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

Table of Contents

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

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

• High-precision positioning using RTK

• New indoor positioning realized with smartphones × LRTK

• Use cases and benefits in factories and warehouses

• How worksites change with simplified surveying using LRTK

• FAQ

High-precision indoor positioning required for location management inside factories

In manufacturing plants and logistics warehouses, location information is critically important in every context—equipment and inventory placement, improvement of work flows, and safety management. Tasks that until now relied on experience and intuition are increasingly being visualized by using digital technologies to make location data visible, driving productivity improvements and waste reduction. In particular, there is growing demand to measure positions inside factories and warehouses with centimeter (cm) -level precision (half-inch accuracy). Precise placements and fine adjustments that were difficult with errors of several meters (several ft) could be achieved if cm level accuracy positioning were possible indoors. The use of high-precision location information is becoming an indispensable element in factory Kaizen (improvement) and efficient warehouse operations.

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

However, measuring position indoors with cm-level accuracy (half-inch accuracy) is by no means easy. Conventional GPS (satellite positioning) cannot be received indoors because it is blocked by the roofs and walls of buildings, and its errors are also large—on the order of several meters to several tens of meters (several ft to several tens of ft)—so it cannot be used as-is in factories or warehouses. Therefore, various indoor positioning technologies other than GPS have been attempted so far. Each has its advantages and disadvantages, but typical indoor positioning technologies include the following.

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

• Positioning by UWB (ultra‑wideband radio): This technique uses very short radio pulses on the order of nanoseconds to perform high‑precision ranging. Multiple dedicated antennas (fixed stations) are installed within buildings. Depending on the environment, accuracy can be improved from several tens of centimeters (several dozen inches) down to about 10 cm (3.9 in). However, hardware and installation/tuning costs are high, which raises barriers to deployment.

• Positioning by ultrasonic (acoustic): Multiple ultrasonic transmitters are placed on ceilings, etc., and positions are calculated from time differences of arrival of sound waves. It is less affected by obstacles, and systems that can acquire three‑dimensional position information have been developed. Some advertise errors of about ±1 cm (±0.4 in), but installation of dedicated infrastructure and pre‑calibration work are still required.

• Positioning using cameras and LiDAR: This technology estimates a device’s position from the surrounding environment by analyzing camera images or LiDAR scans. The advantage is that objects do not need tags or beacons attached, but high‑performance camera/LiDAR equipment tends to be expensive. Also, in some cases, mapping (creating a map) of the entire building or installing markers before measurement is necessary, so it is not necessarily easy.

• PDR (pedestrian dead reckoning): This method estimates a person’s walking movement from smartphone‑built accelerometers and gyroscopes, and integrates relative movement from a known starting position. It is effective for short periods, but errors (drift) accumulate over time, and it cannot maintain accuracy 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 devices or making large initial investments. Also, many technologies tend to remain limited to positions on a two-dimensional plane (X,Y coordinates), making precise measurement in the vertical direction (Z axis) difficult. However, in factory and warehouse sites, height-direction information can also be important—for example, which shelf height an item is at, or how many centimeters (inches) the floor is tilted.

So, how can we more easily achieve cm level accuracy (half-inch accuracy) for indoor positioning? One of the keys is the use of RTK (Real-Time Kinematic) technology.

What is high-precision positioning with RTK

RTK is a technology that achieves centimeter-level (inch-level) accuracy by correcting errors in satellite positioning, such as GPS, in real time. Ordinary GPS positioning has errors of about 5–10 m (16.4–32.8 ft), but by installing a fixed base station separately as a reference point and sending the error information received at that location to the rover to correct it, the positioning accuracy of the rover (the point you want to measure) is greatly improved. As the name suggests, because correction information is received and calculations are performed in real time, you can obtain high-precision positions on the spot.

With positioning using RTK, under good conditions you can achieve accuracy within about ±1–2 cm (±0.4–0.8 in) horizontally and about ±3 cm (±1.2 in) vertically. This is a level of accuracy far beyond conventional standalone GPS.

Originally, RTK was used in outdoor scenarios—such as civil engineering surveying, agriculture, and autonomous driving—where centimeter-level accuracy is required (cm level accuracy (half-inch accuracy)), but in recent years receivers have become cheaper and smaller, making RTK accessible to non-specialists.

In Japan, infrastructure supporting high-precision positioning has also been developed. For example, Japan’s Quasi-Zenith Satellite System “Michibiki” provides a service called CLAS (Centimeter-Level Augmentation Service) that broadcasts correction information from satellites. With a compatible receiver, you can receive correction data for cm-level positioning (cm level accuracy (half-inch accuracy)) directly from the satellites even in environments without internet connectivity.

