RTK dxfでAR施工: 測量座標の現場投影で出来形を即時確認

目次

• RTKとDXFを活用したAR施工の概要

• RTKによる高精度な測位が可能にする現場AR

• DXFデータを用いた設計情報の現場投影

• ARによる出来形即時確認のメリット

• AR施工の活用事例（法面・盛土への適用など）

• AR表示の精度を支えるポイント

• LRTKによる簡易測量で誰でも高精度ARを実現

• FAQ

RTKとDXFを活用したAR施工の概要

In recent years, a method called AR construction has been attracting attention on construction sites. This is a new construction management style that combines high-precision positioning using RTK (Real Time Kinematic) in surveying terminology with AR (augmented reality) technology that overlays digital information onto the real world. Concretely, pre-prepared design data (for example, CAD drawings in DXF files) are displayed in AR on a smartphone aligned to the site coordinate system, and by comparing them on site with the actual conditions, discrepancies in the as-built shape (final form) can be instantly checked and corrected during construction. Because this enables checks that used to be done by surveying after construction to be performed in real time while constructing, it greatly contributes to reducing rework and improving quality. It is also highly compatible with *i-Construction* and ICT construction promoted by the Ministry of Land, Infrastructure, Transport and Tourism, and is expected as a technology that symbolizes on-site digital transformation (DX).

RTKによる高精度な測位が可能にする現場AR

The key to making AR construction feasible is centimeter-level (inch-level) high-precision positioning by RTK. The GPS built into a typical smartphone has errors of several meters, so simply overlaying design drawings will result in large position mismatches with the real world and cannot be used for precise construction checks. This is where RTK positioning comes in. RTK is a technique that uses correction information from base stations to correct positioning errors of GPS and other systems in real time; with this mechanism, you can determine your position outdoors with accuracy within a few centimeters (within a few inches). For example, in Japan, network-type RTK services (Ntrip) using the GEONET of the Geospatial Information Authority and the centimeter-level positioning augmentation service (CLAS) provided by the Quasi-Zenith Satellite System "Michibiki" have been established, and with compatible receivers and a communication environment, high-precision positioning is easily achievable. RTK, which used to require expensive fixed GNSS equipment, has recently become much more accessible due to miniaturization and cost reduction, and receivers that can be attached to smartphones and tablets have emerged. The era has arrived in which anyone on site can easily use centimeter-precision positioning with a smartphone + RTK combination. Only with such high-precision location information can AR construction that overlays digital drawings exactly onto the real scene be realized.

DXFデータを用いた設計情報の現場投影

In AR construction, the construction target’s design data is prepared in digital form and used by projecting it on site. There are various formats for design data, but the commonly used format is 2D CAD drawing data (for example, DXF format). If a detailed 3D BIM/CIM model is available, it can display the heights of columns, walls, and other three-dimensional structures in AR and is very intuitive, but even if only plans or cross-sections are available, there is no need to worry. Even 2D design information such as DXF drawings can be displayed in AR by "laying" the drawing on the ground or rendering lines from the drawing as virtual luminous lines on the ground, allowing you to understand discrepancies between the site and the drawing. The essential point is to overlay the points, lines, and shapes contained in the design drawing on site at the correct scale and coordinates. For example, displaying a site plan in AR lets you confirm on the spot whether it fits within the site and does not interfere with adjacent structures, and projecting road design lines onto the ground allows you to intuitively check curve geometry and width. By leveraging digital drawings such as DXF, you can instantly verify on site the final form and positional relationships that were difficult to imagine from paper drawings.

ARによる出来形即時確認のメリット

There are many advantages to visualizing design information on site using AR. Here we organize the main benefits from the perspective of immediate confirmation of the as-built shape (final form).

• Intuitive sharing of the completed image: The appearance after completion, which is hard to grasp from plans or cross-sections alone, can be experienced realistically by matching it to the actual scenery. Everyone from site supervisors to craftsmen can view the same AR imagery and share "what and how things will be built here," preventing mistakes due to misunderstandings.

• Early detection of construction errors and reduced rework: Because you can continuously overlay design data and the current situation on AR, even small deviations or errors during construction can be discovered immediately. For example, you can check the position of formwork in AR before concrete placement and correct it on the spot if it is off. Correcting errors early can greatly reduce the risk of rework later.

• Streamlining surveying and layout work: Positioning tasks such as stake driving and stringing lines, which were performed by surveying technicians, can be streamlined using AR. If design baseline lines and points are displayed on the ground in AR and you can mark those locations directly, accurate layout can be achieved without skilled personnel. One person can quickly check and mark multiple points, reducing work time and personnel burden.

• Improved safety by visualizing buried objects and boundaries: Underground buried objects and site boundaries that are normally invisible can be displayed in AR, allowing machine operators and workers to know their positions in advance. This helps prevent accidents like accidental damage to gas pipes or communication cables during excavation, and prevents structures from extending outside site boundaries.

