GNSS such as GPS typically exhibits errors of about 5–10 m (16.4–32.8 ft) when used standalone. By using "correction information services" that supplement these signals, positioning accuracy can be improved to the level of several centimeters (a few inches). Currently available correction information services include several types: the network-based type, which distributes error data from regional base station networks; the satellite-only type, which receives augmentation signals directly from satellites; and the smartphone-integrated type, which enables convenient high-precision positioning using a receiver integrated with a smartphone.

This article compares the characteristics of each correction information service, with a particular focus on rigorously evaluating the area coverage capability of smartphone-integrated CLAS-compatible methods (how wide the service area is and whether use is possible outside of cellular coverage). It also explains differences among the methods from the perspectives of positioning accuracy, correction data update frequency, required equipment, ease of deployment, and cost, and touches on use cases in urban, mountainous, and disaster scenarios. Finally, it answers common questions in a FAQ format and offers tips for introducing high-precision positioning.

Contents

• What is a correction information service

• Types of correction information services

• Network-based correction information services

• Satellite-only (CLAS) correction information services

• Smartphone-integrated CLAS-compatible method

• Comparison of area coverage ranges

• Coverage area of network-based services

• Coverage area of satellite-only (CLAS) services

• Coverage area of smartphone-integrated CLAS

• Comparison of positioning accuracy and correction frequency

• Accuracy and correction update frequency of network-based services

• Accuracy and update frequency of satellite-only (CLAS) services

• Accuracy of smartphone-integrated CLAS

• Required equipment and ease of deployment

• Required equipment and deployment conditions for network-based services

• Required equipment and ease of deployment for satellite-only services

• Required equipment and ease of deployment for smartphone-integrated CLAS

• Cost comparison

• Cost of network-based services

• Cost of satellite-only services

• Cost of smartphone-integrated services

• Use cases in the field

• High-precision positioning for disaster response

• Positioning in forests and areas outside coverage

• Positioning in urban and built-up areas

• Summary

• FAQ

What is a correction information service

A correction information service provides information to correct GNSS positioning errors. GNSS satellite signals are affected by various error sources such as satellite orbit and clock offsets, ionospheric and tropospheric delays, and signal reflections (multipath) caused by the surrounding environment. As a result, standalone positioning leaves position errors on the order of several meters. Correction information services compensate for these errors in real time by distributing GNSS error information measured at reference stations (control points with accurate coordinates) to users, or by transmitting augmentation signals directly from satellites equipped with such signals. This dramatically improves positional accuracy, shrinking errors to the level of several centimeters (a few inches).

A long-established mechanism for obtaining high-precision positioning is RTK (Real-Time Kinematic). RTK involves a reference station and a rover both receiving the same satellite signals; the error computed at the reference station is transmitted to the rover to correct its position. This principle cancels error components of satellite signals that cannot be removed by standalone positioning, typically achieving very high horizontal accuracy on the order of 1–3 cm (0.4–1.2 in). Applications of RTK have enabled tasks that were previously unacceptable with meter-level errors—such as automated control of heavy machinery and as-built verification against design drawings—to be carried out safely and accurately.

Types of correction information services

There are several methods of providing correction information services, each differing in how they are delivered and the equipment required. The representative types are the network-based type, the satellite-only type, and the smartphone-integrated type, described below.

Network-based correction information services

Network-based correction information services receive GNSS correction data in real time via the Internet (cellular networks, etc.). A common scheme integrates data from national control point networks such as the Geospatial Information Authority of Japan’s Continuously Operating Reference Stations (about 1,300 CORS sites) and from private operators’ reference-station networks in the cloud, then creates virtual reference stations (VRS) near the user and distributes error correction information. Users connect to correction information servers using a protocol called Ntrip with GNSS receivers or positioning apps, acquiring correction data in real time and applying them to their positioning.

