New Applications for Smartphone Surveying: Projecting 3D Models On-Site with LRTK AR Guidance

In construction, civil engineering, and infrastructure work sites, the fusion of smartphone surveying and AR (augmented reality) technology has become a new trend. By combining easy-to-use surveying with a smartphone and intuitive AR displays that project 3D models onto the actual site, labor for surveying tasks can be reduced and construction verification efficiency can dramatically improve. This article introduces the latest method that leverages a small RTK-GNSS device for iPhone called "LRTK", using the highly accurate position information obtained by smartphone surveying to enable AR guidance. From challenges of conventional methods to the technical mechanism and benefits, concrete use cases, implementation steps, accuracy verification, on-site operational cautions, and future possibilities, we provide a systematic explanation from a practitioner’s perspective. Experience the forefront of on-site DX brought by the fusion of smartphone surveying and AR.

Background for the Advancement of Smartphone Surveying and AR Integration

Surveying and as-built verification (post-construction shape confirmation) in construction and civil engineering have long relied on dedicated instruments such as total stations and levels, and on skilled surveyors. Traditional surveying work involves many steps and a lot of time, from establishing control points to observations and cross-checking with drawings, and accurate quality confirmation can be difficult without experienced personnel. Recently, however, the industry-wide issues of workforce shortages and skill transfer have become serious, driving demand for efficiency and labor savings. With initiatives such as the Ministry of Land, Infrastructure, Transport and Tourism–led "i-Construction" promoting construction DX through ICT use, momentum is building on sites to introduce digital technologies.

Against this background, attempts to use smartphones as surveying instruments have been attracting attention. Especially with the advancement of smartphone performance and positioning services, smartphone surveying—acquiring surveying data with a smartphone—has become a new option on site. By combining AR (augmented reality) technology, surveying data and design models can be overlaid on the real world, enabling intuitive understanding and verification of construction status. This makes it possible to perform smart construction: even those without specialized knowledge can instantly check as-built conditions on site, visually share survey results, and more.

Mechanism and Benefits of Projecting 3D Models On-Site with LRTK

The key technology enabling the fusion of smartphone surveying and AR is the small positioning device "LRTK" provided by Lefixea. LRTK is an RTK-GNSS receiver that attaches to iPhone or iPad and turns a smartphone into a surveying instrument with centimeter-level accuracy (half-inch accuracy). It supports Japan’s Quasi-Zenith Satellite System "Michibiki" high-precision positioning service (CLAS), and can receive correction information directly from satellites for high-precision GNSS positioning even without an internet connection. This makes it possible to obtain absolute coordinates—previously requiring GPS surveying equipment costing several million yen or highly skilled technicians—using a palm-sized smartphone + LRTK.

Moreover, the latest iPhones are equipped with LiDAR scanners and high-performance cameras, allowing quick scanning of surrounding terrain and structures to obtain high-density point cloud data. When combined with LRTK, these point clouds and observation points are assigned accurate latitude, longitude, and height information (absolute coordinates) based on the global geodetic system. In other words, point clouds and survey point data obtained on-site can be directly overlaid with design 3D models or existing survey coordinate systems. This eliminates the need for complicated alignment work, enabling immediate comparison and verification of measurement results against design data.

In addition, incorporating AR into smartphone surveying allows digital data to be projected onto the actual landscape in real time. Using the high-precision current position information from LRTK and the smartphone’s attitude detection, AR displays that accurately align the site and the 3D model are possible. Conventional AR required marker placement or initial position alignment and often drifted as the user moved. However, LRTK’s centimeter-level position tracking ensures that once a model is set, it remains fixed at that location even if the user walks around. For example, projecting a completion 3D model of a structure still under construction onto the site allows verification as if the object were actually present there, enabling users to anticipate differences in position and height in advance.

Main benefits: Projecting 3D models on-site with smartphone + LRTK + AR offers the following advantages:

• Non-experts can use it intuitively: Even without specialist knowledge, users can instantly understand differences from the design and target positions by looking at on-screen guides and color-coded displays. Young staff who struggle with reading drawings can grasp on-site conditions intuitively.

