Overlaying Plans in AR with Smartphones × RTK! On-site DX That Supports Precision Construction

The combination of smartphones and RTK (Real-Time Kinematic) technology is drawing attention for its ability to overlay design drawings onto real-world scenes in AR (augmented reality) at construction sites. Traditionally, rework sometimes occurred due to drawing misreading or construction errors, but visualization through AR can address these issues. Also, as part of on-site DX (digital transformation), introducing plan AR overlay smooths consensus-building among stakeholders and enables precise construction management with fewer personnel. This article provides a detailed explanation—over 7,000 characters—of the value of plan AR overlay using smartphones × RTK, concrete implementation methods, application examples, and the effects it brings to the field.

Table of Contents

• Value and challenges brought by plan AR overlay

• What high-precision positioning enabled by smartphones + RTK means

• Integration with design drawing data and the mechanism of AR overlay

• AR application examples at construction sites

• Accuracy of smartphone surveying and simple operation (use of a monopod and spike)

• Applications to 3D point cloud measurement and heat map analysis

• Cloud sharing and office use

• How on-site DX promotes work style reform and addresses labor shortages

• High-precision, simple surveying starting with smartphone RTK

• FAQ

Value and challenges brought by plan AR overlay

Constructing in accordance with design drawings at construction sites is important, but paper drawings or 2D drawings alone have limits for on-site image sharing. Even if positions are indicated by surveying or layout marks, it can be difficult to visualize the finished form, so there was a risk of construction errors caused by human interpretation mistakes. Using plan AR overlay technology, design drawings or 3D models can be overlaid on the site view through the screen of a smartphone or tablet. This allows intuitive comparison of "design intent" and "site conditions," enabling detection of dimensional or positional deviations on the spot and contributing to prevention of construction errors.

Also, projecting the completed image onto the site via AR greatly facilitates consensus-building with clients and site staff. For example, in river or road rehabilitation works, showing the post-construction appearance in AR helps all stakeholders share the vision of the finished product and makes explanations smoother. Furthermore, using plan AR overlay can reduce personnel for confirmation tasks that previously required multiple people such as surveyors and construction crews. Since one person can perform AR display and position confirmation, quality control can be conducted efficiently even on sites with labor shortages.

What high-precision positioning enabled by smartphones + RTK means

Combining a smartphone with RTK positioning overturns conventional wisdom to achieve high-precision position measurement. RTK (Real-Time Kinematic) is an error-correction technique based on GNSS (satellite positioning) that can reduce errors that were meters with GPS-only positioning to a few centimeters or less (a few in or less). Recently, improvements in GNSS chips inside smartphones, augmentation signals from Quasi-Zenith Satellite System (QZSS, Michibiki), and the use of network reference station services have made RTK positioning possible on smartphones without dedicated equipment.

Conventional surveying required a total station or high-performance GNSS receiver, which are bulky and typically assumed two or more operators. They also required sending units to the manufacturer for annual calibration or maintenance, adding hassle. With smartphone + RTK positioning, you can carry a smartphone-sized receiver and a dedicated app to the site and perform single-person immediate positioning. For example, by attaching a dedicated small GNSS receiver “LRTK Phone” (approximately 165 g) to an iPhone and launching the app, you can obtain precise position information with geographic coordinates. Field tests have shown that LRTK’s positioning results recorded an indistinguishable accuracy with errors within 5 mm (0.20 in) compared to a class-1 GNSS surveying instrument, confirming its practical usability on site.

Integration with design drawing data and the mechanism of AR overlay

So how do you realize plan AR overlay based on the obtained high-precision position information? The key is the linkage of digitalized design data and the AR display capabilities of smartphone apps. Specifically, construction drawings (e.g., CAD DWG files or BIM/CIM 3D data) are uploaded to a cloud service in advance and synchronized to a dedicated smartphone app. Within the app, the imported drawing data are associated with the real-world coordinate system so they can be overlaid on the smartphone camera view.