Therefore, even in mountainous areas or remote islands outside mobile phone coverage, RTK can provide high-precision positioning as long as the sky is unobstructed.

RTK technology is extremely precise, but applying it to "indoor positioning" requires some ingenuity. To obtain the benefits of RTK inside buildings where GPS satellite signals do not reach, a new indoor positioning solution using smartphone × LRTK was devised.

New indoor positioning enabled by Smartphone × LRTK

LRTK (pronounced "L-R-T-K") is a compact, high-precision positioning device that operates in conjunction with a smartphone. It houses a high-performance GNSS antenna and receiver in a palm-sized unit, achieving centimeter-level positioning accuracy (cm level accuracy, half-inch accuracy) using the RTK method. Weighing approximately 165 g and 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, so carrying it on-site will not interfere with work.

Using an LRTK device, in an open outdoor location the RTK positioning quickly reaches a Fix solution (fixed solution) in just a few tens of seconds to about 1 minute, and you can obtain your current position with an error of ± several cm (± several in). Unlike conventional fixed RTK base stations or large surveying equipment, a major advantage is that field staff can carry it in their pocket and obtain a high-precision reference position with that portability. For example, it can be used by quickly measuring your position with high precision in a place where satellites can be directly acquired—such as near a factory entrance or on a building rooftop—and then using 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? 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 own 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 you move indoors the smartphone acts as a high-performance pedestrian dead reckoning (PDR) device, continuously calculating your relative movement from the high-precision reference position acquired just before.

This mechanism enables easy high-precision positioning even at points inside factory buildings where GPS signals cannot reach. For example, the location of equipment deep within a factory can be recorded at cm-level accuracy simply by performing RTK position calibration (reference alignment) near the entrance and then walking with a smartphone. There is no need to install special fixed infrastructure indoors; the fact that the system can be completed with just a user's smartphone and an LRTK device is innovative. No complex setup is required, and the ease of being able to start measuring immediately upon arrival on site is a major advantage.

Application Examples and Benefits in Factories and Warehouses

High-precision indoor positioning technology using smartphones × LRTK can be applied to a wide range of scenarios in factories and warehouses. Here we introduce several concrete examples and their benefits.

• Surveying for equipment layout changes and new installations: When installing new machinery or changing the layout of a production line inside a factory, accurate pre-survey position data is indispensable. Using 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 on-site survey results, you can mark machine mounting positions without misalignment, preventing installation errors and reducing the need for readjustments.

• Warehouse inventory management and picking efficiency: In large warehouses, knowing the exact storage locations directly affects efficient picking operations. If you record shelf and product positions in 3D coordinates with LRTK, you can display and navigate the worker’s current position and the target inventory location in real time on a tablet map. This enables optimization of picking routes and reduction of task time, which can lead to lower labor costs and shorter lead times.

• Visualization and improvement of work flow lines: This is for analyzing logistics flows and worker movements within the factory. If you carry an LRTK connected to a smartphone and walk for a certain period, you can continuously position (log) the movement trajectory at cm-level accuracy (half-inch accuracy). From this high-precision movement data, you can identify unnecessary back-and-forth trips and stagnation points and quantitatively verify the improvement effects of layout changes. From a safety management perspective, it’s also possible to accurately grasp the actual passage areas of people and forklifts and use that information to reassess hazardous locations or separate traffic flows.

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

In this way, indoor positioning using smartphones × 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 verifying 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 ○%,” building internal consensus will be smoother. Improvements based on precise data also help reduce the burden on workers and prevent human errors, supporting the creation of a safer and more efficient workplace.

How On-site Work Is Changing with Simplified Surveying Using LRTK

With the advent of smartphones combined with LRTK, surveying at factories and warehouses is becoming something that can be performed as an extension of routine work rather than a specialized professional task. Traditionally, if you wanted to perform highly precise surveying at the centimeter level (cm level accuracy, half-inch accuracy), you had to hire specialists such as surveyors or use expensive dedicated equipment. However, with simplified surveying using LRTK, on-site staff can complete the necessary measurements themselves in a short time.

For example, having to request an outside surveying firm every time the layout changed took time and money, but with LRTK your department can respond immediately. By attaching an LRTK device to the end of an extension pole (monopod), a single person can achieve stable positioning. The app automatically performs the correction calculations for the height offset, so no difficult knowledge is required. Thanks to this usability that thoroughly eliminates complexity, even first-time users can perform surveying tasks intuitively.

When the on-site team can perform surveying themselves, decision-making speed improves markedly. Simulations of layout proposals and measurements of the effects of improvement measures can also collect accurate data on the spot and be analyzed immediately, enabling the PDCA cycle to proceed swiftly. Because measurements can be repeated as often as necessary, flexible responses to changing conditions are easy. This increase in on-site operational agility will also contribute to accelerating continuous improvement activities on the production floor and strengthening competitiveness.