• Major efficiency gains in surveying work: Traditional workflows required surveying → data processing → drawing comparison, which took time. Smartphone surveying allows measurement and comparison verification to be completed on-site. Real-time on-site as-built verification enables immediate decisions on rework, minimizing rework and reconstruction and contributing to shorter construction schedules.

• High-precision alignment: RTK-GNSS enables exact matching of site coordinates with design coordinates, minimizing spatial discrepancies. This removes the need for initial stake-out adjustment or post-processing alignment of point clouds with the design model.

• Data sharing and centralized management: Point clouds and as-built information confirmed via AR can be uploaded to the cloud and shared with stakeholders. Experts at remote locations can easily review data and provide advice, enabling real-time collaboration between the field and the office.

Use Cases for Smartphone Surveying × AR

The combination of smartphone surveying and AR guidance is being used for various purposes on actual construction sites. Here are representative use cases.

Using AR Heat Maps for As-Built Management

For as-built inspection in civil construction, a method gaining attention is instantly comparing the locally acquired point cloud data with the design 3D model on a smartphone, and displaying the differences as a color-coded heat map. Point clouds obtained with LRTK include absolute coordinates, so the height differences at each point can be automatically calculated with a single click in the cloud. Importing the generated heat map to a smartphone and displaying it in AR lets you intuitively check elevation differences of pavement surfaces or embankments on-site. Areas at design height can appear blue or green, and areas that are low or deficient appear red—differences emerge as colored overlays on the actual object so you can instantly see where rework is needed. This greatly streamlines processes that used to require returning to the office to analyze and report survey data.

AR Guidance for Pile Driving and Stake-Out Work

Establishing control point stakes and performing stake-out of structure locations used to be labor-intensive tasks carried out by two people with a transit and tape measure. Smartphone surveying revolutionizes this. With the AR guidance feature in LRTK-compatible apps, arrows and guide lines appear on the smartphone screen indicating the pre-set target coordinates. Users simply walk in the direction indicated on the screen; as they approach the target, an AR marker appears to indicate the exact location. For example, even in a forest with limited visibility, the AR display can show the hidden stake location among vegetation, preventing users from getting lost. Stakes buried under snow or ground markings can be located without digging when using AR guidance. This feature enables one person—even without veteran skills—to perform accurate stake-out, allowing stake-driving work to proceed efficiently even on sites lacking surveying assistants.

AR Visualization of Buried Pipes and Underground Objects

Smartphone surveying + AR is also powerful for visualizing underground buried utilities such as pipes and cables. If the positions of buried pipes are measured and point-clouded with LRTK in advance, projecting that data in AR at the site allows confirmation of underground pipe routes from above ground. When holding up a smartphone during excavation, a semi-transparent model of the underground piping can be displayed on the screen, reducing the risk of accidental damage. In gas, water, and other buried infrastructure construction or maintenance, anyone can intuitively understand underground structures that are hard to grasp from drawings alone, aiding safe and efficient work planning.

On-Site AR Simulation of Design 3D Models

Projecting 3D models in AR is also used during planning and consensus-building before construction. For example, loading a bridge or building design 3D model onto a smartphone and viewing it as an AR display on-site can reproduce the completed appearance at full scale in place. This helps communicate completion images that are difficult to convey with drawings or perspective renderings to clients and nearby residents. AR simulation during the design phase can also verify how the design interacts with the surrounding environment and its visual impact. Because LRTK provides high-precision alignment, the model’s position and height are accurate, helping prevent rework due to mismatch with the surroundings. Easy design reviews using smartphone and AR improve communication and design quality.

Steps to Introduce Smartphone Surveying Using LRTK

Below is an overview of the steps to introduce cutting-edge smartphone surveying + AR technology on-site. Even first-time users can start smoothly by understanding the necessary preparations and workflow.

• Necessary equipment and apps: Prepare an iPhone or iPad (LiDAR-capable models are desirable) and an LRTK device. The LRTK unit attaches to the device via a smartphone case or attachment. Install a dedicated surveying app that supports LRTK. If you have site design 3D data (BIM/CIM models or 3D models created from drawings), load them into the app in advance.