Because the smartphone’s position and orientation are accurately determined in real time by RTK, there is no misalignment between the digital drawing and reality. Conventional AR functions required placing markers on site or manually aligning positions each time, but combining high-precision positioning enables no-setup alignment and always-accurate overlay display. For example, importing AutoCAD drawing data via the cloud to the smartphone and launching the app on site projects design lines and structural models at full scale in place. Boundary lines and reference lines can also be displayed in AR, allowing immediate confirmation of relationships with terrain and existing structures. By linking design data in this way, AR overlay makes intuitive verification possible that cannot be achieved by merely looking at drawings on hand.

AR application examples at construction sites

In practice, plan AR overlay is beginning to be used at various construction sites. Here are some representative use-case examples.

• River and revetment works: For embankment or revetment block installation, AR is used to project design alignment lines and completion models on site to confirm the final positions. For example, the embankment height and slope can be visualized on the spot to ensure they match the design, enabling supervisors and crews to work with a shared understanding. Showing the completed form in AR also makes explanations to clients more persuasive and aids consensus-building during planning.

• Pile driving work: For foundations of bridges and large structures, pile coordinates from drawings can be imported into a smartphone to display pile installation positions in AR on site. Workers simply align with the target mark displayed on the smartphone screen to set piles at the correct locations. Additionally, RTK-enabled app features like a “coordinate navigator” can guide users to specified coordinates, allowing a single person to efficiently carry out pile center positioning.

• Slope works: In tunnel excavation or road slope shaping, design cut-and-fill gradients can be visualized in AR and compared with the current terrain. When a smartphone is held up, the designed inclined surface of the model overlays the field slope, making it easy to tell whether the slope under construction matches the design gradient. For large slopes, it can be difficult to check the whole picture from a distance, but AR brings design lines into view from afar so progress can be checked safely.

• Road and pavement works: AR overlay is also useful in road widening or repaving works. Drawing the design horizontal alignment and finished heights on site allows verification of curve shapes and widths against plans. In urban roads with many buried utilities, displaying buried pipes and cable routes in AR over excavation areas helps prevent incorrect digging. These uses make spatial understanding, including of unseen elements, easier and reduce construction errors and rework.

Accuracy of smartphone surveying and simple operation (use of a monopod and spike)

Surveying with a smartphone and a small RTK receiver offers high accuracy while keeping on-site operation simple. As mentioned earlier, RTK reduces errors to less than a few centimeters (a few in) under proper conditions, allowing point location within approximately a few centimeters (a few in). Because this accuracy is comparable to dedicated equipment, it is reliable enough for layout points and finished-shape measurements in construction management.

Operationally, the ease of smartphones stands out. For example, by attaching a bubble-level-equipped accessory and a spike tip (ishizuki) to a monopod, you can touch the spike tip to the point to be measured and press a button on the screen to record that point’s coordinates. The app can correct the offset between the spike tip and the GPS antenna position, so if the instrument is held plumb you can perform point surveying without error. Single-point surveys that used to require two people with a pole can be done as one-handed operation with just a smartphone—an enormous advantage. When recording multiple moving points, you can walk while holding the smartphone and record each point with a single tap, so even users with limited surveying experience can operate intuitively.

Applications to 3D point cloud measurement and heat map analysis

The smartphone × RTK platform is powerful not only for AR display of design drawings but also for 3D scan measurement. Recent smartphones (especially the latest iPhones and iPads) are equipped with LiDAR sensors and high-performance cameras, enabling capture of site geometry as point cloud data. Combined with precise RTK position information, the obtained point cloud becomes 3D survey data with absolute coordinates such as latitude/longitude and elevation. For example, even for a wide slope, walking while holding a smartphone for about 1–2 minutes can capture tens of thousands of high-density points. Even for long slopes on the order of 100 m (328.1 ft), walking key areas can produce a 3D model capturing surface irregularities in a short time.

