Indoor positioning technology with cm level accuracy (half-inch accuracy) that enables precise location management within factories and its applications

Table of Contents

• High-precision indoor positioning required for location management in factories

• How to achieve cm level accuracy (half-inch accuracy) for positioning indoors

• What is high-precision positioning with RTK

• New indoor positioning realized by smartphones × LRTK

• Use cases and benefits in factories and warehouses

• How simplified surveying with LRTK transforms on-site operations

• FAQ

High-precision indoor positioning required for location management within factories

In manufacturing plants and logistics warehouses, "location" information is critically important in every area, including equipment and inventory placement, workflow optimization, and safety management. Tasks that previously relied on experience and intuition are increasingly being digitized to visualize location data, driving productivity improvements and waste reduction. In particular, demand is growing for performing position measurements inside factories and warehouses with centimeter (cm) level accuracy (half-inch accuracy). Precision placement and fine adjustments that were difficult with errors of several meters (several ft) can be achieved if indoor positioning with cm level accuracy (half-inch accuracy) becomes possible. The use of high-precision location information is becoming an indispensable factor for factory kaizen (improvement) and efficient warehouse operations.

To achieve centimeter-level positioning indoors (cm level accuracy (half-inch accuracy))

However, achieving centimeter-level accuracy (cm level accuracy (half-inch accuracy)) indoors is by no means easy. Conventional GPS (satellite positioning) cannot be received indoors because building roofs and walls block the signals, and its errors are large—ranging from several meters to several tens of meters—so it cannot be used directly in factories or warehouses. For this reason, various indoor positioning technologies other than GPS have been tried to date. Each has its own advantages and disadvantages, but representative indoor positioning techniques include the following:

• Positioning using BLE or Wi‑Fi: A method that installs multiple radio beacons and estimates distance from the received signal strength. It can be introduced at relatively low cost, but accuracy is coarse even at best—on the order of a few meters (a few ft)—and errors tend to be large due to radio reflections and interference.

• Positioning using UWB (ultra-wideband radio): This method uses very short radio pulses on the order of nanoseconds to perform high-precision ranging. It is used by installing multiple dedicated antennas (fixed stations) inside buildings. Depending on the environment, accuracy can sometimes be improved from tens of cm (tens of in) to about 10 cm (3.9 in). However, hardware and installation/tuning costs are high, which becomes a barrier to adoption.

• Positioning using ultrasound (acoustics): A method that places multiple ultrasonic transmitters on ceilings and calculates position from differences in sound arrival times. It is less affected by obstacles, and systems that can obtain three-dimensional position information have been developed. Some advertise errors of around ±1 cm (±0.4 in), but dedicated infrastructure installation and pre-deployment calibration work are still required.

• Positioning using cameras or LiDAR: A technique that estimates a device’s position from its surrounding environment by analyzing camera images or LiDAR sensor scans. It has the advantage that objects do not need tags or beacons attached, but high-performance cameras/LiDAR equipment tends to be expensive. In some cases, mapping the entire building (creating a map) or installing markers before measurement is necessary, so it cannot be described as easy.

• PDR (pedestrian dead reckoning): A method that estimates a person’s walking movement from a smartphone’s built-in accelerometer and gyroscope and integrates the relative movement from a known starting position. It is effective for short periods, but errors (drift) accumulate over time, and accuracy cannot be maintained over long distances or long durations.

As described above, existing methods for high-precision indoor positioning each had their own limitations and challenges. In particular, to achieve centimeter-level accuracy (half-inch accuracy), most cases required deploying numerous specialized pieces of equipment or making large upfront investments. Also, many technologies tend to be confined to positions on a two-dimensional plane (X, Y coordinates), making precise measurement in the height direction (Z axis) difficult. However, at factory and warehouse sites, height-direction information — for example, which height on a shelf something is located at, or how many cm (how many in) the floor is tilted — can also be important.

So, how can we more easily achieve indoor positioning with cm level accuracy (half-inch accuracy)? One key is the use of RTK (real-time kinematic) technology.

