A Smartphone RTK That Even Surveyors Will Be Surprised By! The Field Survey Revolution Opened by LRTK Phone

High-precision positioning using smartphones is now poised to revolutionize field surveying. What once required expensive, specialized equipment such as total stations or survey-grade GNSS devices and the skills of a trained surveyor to achieve centimeter-level positioning can now be accomplished with a single smartphone. Leading the way is the LRTK Phone. This innovative smartphone RTK solution that even professional surveyors find astonishing is beginning to overturn conventional practices for construction site workers and design consultants alike.

This article explains the challenges of field surveying and the importance of cm level accuracy (cm level accuracy (half-inch accuracy)), and describes how the combination of smartphones and RTK technology is changing workflows. It also introduces the technical features and key functions of LRTK Phone and examines its usefulness through concrete use cases such as stake driving, as-built management, inspection, and disaster response. Finally, we compare it with conventional methods, outline the benefits of adoption, and discuss future prospects and the potential for simplified surveying to explore the future scenario that on-site adoption could bring.

現場測量の課題

Accurate surveying on construction and civil engineering sites directly affects project quality and safety. However, traditional surveying methods have several challenges. First is the issue of manpower and time. For example, surveying with a total station required at least two people: one to operate the instrument and another to place and move the prism. From setting up and leveling the tripod to aiming at targets and reading and recording points, many procedures are involved, so measuring a large number of points could easily take an entire day. Additionally, operating equipment and reading measurement points are difficult without experienced personnel, so dependence on specialized knowledge was a major issue. When humans read and write numbers manually, even a small misreading or transcription error can lead to design or construction mistakes.

Moreover, the lack of real-time capabilities was another persistent problem on site. Traditionally, survey data collected on site had to be brought back to the office and compared with design drawings or CAD data before the validity of as-built conditions or installation positions could be confirmed. If discrepancies were found, it was necessary to return to the site for corrective surveying, creating rework. Surveying in dangerous locations was also problematic. Locations that are difficult or hazardous to approach—such as cliff faces or the underside of bridges—could only be surveyed by abandoning the measurement or taking risky actions with conventional methods. This forced compromises on safety and efficiency.

Finally, equipment cost cannot be ignored. High-precision GNSS receivers, 3D scanners, and total stations are all expensive, making it difficult for small and medium-sized companies to equip multiple sites. Limited equipment leads to waiting for devices on site or rising rental costs. With a shortage of experienced surveyors and pressure to improve efficiency, there was considerable room for improvement in traditional surveying styles.

cm精度測位の重要性

On construction sites, surveying accuracy is directly linked to quality. Especially for setting out foundations, managing elevations, and verifying as-built conditions of structures, errors of a few centimeters are usually unacceptable. Surveyors are professionals requiring national certification, and high-precision surveying has traditionally relied on dedicated equipment and advanced methods. The GNSS built into typical smartphones yields errors on the order of meters. Positioning technologies used in commercial AR apps (for example, self-localization using camera and inertial sensors like ARKit) also suffer from drift over long durations and large areas, making them unreliable for surveying. To achieve centimeter-level accuracy, GNSS positioning must be supplemented to remove error factors in some way.

That is where RTK (Real Time Kinematic), broadly referred to as real-time high-precision positioning, has been used. In RTK-GNSS, the rover receiver at the mobile station corrects positioning errors using differential data from a base station placed at a known position. In Japan, a network-type RTK (Ntrip distribution) utilizing the Geospatial Information Authority's permanent GNSS station network (GEONET) has been established, allowing easy access to correction information via the Internet. By activating an RTK-capable receiver with a smartphone and connecting to a correction service, a fixed solution (integer fix) can be obtained in as little as about 1 minute, after which position updates continue with centimeter-class accuracy. Furthermore, receivers that support the Cabinet Office’s Quasi-Zenith Satellite System (QZSS) centimeter-level augmentation service (CLAS) can receive augmentation information directly from satellites, maintaining high accuracy even outside cellular coverage. In mountainous or disaster sites where communication infrastructure is disrupted, CLAS-enabled RTK can provide stable positioning.

