Table of Contents

• Challenges of traditional surveying and achieving centimeter-level positioning

• What is LRTK Phone?

• Technologies enabling centimeter-level positioning

• Main features of LRTK Phone

• Site surveying transformed by a single smartphone

• Simple surveying with LRTK

• FAQ

Challenges of traditional surveying and achieving centimeter-level positioning

There are many situations—such as setting out positions on construction sites, confirming property boundaries, and as-built management—where centimeter-level positioning accuracy (cm level accuracy, half-inch accuracy) is required. For example, placing structures exactly where designed needs precision that cannot tolerate even a few centimeters of error. Traditionally, achieving this level of accuracy on-site required experienced surveyors and expensive equipment. When using optical surveying instruments like total stations, their large size and weight typically require two people to operate, and transporting and setting up the equipment takes effort. Maintenance such as annual calibration and adjustment also incurs costs, making adoption difficult for small contractors and local governments.

On the other hand, lightweight devices like smartphones or handheld GPS units have standalone positioning errors of around 5–10 m, which is acceptable for map apps but unusable for on-site surveying. If building layout or boundary measurements are off by several meters, they are impractical, so tasks requiring centimeter-level accuracy have continued to rely on professional surveying equipment.

Thus, high-precision on-site positioning has long required labor and cost. Recently, the construction industry has been facing labor shortages and a decline in experienced personnel, increasing demand for "an easy way to perform accurate surveying." If anyone could obtain centimeter-level positioning easily, surveying work would be streamlined and more efficient, greatly boosting productivity.

What is LRTK Phone?

To meet this demand, the innovative device "LRTK Phone" was developed to turn a smartphone into a high-precision surveying instrument. Developed by Refixia, a startup from Tokyo Institute of Technology, the system consists of an ultra-compact RTK-GNSS receiver used with an iPhone or iPad. The receiver attaches to a smartphone via a dedicated case or attachment; by launching the dedicated app, it enables centimeter-level positioning (cm level accuracy, half-inch accuracy) that previously required specialized equipment. The pocket-sized receiver weighs just over 100 g and has a thickness of about 1 cm (0.4 in), making it easy to carry to the site and use whenever needed.

When attached to a phone, LRTK Phone turns the device into a universal surveying tool. In addition to acquiring highly accurate positions from satellite positioning, it leverages the phone’s built-in camera and LiDAR sensor for 3D point-cloud captures (scans), stake placement guidance, and augmented reality (AR) overlays of design data—completing tasks with a single smartphone. An era has arrived in which surveying tasks that previously required multiple devices and personnel can be handled with just a smartphone. Each field technician can carry their own surveying device in their pocket and use it when needed—realizing the concept of "one device per person."

Technologies enabling centimeter-level positioning

The key technology that converts a smartphone into a surveying instrument is RTK (real-time kinematic) positioning. While standard GPS (GNSS) positioning suffers errors of about 5–10 m as noted earlier, RTK uses satellite data received simultaneously at a base station and a rover to subtract common errors, dramatically improving accuracy. LRTK Phone adopts this RTK approach and, despite being a compact device for iPhone, achieves professional surveying-grade accuracy of about ±1–2 cm (±0.4–0.8 in) horizontally and ±3 cm (±1.2 in) vertically. In tests comparing it with a class-1 high-precision GNSS unit, average errors were reported below 5 mm (0.20 in), confirming its high positioning accuracy.

The LRTK receiver includes a high-performance GNSS antenna supporting multiple frequencies and captures signals from all available constellations such as 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-level augmentation service (CLAS) (cm level accuracy, half-inch accuracy). With CLAS support, correction information can be received directly from Michibiki, enabling centimeter-level positioning in real time even in areas without cellular coverage, such as mountainous regions or the open sea. Where mobile communication is available, LRTK also supports network RTK corrections (Ntrip) using networks like the Geospatial Information Authority of Japan’s reference station network, maintaining high-precision positioning nationwide.

In addition, the dedicated LRTK app includes an averaging positioning function. By measuring a stationary position continuously for several seconds and computing the average, single-sample errors are reduced. Under favorable conditions, averaging dozens of measurements can improve accuracy to below 1 cm (below 0.4 in). This combination of hardware and software delivers positioning accuracy that belies its smartphone form factor. RTK also enables accurate altitude (elevation) measurements that were difficult with conventional smartphones, making LRTK Phone useful across a wide range of civil engineering and construction applications.

Main features of LRTK Phone

LRTK Phone lowers the barriers to on-site surveying through portability and high-precision positioning. Key points include:

• Ultra-compact, lightweight design: The device body is approximately 165 g and only about 1 cm (0.4 in) thick. It attaches to the back of a smartphone for compact portability, so you can keep it in your pocket. You can quickly attach it when needed and avoid carrying heavy tripods or surveying instruments.