What is high-precision positioning with RTK

RTK is a technique that corrects errors in satellite positioning systems such as GPS in real time to achieve centimeter-level accuracy (cm level accuracy (half-inch accuracy)). Normal GPS positioning produces errors of around 5–10 m (16.4–32.8 ft), but by installing a separate fixed base station at a known location and sending the error information received there to the rover to apply corrections, the position accuracy of the rover (the unit being measured) is greatly improved. As the name implies, because it receives correction information and performs calculations in real time, it can provide high-precision position information on the spot.

With RTK positioning, under good conditions you can achieve accuracy within approximately ±1-2 cm (±0.4-0.8 in) horizontally and about ±3 cm (±1.2 in) vertically. This is accuracy far beyond that of conventional standalone GPS. RTK has traditionally been used in outdoor scenarios such as civil engineering surveying, agriculture, and autonomous driving that require centimeter-level accuracy (cm level accuracy (half-inch accuracy)), but in recent years receiver costs have fallen and sizes have decreased, making them easy to use even for non-specialist operators.

Also, infrastructure to support high-precision positioning has been established in Japan. For example, Japan’s Quasi-Zenith Satellite System “Michibiki” provides a satellite-based correction information distribution service called CLAS (centimeter-class positioning augmentation service). Using a compatible receiver, even in environments where an Internet connection is not available, you can receive correction data for cm-level positioning (cm level accuracy (half-inch accuracy)) directly from the satellites. Therefore, even in mountainous areas or remote islands where mobile phone coverage is unavailable, RTK can provide high-precision positioning as long as the sky is open.

RTK technology is highly precise, but applying it to "indoor positioning" requires ingenuity. The solution devised to bring RTK’s benefits indoors, where GPS satellite signals cannot reach, is a new indoor positioning solution using smartphone × LRTK.

A new indoor positioning realized by smartphone × LRTK

LRTK (L-R-T-K) is a compact, high-precision positioning device that operates in conjunction with a smartphone. The palm-sized device houses a high-performance GNSS antenna and receiver, and employs the RTK method to achieve centimeter-level positioning (cm level accuracy (half-inch accuracy)). Weighing approximately 165 g and only about 1 cm (0.4 in) thick, it is very compact, and with a built-in battery it can operate continuously for about 6 hours. It can connect wirelessly to a smartphone via Bluetooth and the like, and won't get in the way when carried around on site.

LRTK devices can achieve RTK positioning Fix solution (fixed solution) in just a few dozen seconds to about one minute in an open outdoor area, allowing you to obtain your current position with an error within ± a few cm (± a few in). Unlike conventional fixed RTK base stations and large surveying equipment, a major advantage is that field staff can carry them in their pockets and easily obtain a high-precision reference position. For example, you can quickly take a high-precision measurement of your position at locations that can directly capture satellites—such as near a factory entrance or on a building rooftop—and use that coordinate as a reference to begin surveying and position checks inside the factory.

So, once you enter a building and can no longer receive GPS signals, what happens then? This is where smartphone sensor technology comes into play. Modern smartphones are equipped with high-performance cameras, LiDAR, accelerometers, and gyroscopes, and AR (augmented reality) technology can capture the device’s movement in real time. In a smartphone × LRTK system, even after you go indoors and satellite positioning becomes unavailable, the phone’s AR functions can continue to track your position. In short, while moving indoors the smartphone acts as a high-performance pedestrian dead reckoning (PDR) device, continuously calculating relative movements from the last high-accuracy reference position it had acquired.

With this system, even points inside factory buildings where GPS signals do not reach can easily achieve high-precision positioning. For example, the location of equipment deep inside a factory can be recorded with cm-level accuracy (half-inch accuracy) simply by performing RTK-based position correction (alignment) near the entrance and then moving with a smartphone. It is innovative that there is no need to install special fixed infrastructure indoors and that everything can be completed with just the user’s smartphone and an LRTK device. No complex setup is required, and the ease of being able to start measuring as soon as you arrive on site is a major advantage.

Examples of Use and Benefits in Factories and Warehouses

High-precision indoor positioning technology combining smartphones and LRTK can be utilized in a variety of scenarios in factories and warehouses. Here we introduce some concrete examples and their benefits.

• Surveying for equipment layout changes and new installations: When installing new machinery in a factory or changing a production line layout, accurate pre-installation surveying data is essential. With LRTK, you can measure planned installation points on the floor with cm-level accuracy (half-inch accuracy). By matching the planned coordinates on drawings with onsite survey results, you can mark machine installation positions without deviation, preventing construction errors and reducing the need for readjustment.