• Initial positioning setup: Before starting work on-site, power on the LRTK device and confirm satellite acquisition. In Japan, receiving Michibiki (QZSS) CLAS signals enables RTK positioning without the internet (if network connectivity exists, network RTK such as NTRIP can also be used). It’s advisable to measure your current location at a known control point to verify positioning accuracy. Confirm that the app shows an RTK-FIX solution before proceeding with surveying.

• On-site scanning survey: To check the target terrain or as-built conditions, walk the site while performing LiDAR scanning with the smartphone. Start scanning in the app and walk slowly to cover the target area; high-density point cloud data will be recorded in real time. Because LRTK provides absolute coordinates for each point, no extensive alignment adjustments are required even over wide areas. Typically, scanning a common road section or embankment area completes within a few minutes of walking.

• On-site checking with AR: After scanning, you can immediately compare the acquired point cloud and the design 3D model on the smartphone. The app will automatically overlay them and switch to a mode that displays differences in AR. Looking through the screen at the actual terrain or structure, you will see design discrepancies projected into the real world as heat maps or 3D model overlays. For stake-out, select the target coordinate and start AR navigation. Follow the arrow display, and as you approach the target a marker or virtual object (e.g., a stake model) appears so you can mark the location.

• Data saving and sharing: Survey results are saved in the app and can be synced to the cloud with a single touch if needed. Uploading to the cloud enables immediate sharing with supervisors or clients. Point cloud data and AR confirmation screenshots/videos are automatically organized and can be used later as as-built inspection materials or in reports. Sharing what was checked on-site with stakeholders enables swift communication of issues and verification of corrective actions.

With these steps, even staff without special training can start surveying and using AR with a smartphone and LRTK. It is recommended to trial on a small area first, get accustomed to the operation, and then roll out fully.

Accuracy Verification of Smartphone Surveying: How Trustworthy Is It?

A key concern when introducing new technology is positioning and measurement accuracy. Although smartphone surveying + LRTK uses a small device, various verifications have shown it can achieve accuracy comparable to conventional surveying instruments.

The RTK-GNSS positioning accuracy of the LRTK device is published as within a few cm (within a few in), and in some cases less than 1 cm (less than 0.4 in) for planar position. For example, experiments measuring a fixed LRTK unit multiple times reported a single-measurement horizontal error (standard deviation) of approximately 12 mm (0.47 in), and averaging about 60 measurements at the same point improved accuracy to approximately 8 mm (0.31 in). This level of precision is practical for on-site surveying equipment and meets the strictness required for establishing control points and as-built checks. Vertical accuracy is also within a few cm (a few in), which is sufficient for general civil engineering quality control.

LiDAR scanning on smartphones also captures surface geometry with centimeter-level accuracy (half-inch accuracy) at close ranges (within a few m (within a few ft)). Since point clouds are tagged with coordinates derived from LRTK, the overall positional accuracy is preserved for wide-area 3D models. The output quality can meet the Ministry of Land, Infrastructure, Transport and Tourism’s “As-Built Management Guidelines (Photogrammetry Edition),” making it possible to produce deliverables acceptable as formal as-built management documents.

That said, actual accuracy depends on satellite reception conditions and environmental factors. In open sky conditions, RTK high-precision solutions are almost always attainable, but in areas like high-rise cityscapes or mountainous regions, multipath (reflections) and satellite blockage can degrade accuracy. Therefore, when establishing important control points, it is recommended to increase reliability through techniques such as averaged positioning or multiple observations. Overall, however, smartphone + LRTK provides positioning accuracy comparable to conventional manual surveying and can be relied upon for routine as-built checks and quantity measurements.

On-Site Cautions When Using Smartphone Surveying

To operate smartphone surveying and AR safely and effectively on-site, consider the following points.

• Ensure satellite reception: To maintain RTK-GNSS accuracy, use the system where the sky view is as open as possible. In tunnels, inside buildings, or in dense urban areas, satellites may not be captured and accuracy can degrade to standard GPS levels. Consider taking control point measurements in open areas and measuring relative to them as needed.

