Evolution of RTK Positioning on Smartphones

The advancement in high-precision GNSS chips designed for smartphones has driven significant improvements in smartphone-based RTK positioning. Beginning with the Xiaomi Mi 8, the world's first dual-frequency GNSS smartphone introduced in 2018, devices supporting dual-frequency positioning (L1 and L5 bands) have rapidly increased, including models such as Google Pixel and the latest iPhones. Dual-frequency GNSS enables ionospheric error correction and enhanced use of multiple GNSS constellations, significantly improving standalone smartphone positioning accuracy to the decimeter-level.

Another key development is the enhancement of Android OS capabilities. Starting from Android 7.0 (Nougat), released in 2016, developers gained access to APIs for extracting raw GNSS measurements from smartphones. This allowed direct access to raw data such as pseudorange and carrier phase (accumulated delta range), enabling the implementation of sophisticated positioning algorithms directly on smartphones. Consequently, extensive research has flourished on applying high-precision techniques, previously limited to expensive surveying equipment—such as PPP (Precise Point Positioning) and RTK—using smartphone GNSS data.

In fact, experiments utilizing raw GNSS measurements from smartphones have demonstrated instantaneous centimeter-level accuracy over short baseline distances using RTK methodologies.

However, implementing RTK positioning with smartphones alone poses several challenges. Due to their compact form factor, internal smartphone antennas often have lower sensitivity and are more susceptible to signal noise and multipath interference.

Furthermore, RTK positioning requires receiving correction data from a reference base station, which presents practical barriers for ordinary users regarding acquisition and data processing. Initiatives like Google's "Smartphone Decimeter Challenge," described next, aim to address these hurdles, significantly contributing to the continuous improvement of GNSS positioning accuracy on smartphones.

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Benefits of Smartphone RTK Positioning Using LRTK

By attaching the LRTK Phone to your smartphone, you can easily achieve RTK positioning. Our LRTK Series provides a high-precision GNSS solution designed specifically for use with smartphones. Among these, the LRTK Phone stands out as a pocket-sized RTK-GNSS receiver that attaches directly to smartphones. This compact device, integrating both antenna and battery, easily mounts onto smartphones (primarily iPhones) using a magnetic dedicated cover. By simply connecting via Bluetooth, it receives network-based RTK correction data (via Ntrip), enabling centimeter-level positioning accuracy. Smartphones previously limited to a GPS accuracy of just a few meters can now achieve precision within mere centimeters by simply attaching the LRTK device.

A major advantage is the ease of use—there's no need for any special cable connections, enabling your smartphone to instantly transform into a high-precision positioning device.

Compared to typical standalone smartphone RTK positioning, using LRTK offers several distinct advantages. As mentioned earlier, built-in smartphone GNSS systems often face limitations due to antenna performance and signal noise. In contrast, LRTK devices feature high-sensitivity, multi-band GNSS modules, enabling stable centimeter-level accuracy. For example, the LRTK Phone 4C is a high-performance receiver supporting all major satellite constellations including GPS, GLONASS, Galileo, and QZSS (Michibiki), and is capable of receiving signals across three frequency bands: L1, L2, and L5.

As a result, it becomes easier to capture signals from multiple satellite constellations even in urban areas, significantly increasing the probability of obtaining RTK solutions. Previously, achieving RTK positioning with smartphones required acquiring external base station data and managing complex computational setups. However, LRTK simplifies this process with its dedicated “LRTK App,” enabling intuitive connection to correction services and easy initiation of precise positioning. The ability to start positioning with just a single button press—without requiring specialized knowledge—is a significant advantage for fieldwork operations.

Furthermore, a distinctive feature of the LRTK series is its expandability through the integration of smartphones with external RTK devices. By combining the smartphone's camera, communication capabilities, and cloud integration with the LRTK device's high-precision GNSS, it enables solutions that go far beyond mere positioning. For example, the LRTK app supports continuous positioning at a rate of up to 10 measurements per second (10Hz), allowing users to record movement trajectories and immediately share and review them on cloud-based maps.

It also includes features that enable photos taken on-site to be tagged with high-precision coordinates and orientation data, allowing users to easily verify the precise photo locations later on an office PC.

This capability streamlines the workflow by enabling on-site positioning data and records to be instantly uploaded to the cloud and shared with stakeholders in real-time. By combining the versatility and connectivity of smartphones with LRTK's high-precision positioning capabilities, it is expected to significantly accelerate the digital transformation (DX) of field operations.