• Inventory management and picking efficiency in warehouses: In large warehouses, accurately knowing storage locations directly impacts efficient picking operations. If shelf and product locations are recorded as three-dimensional coordinates using LRTK, a tablet map can display and navigate the "worker’s current position" and the "target inventory item’s position" in real time. This enables optimization of picking routes and reduction of work time, ultimately lowering labor costs and shortening lead times.

• Visualization and improvement of workflow and movement paths: This is used to analyze in-factory logistics flows and worker movements. By carrying an LRTK connected to a smartphone and walking for a set period, you can continuously log movement trajectories at cm-level accuracy (half-inch accuracy). From this highly accurate movement data, you can identify unnecessary back-and-forths and dwell points and quantitatively verify the improvement effects of layout changes. For safety management, it is also possible to accurately determine the actual traffic areas of people and forklifts and use that information to review hazardous spots and separate movement paths.

• Use in inspection and maintenance operations: Accurate location information is also useful in inspection records for factory equipment when identifying problem areas. With LRTK, you can tag and save the coordinates and orientation information of the photo location to photos taken during inspections. Because the photos can later be viewed in the cloud together with maps and 3D models, you can instantly share "which part of which equipment was repaired" and "where the next inspection is." Compared to the traditional method of handwriting notes on paper drawings, this will significantly advance the DX (digital transformation) of equipment management.

In this way, indoor positioning using smartphones combined with LRTK becomes a powerful tool that supports all improvement activities on the production floor behind the scenes. By leveraging high-precision location data, you can increase the accuracy of the entire process—from understanding the current situation to planning and to evaluating the effectiveness of measures. For example, if you can objectively demonstrate by comparing movement-path data before and after a layout improvement that “unnecessary movement was reduced by X%,” building consensus within the company will be smoother. Improvements based on precise data also help reduce the burden on workers and prevent human error on the shop floor, supporting the creation of a safer and more efficient workplace.

How simplified surveying with LRTK is changing job sites

With the arrival of smartphone-based LRTK, surveying in factories and warehouses is becoming less of a specialized task and more something that can be handled as an extension of everyday work. Traditionally, if you wanted to perform precise, centimeter-level surveying, you had to hire specialists such as surveyors or use expensive dedicated equipment. However, with simplified surveying using LRTK, on-site personnel can complete the necessary measurements themselves in a short time.

For example, repeatedly relying on external surveying contractors for every layout change was time-consuming and costly, but with LRTK your department can respond immediately. By attaching the LRTK device to the tip of an extension pole (monopod), a single person can achieve stable positioning. The app automatically performs the height-offset correction calculations, so no specialized knowledge is required. This usability that thoroughly eliminates complexity enables even first-time users to carry out surveying tasks intuitively.

When on-site personnel are able to carry out surveying themselves, decision-making becomes significantly faster. Simulations of layout proposals and measurements of the effectiveness of improvement measures can also collect accurate data on the spot and be analyzed immediately, allowing the PDCA cycle to move quickly. Because measurements can be retaken as often as necessary, flexible responses to changing conditions are easy. Such on-site gains in agility will also contribute to speeding up continuous improvement activities at production sites and strengthening competitiveness.

Also, simplified surveying with LRTK offers a major cost advantage. Once you have prepared the device and a smartphone, there are no additional costs for subsequent measurement work (if you use Michibiki's CLAS signal for satellite augmentation services, no communication fees are required). It can reduce the surveying costs that were outsourced, and because you can perform measurements yourselves at the timing you want, there is no waste. The initial investment can also be kept far smaller than introducing stationary large surveying equipment or other indoor positioning infrastructure.

In this way, the changes that simplified surveying with LRTK can bring to worksites are immeasurable. By creating an environment where everyone can utilize high-precision positioning information, the very methods for managing factories and warehouses will be updated. If your workplace also faces issues such as "we want to measure but can't" or "we are troubled by positional errors," why not consider the new option of smartphone × LRTK? It will surely become a reliable ally in improving operations on-site.