The advantage of this method is that users do not need to set up their own base stations; within the service area, centimeter-level positioning is possible with just a single receiver. Network corrections computed from multiple reference stations largely eliminate accuracy degradation due to distance from a single reference station, providing stable accuracy over wide areas. On the other hand, a contract with the service provider is required and monthly or annual usage fees apply. Also, in areas outside cellular coverage the correction data cannot be received, so real-time positioning cannot be performed.

Satellite-only (CLAS) correction information services

In satellite-only correction services, correction information is provided directly from satellites rather than through terrestrial communication networks. In Japan, a representative example is the Quasi-Zenith Satellite System (QZSS) Centimeter Level Augmentation Service (CLAS). CLAS distributes high-precision error correction data nationwide via the QZSS L6-band signal, and users with compatible receivers can use it free of charge.

The major characteristics of this method are that "users do not need to prepare their own base stations" and "no communication line is required to obtain the correction information." Error information derived from observations at the government-maintained control-point network (GEONET) is sent directly to users via the Quasi-Zenith Satellites, eliminating accuracy degradation due to distance from reference stations and providing uniform augmentation information anywhere in Japan, from mountainous regions to the open sea. Because it only requires receiving augmentation signals from satellites, no Internet connection is necessary, so it can be operated in areas without cellular coverage. Another major advantage is that the augmentation signal reception is free of charge (the purchase cost of a compatible receiver is separate).

A point to note is that a dedicated GNSS receiver capable of receiving CLAS signals (L6D) is required. Typical commercial GNSS devices or smartphone-embedded GPS cannot handle L6-band signals, so you need equipment explicitly marketed as "CLAS-compatible." In terms of accuracy, CLAS may be somewhat inferior to traditional RTK that communicates directly with a reference station. For example, whereas RTK fixed solutions can provide about 2 cm (0.8 in) horizontal accuracy, CLAS is reported to provide about 5–6 cm (2.0–2.4 in). Also, it generally takes several tens of seconds to about 1 minute for initial convergence to reach high-precision positioning; during this period the solution may remain a float RTK solution with errors on the order of tens of centimeters, so care is needed when immediate extreme accuracy is required. However, after about 1 minute the error typically converges to within a few centimeters and remains stably high-precision. Note that CLAS service coverage is limited to Japan (the visible range of Michibiki satellites), so it cannot be used overseas.

Smartphone-integrated CLAS-compatible method

The recently introduced smartphone-integrated method combines satellite augmentation services (CLAS) with smartphones to make high-precision positioning extremely convenient. A compact GNSS device with an integrated antenna, receiver, and battery is attached to a smartphone (mainly iPhone or Android), and connects via Bluetooth, etc., to perform positioning. By launching a dedicated smartphone app, reception of correction information and high-precision positioning are completed on the phone, effectively turning the smartphone into a high-precision surveying instrument.

The advantage of this method is its excellent portability and simplicity. There is no need to carry heavy surveying equipment or cumbersome cables; the receiver device (often weighing under several hundred grams) and a smartphone are all that’s required on site. The antenna is built in and the device is pocket-sized, greatly reducing transport burden. Because it can be used one-per-person, each worker can immediately perform positioning and recording when needed, significantly improving field productivity. The app UI is designed to be familiar and intuitive, enabling workers without specialized training to operate it easily, facilitating field deployment.

Smartphone-integrated devices that support CLAS can perform high-precision positioning even outside cellular coverage. Tasks that were previously impractical—such as surveying in remote mountainous areas or operating during disasters when communication infrastructure is cut off—can obtain centimeter-level positioning directly from satellites if the smartphone-integrated device is available. Integration with the phone’s camera and cloud functions is another benefit. For example, using a smartphone-integrated device and a dedicated app, you can easily take photos with high-precision location tags and visualize photo locations on a map on the spot. Photos are automatically tagged with accurate positioning data, allowing efficient post-processing in the office to match photos with map information for reporting.

Comparison of area coverage ranges

This section compares the coverage areas (service delivery ranges) of each correction information service type from perspectives such as urban areas, mountainous regions, and areas outside cellular coverage.