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Examples of Smartphone RTK Applications

Construction Industry: At construction sites, tasks such as staking out reference points and performing as-built checks are routinely conducted using surveying equipment. With the practical implementation of smartphone-based RTK positioning, supervisors and individual workers can perform precise surveying and marking tasks conveniently using their own smartphones.

In fact, devices like the LRTK Phone have been developed around the concept of providing "one field tool per person." Its compact size and lightweight design (just 125 grams) allow users to easily carry it in a pocket and instantly perform precise positioning and recording whenever necessary.

As a result, tasks traditionally assigned to specialized surveying teams can now be quickly and independently conducted by on-site personnel, significantly improving operational efficiency and reducing labor requirements. Furthermore, high-precision as-built measurement data can be immediately uploaded to the cloud and shared with headquarters or designers for prompt decision-making, thus streamlining and enhancing construction management.

Surveying and GIS Industries: Smartphone RTK technology has had a significant impact on surveying and GIS industries. Tasks traditionally performed using total stations or GNSS receivers, such as control point surveys and on-site inspections, can now potentially be completed using just a smartphone and compact RTK device. For example, during cadastral surveys or land boundary measurements, boundary markers and feature points can be accurately recorded using smartphone RTK and then immediately integrated into GIS systems. With LRTK's cloud connectivity, point cloud data and trajectory data collected in the field can be reviewed remotely from an office, and surveying results can be simultaneously shared among multiple staff members.

Additionally, smartphone RTK is increasingly utilized for infrastructure maintenance tasks such as bridge inspections and displacement monitoring. Even surveying in remote mountainous areas, previously challenging due to limited cellular coverage, has become feasible with LRTK devices that receive QZSS (Michibiki) CLAS augmentation signals. Such capabilities have proven highly effective in mountain surveys and disaster site investigations. The combination of a smartphone and LRTK device enables the collection of highly accurate positioning data even at sites where carrying extensive equipment is impractical.

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Integration with Drone Surveys and Autonomous Driving: High-precision positioning technology is highly compatible with drone-based aerial mapping and autonomous driving. RTK-equipped drones already perform highly accurate autonomous flight and aerial surveying by utilizing centimeter-level positional data. When combined with smartphone RTK technology, ground-based control points can be quickly established using just a smartphone, or network RTK correction data received via a smartphone can be utilized directly by drones. Furthermore, GNSS and RTK technologies are increasingly applied in autonomous vehicles and construction equipment. The compact and cost-effective high-precision positioning know-how cultivated through smartphone RTK is likely to extend into future in-vehicle systems and robotics. By enabling smartphones to communicate positional correction data to vehicles or drones, there is significant potential to achieve safer and more precise navigation systems. Indeed, autonomous agricultural equipment like tractors already utilize RTK technology to achieve practical driving accuracy down to a few centimeters. Smartphone RTK is well-positioned to contribute to such fields as smart agriculture and smart mobility in the near future.

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Future Prospects and LRTK Implementation Guide

Smartphone positioning technology is expected to achieve even greater accuracy and convenience in the future. Dual-frequency GNSS capabilities are rapidly extending to mid-range smartphones, and it is highly possible that all smartphones will eventually feature high-precision positioning as a standard function. Thanks to advancements in satellite constellations (such as expanded Galileo and QZSS/Michibiki satellite coverage) and the introduction of new augmentation signals (such as Europe’s GALILEO HAS and Japan’s sub-meter level augmentation services), an era where smartphones alone achieve accuracy within tens of centimeters is imminent. Additionally, continued developments in internal sensor fusion, cloud-based correction services, and AI-driven positioning error correction methods are further enhancing reliability, especially in challenging environments like tunnels or urban high-rise areas. Thus, ongoing progress is not limited to positioning accuracy alone but extends steadily to overall usability and robustness of smartphone-based positioning solutions.

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In this context, solutions combining the LRTK series and smartphones will strongly accelerate the widespread adoption of high-precision positioning. With easy-to-use devices such as the LRTK Phone, the traditional notion that "high-precision positioning is exclusively for specialists" will be overturned. By enabling everyone on-site to access centimeter-level location data, tasks previously done manually or analogically will transition to digital processes, resulting in new efficiencies and labor-saving opportunities.

The LRTK series offers a diverse product lineup tailored to various needs, including the smartphone-compatible Phone models, advanced Pro models, and products integrated with 360° cameras designed to streamline on-site documentation. By leveraging these solutions, industries ranging from construction and surveying to disaster management and agriculture can enable "easy, high-precision positioning for everyone, everywhere," significantly driving digital transformation (DX) at worksites.