Being able to determine absolute positions to the centimeter order via RTK is indispensable for applying AR technologies and point-cloud measurements to surveying. It enables accurate spatial alignment that was difficult with a smartphone alone, making advanced on-site decisions—such as overlaying measured points on drawings or design models for immediate verification—possible. High-precision positioning is the foundation for promoting DX (digital transformation) on site, and RTK plays a key role.

スマホ×RTKがもたらす業務変化

So what changes does “smartphone RTK,” the combination of smartphones and RTK, bring to the field? In short, it comes down to “enabling a single person to perform safe, high-precision surveying in a short time.” Survey tasks that previously required two or more people can be completed by one person with smartphone RTK. Preparation is simply powering on the smartphone and a compact receiver—no special installation is needed. Walk to the desired point and press the measurement button to obtain high-precision coordinates. There is no longer a need to spend long hours and deploy multiple staff as before, dramatically improving surveying efficiency.

Intuitive operation is another major change. The smartphone app provides AR guidance and automatic recording, making it easy to use even for non-experts. For example, measured points appear as markers on maps or camera views in real time. There is no worry of accidentally measuring the same position twice or missing records. This enables less experienced workers to take on aspects of field surveying, reducing the burden on veteran surveyors and aiding skill transfer.

Also, the ability to confirm results on the spot greatly changes site workflows. Smartphone RTK allows immediate comparison of acquired coordinate data with design data or overlaying a completed model in AR. The situation of “having to bring data back to the office to check whether the as-built condition is correct” is transformed. Because you can check as-built measurements and installation positions on site, errors can be corrected immediately, significantly reducing rework.

The cost implications are also significant. Smartphone RTK requires only a commonly used smartphone, a compact receiver, and a service subscription. It is far lower cost than purchasing and maintaining a fleet of dedicated high-end equipment. Compact devices are easy to carry, making it realistic to equip each worker with “one surveying device per person.” As a result, losses from equipment waiting and personnel scheduling are reduced, improving overall construction efficiency and productivity.

Thus, the advent of smartphone × RTK enables surveying with fewer people, in less time, and at lower cost, fundamentally changing onsite surveying practices. Of course, highly specialized control surveys that demand millimeter accuracy still require traditional optical instruments, but for routine civil surveying and as-built verification, smartphone RTK can now strike a practical balance between accuracy and convenience.

従来手法との比較

How exactly does the new surveying method using smartphone RTK differ from conventional methods? Below is a comparison between typical traditional methods and using LRTK Phone.

• Personnel and time required: Traditional total station surveys were performed by two-person teams and took long hours; smartphone RTK can be completed by one person in a short time. Surveying that once took a full day can sometimes finish in a few hours, greatly reducing personnel and labor costs.

• Required expertise: Previously, operation and reading by skilled surveyors were indispensable. With smartphone RTK, the app guides measurement and recording, making it accessible to non-specialist workers. This levels out reliance on veterans and benefits skill transfer.

• Real-time verification: Traditionally, data had to be taken back to the office for drawing comparison and re-measured if errors were found. With smartphone RTK, measured values can be immediately compared with design data on site, enabling detection and correction of discrepancies on the spot. This prevents rework and improves quality.

• Equipment and cost: Traditional high-precision equipment required large initial investments and maintenance costs. Smartphone RTK can be introduced by combining an existing smartphone with a dedicated receiver, lowering initial costs. Providing devices to multiple people is relatively inexpensive, reducing rental fees and waiting times.

• Safety: Traditional surveying in high or hazardous places carried risk. Smartphone RTK offers non-contact distance measurement using the camera (target measurement) and AR guidance, allowing acquisition of necessary points from a safe distance. This contributes to reduced accident risk during surveying.

As described above, smartphone RTK innovates traditional methods across many aspects, bringing the site benefits of “fewer people, shorter time, high precision, safety, and low cost.”

LRTK Phoneの技術的特長

A noteworthy concrete example of smartphone RTK is the LRTK Phone. Developed by Lefixea, a Tokyo Institute of Technology spinoff startup, it is a high-precision GNSS positioning platform that supports iPhone and iPad. The LRTK system mainly consists of the following components.

