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Table of Contents

• Introduction: Challenges of verifying inflection points on site

• Visualizing inflection points with AR technology

• Conventional AR technology and its problem: positional drift

• What is coordinate navigation?

• Benefits of coordinate navigation

• High-precision AR display made possible by recent technologies

• Use case: improving stake-driving work with coordinate navigation

• Simple surveying and AR utilization starting with LRTK

• FAQ

Introduction: Challenges of verifying inflection points on site

Inflection points (points where the curvature of a curve changes) on road curves or lot boundary lines are shown as coordinates on drawings, but accurately identifying them on an actual site is not easy. Traditionally, survey instruments or tape measures were used to calculate positions from the dimensions on drawings, and the locations were marked with stakes or markings to confirm them. However, it is difficult to visualize positions from paper drawings or numbers alone, and without experienced staff it is hard to place markers without error. Even slight positional deviations can lead to later construction defects or rework, so careful work is required. In particular, inflection points that lie along a curve have no ground-level markers, making it hard to grasp the exact spot where “the curvature changes,” and work tended to rely on intuition.

In addition, on complex terrain or large construction sites, the task of projecting design points onto the actual ground itself consumes time and effort. Usually a surveyor sets up a transit (a surveying instrument on a tripod) while another worker is guided to drive stakes, so it is not uncommon for a two-person team to spend half a day on the task. Human measurement errors or misreadings can also occur, requiring repeated checks and rework to confirm accuracy. This inefficiency directly affects schedules and was a major problem for sites. As described above, verifying and marking inflection points accurately on site has been cumbersome, and in practice it has depended on experience and manpower.

Visualizing inflection points with AR technology

A promising solution to these issues is the visualization of inflection points using AR (augmented reality) technology. With AR, digital information can be overlaid on the real-world view seen through a smartphone or tablet screen. Specifically, virtual markers or flags can be displayed in AR space at the coordinates of inflection points shown on the design drawings, visually indicating those points on site. This makes it possible for even non-experts to immediately understand “this is the design inflection point,” as if the point on the drawing had appeared on the ground.

For example, if an inflection point along a curve is shown via AR at a road construction site, workers can see virtual stakes or lines rendered within the live camera view on a smartphone. By driving an actual stake at that location, they can mark the exact point specified in the drawings. Compared to traditional methods that rely on intuition and experience to determine positions, this is expected to dramatically improve both efficiency and accuracy. If everyone on site can share the same position through AR, it will also greatly help prevent surveying mistakes. In this way, AR can bridge the gap between design data and the field, enabling anyone to place points accurately.

Conventional AR technology and its problem: positional drift

However, conventional smartphone AR technologies have had drawbacks. Typical AR apps can roughly align positions using GPS and camera image analysis, but their accuracy is at best on the order of several meters (several m (several ft)), which does not meet the accuracy of a few centimeters (a few cm (a few in)) required for construction surveying. Also, when walking around with a smartphone, virtual objects displayed can gradually drift away from their true positions. This is because traditional AR primarily tracks device motion using the phone’s built-in accelerometers, gyros, and camera-based image recognition (markerless AR). While convenient for local alignment, when moving across a wide site errors accumulate, and virtual markers that were initially aligned can end up visibly offset from their intended points.

Furthermore, standalone smartphone GPS inevitably has positioning errors on the order of about 5–10 m (16.4–32.8 ft). In outdoor, location-based AR, this error translates directly into display misalignment, making it unsuitable for pinpoint displays such as inflection points. Therefore, using AR for precise point-setting traditionally required special dedicated equipment or was impractical. In other words, with older technologies it was not realistic to use AR to determine exact stake-driving positions.

What is coordinate navigation?

Enter the latest approach called “coordinate navigation.” Coordinate navigation refers to a function that loads target coordinates from the design drawings (such as inflection points or boundary points) into a digital map and lets a smartphone navigate the user to that location. Specifically, when design coordinate data prepared in advance is loaded into a smartphone app, the app displays the direction and distance to the target point on the screen in real time at the site. The phone screen shows compass-like arrows or guiding lines, and the user can simply walk following them to reach the target point.

For example, the app might indicate “5 meters ahead, slightly to the right,” providing continuous updates of distance and bearing. As you approach the target coordinate, the guidance becomes finer until finally a screen marker overlaps the target point to indicate “this is the target.” At that moment, looking at your feet you will be standing exactly at the inflection point. Coordinate navigation transforms what used to rely on expert intuition and manual labor into a simple task of following smartphone guidance.