Coverage area of network-based services

Network-based services are basically available wherever cellular service coverage exists. In Japan, major mobile carriers’ networks cover most of the country, so correction information can be received at most urban and suburban sites. However, in deep valleys, remote forests, and isolated construction sites where cellular service is unavailable, real-time network-based correction information cannot be obtained. Likewise, on the open sea far from shore where terrestrial cellular signals do not reach, network-based services are generally not usable for high-precision positioning.

Note that the service provider’s network coverage (the area where their correction network is established) varies by operator. Some local VRS services only cover limited regions, but nationwide commercial services have been proliferating recently, and by contract many providers now enable nationwide use. Nevertheless, as noted above, service cannot be used outside cellular coverage, so it is important to check radio conditions before heading to mountainous areas.

Coverage area of satellite-only (CLAS) services

The coverage area of satellite-only (CLAS) services extends across Japan. Because CLAS uses augmentation signals transmitted from the Quasi-Zenith Satellites, users can receive uniform correction information from Hokkaido to Okinawa as long as they have a view of the sky. High-precision positioning is possible even in remote mountain valleys, on uninhabited islands, or at sea while underway, provided satellites can be observed overhead. This wide-area coverage is a major advantage not available with network-based services.

However, because the signal comes from satellites, reception can become unstable in environments where sky visibility is severely obstructed—such as urban canyons formed by buildings or dense forests. CLAS is designed so that at least one Michibiki satellite is positioned over Japan at all times, allowing signals to be obtained from relatively high elevation angles even in urban areas, but it still cannot be used entirely indoors or inside tunnels (this limitation applies to other GNSS methods as well). Also, as noted repeatedly, CLAS is a domestic service for Japan and cannot be used overseas where the satellites are not visible.

Coverage area of smartphone-integrated CLAS

Since smartphone-integrated CLAS-compatible methods use CLAS satellite augmentation, their coverage is essentially the same as CLAS. In other words, they are usable in cellular dead zones across Japan, enabling users to perform high-precision positioning while holding a smartphone even when visiting forests or remote islands. For mobile inspection work across multiple sites, there is no need to change base station installations or switch service areas. For example, when taking measurements continuously while traveling a long distance from north to south, the correction service does not interrupt and positioning can be maintained with consistent accuracy.

Even in disaster sites where communication infrastructure has failed, a smartphone-integrated device can receive correction signals directly from satellites, so field positioning and data recording can continue. There are reports of earthquake-affected areas where mobile base stations were down but a smartphone-mounted CLAS receiver enabled accurate recording of damage with photos. In this respect, smartphone-integrated CLAS has a strong advantage in enabling stable, high-precision positioning nationwide regardless of communication conditions.

Comparison of positioning accuracy and correction frequency

This section compares each method’s positioning accuracy (final positional error) and correction data update frequency (intervals of real-time correction information distribution).

Accuracy and correction update frequency of network-based services

Network-based RTK achieves high accuracy (fixed solution) of about 2 cm (0.8 in) horizontally and a few centimeters vertically by continuously receiving data from reference stations. Initial fixed solutions are often obtained within a few seconds, so centimeter-level accuracy is typically reached immediately after starting positioning. Correction data are usually transmitted at roughly 1 Hz, continuously compensating for time-varying errors such as satellite orbit and ionospheric errors. This enables maintenance of centimeter-level accuracy even for continuous positioning while moving or for machine guidance of heavy equipment where real-time performance is required.

However, continuous reception of correction information in a stable communication environment is a prerequisite for maintaining high accuracy. In unstable communication environments, missing correction data may cause loss of the fixed solution and a reversion to float solutions with errors on the order of tens of centimeters. Also, in single-base independent RTK using a single base station set up by the user, accuracy gradually degrades as the distance from the base station increases; generally, errors become larger beyond about 10 km (this distance-related degradation is largely mitigated in network VRS approaches).

