Table of Contents

• cm-level RTK positioning achievable with an iPhone

• Strengths of cloud-connected RTK services

• Easy adoption with subscription-based services

• Comparison with traditional approaches: outright purchase / rental vs subscription

• On-site use cases: surveying to point-cloud capture and AR

• Simple surveying, point-cloud capture, and AR navigation using LRTK

• FAQ

cm-level RTK positioning achievable with an iPhone

In recent years, the accuracy of GPS/GNSS modules built into smartphones has improved dramatically, and the latest iPhones can now handle multi-frequency satellite signals, enabling positioning with errors on the order of tens of centimeters (tens of inches). In Japan, augmentation signals from the quasi-zenith satellite system "Michibiki" have further improved standalone smartphone positioning accuracy. However, on surveying and civil engineering sites, situations often demand 1-2 cm (0.4-0.8 in) accuracy, requiring even higher-precision positioning.

What addresses this need is the fusion of RTK (Real-Time Kinematic) positioning with smartphones. RTK is a method that exchanges GNSS data between a base station (reference) and a rover (positioning device) to perform real-time error corrections and achieve centimeter-level position accuracy. Traditionally this required dedicated, bulky equipment, but recently ultra-compact RTK-GNSS receivers that attach to iPhones and iPads have emerged, making cm-level positioning with only an iPhone possible. By attaching a small device weighing in the 100 g range to a smartphone and receiving correction information, smartphone positioning that once had errors of several meters (several ft) can be rapidly improved to the level of a few centimeters (a few in).

With these solutions, the smartphone used on site becomes a high-precision surveying instrument. Because the devices are pocket-sized and include an internal battery, they are easy to carry and handle on site. The era is beginning where each worker can carry one smartphone RTK per person, and the convenience of being able to position oneself immediately when needed is a major advantage.

Strengths of cloud-connected RTK services

A major strength of smartphone-based RTK positioning solutions is the ability to instantly upload acquired data to the cloud, enabling real-time sharing between the field and the office. Coordinates of measured points, photos, and notes are recorded to the cloud on the spot, and all stakeholders can view them through a web browser. Since measured locations are automatically plotted on a map, there is no need to record by hand or bring data back via USB.

For example, if a site supervisor uploads high-precision photos and positioning data taken with an iPhone to the cloud, office-based engineers can immediately view those photos and their locations on a map to understand the situation. This eliminates analog procedures like verbally relaying measured values over the phone or writing notes for later entry, dramatically speeding up information sharing. Also, with data accumulated in the cloud, daily reports and summaries become easier to produce, and it is simple to review past measurement histories. Because photos and point-cloud data are tagged with precise location information, it is possible to track changes over time or integrate the data with CAD drawings and GIS systems.

Cloud connectivity centralizes on-site positioning data. There is no risk of data scattering across devices, and if a device is lost, a backup remains in the cloud. With proper access controls, positioning results can also be shared with external contractors or clients, enhancing project-wide transparency and collaboration. These features not only provide high-precision positioning but also offer significant advantages for promoting on-site DX (digital transformation).

Easy adoption with subscription-based services

Another factor lowering the barrier to on-site adoption of high-precision positioning is that these solutions are offered as subscription (flat-rate) services. Traditionally, deploying RTK-GNSS equipment required an initial investment of several million yen for a receiver and base station set. In contrast, subscription services include the full set of equipment and software usage fees in a monthly rate, allowing users to reduce initial costs and get started. Because equipment can be used in a leasing-like manner, it is easier to adopt as an operating expense rather than capital expenditure.

Subscription services provide the latest devices and applications continuously. While subscribed, updates and maintenance are applied automatically, so users do not need to handle complex management themselves. If equipment fails, the service provider typically supports or replaces it, reducing operational concerns on site. Many services also allow flexible scaling of contracts by the number of devices or duration required, enabling scalable use according to project size.