• LRTK Phone (dedicated GNSS receiver): A pocket-sized, smartphone-sized RTK-GNSS receiver. It weighs approximately 165 g and has a thin profile with a thickness of about 13 mm (0.51 in), but it contains a high-performance antenna and a battery. By attaching it to an iPhone via a dedicated snap-on case, your existing smartphone instantly becomes a surveying device capable of centimeter-level positioning. Connection is via Bluetooth or a Lightning cable, and it supports network-type RTK (Ntrip) and CLAS reception from the Quasi-Zenith Satellite System, enabling real-time high-precision positioning anywhere in Japan. Battery life is about 6 hours, and it can be extended via USB-C power supply. It also offers dustproof and waterproof performance, ensuring robustness for demanding field use.

• LRTK App (iOS app): A dedicated app that provides all-in-one functions required for field surveying, from positioning and recording to AR display and navigation. It supports single-point measurements and continuous positioning (up to 10 points per second), and includes point averaging functions to improve accuracy. Acquired points are plotted on a map in real time, and conversion to Japan’s plane rectangular coordinate system and geoid height calculations are performed automatically. Photos taken are tagged with high-precision position and orientation data and can be uploaded to the cloud with one tap. Recorded points can be set as targets and navigated to using maps or an AR radar. A variety of tools for measuring, recording, and communicating—such as virtual stake placement, target guidance, and remote target positioning—are integrated into a single app.

• LRTK Cloud (web platform): A service to instantly share and store survey data and photos collected on site to the cloud. Data can be visualized on maps and 3D models via a browser, and CSV or point cloud data can be downloaded. Time-series organized data and photos facilitate collaboration among stakeholders, and password-protected viewing links can be generated for internal and external information sharing.

LRTK Phone is characterized by providing consistent support from hardware to software and cloud services. It is more than a GNSS receiver; it is a comprehensive platform that envisions the utilization and sharing of acquired data, dramatically streamlining the workflow of measuring, verifying, and communicating on site. Utilizing existing smartphones, it delivers precision and functions comparable to dedicated devices in a more accessible form factor, which is another major attraction.

LRTK Phoneの主な機能

LRTK Phone and its app include a variety of features that transform on-site surveying and measurement work. The main ones are listed below.

• Visual surveying support with AR: An AR function that overlays virtual objects onto the site through the smartphone screen. It can display virtual stakes or markers at positions from the design to indicate stake-driving locations, or synthesize planned 3D models into the site scenery to intuitively share construction imagery. Additionally, measured points and checkpoints can be shown as AR markers to visually identify discrepancies between as-built and design on the spot or to prevent missed inspection points.

• 3D point cloud scanning: Using an LiDAR-equipped iPhone to scan surrounding 3D point cloud data and assigning RTK-derived precise coordinates to those points. Typical smartphone point cloud scans tend to have positional drift or unstable scale, but correcting each point with RTK allows scanned point clouds to be placed immediately into geodetic coordinates. This enables on-site tasks such as comparing ground shapes before and after excavation to calculate volumes or recording detailed as-built shapes.

• Coordinate guidance navigation: A function that guides the user on site to pre-determined coordinate values or design reference points. The app displays arrows or guidance on the map or in AR toward the specified target coordinate. This enables accurate navigation to stake-driving or layout positions with a smartphone in hand, replacing traditional methods of marking lines with wooden stakes or chalk. It makes work significantly easier in locations where physical stake installation is difficult, such as slopes or rocky terrain, by indicating positions with virtual markers.

• Target positioning (remote target measurement): A non-contact measurement function that uses the smartphone camera and sensors to measure coordinates of distant objects. For example, points on a cliff top that are out of reach or structures under an overpass can be measured from a safe distance by simply capturing the object with the smartphone camera, instantly deriving latitude, longitude, and elevation for the point. This is achieved by combining smartphone attitude (orientation and tilt) sensors, LiDAR-based distance estimation, and RTK-enhanced self-positioning. It dramatically improves safety and efficiency when surveying hazardous or hard-to-access locations.

• High-precision photo recording: Photos taken with the LRTK app are automatically recorded with high-precision position and camera orientation. For instance, when photographing damage at a disaster site and sharing it to the cloud, each photo will have an accurate location and direction, making it immediately clear which area the photo represents during later office analysis. When performing periodic observations of the same location over time, the app can guide the camera location and angle with AR based on the previous shot, enabling consistent composition and angle for photographic records. This makes high-repeatability photographic measurement—such as crack width comparison or fixed-point monitoring of construction progress—easy to perform.