Accuracy and update frequency of satellite-only (CLAS) services

Satellite-only (CLAS) positioning accuracy is reported to be about 5–6 cm (2.0–2.4 in) horizontally. While slightly larger than conventional network RTK fixed-solution accuracy, this is practically small enough for most applications. With CLAS, initial positioning may remain as a float solution with errors of several tens of centimeters, but it typically converges within several tens of seconds to about 1 minute to an error range of a few centimeters and then maintains stable high precision. The correction information itself is continuously transmitted from the satellites, so if the user continuously receives it while moving dynamically, positioning accuracy can be maintained.

On the other hand, although CLAS does not depend on communication networks, it requires time for initial convergence. For tasks requiring immediate highest accuracy from the start, it is advisable to monitor the quality of positioning after start-up and proceed accordingly. If a receiver temporarily loses satellite signals, some time may be required to return to high precision. Still, since CLAS generally stabilizes to centimeter-level accuracy within about 1 minute, it is usable for typical surveying and construction tasks.

Accuracy of smartphone-integrated CLAS

The positioning accuracy achievable with smartphone-integrated devices is essentially the same as the aforementioned CLAS method. Both horizontal and vertical accuracies on the order of a few centimeters can be obtained, though initial convergence requires some time. Many smartphone-mounted receivers support multi-band GNSS and receive multiple-frequency satellite signals, which helps maintain positioning performance even in urban or forested environments. Some models also support network RTK corrections via cellular networks, allowing hybrid operation that prioritizes network RTK when in coverage and automatically switches to CLAS when out of coverage, thereby maintaining continuous high accuracy. This flexibility enables smartphone-integrated systems to always utilize the optimal correction information for the field conditions.

Field accuracy verifications have shown that smartphone-integrated devices produce positioning results comparable to conventional fixed high-precision GNSS receivers. Despite their small size, they are equipped with high-performance antennas and GNSS modules and can achieve professional-level centimeter accuracy in open environments. However, like conventional equipment, positioning may become unstable in environments with disturbed GNSS signals such as narrow urban canyons. In degraded environments, basic accuracy control measures—such as taking multiple observations and averaging, or moving to a place with better sky view—are necessary.

Required equipment and ease of deployment

This section compares the equipment required for each method and the ease of deploying them in the field, along with setup effort, radio requirements, and whether operations can be completed by a single person.

Required equipment and deployment conditions for network-based services

To use network-based correction services, a centimeter-capable GNSS receiver (rover) is required. In addition, communication conditions (cellular lines or mobile routers) and Ntrip client configuration are needed so the receiver can obtain correction data via the Internet. Specifically, you prepare a receiver with built-in communication modules or connect the receiver to a tablet/smartphone via Bluetooth, then enter the Ntrip ID and password issued when contracting with the service into the receiver or positioning app to connect to the correction distribution server. Many modern GNSS devices include Ntrip client functions, and such connection settings can be made on dedicated apps or field controller terminals.

Deployment requires completing contract procedures with the service provider in advance to obtain account information, but once contracted, use can begin relatively smoothly. Because users do not need to install their own base stations, a single worker can bring a receiver to the site and complete surveying. If communication can be secured, advanced adjustments are unnecessary, and the complications of base station placement or radio frequency settings are avoided. However, if the field is outside cellular coverage, the service cannot be used; for work in mountainous areas, it is necessary to check radio conditions in advance and consider temporary communication relays or, if real-time operation is impossible, post-processing as a countermeasure.

Required equipment and ease of deployment for satellite-only services

When using satellite-only (CLAS), a CLAS-compatible GNSS receiver is required. Compatible devices include high-precision GNSS receivers marketed by established surveying equipment manufacturers and compact receiver modules from emerging manufacturers. The important point is the ability to receive and process the L6-band CLAS signal; general GNSS devices and smartphone-embedded GPS do not support it, so choose equipment explicitly labeled "CLAS-compatible."

Deployment procedures are relatively simple. No communication contracts are necessary: power on the receiver and capture satellites—CLAS reception will begin automatically. Initial settings typically involve selecting the reference coordinate system (e.g., WGS84 or Japanese geodetic systems) and checking output formats; there are few difficult settings. Because there is no need to set up your own base station or obtain special radio licenses for correction reception, once the hardware is purchased you can start using it on site immediately. The simplicity of being able to carry the receiver and power it on alone to begin high-precision positioning is a major advantage.