On the other hand, outright purchase entails not only a large upfront cost but also risks of obsolescence due to technological advances and idle costs during unused periods. With a subscription model, these risks are mitigated while always providing access to up-to-date equipment, making it an attractive option even for companies cautious about adopting new technologies. The small initial burden and comprehensive post-adoption support greatly accelerate on-site deployment speed.

Comparison with traditional approaches: outright purchase / rental vs subscription

Before the advent of smartphone RTK, there were mainly two typical ways to utilize RTK positioning on site. Below we compare these with subscription-based services.

• Dedicated equipment purchased outright: If a company purchases RTK-GNSS receivers and base stations, they can use them whenever they like. However, the initial investment is very large, and calibration, maintenance, and software updates also require time and cost. Because these are advanced measurement devices, operational proficiency takes time to develop, and without specialized surveyors, it can be difficult to use them effectively on site. Additionally, purchased equipment may not be in full use at all times, creating inefficiency by holding idle assets.

• Renting equipment as needed: Renting RTK equipment per project reduces initial investment while allowing use of the latest models. However, rental costs can accumulate if used frequently. There is a risk that equipment may not be available when needed, and handling pickup and return is an extra burden. Temporarily rented gear also makes it harder to accumulate in-house know-how, requiring repeated checking of settings and operation, and thus may not be ready for immediate use on site.

• Using a subscription service: Subscription-based RTK positioning services resolve the above issues. They substantially reduce initial costs while ensuring high-precision tools are always on hand, so you can use them immediately whenever needed. Smartphone-app-centered, intuitive user interfaces make them easy to handle even for non-experts, reducing training costs. Devices and software remain up to date during the subscription, and maintenance support is included in the fee, allowing site staff to focus on positioning tasks. There is no need for cumbersome arrangements like rental, and organizations can build and retain in-house know-how for continuous use.

Thus, compared with traditional methods, subscription-based smartphone RTK services lower cost and operational hurdles while delivering immediate responsiveness on site and cumulative benefits from continued use.

On-site use cases: surveying to point-cloud capture and AR

Smartphone RTK solutions can be applied across a wide range of field operations. In construction and civil engineering, tasks that previously required a surveying team—such as stakeout (layout) and setting control points for as-built management—can now be performed on-site by supervisors or workers themselves. Transferring coordinates from drawings to the field can be guided by the smartphone display, allowing single-person accurate placement. This reduces project delays due to waiting for survey teams and enables immediate positioning, greatly improving work efficiency. The app can also automatically calculate distances, elevation differences, and areas between measured points, providing rapid measurement results on site.

Smartphone RTK is also powerful for infrastructure inspection and disaster surveys. When photographing bridge or road cracks or ground subsidence with an iPhone, each photo is tagged with cm-level position information and shooting orientation. These photos can later be precisely located on a map, and re-surveys at different times can easily capture the same location and angle.

For example, in an earthquake-affected area, smartphone RTK was used to measure and record utility pole tilts and road cracks, then quickly share the data with stakeholders via the cloud. In confined sites or mountainous areas where bulky equipment cannot be brought in, high-precision positioning data can still be obtained with just a smartphone and a small receiver, aiding rapid disaster response documentation.

Moreover, smartphone RTK is being applied to 3D point-cloud capture. Recent iPhones include LiDAR scanners that can conveniently scan surrounding structures and terrain to create point clouds. If high-precision coordinates from RTK are appended to these point clouds, the data can be unified in a public coordinate system. Use cases include scanning excavation shapes to check as-built conditions or recording displacements of structures and relics with high precision. Where fixed laser scanners were once necessary, smartphone + RTK point-cloud capture enables anyone to perform simple 3D documentation.

A distinctive advanced feature of smartphone RTK is AR navigation for positional guidance. Based on RTK-acquired coordinates, arrows or targets are displayed in AR on the smartphone screen to guide users to target locations. This allows you to return precisely to a previously surveyed or photographed point. Applications include repeat monitoring and locating underground utilities. As you approach the target, real-time offsets in up/down/left/right directions are shown on screen, guiding you to the target with centimeter accuracy—almost like solo surveying with a total station. Such AR usage further expands scenarios for positioning data.

