Achieving Centimeter-Level Positioning Accuracy with LRTK Phone – Site Surveying Changed by a Single Smartphone

Table of Contents

• Challenges of Conventional Surveying and Centimeter-Level Positioning

• What is LRTK Phone?

• Technologies Enabling Centimeter-Level Positioning

• Main Features of LRTK Phone

• How a Single Smartphone Changes Site Surveying

• Simplified Surveying with LRTK

• FAQ

Challenges of Conventional Surveying and Centimeter-Level Positioning

There are many situations—such as laying out positions on construction sites (staking), verifying land boundaries, and managing as-built measurements—where centimeter-level positioning accuracy is required. For example, installing structures in the exact positions specified by design requires tolerance of only a few centimeters. However, achieving this level of accuracy in the field traditionally required experienced surveyors and expensive equipment. When using optical surveying instruments like total stations, the equipment is large and heavy, so work is usually carried out by two-person teams, and transporting and setting up the equipment is time-consuming. Maintenance such as annual calibration and adjustments also incurs costs, making adoption difficult for small contractors and local governments.

On the other hand, lightweight devices such as smartphones or handheld GPS units typically have standalone positioning errors of about 5–10 m (16.4–32.8 ft), which is acceptable for map apps but unusable for on-site surveying. A few meters of offset in building layout or boundary measurement is impractical, so centimeter-level tasks have historically depended on dedicated surveying equipment.

Thus, high-precision field positioning has long required personnel and expense. Recently, labor shortages and the decline of veteran workers in construction have intensified the demand for “an easy way to perform accurate surveying.” If anyone could easily achieve centimeter-level positioning, surveying tasks would be streamlined and made more efficient, significantly boosting productivity.

What is LRTK Phone?

Responding to this need, the innovative device “LRTK Phone” transforms a smartphone into a high-precision surveying instrument. Developed by Reflexia, a Tokyo Institute of Technology spin-out startup, the system consists of an ultra-compact RTK-GNSS receiver used with an iPhone or iPad. Attached to a smartphone via a dedicated case or accessory and activated with a dedicated app, it enables centimeter-level positioning that previously required specialized equipment. The pocket-sized receiver weighs only about 100-odd grams and is about 1 cm (0.4 in) thick, allowing it to be carried to the field and used whenever needed.

When attached to a smartphone, the device turns the phone into an all-purpose surveying instrument. In addition to obtaining high-precision positions from satellite positioning, it leverages the smartphone’s built-in camera and LiDAR sensor for 3D point cloud scanning, guidance for stake positions, and augmented reality (AR) overlays of design data—completing the workflow with a single smartphone. The era where multiple devices and personnel were required for surveying is giving way to one where each field technician can carry their own surveying device in their pocket, enabling a “one person, one device” mobile surveying workflow.

Technologies Enabling Centimeter-Level Positioning

The key technology that turns a smartphone into a surveying instrument is RTK (real-time kinematic) positioning. As noted above, standard GPS (GNSS) positioning typically yields errors of about 5–10 m (16.4–32.8 ft), but RTK uses satellite data received simultaneously at a base station and a rover to subtract common errors and dramatically improve positioning accuracy. LRTK Phone adopts this RTK method and, despite being a compact device for iPhone, achieves accuracy comparable to professional surveying instruments—approximately ±1–2 cm (±0.4–0.8 in) horizontally and about ±3 cm (±1.2 in) in height. Tests comparing it with first-class high-precision GNSS equipment showed average errors under 5 mm (0.20 in), confirming its high positioning accuracy.

The LRTK receiver includes a high-performance GNSS antenna that supports multiple frequencies and captures signals from all available constellations: the U.S. GPS, Russia’s GLONASS, Europe’s Galileo, and Japan’s quasi-zenith satellite system “Michibiki.” A major feature is support for Michibiki’s centimeter-class augmentation service (CLAS). With CLAS support, sites outside of mobile network coverage—such as mountainous areas or at sea—can receive correction information directly from Michibiki and achieve centimeter-level positioning in real time. Where mobile communications are available, the device also supports network RTK corrections (Ntrip) using networks such as the Geospatial Information Authority of Japan’s Continuously Operating Reference Station network, maintaining high-precision positioning nationwide.

In addition, the LRTK dedicated app includes an averaging-position feature. By measuring position continuously for several seconds while stationary and computing the average, it reduces errors compared to single measurements. Under favorable conditions, averaging dozens of measurements can improve accuracy to below 1 cm (<0.4 in). This hardware–software combination is what makes LRTK Phone’s smartphone-based positioning achieve unexpectedly high accuracy. RTK also enables accurate elevation measurements, which were difficult with conventional smartphones, making LRTK Phone useful across civil engineering and construction site workflows.

Main Features of LRTK Phone

LRTK Phone’s portability and high-precision positioning technology lower the barriers to field surveying. The main points are as follows.