As described above, LRTK Phone includes a range of features that leverage AR and sensor technologies beyond simple positioning. Because these functions are integrated within a single smartphone app, the need to switch among multiple devices or software on site is eliminated, allowing necessary information to be obtained, verified, and shared in real time.

杭打ち・丁張り作業への活用

One representative case where LRTK Phone’s power is demonstrated is in stake driving and layout tasks. Traditionally, surveyors measured distances on site from coordinates on drawings and drove wooden stakes or stretched strings to indicate reference positions and elevations. These tasks required experience and intuition, and it could be difficult to drive stakes into bedrock or steep slopes.

Using smartphone RTK dramatically streamlines such stake driving and layout tasks. By inputting coordinates from the design into the LRTK app and setting them as targets, the smartphone will guide you to the location. As you approach the target, the screen displays remaining distance and direction, and when the accuracy converges, a virtual marker indicating “this is the design position” appears in AR. Even where physical stakes cannot be placed, the exact position can be indicated on the smartphone screen, freeing you from the dilemma of “wanting to mark it but unable to.” Virtual stakes can be displayed repeatedly, shared with other workers, or rechecked later.

As a result, the effort and time required for layout and foundation setting are greatly reduced. One person walking with a smartphone is sufficient, enabling rapid work with fewer people. Even on sites with large elevation differences or poor visibility, accurate point indication is possible, providing more reliable layout than before. Mistakes such as driving stakes in the wrong place or remeasuring are reduced, improving overall construction efficiency and quality.

出来形管理への活用

LRTK Phone is also a powerful tool for as-built management after embankment, excavation, or concrete placement. Traditionally, checking as-built conditions required staff to measure numerous point elevations with surveying instruments, bring data back to the office, and compare with design sections and reference elevations to detect excesses, shortages, or irregularities. This process was time-consuming and often caused rework because immediate on-site confirmation was not possible.

With LRTK Phone, as-built checks can be performed on site in real time. For example, when checking grading status, an iPhone LiDAR scanner can scan the ground surface point cloud while RTK assigns coordinates to each point. Overlaying that data with the design model or reference elevations on site allows you to intuitively see, in color-coded form, where the embankment is overfilled or where excavation is insufficient. This is essentially a field 3D as-built inspection, enabling immediate quality checks without waiting for later analysis.

When spot-checking pavement thickness or as-built dimensions of structures, points measured with LRTK Phone can be displayed in AR to visually confirm deviations from design values. If areas requiring correction are found, they can be marked or remeasured on the spot, greatly contributing to preventing rework. Furthermore, acquired as-built data can be shared via the cloud immediately, allowing supervisors and designers to respond remotely, realizing rapid inspection cycles.

点検・維持管理への活用

Smartphone RTK is also expected to play an active role in routine inspection and maintenance of infrastructure and structures. For bridge and tunnel patrol inspections, managing inspection points on a map and ensuring no omissions are critical. LRTK Phone can display pre-registered inspection point coordinates as AR markers on site. With “what to inspect next” visible at a glance, the risk of overlooking points is reduced.

Notably, it improves reproducibility of photo records. For example, when comparing crack widths on a tunnel wall over time, accurate comparison requires photographing from nearly the same angle and distance each time. Previously, only skilled personnel could approximate this in the field. The LRTK app records the previous camera position and orientation and guides you with AR on the next inspection to reproduce the same composition. This greatly enhances the accuracy of fixed-point observations, allowing accumulation of reliable maintenance data.

High-precision geotagged photos and measurement data collected during inspections can be uploaded to the cloud for internal sharing or used in report preparation. Because location information is accurate, it is clear “which location this photo shows,” improving the reliability of reports. Introducing LRTK Phone transforms inspection work into an efficient process with fewer omissions, contributing to advanced infrastructure maintenance.

災害対応への活用

Smartphone RTK is also highly effective in disaster response situations such as earthquakes and heavy rainfall. Rapid, accurate situational awareness and planning for recovery are required at disaster sites. However, immediately after a disaster, on-site communications may be disrupted, heavy machinery may be unable to access areas, and secondary hazards may exist, making surveying and investigation difficult.