• Built-in battery for long operation: The device has a built-in battery that provides about 6 hours of continuous operation. Charging is via USB Type-C, and you can power it from a mobile battery in the field, ensuring long-term operation even outdoors where power is hard to secure.

• One-touch attachment and simple connection: Using a dedicated phone case or magnetic attachment, the device can be attached and detached from an iPhone/iPad with one touch. Attach it only when needed and remove it when not in use. Pairing to the phone is done via Bluetooth or Lightning, and high-precision positioning begins simply by launching the app—no complicated initial setup or special operations are required.

• Centimeter-level high-precision positioning: Thanks to the RTK technique and the high-performance antenna, current position can be measured with an accuracy of about ±2 cm (±0.8 in) horizontally and a few centimeters vertically. This precision covers a wide range of surveying needs from stake-out on construction sites to infrastructure inspections. Precise elevation information, which could not be obtained with built-in smartphone GPS, is also available for use as survey results.

• Michibiki CLAS support—reliable even out of coverage: Because it can receive the high-precision correction signal CLAS from Japan’s Michibiki satellites (cm level accuracy, half-inch accuracy), LRTK Phone can maintain centimeter-level positioning even where there is no mobile network coverage. As long as the satellites are visible, high-precision measurements are possible in remote construction sites or areas where base stations are down due to disasters. (Where communication is available, Ntrip network RTK can also be used.)

• Surveying tasks possible by one person: The LRTK device can be mounted on an optional monopod or a pole with a spike at the tip. With the smartphone attached, stake-out work or single-point surveying that previously required two people can be performed accurately by one person. Height offsets (instrument height above ground) can be set with a single button in the app, and by leveling with a bubble level you can achieve precise positioning even with one hand.

• Diverse surveying functions: The dedicated LRTK app enables a wide range of functions on a single smartphone: - High-precision single-point positioning: With one tap you can measure and record latitude, longitude, and height. It supports Japan’s plane rectangular coordinate system and automatically calculates geoid height, allowing the obtained coordinates to be used directly in designs and reports. - Continuous positioning and averaged positioning: In continuous mode you can record a track by acquiring up to 10 high-precision position points per second while moving. In average mode you can compute the averaged coordinate over a specified number of seconds. Taking multiple measurements improves accuracy. - 3D point-cloud scanning: By capturing the surroundings with an iPhone/iPad camera or LiDAR scanner while adding LRTK’s high-precision coordinates in real time, you can easily generate 3D point clouds with absolute coordinates. This revolutionary function lets you measure extensive terrain in 3D by simply walking around—without a dedicated laser scanner. - Coordinate navigation (guidance): The app guides you toward preset target coordinates with arrows and distance on the phone screen. By following the map and bearing, you can reach the target point, making stake marking and locating buried objects straightforward. AR guidance displays help you intuitively locate points. - AR overlay of design data: If you import 3D design models or drawings such as BIM/CIM into the app, you can overlay them onto the camera view in AR. Because the model is aligned in absolute coordinates, you can instantly check whether installed elements match their designed position and elevation. Marker-free, non-drifting AR displays also help stakeholders reach consensus. - Geotagged photos: Photos taken while positioning with LRTK are automatically tagged with the photo location’s latitude, longitude, height, and camera orientation (bearing). They are saved with timestamps and notes, so when you review them later you can immediately tell from where and in what direction a photo was taken. This eliminates the need to annotate maps or organize photos manually, dramatically streamlining inspection records and comparisons over time. - Various measurements: On the acquired point-cloud data you can measure distances between any two points and calculate area or volume for a specified region. For example, you can compute embankment or excavation volumes on-site or generate cross-sections from the point cloud. Performing analyses on-site that previously required dedicated software is a big advantage.

• Integration with cloud services: Data collected on site can be uploaded and synchronized to LRTK Cloud with one tap. On the cloud-based web map, measured points and tracks are plotted and you can view coordinates, photos, and notes for each point. You can issue a sharable URL so stakeholders can view survey results in a browser 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 syncing to the field phones lets the app guide users to specified points. Seamless field↔office information sharing greatly shortens the time needed to compile and check survey results.

Site surveying transformed by a single smartphone

With the features above, LRTK Phone is changing how on-site surveying is done. Its ease and speed overturn conventional surveying practices. Because you can take a smartphone and the compact device from your pocket and start high-precision positioning within minutes, there is no time lost to "preparing for surveying." You can obtain coordinates of points you need to measure on the spot, improving agility for field surveys and as-built management.

