Table of contents

• What is LRTK Phone?

• How smartphones achieve centimeter-level positioning (RTK technology)

• Verifying the accuracy of LRTK Phone

• Use cases enabled by centimeter-level positioning

• What is simple surveying with LRTK

• Conclusion

• FAQ

When it comes to smartphone GPS positioning, errors of several meters have generally been the norm. However, in recent years, remarkably high-precision positioning with smartphones has become possible. A representative example is Refixia’s LRTK Phone. With LRTK Phone, the typical GPS errors of around 5-10 m (16.4-32.8 ft) can be reduced to approximately about 1 cm (0.4 in). How accurate can LRTK Phone actually be? In this article we explain in detail the mechanism and performance of smartphone-based centimeter-level positioning and the use cases it enables. At the end, we also introduce simple surveying using LRTK.

What is LRTK Phone?

LRTK Phone is a GNSS receiver device that can be attached to a smartphone to achieve centimeter-level high-precision positioning. It was developed by Refixia Inc., a startup originating from Tokyo Institute of Technology, with the concept of “turning a smartphone into a pocket-sized all-purpose surveying instrument.” In practice, simply attaching LRTK Phone to an iPhone or Android smartphone (or tablet) allows high-precision position measurements and surveying work that previously required specialized surveying equipment to be performed with just a smartphone.

The LRTK Phone unit is compact and lightweight—weighing approximately 125 g and about 13 mm (0.51 in) thick—small enough to fit in a pocket. It houses a high-performance RTK-GNSS receiver, antenna, and battery, and is used integrated with a smartphone. It attaches and detaches with one touch to a dedicated smartphone case, offering the convenience of quick installation when needed. Because the battery is built in, there is no need to worry about power during long on-site use (almost all day). The device connects to the smartphone via Bluetooth or similar means and position measurements are performed through a dedicated app. Because positioning, data recording, and sharing can all be completed with this one unit, it truly functions as an “all-purpose surveying instrument.”

How smartphones achieve centimeter-level positioning (RTK technology)

Why can a smartphone achieve ultra-high precision positioning at the centimeter level? The key is a positioning technique called RTK (Real Time Kinematic). RTK is a method that uses signals from multiple GNSS satellites and determines the relative position to a base station with high precision. Ordinary GPS positioning yields errors of several meters due to satellite signal errors (ionospheric delays, satellite clock errors, etc.). RTK, however, compares the known position of a nearby reference point (base station) with the observation data from the rover (the smartphone) in real time, canceling out atmospheric errors and enabling relative positioning on the order of centimeters.

LRTK Phone contains a GNSS receiver that supports this RTK high-precision positioning. A notable feature is that it is three-frequency compatible. While many conventional GNSS receivers were single-frequency, receiving only the L1 band, LRTK Phone can receive signals on multiple bands such as L1, L2, and L5. Multi-frequency support improves correction accuracy for ionospheric errors and allows the device to achieve a fixed solution (Fix) more quickly and stably. As a result, smartphone-based centimeter-level positioning with reliability beyond traditional solutions becomes possible.

RTK positioning normally requires correction information (data that compensates for errors) from a base station, but LRTK Phone can use an Internet-based network of reference stations as well as the centimeter-level augmentation service (CLAS) broadcast from Japan’s quasi-zenith satellites, Michibiki. By receiving CLAS, high-precision positioning is possible even in environments without Internet connectivity, such as mountainous areas or at sea where cellular service may be unavailable. In fact, the ability to perform RTK positioning even outside of communication coverage thanks to Michibiki’s augmentation signals has proven valuable in disaster sites. For example, during the 2023 Noto Peninsula earthquake damage survey, where communications infrastructure was disrupted, LRTK Phone proved effective, enabling accurate positioning and recording with only small equipment.

Thus, by combining advanced GNSS positioning technology with communications technology, LRTK Phone enables acquisition of precise location information that was previously unattainable with a smartphone alone.

Verifying the accuracy of LRTK Phone

So, how about the crucial matter of accuracy? LRTK Phone is nominally described as “centimeter-level,” but let’s look at specific figures. According to manufacturer tests, when repeatedly measuring the same fixed point, the single-measurement error (standard deviation) was about 12 mm (0.47 in). This is an error of roughly 1.2 cm (0.5 in), already vastly more precise than conventional GPS. Furthermore, by averaging multiple observations using features in the LRTK app, an astonishing error of about 8 mm (0.8 cm, 0.31 in) was achieved. Eight millimeters is under 1 cm, truly in the “sub-centimeter” realm. Under favorable conditions, horizontal positioning has been confirmed to achieve accuracy below 1 cm (0.4 in).

