What is CLAS? A clear explanation of how to use it, differences from RTK, and practical use cases

When practitioners want to learn how to use CLAS, many first wonder what CLAS actually is, how it differs from RTK, and whether it can really be used on their own sites. In workplaces that handle high-precision position information, you cannot judge based on “higher accuracy” alone. You need to consider communication environment, sky visibility, working time, positioning stability, portability, and ease of operation.

CLAS is an approach that has attracted attention as one option for high-precision positioning. However, in practice RTK is often more familiar, and many people who have heard the name CLAS have not organized how to choose between them. This article therefore organizes, from a field perspective, the basics of CLAS, how to use it, the differences from RTK, suitable use cases, and points to check before introduction. It is intended to be useful as material for decision-making both for those who want to introduce high-precision positioning and for those already operating systems who are considering a review.

Table of Contents

• What is CLAS

• Understanding how CLAS works, simply

• How to use CLAS and the basic workflow

• Differences between CLAS and RTK

• Use cases suited to CLAS

• Situations where CLAS is not suitable and cautionary points

• Common pitfalls in CLAS operation

• How to choose a positioning method that is easy to use on site

• Summary

What is CLAS

CLAS is a system that uses augmentation information transmitted from satellites to achieve higher-precision positioning. With normal satellite positioning, you can determine your current location, but it can be difficult to achieve the fine positional alignment required for fieldwork. For example, confirming construction positions, recording installation locations, understanding as-built conditions, and revisiting inspection points cannot be satisfied by errors on the order of several meters. CLAS is used in such situations to obtain higher-precision position information.

What makes CLAS attractive on site is how the augmentation information is received. Typical high-precision positioning widely uses methods that receive correction information via communication lines, but CLAS improves positioning accuracy by receiving augmentation information transmitted from satellites. For that reason, it tends to be less affected by the communication environment, and may be easier to operate in locations where mobile communications are unstable.

However, it is important not to misunderstand that CLAS will always provide stable high accuracy in every site. Performance can deteriorate where satellites are difficult to see, and it cannot be used unless the receiver supports CLAS. Also, depending on the accuracy required for the task, acceptable initialization time, and ease of continuous operation, RTK may be more suitable in some situations. In other words, CLAS is not a universal substitute; practically speaking, it is a strong option when conditions match.

When understanding CLAS, it is important not to consider accuracy alone. What really matters to field personnel is whether today’s work can proceed without stopping, whether positions can be recorded reproducibly, and whether the operational burden is not too high. CLAS can deliver great benefits depending on these conditions. That is why it is important not just to know the name, but to understand how it works, how to use it, and which tasks it suits.

Understanding how CLAS works, simply

Many find the mechanism of CLAS difficult, but what is needed on site is not to memorize technical terms in detail. The important thing is to grasp why it can achieve higher accuracy than normal satellite positioning and why it can be a candidate even where communications are weak.

In normal satellite positioning, a receiver receives signals from multiple satellites and calculates its position from that information. However, satellite signals contain various error factors: satellite-side errors, atmospheric effects, reception environment influences, and reflections from surrounding buildings or trees. When these combine, positions can easily be offset. For general map display or navigation this is still practical, but for practical work such as construction, surveying, inspection, and maintenance, those errors become a major problem.

CLAS makes it easier to obtain higher-precision positions by using augmentation information that reduces such errors. The image is that where standard satellite positioning left position information ambiguous, additional correction information is added to bring accuracy closer to what is needed on site. Where this additional information comes from is what distinguishes CLAS from other methods.

With RTK, it is common to receive correction information from base stations or a network via communication lines. In contrast, CLAS uses augmentation information transmitted by satellites that CLAS-compatible receivers receive and use. This is why CLAS is said to be less dependent on the communication environment. In mountainous areas, reclaimed land, suburbs, and infrastructure sites where communications are unstable, this difference can directly affect ease of operation.

On the other hand, receiving augmentation information from satellites means that good sky visibility becomes more important. In places with poor overhead visibility, near tall walls or buildings, or with heavy tree cover, expected performance may be harder to achieve. In other words, while CLAS is strong where communication is a weakness, there are cases where clear satellite visibility is more critical.

Also, in practice you cannot ignore differences in receiver performance. Even among CLAS-compatible devices, antenna performance, reception processing, ease of fixing, positional stability, clarity of display, and methods of checking positioning status vary by device. Therefore, do not judge performance by the CLAS mechanism alone; evaluate which terminal and which workflow you will use.

To summarize the mechanism in one sentence: CLAS is a method that makes it easier to achieve high-precision positioning by using augmentation information from satellites. However, to achieve results on site, you must consider satellite visibility, receiver performance, and compatibility with working conditions together.