The fact that surveying can be completed by a single staff member is also significant. Tasks such as stake-out and batter-board layout that used to require survey specialists or multiple assistants can now be performed by the construction manager alone. Even those without surveying expertise can follow on-screen directions and press buttons to make accurate measurements, making LRTK Phone an attractive solution for addressing labor shortages. Single-person operations also reduce the need for someone to hold equipment, enabling safer surveying in hazardous locations.

Real-time information sharing further improves efficiency. By using LRTK Cloud, field data can be shared instantly with the office team. For example, if measured point coordinates and photos are uploaded to the cloud, stakeholders can review the information before the field team returns. This speeds up checks and updates to drawings, reducing idle time. The field can send new target coordinates via the cloud and another worker can immediately go measure that spot—facilitating real-time two-way collaboration. Digitalization and cloud integration considerably shorten the workflows for processing and approving survey data that used to take days, dramatically improving overall field productivity.

LRTK Phone is also proving capable in harsh environments. Reports from veteran surveyors indicate that it maintained high-precision positioning in forests and mountain areas where satellite positioning is normally difficult. Its multi-frequency stability helps preserve accuracy even under conditions where conventional GPS units might deviate by more than 5 m (more than 16.4 ft). This high reliability of positioning suggests LRTK can be actively used in situations where GNSS surveying was previously avoided.

The style of "one smartphone per person" for surveying may become the new norm for field operations. LRTK Phone has started to be featured in various media as cutting-edge technology, and real-world deployments are steadily increasing. At one civil engineering site, introducing LRTK reportedly reduced the time required for stake-out surveying to less than half of what it used to be. As portable, responsive smartphone surveying spreads, field work efficiency and quality control are expected to improve further.

Simple surveying with LRTK

LRTK Phone enables a new workflow in which even non-specialists can perform simple surveying. With only a smartphone and a small receiver, situations like "work is halted today because the surveying team isn't available" can be reduced. For example, in local governments without dedicated surveying departments, responsible staff can perform surveying with their own smartphones, speeding up infrastructure inspections and disaster response. In fact, Fukui City was an early adopter of this smartphone surveying system (LRTK) in 2023 for disaster recovery. Staff who discovered damaged sites could immediately take high-precision measurements on site, reducing round trips between field and office and achieving faster response and cost savings. With limited personnel, they could quickly record damage and streamline recovery planning. Smartphone surveying with LRTK thus has great value as a simple surveying method in emergencies.

Allowing anyone on site to perform tasks that used to require specialists has immeasurable impact. By adopting simple surveying with LRTK Phone, you can eliminate the time and effort involved in arranging surveying services and enable autonomous, flexible field responses. This new surveying solution, which balances accuracy and efficiency, is likely to be adopted at an increasing number of sites. If you are facing challenges with on-site surveying, consider introducing LRTK Phone’s simple surveying approach.

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 a compatible iOS device to the dedicated case and mount the LRTK receiver, then launch the app to start using it. Other than 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 around ±3 cm (±1.2 in) vertically. Averaging measurements while stationary for several seconds can achieve sub-1 cm (sub-0.4 in) accuracy. This rivals high-end GNSS survey instruments.

Q: Can it be used where there is no mobile signal? A: Yes. LRTK Phone supports Michibiki’s high-precision augmentation service CLAS (cm level accuracy, half-inch accuracy), enabling centimeter-level positioning even outside mobile coverage. In mountainous areas or disaster sites where internet connectivity to base stations is unavailable, corrections can be received directly from satellites to maintain high accuracy.

Q: Is it really possible for one person to perform stake-out and surveying? A: Yes. LRTK Phone can be mounted on a monopod or pole, allowing tasks that formerly required two or more people to be carried out by one person. The app guides the operation, so you simply move the smartphone to the indicated location and press a button. The app also displays arrow guidance for stake-out, helping even inexperienced users locate target points without difficulty.

Q: How can measurement data be used? A: Positioning results, point clouds, photos, and more can be stored and shared in the cloud. Data can be downloaded from the cloud in CSV or SIMA formats for import into CAD software, and it’s easy to share with stakeholders. The cloud can also perform coordinate transformations and distance/volume calculations, helping directly with report creation and drawing revisions.

Q: What happens in places where GPS signals are blocked, such as between skyscrapers or under trees? A: Real-time RTK positioning becomes difficult where satellite signals are extremely weak. However, the LRTK app offers an indoor positioning mode that uses the phone’s camera and inertial sensors to continue positioning for short periods when satellites are temporarily lost. For example, if you pass under a bridge, having previously captured position where the sky was visible allows the system to estimate and record the current position autonomously until satellites can be reacquired. Errors will accumulate over long durations, but the ability to continue data acquisition in locations that were previously unmeasurable is a major advantage.