• Ultra-compact, lightweight design: The device itself weighs approximately 165 g and is only about 1 cm (0.4 in) thick. It is compact enough to attach to the back of a smartphone and carry in a pocket. You can quickly take it out and attach it on site, eliminating the need to transport heavy tripods or surveying instruments.

• Built-in battery for long operation: The device contains a battery that allows approximately 6 hours of continuous operation. Charging is via USB Type-C, and it can be powered from a mobile battery in the field, enabling extended surveying even where power is hard to secure.

• One-touch attachment and simple connection: Using a dedicated smartphone case or magnetic attachment, it can be attached to iPhone/iPad with one touch. Attach it only when needed and remove it when not in use. Pairing with the smartphone is via Bluetooth or Lightning, and high-precision positioning starts as soon as the app is launched—no complicated initial setup or special operations are required.

• Centimeter-level high-precision positioning: Thanks to the RTK technology and high-performance antenna mentioned above, it can measure current position with approximately ±2 cm (±0.8 in) horizontal accuracy and a vertical accuracy of a few centimeters (a few inches). This level of precision supports a wide range of surveying needs, from construction staking to infrastructure inspections, and provides precise elevation data that built-in smartphone GPS could not achieve.

• Michibiki CLAS support—reliable even outside network coverage: Because it can receive the high-precision correction signal CLAS from Japan’s Michibiki satellites, it can maintain centimeter-level positioning even at sites without mobile coverage. As long as satellites are visible, high-precision positioning is possible in remote mountain sites or in areas where base stations are down due to disasters. (Where communications are available, network RTK via Ntrip can also be used.)

• One-person surveying tasks: The LRTK device can be mounted on optional monopods or poles with a metal tip. With the smartphone mounted, tasks that previously required two people—such as staking and single-point measurements—can be performed accurately by one person. The app allows height offsets (instrument height above ground) to be set with a single button, and using a bubble level to level the device enables precise positioning even with one hand.

• Wide range of surveying functions: The dedicated LRTK app enables many functions with just one smartphone: - High-precision single-point positioning: With a single tap you can measure and record latitude, longitude, and height. It supports Japan’s plane rectangular coordinate systems and automatically computes geoid height, allowing captured coordinates to be used directly for design and reporting. - Continuous positioning and averaging: In continuous mode, you can acquire up to 10 high-precision points per second to record tracks while moving. Averaging mode computes the mean coordinate over a specified number of seconds, improving accuracy by repeated measurements. - 3D point cloud scanning: While capturing the surroundings with an iPhone/iPad camera or LiDAR scanner, LRTK adds high-precision coordinate data in real time to easily generate 3D point clouds with absolute coordinates. This groundbreaking function enables large-area topographic measurement simply by walking around, without the need for a dedicated laser scanner. - Coordinate navigation (guidance): The app guides you to pre-set target coordinates with arrows and distance readouts on the smartphone screen. By following map and bearing instructions, you can reach the target point—useful for marking stake positions or locating buried utilities. AR guidance displays make it intuitive to find locations. - AR overlay of design data: If you import 3D design models or drawing data such as BIM/CIM into the app, you can display them as AR overlays on the live camera image. Because models are aligned with absolute coordinates, you can instantly verify whether constructed elements are in the correct position and elevation relative to the design. Marker-free, stable AR overlays help stakeholders reach consensus. - Geotagged photos: Photos taken while LRTK is fixing position are automatically tagged with latitude, longitude, height, and camera orientation (bearing). Saved with timestamps and notes, the photos make it easy to see “where and in which direction a photo was taken” later, eliminating the need to annotate maps or manually organize photos. This greatly improves efficiency for inspection records and change-over-time comparisons. - Various measurements: On acquired point cloud data you can measure the distance between any two points or calculate area and volume for a specified region. For example, you can compute embankment or excavation volumes on site or generate arbitrary cross-sections from the point cloud. Analyses that used to require specialized software can now be performed easily in the field.

• Integration with cloud services: Field-acquired data can be uploaded and synchronized to LRTK Cloud with one tap. On the cloud web map, measured points and tracks are plotted and you can view coordinates, photos, and notes for each point. You can issue a shareable URL so stakeholders can view survey results in a browser even without the dedicated app. Data can be downloaded in CSV or SIMA formats for smooth import into CAD or GIS. Conversely, uploading design coordinate data or boundary point lists to the cloud and synchronizing with field smartphones allows on-site devices to navigate to specified points. Seamless field–office data sharing greatly shortens the time needed to compile and check survey results.

How a Single Smartphone Changes Site Surveying

With the features and capabilities described above, LRTK Phone is transforming how field surveying is done. First, its ease of use and speed overturn traditional expectations. You can take a smartphone and the small device from your pocket and begin high-precision positioning within minutes, eliminating time spent preparing equipment. Because coordinates can be obtained the moment you decide to measure, mobility for field surveys and as-built management is dramatically improved.