Note that the lineup of CLAS-compatible devices is still somewhat limited compared to general RTK-capable devices, so choices are fewer. Also, since satellite signal reception requires open sky, if attaching an external antenna arrange it in a location with good visibility; depending on the form factor, mounting on a survey pole or installing on a vehicle may be necessary to secure stable reception—but this remains far simpler than setting up a base station.

Required equipment and ease of deployment for smartphone-integrated CLAS

To introduce a smartphone-integrated CLAS-compatible device, you only need the compatible device itself and your smartphone. For example, devices that attach to an iPhone use a dedicated smartphone case (adapter) into which a ultra-compact receiver module is fitted and connected to the phone via Bluetooth. After installing and launching the dedicated app, positioning starts. Antenna and battery are built into the device, so no cumbersome wiring or external power is required. The devices are lightweight—typically under several hundred grams—and compact enough to fit in a jacket pocket, significantly reducing the burden of carrying equipment to the field.

Setup is extremely simple and intuitive even without specialized knowledge. On the app, select the correction method to use (e.g., CLAS) and press the start positioning button; satellite-augmented high-precision positioning begins automatically. The current position is displayed in real time on the phone’s map, and positions can be saved or shared with a single tap. This enables immediate digital recording of survey point data that would previously have been written in paper field books, and easy cloud synchronization to share progress with the office.

The smartphone-integrated approach’s one-device-per-person readiness is a major attraction. Survey work can begin within minutes of arriving on site, and packing up simply involves putting the device and phone into a bag. Because the UI is that of a smartphone everyone is familiar with, non-specialist staff can operate it after a short lecture, reducing the burden of in-house training.

Cost comparison

This section compares costs for each method from the viewpoints of initial investment and running costs. Specific price figures are not given here, but we will outline relative cost differences.

Cost of network-based services

Network-based services require initial investment to purchase a high-precision GNSS receiver, antenna, and communication devices. Traditionally, such surveying equipment was specialized and expensive, commonly requiring initial investments on the order of several million yen. In addition, service provider contracts require monthly or annual fees. Depending on usage and provider, annual contract fees can be substantial, making running costs significant for long-term use. For small and medium businesses that do not own high-precision equipment or for infrequent users, these recurring fees can be a barrier to adoption.

However, prices have been gradually becoming more affordable due to competition and technological progress. Options such as device leasing with zero upfront cost and paying only monthly are emerging. In construction, productivity gains from high-precision positioning often justify the expenditure, and network-based services sometimes offer robust support and accuracy guarantees, so cost considerations should be weighed along with such added value.

Cost of satellite-only services

The biggest advantage of satellite-only (CLAS) is that the correction information itself is free. There are no usage fees for receiving the Michibiki CLAS signal, so once a compatible receiver is purchased, no monthly service fees are incurred. This absence of ongoing subscription fees can greatly reduce long-term operational costs.

Nevertheless, the purchase cost of CLAS-compatible equipment must be considered as an initial investment. High-precision GNSS receivers have traditionally been expensive, but CLAS reduces required hardware to a single rover receiver, potentially compressing total equipment costs by removing the need for base station hardware and communication modems. If you already own RTK-capable GNSS equipment, firmware updates may make CLAS reception possible without buying new hardware.

Overall, while initial costs are required to adopt CLAS, zero running costs thereafter make it economically attractive, especially for frequent high-precision positioning. For small operators with limited budgets for maintaining their own base stations or subscription services, adopting CLAS-compatible equipment can significantly lower cost barriers.

Cost of smartphone-integrated services

Smartphone-integrated CLAS-compatible devices are extremely cost-effective. Whereas traditional high-precision GNSS systems once required investments of several million yen, smartphone-mounted devices are offered at a dramatically lower price point. By utilizing a general-purpose smartphone and consolidating the dedicated high-precision receiver into a small add-on device, hardware costs are greatly reduced. As a result, centimeter-level positioning is now affordable for small businesses and individuals.