Simple surveying, point-cloud capture, and AR navigation using LRTK

As a concrete service embodying the benefits of smartphone RTK described above, there is LRTK from Reflexia, a venture originating from Tokyo Institute of Technology. LRTK is a cloud-connected subscription service composed of an ultra-compact RTK-GNSS device that attaches to iPhones and iPads, plus a dedicated app and cloud service. By mounting a pocket-sized receiver weighing approximately 125 g and with a thickness of 13 mm (0.51 in) to a smartphone using a dedicated case and connecting via Bluetooth, the smartphone instantly becomes a versatile centimeter-level surveying instrument.

LRTK uses Ntrip-compatible network RTK correction information and Japan’s satellite positioning augmentation service (Michibiki CLAS) to achieve real-time high-precision positioning. Acquired coordinates can be recorded with a single tap in the app and are automatically uploaded to the cloud with point names and timestamps. Recorded data can be immediately displayed and shared on the web-based LRTK Cloud, which also includes distance measurement between points and daily report output features. When taking photos, latitude, longitude, elevation, and shooting direction are automatically recorded, enabling office staff to view site photos with precise location information. Additionally, AR navigation to previously recorded points facilitates smooth re-measurement and repeat observations on site.

Despite its rich functionality, LRTK is developed with the goal of easy adoption as a one-per-person field tool. Because it is available at a reasonable subscription fee compared to traditional equipment, it is easy to deploy at the department or team level, directly contributing to improved on-site productivity. In actual deployments, users report reduced waiting time for surveying tasks and the ability to perform measurements autonomously, along with dramatic improvements in the accuracy and speed of site records. The triad solution of iPhone + RTK + cloud is acting as a driver for on-site DX. The centimeter-level positioning solution resulting from the fusion of smartphones, RTK, and cloud services is expected to be adopted more widely across worksites in the future.

FAQ

Q: Can an iPhone really achieve centimeter-level accuracy on its own? A: By combining a dedicated RTK-GNSS receiver and correction information services, an iPhone can achieve cm-level positioning. The latest iPhones are equipped with high-performance GNSS chips, but alone they typically provide accuracy on the order of tens of centimeters. By using an external device like LRTK together with network RTK (or satellite augmentation signals), positioning errors of a few centimeters can be achieved. It has been demonstrated that in open outdoor environments, smartphone positioning can reach accuracy comparable to traditional surveying instruments.

Q: Do I need my own base station or radio license for RTK positioning? A: No. Subscription services use correction information provided by existing reference-point networks or satellite augmentation systems, so you do not need to install your own base station. Also, smartphones only receive cellular networks and satellite signals, so no special radio license is required (if you operate your own base station, a license may be required in some cases, but this is not a concern when using the service).

Q: What is provided when using a subscription service? A: Typically, the package includes the high-precision GNSS receiver device, a dedicated app for smartphones/tablets, a cloud platform for managing and sharing positioning data, and access rights to correction information (such as network RTK). In other words, the hardware, software, data-sharing system, and correction information services needed for on-site positioning are generally provided as a single set.

Q: Can positioning data be linked or exported? A: Yes. Recorded positioning data and photos can be stored and managed in the cloud and, if needed, downloaded in CSV or DXF formats or imported into GIS/CAD software. Some services and apps also allow direct report output from the field or API integration with other business systems. Because coordinates are high-precision, it is easy to cross-check with other survey results or reflect them in BIM models.

Q: Can it be used in mountainous areas with no cell coverage or indoors? A: If satellite signals can be received outdoors, there are mechanisms that allow use even in areas without cellular coverage. For example, LRTK supports the CLAS signal provided by Japan’s Michibiki, enabling cm-level positioning using satellite augmentation even in mountainous areas without cellular service. However, positioning is difficult in tunnels or indoors where GNSS signals themselves are not available. In such cases, alternative measures—such as reference-point positioning at tunnel exits or combining with an IMU (inertial measurement unit)—are required.