The acquired point cloud data can be used on the spot for volume calculations and shape comparison analysis. For instance, comparing the current terrain point cloud with design data can visualize differences in earthwork volume as a heat map (color distribution map). This intuitively shows “where and how much soil should be added/removed,” facilitating instructions to machine operators and verification of finished shapes. Complex earthwork calculations can be completed in seconds with an app button, so non-specialist site staff can perform instant volume checks and finished-shape management. Additionally, the point cloud can be saved and submitted as electronic delivery data, and is positioned as a measurement method consistent with the Ministry of Land, Infrastructure, Transport and Tourism’s “Finished Shape Management Procedures.” Tasks that previously required craftsmanship for finished-shape measurement are being digitized, improving efficiency and reducing labor.

Cloud sharing and office use

Survey data and AR usage obtained with a smartphone do not remain solely on site. Integration with cloud services enables easy data sharing and collaboration between the field and the office. Point cloud data, coordinate information, photos, etc., captured with the dedicated smartphone app can be uploaded to the cloud with a single button. Uploaded data can be immediately viewed from an office PC via a web browser. For example, if positioned photos (photos with position and orientation) taken on site are synced to the cloud, the office can visually grasp shooting locations on a map or corresponding street-view and remotely check site conditions.

Cloud platforms allow the uploaded point clouds and measured points to be displayed on 2D maps or 3D viewers for measurement of dimensions, checking cross-sections, and other analyses. They often support overlaying multiple point clouds and design 3D models simultaneously, making office-based comparison of as-built versus design convenient. For instance, overlapping a scanned embankment point cloud with the design model on the cloud lets you immediately check volume differences—design verification can be done instantly. Since everything can be completed in the browser without expensive dedicated software, the hurdle for data utilization is greatly reduced.

Furthermore, cloud linkage streamlines report and form output. Lists of surveyed point coordinates and memo information attached to photos can be exported as automatically formatted PDF reports. For example, printing a set of position-tagged photos from inspections generates a one-button report organized by date and location. Report creation, which site supervisors used to compile manually, is simplified, reducing clerical workload. By directly connecting field and cloud, field-office collaboration is strengthened, accelerating the construction PDCA cycle and improving quality.

How on-site DX promotes work style reform and addresses labor shortages

The spread of plan AR overlay and smartphone surveying contributes to work style reform and alleviation of labor shortages in the construction industry. First, because surveying and finished-shape verification can be completed by one person, sites with personnel shortages can operate with a minimal workforce. Even without veteran technicians, smartphone apps can supplement surveying know-how, enabling younger or non-specialist staff to perform tasks at a certain level of accuracy. This can be an effective countermeasure to the decline in skilled workers.

Also, reducing the physical burden of transporting heavy equipment or spending long hours on layout improves technicians’ working conditions. Automated recording of survey results and automatic report generation can reduce overtime and improve work-life balance. Sites that master digital tools are more attractive to younger workers, contributing to the industry’s image improvement and potentially increasing new entrants. Moreover, real-time sharing of site conditions allows checks that previously required on-site visits to be done from a desk, reducing management burden for remote projects. By promoting on-site DX, workplaces more favorable to workers can be established, helping address chronic labor shortages.

High-precision, simple surveying starting with smartphone RTK

Finally, here are some points to consider when introducing high-precision surveying using smartphone × RTK. There are now market solutions combining small smartphone-compatible RTK receivers and dedicated apps; a representative example is LRTK. LRTK is an integrated platform that completes positioning, point cloud measurement, and plan AR with a single smartphone, and its initial introduction cost is lower than conventional equipment. By attaching dedicated hardware to a smartphone and launching the app, centimeter-class positioning becomes immediately available, enabling anyone to start using it easily.

These smartphone RTK solutions are compact, portable, and flexible enough for various on-site scenarios. Even companies without a dedicated surveying department can have site supervisors or construction managers perform accurate measurements themselves, promoting the democratization of high-precision surveying. In fact, many construction firms and consultants are beginning to feel the efficiency gains from smartphone RTK, with some saying, “Once you use it, you can’t go back to the old methods.” If your company is considering plan AR overlay or smartphone surveying as part of DX initiatives, taking advantage of these latest tools is advisable. By adopting evolving smartphone × RTK technologies, you can aim to balance precision construction and operational efficiency.