Benefits of coordinate navigation

Using the coordinate navigation function brings significant benefits to on-site work efficiency and accuracy. The main advantages are summarized below.

• Stake-driving can be done quickly by fewer people: Because the smartphone guides the user, tasks that used to require two people (one handling the surveying instrument while the other drove stakes) can be performed by a single person. Following the guidance alone allows reaching the correct points, so reference staking that used to take half a day can be completed in a short time, shortening schedules and reducing labor costs.

• Reduction of human error: Human mistakes and performance differences due to experience, common in analog surveying, are reduced. Clear instructions are displayed on the smartphone, so even beginners can place points with consistent accuracy without hesitation.

• Visually intuitive: Switching to AR display shows virtual flags or markers standing on the target coordinates, allowing stakeholders to see the completed image that was hard to share from drawings alone. For example, lot boundaries or curve inflection points can be visualized on site, making it easier for clients and contractors to reach a common understanding.

• Height information can also be confirmed: If the design includes a height (elevation) value for the target point, that height can be reflected in the AR marker. For example, it is possible to “display a virtual line 50 cm (19.7 in) above the ground,” allowing visual confirmation of design elevations and smoothing height checks that would otherwise use a level sheet.

• Easy data sharing and recording: Coordinates and photos of points set in AR can be saved and shared as digital data. Recording stake positions to the cloud on site saves the office-side effort of reconciling with drawings later and makes report creation easier.

In this way, the combination of coordinate navigation and AR display integrates surveying and marking workflows. As a result, on-site preparation time is drastically reduced and design intent can be accurately reflected on site.

High-precision AR display made possible by recent technologies

Why has high-precision AR display via coordinate navigation become possible now? The answer lies in the dramatic recent improvements in positioning technologies and device capabilities.

The biggest factor is the emergence of high-precision GNSS (global navigation satellite system) usable with smartphones. By using augmentation techniques such as RTK (real-time kinematic), GPS errors that used to be on the order of meters can now be reduced to below a few centimeters (below a few cm (below a few in)). RTK positioning, which once required expensive specialized equipment, can now be used with a small GNSS receiver attached to a smartphone. Furthermore, Japan’s quasi-zenith satellite system “Michibiki” provides a centimeter-class positioning augmentation service (CLAS) that can ensure stable accuracy even in mountainous areas or sites outside typical communication coverage. Using devices that connect to smartphones (for example, devices like LRTK Phone), centimeter-class positioning can be achieved easily on site.

In addition, advances in built-in smartphone sensors and AR software are notable. Improvements in camera image analysis and the accuracy of electronic compasses allow the device to determine its orientation and motion more precisely. This makes it possible to stably place virtual objects based on absolute coordinates. In coordinate navigation, you perform an initial heading calibration by pointing the smartphone toward a known reference direction to align the north on the digital map with true north on site. By following these procedures, AR objects remain aligned with real-world positional relationships even when walking around a wide site, maintaining high-precision displays without drifting.

In other words, the fusion of high-precision GNSS and AR technologies has created an environment where virtual markers continuously coincide precisely with real-world coordinates.

Use case: improving stake-driving work with coordinate navigation

The effectiveness of coordinate navigation has been confirmed at actual construction sites. In one benchmark point installation, single-point positioning using LRTK was performed at a pre-established known point on site, and that coordinate was registered to the cloud. Using the coordinate navigation function to guide workers to stake locations based on design drawings reduced a task that previously took two people half a day to a single person finishing in under about 2 hours. Survey accuracy was satisfactory, and workers praised it, saying “there’s no hesitation because you just follow the phone’s directions.” The ability to achieve required accuracy without relying on veteran surveyors makes personnel allocation more flexible. Sites are experiencing real efficiency and labor-saving effects from coordinate navigation. In this way, digital guidance has been shown to dramatically improve surveying productivity.

Simple surveying and AR utilization starting with LRTK

The surveying revolution using coordinate navigation and AR described above can now be realized with nothing more than a smartphone. A representative solution is LRTK, a DX solution for civil engineering and surveying. LRTK consists of a small GNSS receiver that attaches to a smartphone, a dedicated app, and cloud services, enabling anyone to easily use high-precision positioning, 3D scanning, and AR construction support features.

