Visualizing Inflection Points with AR: High-Precision Coordinate Navigation Useful on Site

Table of Contents

• Introduction

• What Is an Inflection Point?

• Traditional Surveying Methods and On-Site Challenges

• Benefits AR Technology Brings to the Field

• How High-Precision Coordinate Navigation Works

• How to Visualize Inflection Points with AR

• Use Cases for AR

• Simple Surveying with LRTK

• FAQ

Introduction

In recent years, the use of digital technology on construction and surveying sites has accelerated, and on-site DX (digital transformation) has become a major trend. Facing industry challenges such as labor shortages and an aging workforce, expectations are rising for smart measurement solutions that anyone can operate. Among these, high-precision AR (augmented reality) applications that combine smartphones with GNSS (satellite positioning) technology are attracting attention. Efforts to display inflection points with AR and visualize site conditions are being noticed for their potential to improve construction management and surveying efficiency.

This article explains what inflection points are and why confirming them is important, then outlines the benefits and concrete methods for visualizing inflection points on site using AR technology. It also introduces the RTK-GNSS technologies that are key to achieving high-precision coordinate navigation and presents on-site AR use cases. Finally, as an easy-to-introduce solution, we touch on simple surveying using LRTK and offer tips for field deployment. Now, let us guide you into the world of AR high-precision navigation that supports the sites of the future.

What Is an Inflection Point?

An inflection point generally refers to a point where the curvature of a line or curve changes. Mathematically, it is defined as the point where a curve’s concavity switches (the sign of the second derivative changes), but in civil engineering and surveying it is used in a more practical sense. For example, in longitudinal road design, the crest where an upward slope switches to a downward slope or the sag where a downward slope turns to an upward slope are inflection points. On a plan view, locations where a straight line changes to a curve (near the curve’s entry or exit) or corners where property boundary lines bend are also broadly referred to as inflection points.

On the site, inflection points serve as important reference points. For changes in road alignment, they mark where to construct curves correctly, and for land boundaries they indicate where boundary markers should be placed. However, these inflection points are not visible on the actual ground. Accurately identifying the points shown on drawings in the field has traditionally required time-consuming work such as surveying-based layout (commonly called "boke-dashi") and setting batter boards. Misplacing an inflection point can significantly affect construction quality—distorting road alignment or shifting structures—so accurate identification is essential.

Traditional Surveying Methods and On-Site Challenges

To accurately mark important points such as inflection points on the ground, meticulous layout work by experienced surveyors was traditionally indispensable. For example, using a total station to derive on-site positions from design coordinates and driving stakes to mark locations, or setting elevation and reference lines with levels and layout tools. Such traditional surveying typically requires two or more personnel, and transporting and setting up equipment takes time. Also, the work often does not finish in a single survey; after construction, a surveying team would revisit the site to perform as-built inspections to confirm whether the work matches the drawings.

However, as the shortage of surveyors and constraints on work hours have become more serious, relying solely on these traditional methods creates efficiency and cost issues. Missing required points or marking in the wrong place can lead directly to schedule delays and additional costs. Moreover, mentally mapping drawing points into the physical space relies heavily on experience, making the process dependent on the intuition of skilled personnel. There is a need for surveying methods that allow everyone to reliably share the same accurate spatial image.

Benefits AR Technology Brings to the Field

AR technology offers various benefits to address these challenges. By overlaying lines and points from drawings onto the real world through a smartphone or tablet camera—an AR display—inflection points and other locations can be intuitively identified. You can visualize on the screen where a curve’s transition will occur on site or the extent of the design area, enabling all workers to share a common spatial understanding.

AR is also effective for early detection of misalignment. If the design model or reference lines are continuously projected in AR during construction, you can verify in real time whether completed structures or terrain deviate from the drawings. For example, during embankment works, when the soil reaches the specified height, the design height line on the screen will coincide with and be hidden by the terrain, making it immediately obvious that the required height has been reached. As-built inspections that used to be done after completion can be accomplished on the spot, leading to reduced rework.

Following AR-guided virtual guides can also enable labor savings and improved safety. Even without relying on a veteran’s experience, workers who follow on-screen instructions can reach accurate points, so even newcomers can perform stake driving or layout at multiple locations by themselves. If the locations of buried pipes or structures are registered in advance, AR can display them in a see-through manner during excavation to help reduce the risk of damaging buried utilities. In these ways, AR contributes to more efficient construction management and quality assurance, aligning with the Ministry of Land, Infrastructure, Transport and Tourism’s initiative *i-Construction* (productivity improvement through ICT utilization).