These figures are comparable to specialized surveying equipment. High-precision GNSS receivers and surveying instruments are generally said to have errors of several centimeters in RTK positioning on flat ground, so LRTK Phone can be considered to have performance on par with them. Of course, actual accuracy depends on environmental conditions. Open areas without obstructions provide the best results, whereas urban canyons with tall buildings or forests, where satellite signals are reflected or attenuated, can cause unstable positioning or increased errors. Even so, the precision improvement over smartphone-only GPS is indisputable. The CEO of Refixia has stated that “while normal GPS has errors of about 5-10 m (16.4-32.8 ft), LRTK can measure accurately at about 1 cm (0.4 in),” emphasizing the high positioning accuracy of LRTK Phone.

LRTK Phone also shows good vertical (height) accuracy. RTK positioning typically has slightly larger errors in altitude than in the horizontal plane, but the errors still remain on the order of a few centimeters. For example, the above tests measured horizontal positions under 1 cm and vertical positions within a few centimeters. This level of accuracy is sufficient for tasks such as checking finished heights on construction sites.

Overall, LRTK Phone’s accuracy lives up to its “centimeter-level” name. It offers precision that sets it apart from conventional smartphone GPS and has been demonstrated to be suitable for serious positioning and surveying applications.

Use cases enabled by centimeter-level positioning

When centimeter-level accuracy becomes available on a smartphone, the scope of on-site work and services expands greatly. Here are the main use cases and benefits enabled by LRTK Phone.

• Streamlining surveying and layout work: On construction and civil engineering sites, surveyors often perform tasks such as setting reference points (layout) and as-built management using high-precision equipment. With LRTK Phone, site supervisors and workers themselves can carry out simple surveying tasks and immediately obtain and verify coordinates of required points. For example, checking building placement or guiding the installation position of structures (coordinate navigation) can be done accurately while viewing real-time coordinate information on the smartphone screen.

• Use in infrastructure inspection and surveys: For inspections of roads and bridges or damage surveys after disasters, it is important to attach accurate position coordinates to photographs for records. With LRTK Phone, photos taken on a smartphone can be automatically tagged and saved with cm level accuracy (half-inch accuracy) location information and capture orientation. This enables recording the exact location of, for example, concrete cracks or the extent of landslides; because photos and geographic coordinates are shared on the cloud immediately, the situation can be accurately understood later on maps. In urgent data-collection scenarios such as disaster sites, one-stop positioning and recording is highly useful.

• AR visualization and design verification: LRTK Phone’s high-precision location data can be combined with a smartphone’s AR (augmented reality) features. For instance, if you have location data for underground pipes or cables, you can display 3D models or markers precisely in AR at the correct positions on-site through the smartphone. During a subsequent excavation, workers can view the positions of buried utilities through the phone and avoid damaging pipes. You can also project design lines or structural models on-site before construction to verify whether placement matches plans. AR displays have traditionally suffered from positional drift, but with LRTK accuracy, a stable AR experience that doesn’t drift while walking around becomes possible. This facilitates sharing completion images among project stakeholders and smooth consensus-building.

• 3D measurement and point-cloud acquisition: Combining LRTK Phone with a smartphone camera allows easy 3D point-cloud surveying. By moving the smartphone as if scanning the scene within a dedicated app, you can capture surrounding terrain and structures as point-cloud data. On iPhone models without LiDAR, photogrammetry techniques still enable point-cloud generation. Because the resulting point clouds are tagged with absolute (world) coordinates from the start, they can be directly overlaid on maps or CAD drawings in post-processing. This makes advanced analyses such as on-site earthwork volume calculations or automatic generation of as-built drawings feasible in a short time. For example, you can measure the filled volume of a large reclaimed area on-site and instantly compare it to plan values.

As shown above, enabling centimeter-level positioning on everyday smartphones makes the on-site workflow of “measure and check immediately” much easier to adopt. Tasks that once relied on specialized contractors or expensive equipment can be performed quickly in-house, leading to shorter schedules, improved quality, and cost savings.

What is simple surveying with LRTK

One of the productivity-enhancing initiatives enabled by LRTK Phone is “simple surveying.” Simple surveying refers to allowing on-site personnel to perform part of the measurements that previously required professional surveyors. With LRTK, even people without extensive training can achieve centimeter precision with minimal operations. For example, routine dimensional checks, as-built verification, or boundary checks that occur daily on construction sites can be carried out immediately as simple surveying tasks.

Specifically, by mounting an LRTK Phone-equipped smartphone on a pole or monopod and pointing it at a point, pressing a button in the app records the coordinates (latitude, longitude, height) of that location. Recorded points are automatically synchronized to the cloud and can be shared in real time with staff in the office. This allows on-site questions to be answered quickly with numbers, and stakeholders can share information and make decisions promptly.

