Centimeter-level high-precision positioning to improve field efficiency! Benefits of introducing LRTK

Table of contents

• Why centimeter-level positioning is necessary for field efficiency

• Issues with conventional surveying methods

• RTK method that enables centimeter-level positioning

• Emergence of smartphone surveying “LRTK”

• Main features of LRTK Phone

• Surveying functions available with LRTK Phone

• Field benefits of introducing centimeter-level positioning

• Case study: use in disaster recovery

• Simple surveying with LRTK Phone

• FAQ

Why centimeter-level positioning is necessary for field efficiency

To improve work efficiency on construction and surveying sites, positional accuracy—i.e., positioning precision—is critically important. For mapping and construction management, position information with errors of several meters is not practical. For example, when marking site boundaries or laying out building positions (staking/marking), if positioning error is as large as 5 m (16.4 ft) you cannot place marks at the correct locations, leading to rework and redo. This not only fails to improve field efficiency but can also cause construction errors and project delays.

On the other hand, satellite positioning systems (GNSS) allow easy measurement of positions over wide areas, but conventional consumer GPS receivers can have positioning errors on the order of several meters (about 5–10 m (16.4–32.8 ft)). This accuracy is insufficient for the construction and civil engineering tasks described above. For field efficiency, centimeter-level (cm level accuracy, half-inch accuracy) high-precision positioning is indispensable. If errors are within a few centimeters, structures can be built at the designed positions and elevations, greatly reducing additional surveying checks and rework. In other words, high-precision positioning directly prevents rework and improves quality on site, resulting in cost reduction and shortened schedules.

Moreover, the construction and surveying industries have been facing severe labor shortages and a decline in experienced technicians. As a result, the demand for performing high-precision surveys with reduced labor is increasing year by year. If easy-to-use centimeter-level positioning technology becomes widespread, site staff themselves will be able to quickly perform necessary surveys without relying on dedicated survey teams, improving overall operational efficiency.

Issues with conventional surveying methods

Obtaining high-precision positioning traditionally required dedicated surveying equipment and methods. However, these conventional approaches have several issues. For example, when using optical surveying instruments such as total stations, the equipment is large and heavy and basically requires a two-person team. Every time the instrument is set up, a tripod must be erected and leveled and targets aligned, which consumes personnel and time. Regular calibration and maintenance to preserve accuracy also incur time and cost. Precise operation often requires experienced operators, so training technicians also takes time.

Meanwhile, GNSS-based surveying also had high hurdles. Achieving high precision required high-performance GNSS receivers that support the RTK method, and obtaining correction information from a base station or via a network required dedicated equipment or service contracts. As a result, the initial cost of the full equipment set was very high, and specialized knowledge was needed for operation. Due to these cost and personnel burdens, many small sites and municipalities could not adopt high-precision positioning and had to rely on conventional manual methods or tolerate larger errors.

In short, the long-standing problem was the lack of a positioning method that combined ease of use and high precision. The solution filling this gap is a new positioning technology that leverages smartphones.

RTK method that enables centimeter-level positioning

So how does RTK achieve centimeter-level positioning? RTK (Real Time Kinematic) is a technique that improves GNSS positioning accuracy by correcting error sources. Satellite positioning errors arise from various factors such as atmospheric effects (ionosphere and troposphere delays), satellite clock errors, and multipath (reflected signals), which can lead to meter-level errors. RTK installs a reference station (base station) with known accurate coordinates and computes the real-time difference between the GNSS signals received at the base station and the rover. The correction values are then transmitted to the rover in real time, enabling positioning with errors of only a few centimeters or less.

The advantage of RTK is its very high relative positioning accuracy and the ability to obtain results in real time. This allows surveyors to acquire high-precision coordinates on site and immediately use them for staking and layout. However, traditionally one had to either deploy their own base station or subscribe to correction services via existing reference station networks (e.g., electronic reference point networks) over the Internet (Ntrip service). Thus, RTK was difficult to use in areas without mobile coverage, such as mountainous regions, or in locations lacking infrastructure.

Recently in Japan, the Quasi-Zenith Satellite System “Michibiki” provides a high-precision augmentation service (CLAS), and receivers capable of receiving these satellite corrections can achieve centimeter-level positioning without a base station or communications. In other words, RTK positioning can be completed by receiving correction signals from satellites overhead, without installing a dedicated base station. Small devices that combine RTK methods with CLAS support and are usable with smartphones have begun to appear. This is the LRTK introduced next.

Emergence of smartphone surveying “LRTK”

Bringing this innovation to market is LRTK Phone, developed by Reflexia, a startup from Tokyo Institute of Technology. It is an ultra-compact RTK-GNSS receiver device that attaches to a smartphone (currently mainly iPhone and iPad), turning a handheld smartphone into a surveying instrument capable of centimeter-level positioning. Tasks that previously required carrying heavy equipment and two-person teams can now be completed with a pocketable smartphone and a small device. Each field technician can carry their own surveying tool and use it whenever needed—making the idea of a one-per-person mobile surveying instrument a reality.