How to use CLAS and the basic workflow

What field personnel who want to know how to use CLAS should first grasp is not the operation steps themselves but what to check before starting work. High-precision positioning is not decided at the moment you press the positioning button. Preparatory decisions greatly affect work efficiency and the stability of accuracy.

The very first thing to confirm is whether the receiver or terminal you will use supports CLAS. This is a prerequisite. Devices that do not support CLAS cannot, of course, use it. Even if supported, mode switching may be necessary. Some devices automatically select the high-precision positioning method, while others are better if you explicitly check the positioning mode. In practice, if you are unsure of settings after arriving on site you can easily lose time, so confirming before departure is important.

The next important point is checking the environment where you will start positioning. Because CLAS makes satellite signal reception very important, it is basic to initialize in a location with a wide open sky. Near tall buildings, at the edge of slopes, under tree canopies, or in areas with many metal structures, positioning tends to be unstable. Even if the work point itself is in a blocked environment, it may be faster overall to first confirm a stable state in an open location and then move.

In actual workflow, upon arrival at the site start the device in a place with good reception and check satellite reception status and positioning mode. Rather than rushing to measure, determine whether the positioning state is stable. In high-precision positioning, a position may appear to be displayed but not yet be stable. In practice, proceed while checking not only the displayed value but also current positioning state, accuracy indicators, and solution stability.

Once positioning is stable, record the target points. At this time, avoid deciding with just a single measurement; it is important to confirm multiple times even over a short period. For example, re-check the same point after a short interval, verify relative relationships with nearby points for inconsistencies, or check alignment with a known point or a visible reference. Simple verifications like these reduce misidentification and recording errors on site. CLAS is convenient, but because it is high-precision positioning, do not leave final judgments to the device alone.

Recording how you save field data is also important. Save not only the positioning results but also when, where, and under what conditions they were acquired so that later comparison or re-checking is easier. For example, keeping the work time, surrounding environment, sky visibility, whether re-measurement occurred, and photos of the target together makes decisions on return visits much easier. The value of high-precision positioning lies not only in obtaining coordinates but in storing them in a reproducible way.

Also, consider whether you will use CLAS while moving or by stopping at points. For operations that secure positions one point at a time, stability checks and re-observations are more meaningful. For use while walking to reference positions or to guide to target points and for rough checks, continuous position updates and ease of handling on site are more important. In short, how you use CLAS is not single-purpose; you must adapt operation to your business objectives.

From a practical perspective, the CLAS workflow is: prepare CLAS-compatible equipment, stabilize positioning in a place with open sky, confirm accuracy status while recording target points, and save results in a reproducible form. Understanding this series of steps brings you closer to an operation that is less prone to failure on site rather than just learning button operations.

Differences between CLAS and RTK

When asked “What is the difference between CLAS and RTK?”, answering only in terms of accuracy is insufficient for practical work. Both are methods for high-precision positioning, but they differ in how correction information is received, the required environment, ease of operation, and the types of sites they suit. On site, what matters is not which is superior but which fits the task.

The first major difference is the route by which correction information is received. RTK receives correction information from base stations or networks and performs high-precision positioning based on that. Depending on the operational form, communication lines are important. Therefore, RTK is easy to use where communications are stable but difficult to operate in areas without coverage or with unstable communication quality. In contrast, CLAS uses augmentation information from satellites and can reduce dependence on communication lines. This difference is particularly meaningful in mountainous areas, suburbs, and large-scale construction sites.

Another important difference is compatibility with site conditions. If a stable correction environment can be secured, RTK is very practical and often suitable for continuous operations. CLAS, while a choice where communication cannot be relied upon, places greater importance on satellite visibility. So you can view it as RTK being keyed to communication conditions, while CLAS is keyed to the overhead environment.

Initial fix ease and stability of positioning state also depend on site environment and device. On sites where many are familiar with RTK, settings and state interpretation are shared and troubleshooting can be quick. CLAS may feel operationally simpler in some cases, but without understanding receiver conditions and appropriate use cases, it can be judged disappointing.

The notion of accuracy needs some clarification. In general, both aim for high precision, but in practice what matters is not nominal values. Actual outcomes change significantly depending on sky openness, obstructions, working posture, movement, holding method, surrounding reflections, observation time, and device characteristics. Therefore, do not mechanically choose CLAS or RTK based solely on accuracy; check whether it can be reproduced stably on your site.

From an operational standpoint, RTK may require preparation of base stations, communications, and network connections, and is strong if such systems are in place. CLAS allows operations that do not rely on communications, and can be a good match for tasks that emphasize mobility. For example, CLAS tends to show advantages when moving across wide areas for inspection, when quick position confirmations are needed, or when recording in places with unstable communications.