Also, simple surveying with LRTK offers a significant cost advantage. Once you have the device and a smartphone, there are no additional costs for subsequent measurement work (and if you use Michibiki's CLAS signal for the satellite augmentation service, no communication fees are required). It can reduce the surveying costs you previously outsourced, and because you can measure immediately whenever you want, there is no waste. The initial investment can also be kept far smaller than introducing stationary large surveying instruments or other indoor positioning infrastructure.

Thus, the changes that simplified surveying with LRTK brings to worksites are immeasurable. As environments are established in which everyone can utilize high-precision location information, the management methods of factories and warehouses themselves will be updated. If your workplace is also facing issues such as "we want to measure but can't" or "we're troubled by positional errors," why not consider a new option: smartphones × LRTK? It will surely become a reliable ally in improving on-site operations.

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 an iPhone or iPad). Install the dedicated LRTK app on the smartphone and connect it to the device via Bluetooth or similar. When performing positioning, you first need to receive satellite signals in a location with a clear view of the sky to establish an initial position with RTK. Even when measuring indoors, make sure to obtain an RTK fix once outside the building or near a window before starting measurements. After that, carry the smartphone indoors and simply press the record button at the points you want to measure. No complicated setup of base stations or pre-calibration work is required, so you can start measuring as soon as you arrive on site.

Q. Is the positioning accuracy really on the centimeter level? Doesn't the accuracy drop when you go indoors? A. Yes, with proper operation you can obtain high accuracy with errors of a few centimeters or less (a few inches or less). If an RTK fix (cm-level positioning; cm level accuracy (half-inch accuracy)) is available in an open outdoor area, moving indoors immediately afterward will not cause a large drop in accuracy. Thanks to smartphone AR technology, positional accuracy can be maintained for a short time, so coordinates can be obtained indoors with approximately a few cm (a few in) of accuracy. However, if no satellites are tracked at all for an extended period, errors will gradually accumulate, so when moving long distances within very large facilities it is advisable to go outside midway to reacquire satellites (reset the position). In actual use, it has been confirmed that for point surveys of about 10 points 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 several dozen times and averaging, accuracy approaching less than 1 cm (less than 0.4 in) can be achieved.

Q. How portable is the LRTK device? How much does it weigh and how long does the battery last? A. The LRTK device is designed to be extremely compact and lightweight. It weighs approximately 165 g, about the same as a smartphone, and its thickness is only about 1 cm (0.4 in). It’s pocketable and won’t get in the way when carried on site. The device has a built-in battery and runs for approximately 6 hours on a full charge. Charging is done via USB Type-C, and it also supports power from a power bank. This lets you operate it for extended periods without worrying about the power running out.

Q. Can it be used in environments without internet access? A. Yes, it can be used. LRTK devices support receiving Japan’s quasi-zenith satellite "Michibiki" CLAS signal (centimeter-level augmentation information (half-inch accuracy)). Therefore, even in remote mountains or underground facilities where cellular reception is unavailable, as long as the sky is visible, correction information can be received directly from the satellite for high-precision positioning. For indoor positioning, if the Michibiki signal can be received from a building rooftop or near a window, RTK accuracy can be maintained without a network connection. However, in places where the sky is completely obscured, such as deep underground, satellite signals cannot reach and it will be difficult. In such cases, workarounds include relative surveying from a control point measured once on the surface or aligning positions with existing drawing data.

Q. How are survey data and recorded information handled? Can they be shared within the company? A. Positioning data, captured images, scanned point cloud data, and other information obtained with the LRTK app can be synchronized to a cloud service and put to use. Coordinate values and photos of each point measured on site can be uploaded to a dedicated cloud over the internet. After uploading, you can view the data as 2D maps or 3D views in a browser and measure distances. You can also issue a web sharing URL so members of other departments or external partners who do not have the dedicated software can view the data. The coordinate system also supports Japan’s plane rectangular coordinate system (any system selectable), making it easy to overlay acquired data onto CAD drawings or other GIS data. In short, this allows you to smoothly compare on-site position data with design drawings or existing documents and to share information among stakeholders.

Q. Is specialized knowledge required for installation or operation? Can beginners handle it? A. No specialized knowledge or qualifications are necessary. 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 the device to an extension pole and standing it vertically; 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, so even beginners can easily grasp the current accuracy status. Operation manuals and tutorials are provided, and if anything is unclear a support desk will assist. In practice, factory equipment managers and staff with no surveying experience have been able to perform surveys with LRTK after a short briefing. Please feel confident introducing it to your site.