ARマーカーがずれる…LRTKで現場誤差をゼロに

目次

• ARマーカーがずれるとは

• ARマーカーがずれる原因

• 現場で生じる問題点

• 従来の対策と限界

• RTKで実現する高精度AR

• LRTKで現場誤差をゼロに

• FAQ

ARマーカーがずれるとは

When using AR technology on site, you may encounter the phenomenon where "AR markers shift and the display does not match the real object." This is the problem where the position of virtual markers or models viewed through a smartphone deviates from the intended position on the actual site. For example, even if a point from construction drawings is displayed on the ground in AR, it may appear several meters away from where it should be. If the AR display on site does not align with the real object, you cannot use AR effectively for position checks or guidance. Especially in fields like construction and surveying that require high accuracy, this discrepancy in the AR display becomes a major issue that cannot be overlooked.

ARマーカーがずれる原因

Such AR marker position shifts are mainly caused by the following factors.

• GNSS (GPS) positioning errors: The accuracy of typical smartphone-built-in GPS is said to be on the order of several meters. If you use a smartphone's GPS coordinates to align AR content outdoors, the virtual model will be displayed offset from reality by that amount of error.

• AR system tracking errors: AR apps track device movement using the camera feed and sensors, but slight measurement errors accumulate and cause model position drift. Even if you think you have placed a model correctly, the model may gradually shift as the user moves or its position may become misaligned over time.

• Device sensor accuracy: Smartphones and tablets have compass (orientation sensor) and gyroscope errors, so deviations in north reference or tilt affect AR display. If the compass is off by a few degrees, lateral display errors grow larger for distant objects.

• Environmental influences: AR self-localization also relies on feature points captured by the camera, so accuracy depends on the environment. For example, in areas with plain, patternless walls or floors, in dark places, or where there are many glass surfaces, AR may fail to detect position well and the content may wobble or jump.

When these factors combine, AR displays on site fail to lock onto the intended positions, resulting in the "marker shifting" state.

現場で生じる問題点

If AR marker shifts remain large, the benefits of AR on site are lost. Specifically, the following problems arise.

• Risk of construction errors: If AR positions do not match reality, construction errors can occur such as "I installed it where the display indicated, but it was offset from the correct position." Installing structures at incorrect positions leads to rework and significant loss.

• Inefficient verification work: If AR display accuracy cannot be trusted, manual verification with tape measures or surveying instruments becomes necessary. If you spend time aligning positions each time, you lose the efficiency benefits of introducing AR.

• Safety concerns: Even for uses like indicating the location of underground utilities or hazardous areas in AR, display misalignment can lead to excavating the wrong spot and damaging lifelines. AR intended to ensure safety could instead produce near-miss incidents.

• Distrust in AR technology: If using AR on site results in "the positions are always off and unreliable," site staff will gradually stop trusting AR. As a result, introduced digital technology may fail to take root and remain unused.

Leaving the AR display error unaddressed thus negatively affects site productivity, quality, and safety, and undermines trust in digital tools.

従来の対策と限界

Several measures have been tried on site to reduce AR marker shifts, but each has its limitations.

• Marker placement or manual calibration: One method is to pre-install markers such as QR codes on site and have the AR app read them to align positions. Alternatively, manual calibration where users fine-tune the model on the screen to match known reference points is also used. Even if these temporarily align positions, moving over a wide area causes renewed shifts, and repeated adjustments are time-consuming. Placing reference markers requires pre-survey work, which is a significant preparation burden for each site.

• Use of high-precision dedicated equipment: In some cases, high-precision AR systems for civil engineering (head-mounted display devices, dedicated scopes, etc.) have been used. These offer high tracking accuracy and are less prone to drift, but they come with equipment costs on the order of hundreds of thousands of yen and are burdensome to wear. They are not devices that everyone on site can easily use, so their use was limited to specific scenarios.

In short, the traditional approaches were a choice between "spending labor to align each time" or "relying on expensive dedicated equipment." Neither is a fundamental solution, and both present barriers to widespread on-site use.

RTKで実現する高精度AR

The key to fundamentally solving AR shift problems is a positioning technology called RTK (Real Time Kinematic). RTK corrects satellite positioning errors in real time and can determine positions with centimeter-level precision (half-inch accuracy). While normal smartphone GPS had errors of about 5–10 m (16.4–32.8 ft), RTK can reduce that error to a few centimeters.

