Table of Contents

• Why centimeter-accuracy positioning is needed in factories

• Challenges of indoor positioning: achieving high precision where GPS can't be used

• What RTK-GNSS is: technology that enables centimeter-level positioning

• Easy high-precision positioning realized with smartphones × RTK

• What LRTK is: a compact positioning device ideal for factory indoor positioning

• Benefits of LRTK that will change factory indoor positioning

• Use cases for LRTK inside factories

• Easy deployment: start high-precision positioning with smartphone integration

• Summary: factory DX and simplified surveying enabled by LRTK

• Frequently Asked Questions (FAQ)

On wide factory floors and production lines crowded with equipment, even a difference of a few centimeters can have a major impact. If the installation position of machinery is off by a few centimeters, piping or wiring connections may be obstructed, or production-line efficiency may suffer. For autonomous guided vehicles (AGVs) and robots, route deviations directly affect safety and operational accuracy. The ability to measure positions to the centimeter within a factory is therefore critically important for quality control, productivity improvement, and safety assurance.

However, achieving high-precision positioning indoors is not easy. Ordinary GPS (satellite positioning) cannot receive signals under roofs or ceilings, and even meter-level positioning as outdoors becomes difficult. Until now, knowing positions to centimeter accuracy inside factories required specialized equipment such as surveying total stations operated by professional surveyors. Bringing in large equipment to establish survey reference points and having experienced personnel work as a team takes time and manpower, and may even require temporarily halting production. Isn’t there a way to make high-precision indoor positioning more convenient? A new technology that solves these on-site problems has emerged: “LRTK,” which combines smartphones with the latest GNSS technology. With a small device that can be attached to a smartphone and a companion app, centimeter-class RTK positioning becomes possible inside factories, and an era is beginning in which anyone can easily perform precise position measurements.

Why centimeter-accuracy positioning is needed in factories

In industrial facilities such as factories and warehouses, accurate position information is required in all situations—equipment and product placement, workflow routes, robot travel paths, and more. One reason is to minimize mistakes and losses. For example, when installing machinery on a production line, if installation does not match the design drawings, later processes may experience part mismatches or require additional adjustments. Small deviations can accumulate and lead to product quality variation or accelerated machine wear.

High-precision positioning is also important for automated driving of AGVs and forklifts used in factory logistics. A deviation of just several tens of centimeters increases the risk of contact with shelves or equipment and affects safety. Knowing the exact current position enables more precise autonomous control, allowing efficient and safe transport.

Furthermore, accurate positioning is essential for maintenance and layout changes in factories and plants. If you accurately record reference coordinates when 3D-scanning existing equipment or marking installation locations for new devices, layout changes can proceed smoothly as planned. For example, when bringing in large machinery, if the installation space dimensions are not measured accurately, you may face on-site troubles like “it doesn’t fit” or “it interferes.” Tools that can position to centimeter accuracy directly reduce such on-site risks.

As shown, many factory tasks require centimeter-level positional accuracy. So why has this been difficult? Let’s look at the conventional challenges.

Challenges of indoor positioning: achieving high precision where GPS can't be used

In environments where satellite signals from above cannot reach—indoors, underground, or under elevated structures—conventional GPS positioning hardly works. The number of satellites a GPS receiver can pick up drops dramatically, or signals may not be received at all. Even if weak signals are received, multipath (reflections) from walls and ceilings prevents accurate positioning, producing errors of tens of meters. Thus, typical smartphone GPS functions cannot accurately measure the positions of people or objects indoors.

Various methods have been explored to achieve high-precision indoor positioning. One is installing UWB (ultra-wideband) or Bluetooth beacons throughout a space and deriving positions from their signals. UWB can theoretically achieve centimeter accuracy, but it requires multiple antennas or tags to be installed indoors, entailing high initial cost and maintenance effort. Beacon systems also require installation and upkeep of dedicated devices and can suffer unstable accuracy due to radio interference. Image-recognition or magnetic-field-based positioning have also been researched, but they are sensitive to preparatory work and environmental factors, making them difficult to use in factories where layouts change frequently.