LRTK Phone’s strength lies in combining hardware with smartphone sensors and apps to do much more than simple positioning; it can perform various measurements and tasks needed on site in a single device. By leveraging the iPhone camera and LiDAR scanner, you can perform 3D terrain scans (point cloud measurement), stakeout positions based on design data, and even AR visualization—all with a single iPhone. Truly, the era in which a smartphone itself becomes a surveying instrument has arrived.

Main features of LRTK Phone

• Ultra-compact and lightweight: The device itself weighs about 165 g and has a thickness of about 1 cm (0.4 in). Its compactness allows it to be carried in a pocket at all times.

• Built-in battery for long operation: The built-in battery supports about 6 hours of continuous operation, and it can be charged/supplied via USB Type-C. Using a mobile battery enables worry-free use on site without running out of power.

• Easy attachment/detachment: Using a dedicated smartphone case or magnetic attachment, it can be attached to and detached from an iPhone or iPad with one touch. You can mount it only when needed and remove it when not in use.

• Centimeter-level high-precision positioning: Equipped with a multi-frequency high-performance GNSS antenna and RTK corrections, it achieves positioning accuracy of about ±2 cm (±0.8 in) in plane coordinates. Vertical positioning is also measurable with accuracy on the order of a few centimeters.

• Michibiki (QZSS) CLAS support: It can receive high-precision augmentation signals (CLAS) provided by Japan’s Quasi-Zenith Satellite System “Michibiki,” enabling centimeter-level positioning without the Internet even in mobile dead zones such as mountainous areas. It also supports network RTK (Ntrip) via the Internet, allowing real-time centimeter-level corrections anywhere in Japan.

• Supports one-person operation: By mounting the device on a monopod or a pole with a tip, staking tasks that used to require two people can be performed by one person. Height offsets can be easily set in the app, and if you level with a bubble vial, accurate positioning is possible with one hand.

• Support for indoor positioning: In indoor or underground spaces where GPS signals cannot reach, relative positioning mode using the iPhone’s AR technology allows continued measurement. For example, by using a known reference point near the entrance, you can measure internal positions inside tunnels.

Surveying functions available with LRTK Phone

• High-precision coordinate positioning: With one tap you can measure and record latitude, longitude, and height (elevation). The app supports Japan’s Plane Rectangular Coordinate System and automatically calculates geoid height, so measurement results can be used directly in design drawings and maps.

• Continuous positioning and averaged positioning: You can compute averaged coordinates from continuous observations over several seconds, or log continuous trajectories while moving. Averaging multiple measurements can further improve accuracy, and walking around allows efficient measurement of many points over areas.

• 3D point cloud measurement: By capturing the surrounding terrain and structures with the iPhone camera or LiDAR scanner while simultaneously tagging high-precision LRTK position data in real time, you can easily generate 3D point cloud models with absolute coordinates. Without a special laser scanner or pre-placed targets, you can measure wide areas three-dimensionally simply by walking the site.

• Coordinate navigation (guidance): For pre-set target coordinates (reference points or staking positions), the app displays guidance with arrows and distance on the smartphone screen. Even untrained personnel can follow on-screen instructions to approach the target and locate the specified position to the centimeter.

• AR visualization of design data: Import design drawings or 3D model data into the app and overlay them on the live camera view with AR. With models aligned in absolute coordinates, you can visually confirm at a glance whether constructed elements are at the designed positions and elevations. Registered boundary lines or underground utility locations can also be AR-displayed to warn during excavation or assist in as-built inspections.

• Photogrammetry (geotagged photos): Photos taken with the smartphone camera are automatically tagged with high-precision capture coordinates and camera orientation (bearing). You can accurately plot photo locations on a map for management and easily track changes at the same location over time.

• Use and calculation of measurement data: Using measured coordinate data, the app can compute distances between two points, areas, and volumes. For example, from acquired point clouds you can generate arbitrary cross sections and compute cut-and-fill volumes on-site instantly.

Field benefits of introducing centimeter-level positioning

LRTK Phone is not only highly accurate but also practical in terms of speed and portability. In open areas, turning on the power yields an RTK Fix solution in about 20 seconds, at which point centimeter-level position information is already available. In experiments, when the device was fixed and single-point positioning was performed, the horizontal position standard deviation was about 12 mm (0.47 in), and using an average of 60 measurements improved accuracy to about 8 mm (0.31 in). Achieving accuracy below 10 mm (0.39 in) is comparable to the performance of conventional professional surveying equipment. Once a Fix is obtained, high-precision positioning can be maintained while moving, so tasks that previously required setting up a tripod at each point can now acquire point cloud data over wide areas simply by walking with a smartphone. Fewer measurement omissions and faster on-site results lead to shortened schedules and prevention of rework.

