LRTK brings RTK accuracy to factory indoor positioning at cm level accuracy (half-inch accuracy)! Easy to deploy with smartphone integration

Table of Contents

• Why centimeter-level positioning is needed inside factories

• Challenges of indoor positioning: achieving high accuracy where GPS is unavailable

• What RTK-GNSS is: a technology that enables positioning to within a few centimeters

• Easy high-precision positioning realized by smartphone × RTK

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

• Benefits of LRTK that will change factory indoor positioning

• LRTK use cases inside factories

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

• Summary: factory DX and simple surveying enabled by LRTK

• Frequently Asked Questions (FAQ)

On wide factory shop floors and production lines crowded with equipment, even a deviation of only a few centimeters (a few inches) can make a big difference. If the installed position of machinery is off by a few centimeters (a few inches), piping or wiring connections may be obstructed, or the efficiency of the production line may be affected. For autonomous vehicles (AGV) and robots, route deviations directly affect safety and operational accuracy. Being able to measure positions inside a factory to the centimeter level (cm level accuracy, half-inch accuracy) is therefore crucial for quality control, improved production efficiency, and safety assurance.

However, achieving high-precision positioning indoors is not easy. Standard GPS (satellite positioning) cannot receive signals under building roofs or ceilings, making even meter-level positioning difficult as it is outdoors. Until now, to know positions to centimeter accuracy inside a factory, the only option was to use specialized equipment such as a surveyor’s total station (optical surveying instrument). Bringing in large equipment to set survey benchmarks and having skilled personnel work as a team takes time and manpower, and may require temporarily halting production on site. Is there a way to make indoor positioning more easily high-precision? A new technology that addresses these on-site concerns has emerged: “LRTK,” which combines a smartphone with the latest GNSS technology. With a small device that attaches to a smartphone and an app, RTK positioning to centimeter-level accuracy becomes possible even inside factories, and an era is dawning in which anyone can perform precise position measurements easily.

Why centimeter-level positioning is needed inside factories

In industrial facilities such as factories and warehouses, accurate position information is required in every aspect, including equipment and product layout, work flow lines, and robot routes. One reason is to minimize mistakes and losses. For example, when installing machines on a production line, if they are not placed according to the design, parts may not fit in later stages or additional adjustment work may be required. Even slight deviations, if accumulated, can lead to variation in product quality or early wear of machinery.

High-precision positioning is also important for the autonomous operation of AGVs (automated guided vehicles) and forklifts used in factory logistics. If a route deviates by just tens of centimeters (tens of inches), the risk of contact with shelves or equipment increases, impacting safety. Knowing the exact current position enables more precise autonomous navigation control, allowing efficient and safe transport.

Accurate positioning is also indispensable for maintenance and layout changes in factories and plants. When 3D-scanning the layout of existing equipment or marking the installation locations for new machines, having accurately identified reference point coordinates makes layout changes proceed smoothly. For example, when bringing in a large machine, if the installation space dimensions are not measured precisely, one can encounter problems on site such as “it won’t fit” or interference. Tools capable of centimeter-level positioning directly reduce such on-site risks.

As shown, there are many situations in which centimeter-level positional accuracy is required in factory operations. So why has achieving this been difficult? Let’s look at the traditional challenges.

Challenges of indoor positioning: achieving high accuracy where GPS is unavailable

In environments where satellite signals from the sky cannot reach—indoors, underground, or under elevated structures—normal GPS positioning barely works. The number of satellites a GPS receiver can lock onto drops dramatically, or none at all. Even if a faint signal is received, multipath reflections from walls and ceilings prevent accurate positioning, producing errors of tens of meters. Therefore, a typical smartphone’s GPS function cannot accurately measure the positions of people or objects indoors.

Various methods have been explored to achieve high-precision indoor positioning. One approach is installing UWB (ultra-wideband) or Bluetooth beacons in the space and deriving position from those signals. While UWB is theoretically capable of centimeter-level accuracy, it requires installing multiple antennas or tags indoors, which involves high initial costs and significant maintenance effort. Beacon systems also require dedicated devices to be installed and maintained, and accuracy can become unstable due to radio interference. Image recognition and magnetic-based positioning are also being researched, but they are sensitive to pre-installation work and environmental factors and can be difficult to manage in factories where layouts change frequently.