In the end, to reliably achieve centimeter-level accuracy, reliance on manual optical surveying has been the reality. Using a total station to set reference points and measure relative distances to desired points can achieve millimeter-level accuracy. However, this requires arranging a professional surveying team and bringing equipment into the factory. Work often necessitates temporarily stopping production or restricting access, imposing a heavy burden on the site. The difficulty of achieving high indoor positioning accuracy has long been a source of on-site headaches.

What RTK-GNSS is: technology that enables centimeter-level positioning

A representative technology that enables centimeter-level positioning outdoors is RTK-GNSS. RTK stands for Real Time Kinematic and refers to real-time kinematic positioning. Conventional GNSS (Global Navigation Satellite System) positioning determines position from satellite signals, but by itself suffers meter-level errors from ionospheric effects, clock errors, and so on. RTK dramatically improves positioning accuracy by using data from a nearby reference station (a fixed receiver) to correct errors.

Specifically, the reference station obtains error information (satellite signal biases) and sends that information to the rover (the user’s receiver) in real time; by comparing both sets of observations, errors are subtracted at millisecond resolution. This allows the rover to compute its position at the centimeter order. In short, the concept is “place another GPS nearby as a reference, and determine a highly accurate relative position.”

Recently, environments for easily obtaining RTK reference signals have been improving, such as internet-based networks of electronic reference stations and centimeter-level augmentation services (CLAS) from the Quasi-Zenith Satellite System (QZSS) “Michibiki.” RTK positioning, which used to require specialized high-performance GNSS equipment, has become more accessible thanks to small, low-cost receivers. Now, applying RTK-GNSS on smartphones is attracting attention as a new approach.

Easy high-precision positioning realized with smartphones × RTK

Smartphones are ubiquitous general-purpose devices, and by combining them with a small RTK-capable GNSS receiver, they can be transformed into survey-grade high-precision positioning terminals. Smartphones are equipped with GPS, cameras, accelerometers, gyroscopes, and other sensors. By linking a smartphone measurement app with an external GNSS device, you can ingest high-precision positioning information from satellites while visualizing and saving data on the phone.

In practice, the GNSS receiver attached to the smartphone obtains RTK-positioned location data and sends it to the phone via Bluetooth or a dedicated connector. An app on the phone receives this data and displays the coordinates in real time. By tapping a button at the point you want to measure, the app instantly records the latitude, longitude, and altitude of that spot. RTK corrections keep errors within a few centimeters, so you can achieve accuracy comparable to conventional total stations or expensive GNSS equipment using just a smartphone.

Another advantage is intuitive operation leveraging the smartphone interface. For example, you can plot your current position and measured points on a map or camera view and visually confirm them. After measuring multiple points, you can draw a simple diagram on the phone, and measurement results can be uploaded to the cloud for immediate sharing. Data management that used to be handled manually on site and carried back for processing becomes much faster and more accurate with smartphone utilization.

This smartphone × RTK positioning technology makes “measuring places accurately” more convenient and accessible. So what is LRTK, a prime example of this approach?

What LRTK is: a compact positioning device ideal for factory indoor positioning

LRTK is a super-compact RTK-GNSS receiver that can be attached to a smartphone. It was developed by Reflexia Inc., a startup originating from Tokyo Institute of Technology, and operates via Bluetooth connection with iPhone and iPad devices. The device weighs about 125 g and features a rugged integrated design with an antenna and battery built in. It attaches to the back of the device with a one-touch action through a dedicated smartphone-case-style adapter, eliminating messy wiring. Because it can be carried together with the smartphone, on-site surveying while carrying it is easy.

With LRTK, an iPhone effectively becomes a centimeter-accuracy surveying instrument. By launching the dedicated app “LRTK Phone” and pressing a button at the point to be measured, you can obtain high-precision coordinates for that location. In actual tests, single-epoch LRTK positioning achieved horizontal errors of about ±1–2 cm and vertical errors of ±2–3 cm. Averaging multiple observations can achieve accuracy of less than 1 cm. This performance approaches that of conventional total stations, and obtaining such accuracy with a pocket-sized device is groundbreaking.

LRTK is not only capable of measuring point coordinates but also provides various functions that utilize its high-precision positional data. For example, combined with a smartphone’s built-in LiDAR scanner (available on Pro models) or camera, it can record the surrounding environment as 3D point-cloud data. Tasks that previously required a dedicated 3D laser scanner can be done in a simplified manner with LRTK and a smartphone. Since the captured point cloud is linked with LRTK’s position coordinates, measured data can be reproduced at full scale in drawings or CAD, or easily integrated with other survey data.