Running costs are also low: since smartphone-integrated devices typically use CLAS’s free correction, no additional service fees are required. App usage fees are often included with the device purchase, and subscription-based models are uncommon. Models that can optionally use network RTK allow flexible cost control by enabling short-term subscriptions only when needed.

Lower per-unit costs also make deploying devices to multiple personnel realistic. Where previously a single expensive survey set was shared among a team, smartphone-integrated devices can be distributed so each person uses their own phone to perform positioning tasks simultaneously, dramatically improving productivity. Overall, smartphone-integrated CLAS-compatible methods offer the best cost performance in terms of both initial investment and maintenance.

Use cases in the field

This section introduces specific field scenarios where each correction information service excels. Differences in characteristics make certain methods more suitable for particular use cases.

High-precision positioning for disaster response

Disaster response scenarios create a strong need for high-precision positioning—to rapidly record topographic changes and damage and to provide accurate coordinates for recovery planning. However, cellular and power infrastructure are often disrupted in disasters, making network-based RTK unusable. Satellite-only (CLAS) and smartphone-integrated devices are powerful in such situations because they do not rely on terrestrial communication networks and can receive satellite-based corrections directly, enabling centimeter-level positioning even in isolated areas immediately after a disaster.

For instance, in an earthquake where mobile base stations were down, a smartphone-mounted CLAS receiver was used to accurately record damage locations with photos. Being able to obtain accurate geolocation during emergencies greatly aids damage assessment and emergency planning. Keeping smartphone-integrated devices for disaster use increases resilience of infrastructure maintenance and provides a risk-hedging measure when communication networks are unavailable.

Positioning in forests and areas outside coverage

Differences in correction information services are especially apparent in mountainous or sparsely populated fields outside cellular coverage. In the past, achieving real-time centimeter accuracy in such areas was difficult. Network RTK cannot be used outside coverage, forcing users to set up on-site base stations for short-range independent RTK or to perform static GNSS observations for post-processing. With the advent of CLAS and smartphone-integrated devices, centimeter-level positioning is possible on arrival at the site.

For example, tunnel portal works in remote mountains or dam construction sites can perform as-built control measurements based on design coordinates without worrying about communications. Even in dense forests where visibility is poor, choosing a spot with only a partial sky view can allow reception of satellite augmentation signals and enable precise observations of survey points that were previously difficult. CLAS is also effective for maintaining position references on offshore operations far from shore: buoys or survey vessels can be positioned to within several centimeters if they can receive satellite augmentation signals.

Positioning in urban and built-up areas

High-precision positioning in urban areas and near structures presents different challenges. Near tall buildings and large structures, GNSS satellite signals can be blocked or reflected (multipath), causing unstable positioning even if correction information is available. Both network-based and CLAS-based systems can struggle in such environments. Michibiki’s CLAS provides satellites at higher elevation angles which helps secure satellites in urban areas, but in dense urban canyons the number of visible satellites may still be insufficient to obtain a fixed solution. In practice, measures such as moving to an open intersection or observing at times when the sky view is better are often necessary.

A newer technology for surveying near structures is tilt compensation in receivers. Tilt compensation allows accurate coordinates to be calculated even if the pole-mounted receiver is tilted, enabling point acquisition under eaves, under bridges, and in places where the pole cannot be held vertical. Using tilt-compensation-equipped high-precision GNSS equipment makes it possible to measure points very close to structures and substantially improves urban work efficiency.

Smartphone-integrated devices are suitable for quick surveying in narrow streets and dense urban neighborhoods. Their small size and light weight mean measurements can be taken without spreading a tripod in constrained spaces, allowing fast point recording without obstructing pedestrians or vehicles—useful for infrastructure inspections and maintenance tasks. However, in strong multipath or heavily obstructed urban areas, positioning accuracy may be disrupted, so multiple observations and averaging or using nearby high-accuracy control points are recommended for careful data validation.