In the end, to reliably obtain centimeter-level accuracy, the reality was that manual optical surveying by skilled personnel was unavoidable. Using a total station to establish reference points and measure relative distances to the desired points can achieve millimeter-level accuracy. However, that requires arranging a specialized surveying team and bringing equipment into the factory. During such work, the production line may need to be paused or access restricted, placing a heavy burden on the site. The difficulty of easily achieving high precision indoors has long been a source of on-site frustration.

What RTK-GNSS is: a technology that enables positioning to within a few centimeters

A representative technology that enables centimeter-level positioning outdoors is RTK-GNSS. RTK stands for “Real Time Kinematic,” and in Japanese it is called real-time kinematic positioning. Ordinary GNSS positioning determines position by receiving signals from satellites, but this alone leads to meter-level errors due to ionospheric effects and clock errors. RTK dramatically improves positioning accuracy by correcting errors using data from a nearby reference station (a fixed receiver).

Specifically, error information (deviations in satellite signals) obtained at the reference station is sent in real time to the rover (the user’s receiver), and the two sets of observations are compared and the errors are subtracted at millisecond intervals. This allows the rover to compute its position to the centimeter order. In short, it’s the idea of “placing another GPS device nearby as a reference and determining a high-precision relative position.”

Recently, environments for easily obtaining RTK reference signals have been maturing, such as internet-accessible electronic reference station networks and centimeter-level augmentation services (CLAS) from the quasi-zenith satellite system “Michibiki.” What once required specialized high-performance GNSS equipment for RTK positioning is becoming more accessible thanks to compact, low-cost receivers. Now, a new approach gaining attention is using RTK-GNSS with a smartphone.

Easy high-precision positioning realized by smartphone × 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 tools. Smartphones are equipped with GPS, cameras, accelerometers, gyroscopes, and other sensors. By integrating a measurement app with an external GNSS device, high-precision satellite positioning data can be ingested and visualized and saved on the smartphone.

The specific mechanism is that the GNSS receiver attached to the smartphone acquires position information via RTK and sends data to the phone via Bluetooth or a dedicated connector. An app on the phone receives that data and displays coordinates in real time. Tap a button at the point you want to measure and the latitude, longitude, and elevation of that point are recorded instantly. Because RTK corrections limit errors to within a few centimeters (a few inches), a smartphone can provide accuracy comparable to conventional optical distance meters or costly GNSS equipment.

Another advantage is the intuitive operation afforded by the smartphone interface. For example, you can plot your current position and recorded points on an on-screen map or camera view and visually confirm them. After measuring multiple points you can sketch a simple drawing on the phone, or upload measurement results to the cloud for immediate sharing. Data management that used to require handwritten notes and returning to the office has become significantly faster and more accurate with smartphone usage.

With smartphone × RTK positioning technology, the act of “measuring a place accurately” is becoming more accessible and user-friendly. So what exactly is LRTK, a representative device of this approach?

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

LRTK is an ultra-compact RTK-GNSS receiver that can be attached to a smartphone. It was developed by Reflexia Inc., a startup spun out from Tokyo Institute of Technology, and operates via Bluetooth with iPhone and iPad. 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 installation via a dedicated phone-case-style adapter, eliminating complicated wiring. Because it integrates with the smartphone for portability, carrying it around on site for surveying is effortless.

With LRTK, an iPhone becomes a centimeter-level (cm level accuracy, half-inch accuracy) surveying instrument. Launch the dedicated app “LRTK Phone” and press a button on the screen at the point to be measured to acquire highly accurate coordinates for that location. In actual tests, standalone LRTK positioning produced horizontal errors of ±1–2 cm (±0.4–0.8 in) and vertical errors of ±2–3 cm (±0.8–1.2 in). Averaging multiple observations can achieve accuracy of less than 1 cm (less than 0.4 in). This performance approaches that of conventional total stations, and achieving such accuracy with a pocket-sized device is revolutionary.