• Smoother consensus building and communication: Using AR to explain to clients or neighbors allows you to share the completed image on site that was difficult to convey with paper drawings. This prevents misunderstandings like "this isn't what I expected" and makes it easier to obtain concrete feedback from the planning stage. Aligning the completed image in advance also contributes to higher satisfaction after handover.

AR施工の活用事例（法面・盛土への適用など）

Here are some examples of how AR construction can be used on site.

• Slope as-built inspection: In construction of reclaimed land or road slopes, it is important to check whether the slope and shape match the design. By projecting design slope lines or inclined surface models on site with AR, you can tell at a glance, even from a distance, whether the actual cut or fill faces are within the design lines. Instead of survey staff climbing the slope to measure many points, you can grasp the overall shape from the base with a smartphone in hand, improving safety and efficiency.

• Embankment height control: In embankment work, repeated surveying is required to confirm whether the soil has been placed to the specified height and slope. With AR, you can display a virtual horizontal plate or lines representing the design finished height and compare them with the current ground surface. For example, you can visually recognize statements like "You need to add another ◯cm (◯ in) of fill" or "Some parts are overfilled," allowing immediate height adjustment while moving soil with dump trucks or heavy machinery.

• Pre-check of formwork and structure positioning: Before placing concrete structures, AR is also effective for confirming whether formwork and rebar positions match the design. If you display building or bridge design lines on the floor or ground in AR and check that the formwork position and dimensions align with those lines, horizontal and vertical deviations can be detected early. Detecting issues before work starts prevents the tragedy of discovering "the position was wrong" after completion.

• Site boundary and building layout confirmation: For construction on small lots or structures close to boundaries, it is important to accurately understand the relationship between the boundary line and the planned position. By visualizing site boundaries and building outlines on the ground in AR, you can check clearances and offsets at your feet. This prevents troubles such as the finished structure protruding into neighboring property.

• Locating underground buried objects: If you display drawing data indicating pipes and cable routes under roads in AR, you can mark buried routes on the ground before excavation. While sites often mark general positions with spray or signs, AR can accurately trace even complex curved routes. This makes it easier to take appropriate measures to avoid damaging buried objects during excavation.

AR表示の精度を支えるポイント

To make AR construction successful, there are several points to ensure display accuracy. First and foremost, it is important to match the coordinate system of the design data with the site. Even when using digital drawings (DXF, etc.) as-is, if the design was drawn in a local coordinate system, discrepancies will arise with site-measured coordinates. Therefore, convert the drawing data to a public coordinate system or align it with the site's control points as necessary. If known control points exist on site, placing the device (smartphone) there and receiving RTK and using that to align the drawing for initial positioning increases reliability.

Next, prepare high-precision positioning means. There is a significant difference in AR display reliability between using an RTK-capable GNSS receiver and not using one. Normal smartphone GPS or standalone AR functions can have positional errors from tens of centimeters to several meters (tens of centimeters (tens of inches) to several meters (several feet)), but combining RTK can reduce horizontal and vertical errors to within a few centimeters (within a few inches). In other words, you can overlay design data with almost no offset and perform AR displays with accuracy sufficient for actual construction. Also, using high-precision GNSS makes it possible to display models without installing special markers. On wide outdoor sites, satellite positioning allows the device itself to always know its position in a reference coordinate system, eliminating the need to pre-place target markers on site or manually adjust alignment each time. Conversely, in environments where GNSS cannot be used, such as inside buildings or underground spaces, relative model alignment using the smartphone’s AR functions (ARKit, etc.) with plane detection or image markers is necessary, but for outdoor construction RTK-based coordinate alignment is the most efficient and reliable method.

With the above points addressed, on-site AR displays proceed surprisingly smoothly. With high-precision positioning and appropriate data preparation, you do not need to consciously worry about "discrepancies" between digital drawings and the site, and anyone can intuitively confirm as-built shapes at the correct positions.

LRTKによる簡易測量で誰でも高精度ARを実現

As described above, AR construction using RTK is extremely useful, but some may feel that preparing and operating dedicated equipment is difficult. Enter the small device LRTK, which turns a smartphone into a high-precision surveying instrument. LRTK is an RTK-capable GNSS receiver small enough to fit in a pocket and is attached to a smartphone or tablet. Combined with a dedicated app, it is designed so that with simple button operations you can perform RTK positioning, record survey data, and even display design data in AR without complex settings. Its lightweight nature—on the order of a few hundred grams—and the ease of starting positioning as soon as you turn it on make it a convenient "surveying tool anyone can use," significantly lowering the barrier to on-site use.