With LRTK Phone, a small, lightweight smartphone can be used to quickly walk through hazardous areas and record coordinates and photos of necessary points. As mentioned earlier, CLAS augmentation support allows centimeter-level positioning to continue even where cellular signals are unavailable, via satellite. For example, at a landslide site, remote target positioning can capture points such as the toe of the landslide or extent of damage from a safe distance, and upload high-precision photos to the cloud immediately. Office or remote engineers can receive the data almost in real time, plot it on drawings to analyze damage, and begin considering emergency measures. This enables rapid, synchronized collaboration between the site and headquarters, greatly accelerating initial response.

In fact, some local governments in Japan have begun equipping staff with GNSS-enabled smartphones for recovery of mountain landslide areas, using them for surveying and recording conditions where heavy machinery cannot reach. Cases have arisen where creating a damage map that used to take several days can be completed the same day. LRTK Phone can serve as a “mobile investigation unit” for disaster response, supporting lifesaving and infrastructure recovery efforts.

現場導入メリットまとめ

As we have seen, adopting LRTK Phone on site yields many benefits. Here we summarize the key effects.

• Labor and effort reduction: Because surveying can be completed by one person, tasks that previously required multiple staff can be greatly reduced. This helps create a workflow that can be managed with fewer people even amid a shortage of experienced surveyors.

• Speed improvement: Surveying time is dramatically shortened, and because measurement, verification, and sharing can be done in real time, overall construction speed improves. Waiting and setup losses are also reduced.

• Improved safety: Enabling remote surveying of hazardous locations reduces worker risk. Fewer-person operations also reduce accident risk during personnel movement and human error.

• Improved quality and accuracy: Constant access to cm-level data and immediate verification reduce mistakes and oversights, suppressing variability in construction quality. The reliability of as-built and inspection results increases, enabling data-driven quality control.

• Cost reduction: In addition to labor savings and avoided rework, there is no need to purchase and maintain numerous expensive surveying devices, reducing capital and maintenance costs. Efficiency gains that shorten construction schedules also contribute to total cost savings.

Adopting LRTK Phone delivers significant value across people, time, safety, quality, and cost—effectively a productivity revolution.

今後の展望と簡易測量の可能性

As smartphone RTK becomes widespread, the manner of field surveying will continue to change dramatically. In the trend of construction DX represented by the Ministry of Land, Infrastructure, Transport and Tourism’s “i-Construction,” accessible high-precision positioning tools like LRTK Phone are becoming indispensable. The era of one surveying device per person, where each person carries a smartphone as a surveying instrument and can measure, confirm, and share on the spot as needed, is becoming realistic.

Of course, it will remain important to use the right tool for the job. Tasks requiring millimeter-level precision—such as establishing construction control points or displacement measurements—will continue to rely on levels, total stations, and high-performance laser scanners. However, a large portion of routine surveying and measurement work can be adequately handled by smartphone RTK. The role of surveyors may shift from manual field work to data management and verification, overseeing overall quality. With smartphone RTK lowering the barrier, more people can perform surveying to a certain standard, allowing limited surveyors to focus on higher-level tasks and raising overall efficiency and quality.

Satellite positioning, sensors, and AR technologies are expected to advance further. More compact, higher-performance devices and new measurement methods will enhance the convenience of smartphone RTK. In the future, integrating construction machinery with smartphone RTK to automatically feedback as-built conditions or having AI analyze field data to propose optimal construction plans may become a reality. The field surveying revolution opened by LRTK Phone has the potential not just to improve surveying efficiency but to transform how work is done on site.

The era of simplified surveying has begun, and the important first step is to experience it on site. Adopting high-precision surveying that can be completed with a single smartphone will let you feel its convenience and effectiveness firsthand. LRTK Phone is a powerful partner that supports on-site DX. By proactively embracing new technologies rather than clinging to old conventions, construction site productivity and safety can be dramatically improved. Whether you are a surveyor or a field worker, why not verify this smartphone RTK surveying revolution with your own eyes? The future of field surveying is just around the corner.