FAQ

Q: What equipment and preparations are required to perform AR overlay of plans? A: Basically, you need an RTK-capable GNSS receiver, a smartphone, and a dedicated AR display app. For example, prepare a small RTK receiver that can be attached to a smartphone and an app that supports that receiver. You also need to preload the design drawing data you want to overlay (DWG, LandXML, IFC, or other 3D models) into the app or cloud. If you can receive correction information via a network, a smartphone alone (plus the receiver) can perform real-time high-precision positioning and AR display.

Q: Is the accuracy of smartphone RTK really sufficient for construction? A: Yes. The latest smartphone + RTK solutions can achieve accuracy on the order of a few centimeters (a few in). Under good conditions, errors often fall within 1–2 cm (0.4–0.8 in), which is sufficient for setting out structures and finished-shape verification. In practice, comparisons with dedicated surveying instruments have shown smartphone RTK positioning errors remaining on the order of a few millimeters (a few 0.1 in) in some cases. With proper setup, on-site positioning can be performed with accuracy comparable to conventional total stations.

Q: How does it differ from traditional total stations or GPS surveying? A: The main differences are ease of use and single-person operation. Total stations are high-precision but require specialist knowledge for setup and calibration and consume time and manpower. Smartphone RTK starts positioning as soon as you launch the app and acquire satellites, and one person can carry it and obtain coordinates at desired locations. Another advantage of smartphones is integrated functionality such as on-the-spot AR display and point cloud scanning. With dedicated equipment, surveying data typically required post-processing on a PC, but smartphone RTK enables seamless surveying, visualization, and analysis. Cost-wise, a smartphone plus a small receiver is less expensive than traditional equipment and lowers operational costs.

Q: Can I use my existing design data (CAD drawings or BIM models)? A: Yes, you can use existing CAD data and BIM models. Many smartphone RTK-compatible apps can import 2D drawings like DWG or DXF and 3D models in formats like LandXML or IFC. Data can be synced via the cloud and displayed aligned to the site coordinate system, so drawings created during the design phase can be used directly for AR overlay. However, if the drawings are not aligned with the surveying coordinate system, you may need to align them on site with known control points.

Q: Is positioning and AR display possible indoors or where GPS signals don’t reach? A: In environments where GPS cannot be received, such as indoors or inside tunnels, RTK-based high-precision positioning becomes difficult. However, there are countermeasures. Indoors, you can align relatively using pre-installed known reference markers, or temporarily position using the smartphone’s AR kit dead-reckoning functions. Accuracy will be lower than with satellite reception but may be sufficient for short ranges. Recently, systems that transmit pseudo-satellite signals indoors or QR-code-based positioning systems are also being researched. In the future, technologies that allow seamless positioning and AR display indoors and outdoors are expected to become widespread.

Q: What are the introduction and running costs? A: The introduction cost for smartphone RTK solutions tends to be lower than conventional surveying equipment. High-precision GNSS receivers and total stations can cost several million yen, whereas small smartphone RTK receivers are much less expensive. App and cloud service fees are also typically set more affordably than specialized software. For example, LRTK offers plans with unlimited cloud features for a flat fee. Moreover, indirect cost benefits from reduced labor and improved efficiency mean initial investment can be recouped relatively quickly.

Q: How can the acquired survey data be utilized? A: Coordinates and point cloud data obtained with smartphone RTK have many uses. For finished-shape management, point clouds can be imported into CAD software to compare with the design model or used for earthwork volume calculations. Positioned photos taken on site can serve as evidence in reports. Sharing data on the cloud allows remote checking of construction status and receiving advice. Organizing data for electronic delivery also helps in later design changes and maintenance.