Conventional surveying equipment often requires operator proficiency and has a high unit price. LRTK Phone, however, is usable without training and has lower introduction costs, which is a key feature. Subscription-based usage plans are also available, enabling low initial costs and lowering the barrier to on-site adoption. In this way, simple surveying with LRTK represents a new on-site style anticipating an era of “one device per person.” In fact, LRTK Phone is attracting attention as an essential tool on construction sites, and many companies have started trial deployments. There are also cases of deliveries of 3D as-built results to the Ministry of Land, Infrastructure, Transport and Tourism, showing adoption in public projects.

Incorporating high-precision positioning into daily operations dramatically accelerates the on-site PDCA cycle. If simple surveying with LRTK Phone becomes widespread, more flexible and efficient construction management and maintenance will be realized.

Conclusion

We have reviewed the capabilities and use cases of smartphone-based cm-level positioning. With LRTK Phone, centimeter-level high-precision positioning that was once difficult is now possible in the palm of your hand, contributing to operational efficiency across a wide range of fields from construction and civil engineering to inspection and surveying. Its accuracy has been measured to fall below 1 cm (0.4 in) in practice, equipping it with performance comparable to specialized instruments. The ability to position even outside communication coverage, along with advanced features such as AR and point-cloud measurement, is transforming it into a genuine “all-purpose surveying instrument.”

As high-precision positioning technology becomes more accessible, the barrier to “measuring” tasks has fallen dramatically. From now on, anyone on site can take quick measurements without needing to call in specialists. Simple surveying with LRTK supports this new work style. A world in which precise location information can be handled with a smartphone is upon us, and further expansion of use cases is expected.

FAQ

Q. What kind of product is LRTK Phone?

A. It is a small high-precision GNSS receiver that is attached to and used with a smartphone. It dramatically improves smartphone GPS accuracy to achieve centimeter-level positioning. It is a pocket-sized device that mounts into a dedicated case and contains an antenna, GNSS module, and battery, with positioning data acquired and managed via a dedicated app.

Q. How accurate is LRTK Phone?

A. Horizontal errors are around 1–2 cm (0.4–0.8 in) typically, and under favorable conditions can be below 1 cm (down to the millimeter range). Tests have shown about 12 mm (0.47 in) for single measurements and about 8 mm (0.8 cm, 0.31 in) after averaging data. Height errors are also within a few centimeters, giving accuracy comparable to professional surveying equipment.

Q. How can such high-precision positioning be achieved on a smartphone?

A. Because it uses RTK (Real Time Kinematic) positioning. By using correction information from base stations to cancel satellite positioning errors, centimeter-level accuracy is obtained. LRTK Phone supports multi-frequency GNSS signals and can utilize augmentation signals (CLAS) from Japan’s Michibiki satellites, enabling high-precision positioning even outside cellular coverage.

Q. What preparation or environment is required to use it?

A. Basically, you need a compatible smartphone (iPhone or Android), the LRTK Phone unit, and the dedicated app. Initial setup is simple—install the app and connect the device to start positioning. For high-precision positioning, an outdoor environment where GNSS satellite signals can be received is preferred (indoor or underground positioning is not possible). While Internet connectivity accelerates stable positioning, accuracy can be maintained even without connection by receiving Michibiki’s correction data.

Q. What are the advantages and disadvantages compared to conventional surveying equipment?

A. The biggest advantages are portability, ease of use, and lower cost. LRTK Phone is pocket-sized and ready to use, requires no specialist training, and is intuitively operable. It is also priced lower than many surveying GNSS units, and subscription plans can reduce initial investment. Disadvantages include increased smartphone battery consumption during extended use and inability to use indoors. However, for outdoor positioning, it offers accuracy comparable to conventional equipment and sufficient operational time (the device itself has a long-lasting internal battery), making it suitable for most on-site tasks.

Q. In what situations is LRTK Phone useful?

A. It is useful in a wide range of situations requiring high-precision location data, such as construction and civil engineering site surveying, infrastructure inspections, and disaster area surveys. Examples include setting reference points and as-built verification at construction sites, patrol inspections of bridges and roads, and photographic records at disaster sites. It is also being used in advanced applications such as combining AR to visualize drawings or buried utilities on-site. In short, LRTK Phone is beneficial in any situation where knowing an accurate position is useful.

Q. Will centimeter-level positioning on smartphones become standard in the future?

A. Smartphone-embedded GPS chips are improving year by year, but currently achieving centimeter-level positioning with a smartphone alone is difficult. External devices like LRTK Phone and augmentation services are key. Demand for high-precision positioning is growing, and an era in which smartphones combined with peripherals routinely deliver centimeter-level accuracy is likely to come. LRTK Phone is a pioneer in this area. In the future, smartphones themselves may come standard with multi-frequency GNSS and correction reception functions, but for now, solutions like LRTK remain the easiest way to achieve cm-level positioning.