AR guidance, and 3D scanning can be completed simply by walking around holding the smartphone.

What is most appreciated on site is its labor-saving effect and ease of use. By introducing LRTK, surveying and layout tasks that used to require 2–3 people can be done by 1 person, and even inexperienced technicians can carry out high-precision surveys by following instructions on a smartphone. In actual field deployments of this system, the time required for surveying and stake-driving was greatly reduced compared with conventional methods (in some cases, several days of work were shortened to a few hours), and in addition to cost reductions from reduced staffing, the need to procure expensive dedicated equipment is eliminated, keeping initial investment down; reports also indicate that rework has almost disappeared due to a reduction in human error. Also, at a disaster-recovery site in one municipality, the ability of a small team to rapidly survey a wide area of damage allowed restoration work to begin much earlier than usual. Because it requires no special controllers or long training periods and is designed so anyone on site can master it after a short training, it can be called a simple surveying tool that overturns the conventional wisdom that "surveying can only be done by specialists."

At construction sites in the DX era, intuitive technologies combining GNSS terminals and AR are expected to become increasingly widespread. In the future, combining them with wearable devices such as smart glasses is also expected to enable even more intuitive and efficient work. By introducing such smartphone surveying systems at your company's sites, unprecedented efficiency gains and quality improvements can be expected. Furthermore, shortening work time and reducing mistakes will likely contribute to improved on-site safety and reduced waste. LRTK is the ideal solution as an entry point to that.

Why not actively leverage the latest technologies and take surveying and construction management to the next stage? You will surely be able to experience their effects on site. The benefits brought by GNSS terminals and AR will continue to expand and will significantly transform the future of construction sites.