LRTK is not only capable of measuring point coordinates but also includes various features that leverage its high-precision positioning. For example, combining LRTK with a smartphone’s built-in LiDAR scanner (available on Pro models) or camera allows recording the surrounding environment as 3D point cloud data. Tasks that previously required a dedicated 3D laser scanner can be performed in a simplified manner with LRTK and a smartphone. Since the acquired point cloud is linked to LRTK position coordinates, measured data can be reproduced to scale on drawings or CAD and easily integrated with other survey data.

You can also attach photos and notes to measured points and save them, or use AR (augmented reality) features to guide you to and mark designated coordinates. For example, if you specify a location on the floor where a mark should be placed, the phone can guide you to that spot using on-screen arrows, which is useful for layout marking tasks. All of these functions are completed with just one LRTK device and one 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 above, centimeter-accuracy surveying that once required specialists and expensive equipment can now be done by on-site staff themselves. For example, a line installation worker can measure reference points and check machine placement, or maintenance personnel can record coordinates of repair locations—positioning can be performed as needed. Being able to measure yourself when required, without relying on a skilled surveyor, dramatically increases on-site agility.

LRTK is also small and lightweight, making it suitable for measurements in confined or elevated spaces inside factories. Even in places without room to set up a tripod, you can approach the measurement point with a smartphone as long as a person can fit into the gap. In plant equipment with stairs and many pipes, the compact LRTK is easy to handle. There is no need to carry heavy equipment, and setup time is minimal. The ability to pull it out and measure on the spot is powerful for daily inspections and ad hoc checks.

There are also data utilization benefits. Data acquired 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 layouts measured in the factory can be immediately reviewed at headquarters and remote instructions issued smoothly. While traditional workflows required time to convert field measurements into drawings and share them, LRTK enables immediate data sharing and visualization, accelerating decision-making.

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

LRTK use cases inside factories

Below are several scenarios showing how LRTK can actually be used inside factories.

1\. New equipment installation and layout changes When introducing new machinery or production lines, measuring installation coordinates with LRTK in advance allows you to match the on-site situation to the plan without discrepancy. Accurately measuring distances and heights from reference points can prevent rework on installation day due to “wrong position” or “not level.” Using AR, you can also project marks indicating floor installation positions, speeding up the marking process.

2\. Equipment inspection and maintenance records In equipment maintenance, it is important to accurately record the locations of faults and replacement parts. With LRTK you can record detailed position information as coordinates—for example, “the pipe connection located 2.3 m (7.5 ft) east of the motor on Line 3.” Attach photos and notes and save them to the cloud so that the same location can be easily identified at the next inspection, improving equipment management accuracy.

3\. Measuring dimensions and capturing the current state inside the factory In manufacturing, you often need to measure clearances between machines or walkway widths. While tape measures or laser distance meters can do this, LRTK lets you record multiple points and later compute precise digital dimensions. Analyzing point cloud data captured with a smartphone lets you understand on-site dimensions and shapes as a 3D model. For example, you can derive floor level inclinations from point cloud data and use that to check drainage slopes.

4\. Surveying that spans outdoor to indoor LRTK is powerful when surveying continuously from outdoors into building interiors on a factory site. Outdoors, you can obtain high-precision absolute coordinates with RTK, and when you enter a building where satellite reception becomes impossible, switch to relative positioning using the smartphone’s inertial sensors and camera to continue measurements. For example, establish a reference point near the building entrance and then patrol the interior using pedestrian dead reckoning (PDR) to estimate positions. Some error accumulates with distance, but over short ranges, continuous positioning can be achieved at practically usable accuracy. This enables one person to complete surveys that span indoor and outdoor areas seamlessly.

Easy deployment: start high-precision positioning with smartphone integration

No special infrastructure construction is required to introduce LRTK. Basically, prepare the LRTK device and a compatible smartphone (mainly iPhone/iPad), install the app, and you can start. Correction information required for RTK positioning can be obtained over the internet via an electronic reference station network within Japan, or by directly receiving Michibiki’s CLAS signal in supported areas. The app automatically handles complex settings, so the user only selects the positioning mode to start high-precision positioning.