How High-Precision Coordinate Navigation Works

For AR to be practically usable on site, the most essential requirement is high-precision positioning. Typical smartphone GPS has errors of several meters or more (several ft or more), making it difficult to project points from drawings accurately onto the site. The technology gaining attention recently is the high-precision satellite positioning called RTK-GNSS (real-time kinematic). RTK uses correction information from a reference station to improve positional accuracy to the order of a few centimeters (a few in). This enables centimeter-level positioning even with smartphones, dramatically improving the alignment of AR objects.

High-precision coordinate navigation uses this centimeter-level positioning to guide users to specified coordinates or to present coordinate information of the current location in real time. Concretely, arrows or guide lines to the target point are shown on a map or AR screen on the phone, navigating the user to a pinpoint position. Tasks that previously relied on paper drawings or handheld GPS devices to estimate approximate locations can now reach the intended points without hesitation thanks to this high-precision navigation.

To use RTK-GNSS with a smartphone, combining a dedicated compact receiver is common. By attaching a GNSS module that can be mounted on a smartphone, you can use an existing phone as a high-precision positioning terminal (this approach is sometimes called "smartphone RTK"). As long as GNSS positioning is stable, AR-displayed inflection point markers remain fixed at the correct coordinates and the display stays stable without shifting even when users walk around and view from different angles. This "non-shifting AR" is the foundation of usable AR visualization on site.

How to Visualize Inflection Points with AR

To actually display inflection points in AR on site, several preparations and steps are required. First, prepare the design drawings and point digital data. CAD data of the road centerline or boundary lines (DXF/DWG, etc.) or a list of inflection point coordinates are ideal. If you only have paper drawings, scan or trace them into digital form beforehand so they can be imported into AR.

Next, check the coordinate system of the drawing data. If the data are designed in an absolute coordinate system such as the Geospatial Information Authority of Japan’s plane rectangular coordinate system or the World Geodetic System (WGS84), you can directly map them to on-site positioning coordinates. If the drawing uses a local arbitrary coordinate system, on-site alignment is necessary. For example, measure a field point corresponding to a reference point on the drawing with GNSS, then translate and rotate the drawing data appropriately. If you perform this coordinate alignment beforehand, simply loading the data into the AR app will display virtual objects at the correct locations.

Once preparations are complete, start the smartphone and a high-precision GNSS receiver (RTK-capable) on site and use an app to display the data in AR. If the device position is accurately determined by corrected GNSS, virtual inflection point markers and design lines should appear to align perfectly with the real landscape. If needed, you can measure a known point on site and use an adjustment function to fine-tune the AR display to match the physical object. After one calibration, you only need to hold up the phone and walk to always know where you are relative to the design. As you approach the inflection point you want to see, distance indicators or arrows appear, and when you are directly over the point the marker overlays the ground on the screen. At that location you can drive a stake or mark with paint, completing the physical layout smoothly.

Use Cases for AR

• Improving efficiency of stake driving and layout: By displaying design points and lines on site in AR, stake driving and layout work can be performed intuitively. Workers can follow virtual markers on the smartphone screen to reach accurate positions, reducing the need for surveying assistants and enabling one person to efficiently complete layout tasks. Measurement points on distant slopes can also be "placed" as virtual stakes in AR to check and share positions, minimizing dangerous entries.

• Boundary confirmation and visualization of design areas: If boundary lines and work area data are pre-registered, they can be visualized on site. Normally invisible boundary lines can be displayed as lines or fences in AR, helping prevent encroachment onto adjacent land. You can also overlay building layouts and heights from the design on the spot to check harmony with the surrounding landscape.

• Sharing construction images and building consensus: By overlaying a 3D model of the completed structure (BIM/CIM data, etc.) onto the current terrain before construction, AR becomes a powerful communication tool in meetings with clients or nearby residents. The completed appearance, which is hard to convey with drawings or words alone, can be experienced at full scale through AR, making explanations and persuasion easier. This smooths preliminary consultations and consensus-building and reduces the risk of later changes.

• As-built management and quality checks: By scanning the site immediately after construction and overlaying the acquired point cloud data or as-built measurements with the design model in AR, you can visually check deviations in the finished work. For example, the measured shapes of embankments or structures can be color-coded to show where they deviate from the design, aiding quality management analysis. Tasks that were previously performed separately on a PC—such as as-built inspection and calculation—can be done on site, greatly reducing labor.

Simple Surveying with LRTK

Finally, we introduce LRTK as a solution that makes the AR and high-precision positioning described above easy to realize. LRTK is a compact GNSS receiver that attaches to a smartphone and enables a phone to support centimeter-level positioning (half-inch accuracy). Although lightweight at about 150 grams, pocket-sized, it is equipped with a high-sensitivity antenna and an RTK engine, and in conjunction with a dedicated app provides an all-in-one range of functions from positioning to point-cloud measurement, photography, and AR display.