Applying RTK's high-precision positioning to AR dramatically improves on-site AR display accuracy. Specifically, it becomes possible to overlay designs and models directly onto the correct geographic coordinates (latitude/longitude or planar coordinates). Without the pre-alignment work previously required, virtual models can be placed according to the coordinates in the data. For example, RTK-enabled AR projects lines or points on the ground that perfectly match actual terrain and structures, and the model remains constantly at the designated position as the user walks around. You no longer have to worry about AR stakes shifting as you move.

This method of displaying based on absolute coordinates using RTK is referred to as "absolute-coordinate AR" and is attracting attention as next-generation AR technology. With high-precision positioning information, AR displays stay synchronized with the real-world coordinate system. Once achieved, drift-free AR becomes practically feasible for the first time. You can perform intuitive AR-based construction checks and guidance without worrying about model position errors, directly helping to prevent construction mistakes and improve work efficiency.

LRTKで現場誤差をゼロに

However, using high-precision RTK positioning on site easily may seem to require dedicated equipment or reference station installation. Enter LRTK, a solution that enables easy RTK positioning with a smartphone. LRTK is a system composed of a compact RTK-GNSS receiver and a smartphone app; by simply attaching the receiver to the smartphone, you can perform centimeter-class positioning and AR display. What used to be large-scale high-precision GNSS surveying can now be achieved with a pocket-sized device—an innovative setup.

Using LRTK can reduce the AR display error on site to nearly zero. The main features of LRTK are summarized below.

• High-precision absolute-coordinate AR: With RTK positioning, smartphone AR achieves horizontal position accuracy within a few centimeters (half-inch accuracy). Models can be displayed at the positions shown on drawings, so the AR seen on site does not differ from the actual location.

• No prior calibration required: There is no need to place markers on site or perform surveying to align references. Just hold your smartphone on site and models are projected at the correct positions.

• Easy and versatile: Since it only requires a smartphone combined with a compact receiver of about 125 g, anyone can easily carry and operate it. No special training or complicated settings are necessary, so even newcomers on site can handle it in a short time.

• One-person surveying and staking: Tasks that previously required multiple people or dedicated instruments—such as surveying or marking stake positions—can be done by one person with LRTK by looking at the smartphone. You simply follow the virtual stakes or guidance arrows displayed on the screen to reach the exact point.

• Cloud-linked data sharing: Coordinates of measured points and model information placed in AR can be uploaded to the cloud and shared instantly. Data can be synchronized between the site and the office, making it easy to check progress and measurement results remotely.

• Applicable to a wide range of site uses: LRTK can be used in construction management, surveying, infrastructure inspection, and more. It handles everything from pre-stake position checks and visualization of underground utilities to as-built checks and point cloud acquisition from photogrammetry—an all-in-one capability.

The biggest advantage of LRTK is that "there is no need for any on-site coordinate alignment." With conventional AR, it was essential to set and adjust reference points for each site, but with LRTK models are displayed at accurate coordinates from the outset, so on-site errors themselves do not occur. For example, position deviations of formwork or stakes that previously required checking against paper drawings can be confirmed in real time with LRTK AR as "zero deviation." If the design model shown on the screen always perfectly overlaps the real object, early detection of construction mistakes and prevention of rework follow. Since underground pipe routes are also displayed accurately, you can avoid finding that something "was not where you thought it was" during digging.

Furthermore, LRTK turns a smartphone into a versatile surveying tool. Coordinates of surveyed points are automatically recorded and calculated on site, and distance, area, and volume calculations are available with one tap. Data saved to the cloud can be viewed from the office immediately, aiding report creation and as-built management. These features align with initiatives such as the Ministry of Land, Infrastructure, Transport and Tourism's i-Construction and the broader construction DX (digital transformation) movement. By introducing LRTK, the era where you can truly "perform everything from simple surveying to high-precision AR with just a smartphone" becomes real.

If you are troubled by AR marker shifts on site, why not try the zero-error experience with LRTK? With a dedicated receiver and app, anyone can perform high-precision position checks in a short time. Install the LRTK app on your smartphone first and experience its effects—you may find on-site practices change dramatically.

FAQ

Q1. 高精度なARを実現するにはどんな機材やアプリが必要ですか？ A. Basically, you need an AR-capable smartphone or tablet, an RTK-GNSS receiver that can measure positions with centimeter-level accuracy, and a dedicated app that links them (for example, the LRTK app). AR display itself is possible with a smartphone alone, but precise alignment requires an RTK-capable GNSS receiver (some latest smartphones have built-in RTK reception, but external receivers are more stable). By attaching a dedicated small receiver like LRTK Phone to your smartphone, your iPhone/Android device instantly becomes a high-precision positioning and AR device. Also, you may need an Internet connection (via the smartphone’s mobile network or a mobile router) to receive correction data.