The fact that surveying can be completed by a single field worker is also significant. Tasks such as staking and setting out traditionally required multiple surveying specialists or assistants, but with LRTK Phone a construction manager can perform layout alone. Even those without surveying expertise can follow on-screen guidance and press buttons to take accurate measurements, so the system is gaining attention as a countermeasure against labor shortages. Single-person operation also reduces the need for others to support equipment, enabling safer surveying in hazardous locations.

Real-time information sharing also drives efficiency. Using LRTK Cloud, field data can be shared instantly with office teams. For example, uploading measured point coordinates and photos allows stakeholders to review information before returning to the office, accelerating checks and drawing updates and reducing waiting times. Two-way workflows are possible—sending new target coordinates from the office to the field via the cloud so another worker can immediately measure that location. Digitalization and cloud integration greatly shorten the days previously required for processing and approving survey data, yielding dramatic productivity gains across the site.

Furthermore, LRTK Phone has demonstrated the ability to perform surveying under challenging conditions. Reports from veteran surveyors indicate that high-precision positioning was maintained with LRTK even in forests and mountainous areas where satellite positioning is usually difficult. Its multi-frequency, stable positioning performance helps preserve accuracy under conditions where conventional GPS equipment might deviate by more than 5 m (16.4 ft). This high reliability of positioning suggests that GNSS surveying can be applied in scenarios where it was previously avoided.

The “one person, one smartphone” surveying style could become the new norm for field operations. LRTK Phone has begun to be featured in various media as a cutting-edge technology, and real-world adoption cases are steadily increasing. In one civil engineering project, stake-out surveying time was reportedly reduced to less than half after introducing LRTK. As portable, rapid-response smartphone surveying spreads, site efficiency and quality control are expected to improve further.

Simplified Surveying with LRTK

LRTK Phone enables a new workflow in which non-specialists can perform simple surveying. Because only a smartphone and a small receiver are needed, situations such as “work is halted because the survey team is not available today” can be avoided. For example, local governments that lack dedicated surveying departments can have staff carry out measurements on their own smartphones, speeding up infrastructure inspections and disaster response. In fact, Fukui City was an early adopter of this smartphone surveying system (LRTK) for disaster recovery in 2023. Staff who discovered damaged areas were able to perform high-precision measurements on the spot, reducing trips between field and office and accelerating response while cutting costs. Limited personnel could quickly record damage and streamline recovery planning. LRTK smartphone surveying therefore has great value as a quick surveying method during emergencies.

The impact of enabling anyone on site to perform tasks that previously required specialists is immense. Incorporating the simplified surveying enabled by LRTK Phone reduces the time and effort previously spent arranging surveys and allows autonomous, flexible field response. This new surveying solution, which balances accuracy and efficiency, is likely to be adopted at more and more sites. If you face challenges with field surveying, consider introducing the simplified surveying made possible by LRTK Phone.

FAQ

Q: What do I need to use LRTK Phone? A: Basically, you need an iPhone or iPad, the LRTK device, and the dedicated LRTK app. Attach the dedicated case to a supported iOS device, mount the LRTK receiver, and launch the app—apart from initial pairing, no special equipment or complex setup is required.

Q: What level of positioning accuracy can be achieved? A: Depending on conditions, typical accuracy is about 1–2 cm (0.4–0.8 in) horizontally and about 3 cm (1.2 in) vertically. By averaging measurements taken while stationary for several seconds, sub-centimeter accuracy (<1 cm (<0.4 in)) can be achieved. This is comparable to high-end GNSS surveying instruments.

Q: Can it be used where mobile signals do not reach? A: Yes. LRTK Phone supports the Michibiki satellite system’s high-precision augmentation service CLAS, enabling centimeter-level positioning even outside mobile coverage. In mountainous areas or disaster zones where internet communication from base stations is unavailable, correction information can be received directly from satellites to maintain high accuracy.

Q: Is it really possible for one person to perform staking and surveying? A: Yes. LRTK Phone can be mounted on a monopod or pole, allowing tasks that previously required two or more people to be performed by one person. The app guides operation, so you simply move the smartphone to the instructed position and press a button. The on-screen arrow guidance for staking helps even inexperienced users find target points without confusion.

Q: How can the measurement data be used? A: Positioning results, point cloud data, photos, and more can be saved and shared in the cloud. Data can be downloaded from the cloud in CSV or SIMA formats for import into CAD software, and sharing with stakeholders is simple. The cloud can also perform coordinate transformations and distance/volume calculations, supporting report generation and drawing revisions directly.

Q: What happens in places where GPS signals are blocked, such as between buildings or under trees? A: Real-time RTK positioning becomes difficult in locations where satellite signals are extremely weak. However, the LRTK app includes an indoor positioning mode that uses the smartphone camera and inertial sensors to continue positioning for short periods when satellites are temporarily lost. For example, if you pass under a bridge, having captured position in an open area just before entering allows the system to estimate and record the current position autonomously until satellites are reacquired. Errors accumulate over long periods, but the ability to obtain continuous data in places that were previously unmeasurable is a significant advantage.