Even seemingly difficult tasks like displaying inflection points in AR on site become surprisingly simple with LRTK. Design coordinate data (for example, lists of inflection point or boundary coordinates) can be uploaded to the cloud in advance and accessed from the app on site. Then, simply turning on the coordinate navigation function will have the smartphone guide you to the target inflection point. Walk according to the guidance, and when the on-screen marker aligns with the site location, drive a stake or spray a mark and you’re done. Even without skilled craftsmen, following a digital guide allows accurate surveying and marking, greatly improving on-site efficiency.

LRTK also has features to display acquired point cloud data and survey points directly in AR, allowing visualization of buried pipes or existing structure lines as if seeing through the ground. Information that was hard to share via drawings or in people’s heads can be overlaid on the real scene, greatly improving on-site communication and safety checks. This reduces the risk of accidentally damaging buried utilities and is therefore effective for safety.

By introducing LRTK-based simple surveying, previously labor- and time-intensive surveying and as-built management tasks can change dramatically. Even sites and municipalities lacking specialist surveyors can achieve centimeter-level positioning; specifically, everyone can perform position setting with cm level accuracy (half-inch accuracy) using only a smartphone and a small GNSS receiver. LRTK is compatible with the Ministry of Land, Infrastructure, Transport and Tourism’s i-Construction initiatives and strongly supports digitalization in the construction industry. Why not start a new surveying style that balances “simplicity” and “high accuracy” by adopting the latest technologies?

FAQ

Q. What preparations are needed to display inflection points in AR on site? A. First, you need the coordinate values of the inflection points you want to display. Extract the relevant coordinates from the design drawings and register them with the corresponding app or cloud service. Next, attach a high-precision GNSS receiver (RTK-capable) to your smartphone and perform on-site reference calibration (position and heading correction). After that, start coordinate navigation in the app and simply walk following the digital guidance to the inflection point. When you arrive, a virtual marker will appear on the phone screen, and you can mark that point on the ground.

Q. Is AR display accuracy really on the order of a few centimeters? A. Yes. In environments where high-precision GNSS (RTK) signals can be received, horizontal positioning errors can be kept below a few centimeters (below a few cm (below a few in)). If heading correction with the phone’s sensors is properly performed, virtual markers in AR will be displayed with almost no offset. However, accuracy can degrade in places where satellite signals are lost (such as mountainous areas or inside tunnels). Even then, for short periods the phone’s internal AR-based self-position estimation can maintain a certain level of accuracy.

Q. Besides the smartphone and GNSS receiver, is any other equipment required? A. Basically, work can be done with just a smartphone and a compatible high-precision GNSS receiver. Using a pole or monopod to mount the phone can help stabilize point indication. If you use cloud services, internet connectivity is also needed. However, systems like LRTK that can operate offline offer positioning guidance with maintained accuracy even in areas without network coverage.

Q. I’m worried about introduction costs — is it worth it compared to traditional methods? A. High-precision GNSS receivers and dedicated apps require initial investment, but operation costs are overwhelmingly lower compared to traditional sets of surveying equipment and labor costs. Above all, the efficiency gains from single-person operation and the prevention of rework due to mistakes can yield returns greater than the investment. Subscription-based services have also emerged recently, enabling lower upfront costs for adoption.

Q. Can AR be used to display or utilize things other than inflection points? A. Yes. For example, drawing a virtual line along a property boundary can clearly indicate land limits, and displaying the positions of buried pipes in AR can prevent accidental excavation damage. You can also project models of finished structures on site to share the expected completion image with stakeholders. AR can be applied broadly to visualize many kinds of on-site information, not just inflection points.

Q. Is AR display possible inside tunnels or indoors where satellite positioning is not available? A. Maintaining full accuracy is difficult, but short-term use is possible. LRTK includes an indoor positioning mode for environments where GPS signals do not reach; if you set a reference position outdoors and then move into a tunnel or building, the smartphone’s camera and sensors will continue to track your relative position. For areas on the order of tens of meters (tens of m (tens of ft)), AR guidance can be continued with accuracies on the order of a few cm–several tens of cm (a few cm–several tens of cm (a few in–several in)). However, over long distances or extended durations errors accumulate, so periodic re-calibration at an outdoor reference point is necessary. This feature helps avoid situations where “work stops because GPS is lost,” which is reassuring for sites.

Q. Can staff unfamiliar with on-site AR use it easily? A. Yes. Coordinate navigation is intuitive and you just follow the on-screen instructions, so no specialized knowledge is required. Sites that have adopted LRTK report that “there’s no hesitation because you just follow the phone’s guidance.” With brief training, anyone can start using it, enabling surveying without relying on veterans.