• Handling devices and smartphones: Confirm that the LRTK device attached to the smartphone is securely fixed. As precision equipment, avoid drops and shocks, and consider using dustproof and waterproof cases. Monitor smartphone and LRTK battery levels during long operations and prepare spare power sources.

• Measurement reference and offsets: When using a hand-held smartphone, the antenna position is above the ground, so height offset correction is required. Use the included pole or monopod and set the antenna height in the app for automatic correction. For critical points, perform error checks against known points and, if necessary, restart the device or use averaged positioning to ensure accuracy.

• AR display calibration: AR model projection depends on the smartphone’s orientation sensors and camera tracking. Electronic compasses can be affected by nearby steel structures and become inaccurate, so align a true north reference at the start of surveying or compare the displayed direction with a known bearing to calibrate orientation. Modern AR apps use sensor fusion for stable displays, but if you travel long distances in the field it can be effective to restart the app to reset drift.

• Safety and task division: Working while looking at a smartphone screen can reduce situational awareness. On-site, pay attention to footing and moving machinery, and perform surveying and AR checks only after ensuring safety. If possible, work in pairs so one person can focus on screen operation while the other watches the surroundings to maintain safety.

By observing these points, you can maximize the benefits of smartphone surveying while minimizing risks. Although new technology may cause initial unease, with on-site experience and ingenuity you can achieve safety and quality control that surpasses traditional methods.

Future Possibilities Opened by Smartphone Surveying and AR

The fusion of smartphone surveying and AR guidance is expected to expand into many areas going forward. One foreseeable development is integration with wearable devices such as AR glasses. Currently AR displays are shown on smartphones and tablets, but in the future, incorporating LRTK-equivalent positioning into smart glasses could allow workers to view AR information in real time while keeping both hands free. For example, helmet-integrated AR goggles that display 3D models or navigation directly in the field of view would enable more intuitive and safer transmission of work instructions.

Moreover, analyzing acquired high-precision point clouds and design models with AI could enable automated quality checks and real-time pass/fail determination of as-built conditions. Accumulating daily or weekly scans via smartphone surveying and automatically comparing progress or visualizing quantities would promote digital-twin-style uses. Currently, LRTK cloud services allow overlaying point clouds from multiple days to monitor construction progress, but in the future this may evolve into systems that track the entire construction process with data to detect delays or defects early.

Integration with administrative and public data is also anticipated. Combining smartphone surveying with national 3D urban models like PLATEAU, or integrated underground utility databases, could be applied to urban infrastructure management and inspection. For instance, if routes of nearby water/sewer and communications cables can be confirmed in AR during road works, prior coordination and permit applications could proceed more smoothly. Smartphone surveying could serve as a new on-site information platform across fields such as facilities management, disaster response, and cultural heritage preservation—not limited to construction.

On the technology side, further improvements in positioning satellites and in-device sensors are expected. Multi-frequency GNSS chips and higher-resolution LiDAR becoming standard will further boost accuracy and reliability. With 5G/6G connectivity enabling continuous cloud connections, sharing and processing large 3D data sets in real time will become easier. Such advances could realize full automation and real-time surveying, keeping on-site digital twins continuously up to date.

Conclusion: Start Simple Surveying and AR Use with LRTK

Facing workforce shortages and the need for productivity improvements, the fusion of smartphone surveying and AR guidance is a powerful solution that balances labor savings and quality assurance. The combination of iPhone and LRTK makes it possible for anyone to measure sites with surveyor-like accuracy and visualize and share acquired data on the spot. By adopting advanced technologies beyond traditional methods, you can accelerate on-site DX and step into the next stage of construction management.

If you are struggling with surveying or as-built management burdens or manpower shortages, consider introducing smartphone surveying using LRTK. Linking simple surveying without relying on dedicated instruments with intuitive AR use will remarkably support daily operations in a smart and powerful way. Use the latest technology to make future construction sites more efficient and easier to understand. For example, the [LRTK official site](https://www.lrtk.lefixea.com/) provides product information, case studies, and contact windows—please access it if you are interested. We hope this new use of smartphone surveying × AR brings innovative added value to your sites.