FAQ

Q. What do I need to use a smartphone with LRTK? A. Basically, all you need to prepare is the LRTK device itself and a compatible smartphone (currently iOS devices such as iPhone or iPad). Install the dedicated LRTK app on the smartphone and connect to the device via Bluetooth, etc. When performing positioning, you first need to receive satellite signals in a location with a view of the sky to establish an initial RTK fix. Even when measuring indoors, before starting measurements, perform RTK positioning once outside the building or near a window to obtain an RTK fix. After that, simply carry the smartphone indoors, move to the point you want to measure, and press the record button. No complicated setup of base stations or prior calibration work is required, so you can start measuring as soon as you arrive on site.

Q. Is the positioning accuracy really at the centimeter level? Doesn't accuracy drop when going indoors? A. Yes—if operated properly, you can achieve high accuracy with errors of only a few centimeters or less. If an RTK Fix solution (cm-level positioning, half-inch accuracy) is available in an open outdoor area, moving indoors immediately afterward will not cause an immediate large drop in accuracy. Thanks to smartphone AR technology, you can maintain position accuracy for a short time, so you can obtain coordinates indoors with accuracy on the order of a few centimeters (a few in). However, if a state of complete satellite loss persists for a long time, errors will gradually accumulate, so when traveling long distances inside a very large facility it is safer to go outside again midway to reacquire satellites (reset the position). In actual use, point surveys of about 10 points have confirmed that the scatter of each point falls within a standard deviation of approximately 1–2 cm (0.4–0.8 in). Furthermore, by measuring the same point dozens of times and averaging, you can achieve accuracy approaching less than 1 cm (less than 0.4 in).

Q. How portable is the LRTK device? How heavy is it and how long does the battery last? A. The LRTK device is designed to be extremely compact and lightweight. It weighs approximately 165 g, comparable to a smartphone, and is only about 1 cm (0.4 in) thick. Its size makes it easy to carry in a pocket and it won’t get in the way when carried around on site. The device has a built-in battery and runs for approximately 6 hours continuously on a full charge. Charging is done via USB Type-C, and it also supports power supply from a mobile battery. This allows operation for long tasks without worrying about the power running out.

Q. Can it be used in environments without an Internet connection? A. Yes. LRTK devices support receiving the CLAS signal (centimeter-class augmentation information; cm-level augmentation information (half-inch accuracy)) provided by Japan’s quasi-zenith satellite Michibiki. Therefore, even in remote mountains or underground facilities where cellular signal does not reach, if the sky is visible the device can receive correction information directly from the satellite and achieve high-precision positioning. Even for indoor positioning, if you can receive Michibiki’s signal from the building roof or near a window, you can maintain RTK-level accuracy without a network connection. However, in places deep underground where the sky is completely blocked, satellite signals themselves cannot reach, so it is difficult in such environments. In those cases, you can cope by methods such as performing relative surveying from a reference point measured on the ground once, or aligning positions by matching with existing drawing data.

Q. How are surveying data and recorded information handled? Can they be shared within the company? A. Positioning data obtained with the LRTK app, captured images, and scanned point cloud data can be synchronized to a cloud service and utilized. Information such as the coordinate values and photos of each point measured on site can be uploaded to a dedicated cloud over the Internet. After uploading, the data can be viewed as 2D maps or 3D views in a browser and lengths can be measured. You can also issue a web sharing URL so that members of other departments or business partners who do not have the dedicated software can view the data. In addition, because it supports Japan’s plane rectangular coordinate system (any system can be selected), it is easy to overlay the acquired data onto CAD drawings or other GIS data. In short, this enables smooth comparison of on-site position data with design drawings or existing documents and seamless information sharing among stakeholders.

Q. Is specialist knowledge required for installation or operation? Can beginners use it effectively? A. You don’t need specialized knowledge or qualifications. The LRTK system is designed with a simple UI and automated processing so that even first-time users can operate it intuitively. Equipment setup is at most attaching it to an extension pole and setting it vertically, and there are no complicated calibration procedures. The app displays the current positioning mode (Fix solution / Float solution, etc.) and the number of satellites being tracked, making it easy for beginners to understand the current accuracy status. Operation manuals and tutorials are provided, and if you have any questions our support desk will assist you. In practice, factory equipment personnel and staff with no surveying experience have been able to perform surveys with LRTK after a short lecture. Please feel free to deploy it on-site with confidence.