Q2. 手元の設計図面がPDFデータしかありません。それでもAR重ね合わせに利用できますか？ A. Even with only PDF drawings, there are ways, but they require some work. Ideally, CAD data or 3D data is preferable for displaying drawings or models in AR. If possible, import the PDF into CAD software and convert it to a common format such as DXF/DWG so that line data can be displayed easily in AR. Alternatively, you can rasterize the PDF into an image and display it as a textured plane (this requires scale adjustment). Practically, inquire whether you can obtain the original CAD data from the client; if that’s not possible, create an image with coordinates from the PDF and load it into AR. The LRTK app can handle DXF/DWG format drawings directly, so converting drawings to CAD format is best when possible.

Q3. AR表示の精度は本当に数センチなのでしょうか？どの程度信頼できますか？ A. If RTK positioning is performed properly and the reference between drawing data and positioning coordinates is correct, horizontal position accuracy typically falls within about ± a few centimeters. This is comparable to the accuracy achieved by conventional total stations. However, note that due to device attitude and camera characteristics in smartphone AR, vertical (height) display errors tend to be slightly larger. Especially for distant objects, projected heights may differ from the actual object by a few cm to 10 cm (a few in to 3.9 in). Therefore, when matching heights on a perfectly flat reference plane, careful confirmation is necessary. That said, the accuracy is sufficient for staking positions and verifying structure installations, so it can be trusted for practical on-site use.

Q4. 屋内やトンネル内などGNSSが届かない環境でもARを使えますか？ A. Unfortunately, in environments where satellite signals cannot be received, the high-precision AR described here using RTK is limited. In locations without GNSS, AR will rely on the smartphone’s camera and sensors for self-localization, but errors will inevitably accumulate over long periods or long distances (as a guideline, imagine an error of a few percent relative to travel distance). Therefore, when using AR in long tunnels or large indoor spaces, we recommend periodically resetting position by pointing the device at known points or supplementing with visual markers such as QR codes. With some measures, AR overlays are possible for limited times and areas, but sustaining the same high accuracy as when using GNSS outdoors is difficult.

Q5. 他社の高精度ARシステムとの違いは何ですか？ A. Traditional high-precision AR systems required dedicated surveying instruments or head-mounted display devices, with high upfront costs. They were also large and difficult to handle, so they were not practical as general-purpose on-site tools. In contrast, LRTK achieves comparable accuracy simply by attaching a small GNSS receiver to a handheld smartphone, which is groundbreaking. Using smartphones offers better operability and portability, and features can be extended via software updates. LRTK is also an all-in-one system that covers surveying, photo management, point cloud measurement, and drawing AR, and it allows integrated cloud management of various data. In short, its strength lies in being multi-functional and startable on a general-purpose device. Of course, in some specialized applications, traditional systems may still be more suitable, but for many sites, adopting an all-in-one solution like LRTK and issuing one per person can deliver great effects while keeping costs down.

Q6. 機械操作が苦手な初心者でも使いこなせますか？特別な訓練は必要ですか？ A. LRTK’s basic operations are all handled in a smartphone app with an intuitive GUI, and many report that even field newcomers quickly get used to and can operate it. Coordinate guidance and AR display are especially like a game—just follow the on-screen prompts—so no specialist knowledge is required. However, having basic knowledge of high-precision positioning principles helps for troubleshooting (for example, understanding why an RTK solution may not fix or what a coordinate system is makes problem diagnosis smoother). LRTK provides support sites and manuals covering these basics, so users can learn both operational steps and conceptual knowledge; no special training is needed, and most people can become proficient in a short time.

Q7. LRTKを導入するにはまず何から始めればよいでしょうか？ A. For first-time users, we recommend downloading the LRTK app for smartphones from the official LRTK website and trying the basic functions with a free trial account. You can experience AR model display and point cloud viewing using sample design data in the cloud with just your smartphone. Performing centimeter-level positioning in earnest requires a dedicated GNSS receiver, but device rentals and demo programs are available, so feel free to inquire. When introducing the system, first define which process on site you want to apply it to (e.g., stake accuracy management, as-built verification efficiency), and plan the necessary data preparation and operational flow accordingly. With support from the LRTK team, start with a pilot on a small site or part of a process, and gradually expand the application area as you become familiar. As a first step, try installing and using the app—that is the gateway to site DX.