Additionally, you can attach photos and notes to measured points and save them, or use AR (augmented reality) features to guide you to and mark specified coordinates. For example, if you specify a position on the floor to mark, the app can guide you to that location with on-screen arrows, making layout marking (positioning) tasks efficient. All these functions are completed with just the LRTK device and a smartphone.

Benefits of LRTK that will change factory indoor positioning

The biggest advantage of using LRTK in factories is that anyone on site can immediately perform high-precision positioning. As described, where centimeter-precision surveys used to be done by specialists with expensive equipment, on-site staff can now perform them themselves. For example, a line installation worker can measure reference points and confirm machine placement, or a maintenance person can record coordinates of repair locations—allowing convenient, on-demand positioning according to needs. Not having to rely on expert surveyors and being able to measure when needed dramatically increases on-site agility.

LRTK’s small, lightweight form factor also makes it suitable for measuring in narrow spaces and at heights inside factories. In cramped areas without space for setting up tripods, as long as a person can reach the spot, they can approach the measurement point with a smartphone. In plants with stairs and piping, the one-handed LRTK is easy to handle. There is no need to carry heavy equipment, and preparation time for measurement is minimal. The ability to quickly take out and measure when needed is powerful for daily inspections and ad-hoc checks.

There are also data-utilization benefits. Data obtained with LRTK and a smartphone can be uploaded to the cloud on site and shared in real time within the company. For example, point-cloud data of equipment placement measured in the factory can be immediately reviewed at headquarters and used to give remote instructions. Previously, it took time to convert on-site measurements into drawings for sharing, but with LRTK you can achieve immediate data sharing and visualization, speeding decision-making.

Furthermore, the cost of introducing LRTK is much lower than conventional surveying equipment. It is far less expensive than purchasing a large total station, making it realistic to deploy multiple units so each field worker carries one. Lowering the cost barrier brings closer an era of “one surveying device per person.”

Use cases for LRTK inside factories

Here are some scenarios for how LRTK can be used in factories.

1. Installation of new equipment and layout changes When introducing new machines or production lines, measuring installation coordinates in advance with LRTK allows you to compare the plan and the site without discrepancy. By accurately measuring distances and heights from reference points, you can prevent rework on installation day such as “position is wrong” or “not level.” Using AR functions, you can even project installation marks onto the floor, speeding up marking tasks.

2. Equipment inspection and maintenance records For maintenance inspections, it is important to record the exact locations of faults or replacement parts. With LRTK, you can record precise coordinates—for example, “the piping connection point 2.3 m east of the motor installation on line 3.” By attaching photos and notes and saving to the cloud, the same spot can be easily located during the next inspection, improving equipment management accuracy.

3. Dimensional measurement and as-built documentation inside the factory On the shop floor you frequently need to measure clearances between machines or corridor widths. While tape measures or laser distance meters work, LRTK lets you acquire multiple points and calculate accurate digital dimensions later. By analyzing point-cloud data captured on the smartphone, you can understand on-site dimensions and shapes as a 3D model. For example, you can derive floor slope from point clouds to check drainage gradients.

4. Surveying that spans outdoor and indoor areas LRTK is also powerful when surveying continuously from outside into a building. Outdoors, RTK can provide high-precision absolute coordinates; once inside where satellites are not visible, the smartphone’s inertial sensors and camera can switch to relative positioning to continue measurements. For example, you can set a reference point near the building entrance and then patrol the interior using pedestrian dead reckoning (PDR). While small errors accumulate with distance, over short ranges seamless positioning is practically accurate enough. This enables one person to complete surveying that spans indoor and outdoor areas.

Easy deployment: start high-precision positioning with smartphone integration

No special infrastructure work is required to introduce LRTK. Basically, prepare the LRTK device and a compatible smartphone (mainly iPhone/iPad) and install the app to get started. RTK correction information can be obtained via an internet connection to an electronic reference station network in Japan, or by directly receiving CLAS signals from Michibiki in supported areas. The app handles complex settings automatically, so users only select the positioning mode to use high-precision positioning.