The specific benefits of introducing LRTK Phone include:

• Reduced surveying costs: Survey tasks that previously required expensive dedicated equipment and multiple personnel can be completed with only a smartphone and a small device, significantly lowering costs. Equipment maintenance and outsourcing expenses can also be reduced.

• Shorter work time and improved efficiency: Preparation and equipment setup time are reduced, and the process from data acquisition to processing can be performed quickly, significantly shortening work time. Real-time point cloud generation and volume calculations enable on-site decision-making and progression to the next steps.

• Reduced construction errors: High-precision positioning and AR visualization allow discrepancies between design and construction to be discovered and corrected on site. Mistakes in staking or measurement omissions are reduced, enabling high-quality construction in a single pass.

• Labor savings: One person can perform surveying and staking, eliminating the need for additional assistants. This helps address labor shortages and improves safety by reducing personnel working around heavy machinery.

• Reduced training costs: The intuitive UI of the smartphone app allows people without specialized knowledge to perform accurate positioning by following instructions. Results can be obtained without relying on veteran intuition, reducing the training burden on newcomers and easing skill transfer challenges.

• Smoother data sharing: Survey results can be shared immediately within and outside the organization via the cloud, allowing all stakeholders to view the latest information. There is no need to carry paper drawings or exchange data via USB; reporting to clients can be done smoothly using digital data.

Case study: use in disaster recovery

The innovative LRTK Phone has already begun to be adopted at construction sites and by municipalities nationwide. For example, Fukui City in Fukui Prefecture quickly implemented a smartphone surveying system using iPhones and RTK positioning on disaster recovery sites, enabling faster and lower-cost mapping of damage than before. Its ability to efficiently cover wide areas with limited personnel was highly valued, greatly accelerating the planning of recovery measures. This smartphone surveying system was also used to assess damage after the Noto Peninsula earthquake (2023), contributing to rapid surveying and documentation of affected areas.

These results have attracted attention, and national agencies and other municipalities are now considering and proceeding with LRTK Phone adoption. Use cases for infrastructure inspection of roads and bridges and labor-saving public surveying tasks are increasing. High-precision, easy-to-use smartphone surveying is expected to support DX (digital transformation) of a wide range of field operations beyond disaster prevention.

Simple surveying with LRTK Phone

As shown above, LRTK Phone contributes significantly to efficiency improvements at surveying and construction sites through centimeter-level high-precision positioning and a variety of functions. With accuracy comparable to dedicated equipment but usable with just a smartphone and a small device, this system embodies the concept of “simple surveying.” The introduction cost is relatively low compared to conventional surveying equipment, and real-world adoption across regions attests to its reliability.

LRTK Phone can be a familiar tool for surveyors, construction technicians, and municipal staff responsible for infrastructure management. Sites facing labor shortages and budget constraints stand to gain the most from such a simple surveying system. With a pocketable surveying device for each person, why not take the first step toward field DX? Consider introducing LRTK Phone and experience its effects on your sites.

FAQ

Q: What is LRTK? A: LRTK is a system composed of an ultra-compact GNSS receiver device that connects to a smartphone and a dedicated app, turning a handheld iPhone into a surveying instrument capable of centimeter-level positioning. Developed by a venture originating from Tokyo Institute of Technology, it achieves high positioning accuracy by utilizing RTK technology.

Q: Why can't conventional GPS provide high-precision positioning? A: Standalone GPS suffers meter-level errors due to satellite signal errors, so it cannot meet the centimeter-level accuracy required for surveying or staking. Without correction techniques such as RTK, it is difficult to cancel out the error sources in satellite positioning and achieve high precision. LRTK employs the RTK method to correct positioning errors in real time, enabling centimeter-level accuracy on a smartphone.

Q: Can LRTK Phone be used indoors or outside mobile coverage? A: Yes. LRTK Phone supports Japan’s Quasi-Zenith Satellite “Michibiki” augmentation signal CLAS, allowing high-precision positioning even at sites out of mobile coverage such as mountainous areas. However, in fully indoor environments where satellite signals cannot be received, relative positioning mode using the iPhone’s AR functions is used. If you measure a reference point outdoors once, you can use that reference to measure relative positions inside tunnels or buildings.

Q: Do you need specialized knowledge or qualifications to operate it? A: No, no special qualification is required. The LRTK app has clear Japanese UI, and accurate positioning can be achieved simply by following the on-screen instructions. Complex settings and calculations common to conventional surveying equipment are automatically handled by the app, so users familiar with basic smartphone操作 can begin using it after a short training session.

Q: What is required for introduction? A: You need the LRTK Phone unit (the compact GNSS receiver), a compatible iPhone/iPad, and the dedicated LRTK app. If you want to use correction information via the Internet, you must subscribe to an Ntrip service, but within Japan Michibiki (CLAS) allows high-precision positioning without network connection. Basically, attach the LRTK device to your smartphone and launch the app to start centimeter-level positioning.