Pairing the smartphone with LRTK via Bluetooth is simple. Once pairing is configured, the phone will detect and automatically connect to LRTK when powered on in the field. By following the app prompts, even first-time users can start measurements without confusion. Designed to be usable without specialized knowledge, the training cost is minimal; a few pages of a manual or tutorial videos are usually sufficient for basic proficiency.

Thus, LRTK also excels in terms of ease of introduction. As a tool for promoting factory DX (digital transformation), it is attractive because it allows you to leverage existing smartphones and tablets to begin high-precision positioning. Low initial investment and the ability to start operations in a short period while immediately contributing to on-site productivity make it appealing to management.

Summary: factory DX and simple surveying enabled by LRTK

To address the long-standing challenge of achieving high precision indoors, LRTK offers a practical solution by integrating with smartphones. By combining the accuracy of RTK-GNSS with the convenience of smartphones, centimeter-level positioning is becoming possible anywhere, by anyone. This will accelerate the DX of position information across various factory use cases. Opportunities to utilize positional data in layout planning, equipment management, logistics optimization, and safety management will continue to expand.

LRTK, in particular, has the potential to overturn the conventional wisdom that surveying is only for specialists and to establish a culture of “simple surveying” at worksites. The act of casually measuring with a smartphone can lead to better on-site awareness and identification of improvement points, significantly enhancing on-site capabilities. LRTK, which balances accuracy and ease of use, can be called the next-generation positioning and surveying tool.

In the future, the era may come when every field worker carries a high-precision positioning device. LRTK, as a forerunner, is powerfully supporting on-site DX. Why not bring centimeter-level accuracy into your factory? You may be surprised by the results and find it indispensable.

Frequently Asked Questions (FAQ)

Q: Can centimeter-level positioning really be achieved indoors? A: In fully enclosed indoor spaces where satellite signals cannot reach, LRTK estimates position using the smartphone’s inertial sensors and camera via relative positioning methods (PDR and ARKit technologies). Small errors accumulate over long distances, but over short segments practically maintain accuracy on the order of a few centimeters (a few inches). When near building openings, temporarily capturing satellites to apply corrections can help maintain accuracy. In factory facilities that combine indoor and outdoor areas, combining RTK high-precision positioning with these techniques provides practically sufficient accuracy.

Q: Do I need specialized knowledge to operate LRTK? A: No. It is designed to be operated without special surveying knowledge. The dedicated app has a user-friendly Japanese UI, and you simply follow on-screen prompts from measurement start to save and share. Complex settings are automated, so beginners can perform basic positioning after a short period of use. 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) generally achieves horizontal accuracy of ±1–2 cm (±0.4–0.8 in) and vertical accuracy of ±2–3 cm (±0.8–1.2 in). While it does not reach the millimeter-level accuracy of a total station over short distances, its accuracy is within acceptable limits for many factory tasks. For tasks where a millimeter-level strict accuracy is required, a total station remains appropriate. Using each tool according to the purpose maximizes overall on-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 mainly iPhone/iPad). Install the dedicated app on the phone and connect it to LRTK via Bluetooth. Correction information for positioning is obtained over the internet or by directly receiving Michibiki’s CLAS signal. For outdoor use, be in a location with a clear view of the sky; for indoor use, obtaining reference points outdoors beforehand improves accuracy.

Q: In what formats can I use or export positioning data? A: Position data acquired by the LRTK app is saved with latitude, longitude, and height for each point, along with timestamps, notes, and photos. These can be exported as CSV or survey coordinate formats, or uploaded to the cloud and imported into CAD or GIS on a PC. Point cloud data can be exported in common LAS/PLY formats for comparison with drawings or 3D model construction. Real-time cloud-shared data can be displayed on a web browser map and viewed or edited simultaneously by other personnel. The ability to utilize field-acquired positioning information in various forms is another major attraction of LRTK.