Pairing the smartphone with LRTK over Bluetooth is simple. Once paired, the phone will detect the LRTK device and connect automatically when powered on at the site. Following the app’s on-screen guidance, even first-time users can start measurements without confusion. The design requires no specialized knowledge, so training costs are minimal. A few pages of manual or a tutorial video are usually enough for staff to become proficient.

In this way, LRTK also excels in ease of deployment. As a factory DX (digital transformation) promotion tool, high-precision positioning that leverages existing smartphones and tablets is highly attractive. With low initial investment and rapid operational start-up, it can quickly contribute to on-site productivity—an easy selling point for management.

Summary: factory DX and simplified surveying enabled by LRTK

To address the challenge of “achieving high precision indoors,” LRTK presents a practical solution through smartphone integration. By combining RTK-GNSS accuracy with smartphone convenience, centimeter-class positioning is becoming accessible to anyone, anywhere. This will accelerate position-information DX across factory operations. Opportunities to utilize positional data—for layout planning, equipment management, logistics optimization, safety management, and more—will continue to expand.

LRTK, in particular, has the potential to overturn the conventional notion that surveying is only for specialists, and to establish a new culture of simplified surveying on the shop floor. The simple act of measuring with a smartphone can lead to better understanding of current conditions and discovery of improvement opportunities, dramatically boosting on-site capabilities. With its combination of accuracy and ease of use, LRTK is truly a next-generation positioning and surveying tool.

In the future, factories, construction, and civil engineering sites may see an era in which each worker carries a high-precision positioning device. LRTK is leading the way, strongly supporting on-site DX. Why not bring centimeter-level precision into your factory? You will likely be surprised by the results and find it indispensable.

Frequently Asked Questions (FAQ)

Q: Can you really achieve centimeter accuracy indoors? A: In completely enclosed indoor spaces where satellite signals cannot reach, LRTK estimates position using the smartphone’s inertial sensors and camera (relative positioning such as PDR and ARKit technologies). Small errors accumulate over long distances, but for short ranges accuracy can generally be maintained at around a few centimeters. In areas near openings in the building, temporarily acquiring satellite fixes to apply corrections can help maintain accuracy. If a facility spans both indoor and outdoor areas, combining RTK high-precision positioning with indoor relative positioning can achieve practically sufficient accuracy.

Q: Do you need specialized knowledge to operate LRTK? A: No. It is designed to be usable without special surveying knowledge. The dedicated app has a clear Japanese UI, and you proceed from measurement start to saving and sharing by following on-screen instructions. Complex settings are automated, so even first-time users can perform basic positioning after a short hands-on session. If you do get stuck, manuals and support are available.

Q: How does LRTK’s positioning accuracy compare to a total station? A: LRTK (smartphone surveying) typically achieves horizontal accuracy of about ±1–2 cm and vertical accuracy of ±2–3 cm. While this does not match the millimeter-level accuracy of total stations over short distances, it is within acceptable tolerance for many factory tasks. For layout checks or progress measurements where a few centimeters of error are acceptable, LRTK can be a sufficient substitute. For inspection processes requiring millimeter-level precision, total stations remain appropriate. By choosing the right tool for each task, you can maximize overall site efficiency and accuracy.

Q: What do I need to use LRTK? A: The basic set includes the LRTK device and a compatible smartphone (currently primarily iPhone/iPad). Install the dedicated app on the phone and connect to LRTK via Bluetooth to use it. Correction information for positioning can be obtained via the internet or by directly receiving Michibiki’s CLAS signals. For better accuracy indoors, you can take a reference point outdoors beforehand to serve as a baseline.

Q: In what formats can positioning data be exported and how can it be used? A: Positioning data acquired with the LRTK app is saved with latitude, longitude, and altitude for each point, along with time, notes, photos, and other metadata. These can be exported as CSV or surveying coordinate formats, or imported to a PC via the cloud for use in CAD or GIS software. Point-cloud data can be exported in common LAS/PLY formats and used for comparing with design drawings or building 3D models. Real-time cloud-shared data can be displayed on a web browser map and viewed or edited by other staff simultaneously. The ability to use on-site positioning information in various ways is a major appeal of LRTK.