Summary

Each correction information service method has its own strengths and limitations. Network-based methods offer high responsiveness and stable accuracy provided communication infrastructure is available but cannot perform in areas without coverage. Satellite-only (CLAS) stands out for its area-free capability and is reliable in disasters and remote regions, though device preparation and initial convergence time should be considered. Smartphone-integrated CLAS-compatible methods combine the latest technologies to make high-precision positioning accessible: leveraging ubiquitous smartphones to enable centimeter-level positioning anywhere has the potential to change conventional expectations about positioning.

The advent of smartphone-integrated devices has significantly broadened the user base for high-precision positioning. For example, using products like the LRTK Phone series, non-specialists can immediately perform centimeter-level positioning in the field. Advances in correction information service technology are transforming precision positioning from an expensive, expert-only domain into a more affordable and user-friendly tool. Which system is optimal for your organization depends on use and environment, but if you have hesitated to adopt high-precision positioning so far, consider trying a modern correction information service to enable simple surveying.

FAQ

Q: What is CLAS? Is there a cost to use it? A: CLAS (Centimeter Level Augmentation Service) is a centimeter-level augmentation service provided by the Quasi-Zenith Satellite System (Michibiki). It broadcasts error correction information from satellites so that a compatible receiver can obtain positioning accuracy of a few centimeters. Receiving the CLAS signal itself is free of charge (no contract or communication fees), so it can be used without subscription. However, the purchase of a CLAS-compatible receiver is required separately.

Q: Can a smartphone’s built-in GPS achieve centimeter-level positioning by itself? A: In general, the GNSS receiver built into a typical smartphone cannot achieve centimeter-level accuracy by itself. Smartphone GNSS is designed for standalone positioning and exhibits errors on the order of several meters, and does not provide an interface for inputting real-time correction data, so it cannot be upgraded to high precision. Although some of the latest phones include multi-frequency GNSS chips, without dedicated correction information and a high-performance antenna, positioning errors cannot be reduced sufficiently. Achieving centimeter accuracy requires an external high-precision GNSS receiver (a smartphone-integrated device) or dedicated surveying equipment.

Q: Is CLAS less accurate than conventional RTK (network-based)? A: Both CLAS and RTK provide centimeter-level accuracy, but have different characteristics. Network RTK (VRS) can, in ideal conditions, achieve horizontal errors of about 2 cm (0.8 in) and vertical errors of a few centimeters, while CLAS is reported around 5–6 cm (2.0–2.4 in) horizontally. RTK typically provides a fixed solution within a few seconds after startup, whereas CLAS requires about 30 seconds to 1 minute for initial convergence. Nevertheless, both methods ultimately produce errors within a few centimeters, and for most surveying and construction uses the practical difference is minimal. RTK may be advantageous when immediate responsiveness and the absolute highest accuracy are critical, but CLAS has been shown in various verifications to deliver practically equivalent results.

Q: Can anyone use correction information services? Are special licenses or qualifications required? A: Anyone with appropriate equipment can use GNSS correction information services. Network-based services can be contracted by individuals, and CLAS requires only receiving satellite signals, so no license or registration is needed. Receiving correction information does not require a radio station license (simply receiving is not subject to notification). However, for public surveying tasks or official surveying work, surveyor qualifications or compliance with regulations may be required. For general, non-official use, anyone can try high-precision positioning with modern correction information services.

Q: How can I easily start high-precision positioning (simple surveying) with a smartphone? A: The easiest way is to use a smartphone-compatible high-precision GNSS receiver (a smartphone-integrated device). For example, using a device such as the [LRTK Phone series](https://qzss.go.jp/info/archive/lefixea_240513.html), you can transform your smartphone into a centimeter-precision surveying tool without being a specialist. Attach a compatible device to an iPhone or Android phone, launch the dedicated app, and you will immediately receive satellite correction information (CLAS) and start high-precision positioning. Initial setup is simple, and results are displayed and saved clearly on the phone, so anyone can use it without buying expensive surveying equipment or performing complicated configurations. Try this kind of smartphone-integrated "simple surveying" tool to quickly experience how easily high-precision location data can be obtained.