Historically, introducing high-precision AR systems on site required expensive investments in dedicated equipment and software. With LRTK, however, you only need your smartphone paired with a small device, making it low-cost and easy to bring to the field. Complex setup is unnecessary—anyone can start surveying and AR navigation by following the app’s guidance. There are even reports that novice technicians can handle it like a game, making LRTK a true embodiment of simple surveying.

By adopting simple surveying with LRTK, each person with a device can grasp site conditions, perform as-built checks, and carry out layout tasks. Even on sites short of surveying staff, construction managers can perform necessary measurements on the spot, reducing waiting time and enabling faster progress. With a high-precision coordinate axis always at hand, on-site decision-making becomes quicker and rework due to mistakes drops dramatically. LRTK is a key device that leverages the latest technology to realize a site where "anyone can survey." If you are interested in AR-based surveying and navigation as part of on-site DX, LRTK can make a significant first contribution.

FAQ

Q1. What equipment and preparations are required to display inflection points in AR? A. Essentially, you need an AR-capable smartphone (or tablet), a GNSS receiver capable of centimeter-level positioning, and a dedicated app that links them to provide AR displays. While a smartphone alone can perform simple AR displays, RTK-compatible GNSS is indispensable for high-precision alignment. For example, by using an attachable LRTK device you can make an iPhone or Android device function as a high-precision positioning & AR device. It is also best to have network connectivity for correction information and an environment that can receive CLAS signals from the domestic positioning satellite system (QZSS).

Q2. I only have a PDF or paper drawing. Can I still display it in AR? A. Directly displaying a PDF or paper drawing in AR is difficult, but there are several workarounds. Ideally, obtain the original CAD drawings or coordinate tables. If that is impossible, load the PDF into CAD software and convert to DXF/DWG, or import it as an image and georeference it to a virtual plane after scaling and aligning. Although this takes some effort, digitizing the drawing enables AR overlay. The LRTK app can handle DXF/DWG directly, so preparing CAD data is recommended when possible.

Q3. Is the AR display accuracy really down to a few centimeters? How reliable is it? A. If RTK positioning is properly performed and the drawing data are coordinate-aligned, horizontal positional errors are generally contained within approximately ± several centimeters (± several in). This is comparable to the accuracy of traditional instruments like total stations. However, note that in smartphone AR, vertical errors of a few centimeters can occur depending on device orientation and tilt. Height projection errors tend to increase for distant objects, but for typical stake driving and reference layout the accuracy is sufficient. In short, horizontal accuracy is reliable, but it’s wise to allow a margin of error and confirm heights at critical locations.

Q4. Can AR surveying be used where GNSS reception is not available (e.g., inside forests or tunnels)? A. In environments without satellite signals, the high-precision AR described here is unfortunately limited. Without RTK positioning, you must rely on the phone’s camera and sensors to estimate position, and errors gradually accumulate over long times or distances. However, for short durations the phone’s inertial measurement unit (IMU) can maintain positioning to some extent, allowing limited AR continuity. Installing QR code markers in tunnels and scanning them occasionally to reset position can help supplement accuracy. In summary, you cannot expect outdoor-level precision, but with adaptations you can still use AR to some degree in indoor or underground spaces.

Q5. Compared to traditional methods, what are the benefits of introducing AR on site? A. The biggest benefits are efficiency and labor reduction. Surveying and inspection tasks that once required multiple people and significant time can be carried out quickly with fewer personnel using AR navigation. Digital displays also make aspects that relied on veteran intuition visible to everyone, leading to fewer mistakes and more consistent quality. In addition, on-site information sharing improves communication, and AR can visualize “invisible hazards,” enhancing safety. Overall, AR adoption raises productivity and safety on site, contributing to cost reduction and schedule shortening.

Q6. Can beginners unfamiliar with the technology operate it? Is special training required? A. Basic operation is completed within a smartphone app with an intuitive GUI, so newcomers on site usually become comfortable quickly. Even without specialized knowledge, following on-screen instructions to take measurements or check AR displays is often sufficient, and many find it as easy as playing a game. That said, stabilizing high-precision positioning benefits from some understanding of RTK communications and coordinate systems. Understanding principles such as why satellite corrections improve accuracy or what a reference point coordinate is can help with troubleshooting. LRTK provides support sites and manuals that explain these points in detail, and users can learn while using the system. With practice on site, anyone should become proficient in a short period.