Using an LRTK system, even young engineers without surveying expertise can handle centimeter-precision positioning after a short period of familiarization. For example, by following instructions on the smartphone screen, you can smoothly perform the reception settings for correction information from the reference station, save points, and display the model in AR. Of course, the acquired data is immediately saved on the device and can be shared to the cloud as needed. Furthermore, LRTK supports multi-band GNSS, and in areas without mobile communication, it can directly receive CLAS signals from Japan’s Quasi-Zenith Satellite "Michibiki" to obtain augmentation information, allowing high-precision positioning to continue at sites without network connectivity. Introducing simple surveying with LRTK enables on-site staff to perform surveying and as-built confirmation tasks themselves—previously outsourced to specialists—dramatically improving the efficiency and accuracy of construction management.

Finally, here is a Q&A summarizing common questions about RTK × DXF × AR construction.

FAQ

Q: RTKを用いたAR施工を現場で活用するには、どんな機材や準備が必要ですか？ A: Basically, what you need is a small receiver that supports high-precision GNSS, a smartphone (or tablet) that can connect to it, and a dedicated app that supports AR display. A concrete example is an RTK receiver that can be attached to a smartphone (e.g., an LRTK device), and you should configure it to receive correction information over the Internet. Correction information can be obtained via network-type RTK services (Ntrip) using mobile communications or via CLAS signals from the Quasi-Zenith Satellite. It is also important to preload the design data (drawings or models) coordinates to be overlaid in AR into the device and adjust them to the site’s surveying coordinate system as needed. With these preparations, you can start high-precision AR construction on site without large specialized equipment or surveying specialists.

Q: 2次元の図面データ（DXFなど）しかなくてもAR表示は可能でしょうか？3Dのモデルがないと難しいですか？ A: AR display is perfectly feasible with only 2D drawing data. Even if you only have CAD drawings (DXF files) or scanned images of paper drawings, you can lay them in AR on the ground like a background sheet or display lines from the drawing as glowing virtual lines to check discrepancies with the site. Although you cannot perform vertical checks without height information, 2D data is effective for understanding planar positional relationships. If possible, however, it is desirable to prepare 3D design models as well. 3D models can reproduce the heights and volumes of columns, walls, and other structures in real space, enabling checks that include three-dimensional interference and finished appearance. In short, 2D data like DXF can be used for AR construction, and 3D data is preferable when available.

Q: AR表示の位置精度はどの程度確保できるのでしょうか？ A: Standalone AR using a normal smartphone GPS or markers can have position errors ranging from tens of centimeters to, in some cases, several meters (tens of centimeters (tens of inches) to several meters (several feet)). That level of accuracy may be sufficient for rough checks but is inadequate for precise layout or as-built inspection. By combining RTK high-precision positioning, horizontal and vertical errors can be reduced to within ± a few centimeters (± a few inches). This allows AR overlays with accuracy comparable to measurements by levels or total stations, achieving centimeter-level positioning and enabling AR displays precise enough for construction. In short, using high-precision GNSS yields AR displays almost indistinguishable from the design drawings in terms of positional accuracy.

Q: 特別な知識や訓練が必要そうですが、現場のスタッフでも使いこなせるでしょうか？ A: The operation itself is simple and does not require specialized CG software skills. By following the screens of compatible surveying/AR apps, anyone can perform basic usage. Products like LRTK are designed with intuitive user interfaces so that starting positioning, saving points, and toggling AR displays can be done with one tap. Even those not familiar with smartphone operation can quickly get the hang of it by following on-screen guidance. Many vendors also offer brief on-site training or support for staff, so initial questions can be resolved quickly. In other words, the ease of use for site personnel is a major attraction of smartphone + RTK surveying and AR technology.

Q: AR表示のために事前にマーカーやターゲットを設置しておく必要はありますか？ A: Basically, if you use GNSS (RTK) outdoors, there is no need to place special markers on site. Because the GNSS allows the smartphone (device) itself to always know its position in the world coordinate system, you can display the design model at the prescribed coordinates simply by loading it in the app. With continuous position correction by a high-precision GNSS like LRTK, simply loading the model data in the app will automatically display it in the correct location. Conversely, in GPS-denied environments like building interiors, you must align the model in the camera image using markers or physical reference points; in such cases, placing easily identifiable reference marks like wall corners or floor crosses helps improve accuracy. For wide outdoor construction sites, RTK-based absolute coordinate alignment remains the most efficient approach.

Q: 通信圏外の山間部などインターネットが使えない現場でも、高精度のAR施工は可能ですか？ A: Yes, it is possible. Even where network-based corrections cannot be received, methods exist to maintain high-precision positioning. For example, using the aforementioned Quasi-Zenith Satellite "Michibiki" CLAS allows real-time centimeter-level positioning without the Internet in mountain areas or remote islands where mobile signals do not reach. Alternatively, you can set up your own base station (reference receiver) on site and transmit correction information by radio to build a local RTK system. In these ways, even in locations where network connectivity is difficult, augmentation signals from satellites or operation of your own base station enable continued high-precision GNSS positioning and AR display. Therefore, there is no need to give up on RTK-based AR construction just because the site lacks communication infrastructure.