Put another way, RTK often becomes the primary method for precise site operations, while CLAS tends to perform well in operations that require mobility or face strict communication constraints. However, this is a general tendency; the optimal solution ultimately depends on the devices used, desired accuracy, work procedures, and site environment. Knowing the differences allows you to judge whether each method fits your company’s operations.

Use cases suited to CLAS

CLAS shows its value particularly in situations where communication environment and mobility conditions greatly affect work efficiency. It is not just whether high-precision positioning is possible but whether it can be used continuously on site, whether personnel can handle it without confusion, and whether it can be used the same way on revisits. Viewed this way, there are surprisingly many use cases suited to CLAS.

First, it is well-suited to sites with unstable communications. In mountainous areas, large reclaimed sites under development, suburban infrastructure inspection areas, and construction sites with many temporary facilities, communication quality may be unstable. Even if you want high-precision positioning, operations that assume communications can fail in such places. Because CLAS receives augmentation information from satellites, it is often a viable option in these locations.

Second, it suits inspections and patrol-type tasks where you handle positions while moving across wide areas. For equipment location checks, recording inspection points, managing revisits to abnormal points, and recording photo locations, operations that are portable and allow quick position checks are preferred to time-consuming preparations each time. CLAS tends to provide practical benefits in such mobile-focused scenarios.

It is also suitable for initial surveys and rough confirmation. For example, when you want to grasp general positional relationships on entering a site, record target locations along with photos or notes, or hand over coordinates to subsequent processes, ease of immediate use is valuable. CLAS can leverage its ease of introduction and light operation in these situations.

CLAS is a candidate for broad, linear management tasks such as farmland, forests, and infrastructure lines. For jobs that capture points while moving across a wide area, frequent communication dropouts reduce efficiency. Although sky conditions must be checked, the reduced dependence on communications is meaningful for large-area tasks.

Moreover, CLAS increases value when combined with location-tagged information recording. If you save photos, notes, inspection results, simple sketches, and object attributes together with coordinates, later checking and sharing become easier. In practice, usable position-tagged operational information is more important than coordinates alone. CLAS can be an effective way to raise the quality of such field records.

Also, if you want to switch positioning methods per site, CLAS becomes an option. For example, use another method where communications are stable and CLAS where communications are difficult. Rather than fixing on one high-precision method, switching by use often yields overall optimization. In that mix, CLAS fills the role of complementing operations sensitive to communication conditions.

Situations where CLAS is not suitable and cautionary points

CLAS is convenient, but it does not apply to every site automatically. When deciding whether to introduce it, understanding situations where it is not suitable and cautionary points first helps avoid failure.

First, be cautious in sites with poor overhead visibility. In narrow areas surrounded by high-rise buildings, under heavy tree canopy, beneath bridges, near retaining walls, or in densely packed equipment areas, satellite reception may become unstable. While CLAS reduces communication dependency, it is more affected by satellite environment, so results may fall short where the sky is not visible. In urban confined sites or places at the indoor-outdoor boundary, be careful in method selection.

Second, for tasks that always require high reproducibility and continuous stability, design your operation carefully. For example, for continuous construction guidance, strict as-built verification, or tasks that emphasize coordinate consistency, you must prepare verification procedures as well as the method itself; otherwise, it could affect downstream processes. The key is to determine whether CLAS meets the tolerances required by the work, not simply whether it is usable.

Also be aware that supported devices are limited. CLAS can only be used if the receiver supports it, and even among supported devices the clarity of operation screens and status displays varies. If field personnel cannot read device status, the availability of high-precision positioning is wasted and operational mistakes increase. Before introduction, check not only accuracy specifications but also ease of settings, status confirmation, and recordkeeping.

Furthermore, it is dangerous to assume that because CLAS does not need communications, preparation is trivial. While it does have the advantage of fewer communication settings, on site you must pay more attention to sky visibility, holding posture, initialization location, observation time, and rechecking points. Starting operations with only the impression that preparation is simple can lead to unmet accuracy expectations and failure to use the system properly.

From a manager’s perspective, do not introduce CLAS simply because it seems convenient. Judge whether it can run smoothly for your site conditions and work content. Being strong in communication does not mean being strong in every environment. Understanding this distinction alone can greatly reduce mistakes in method selection.

Common pitfalls in CLAS operation

After introducing CLAS, many cases where users feel it is not as easy to use as expected stem not from the method itself but from operational missteps. High-precision positioning does not automatically work because the equipment is high-performance. Knowing common on-site pitfalls in advance is the quickest route to stable operation.

One common pitfall is recording without sufficiently confirming the positioning state. Under time pressure, field staff tend to record as soon as a position appears. However, displaying a position and being stable are not the same in high-precision positioning. Omitting checks of positioning mode and accuracy state may produce data that is hard to use later.

Another frequent issue is underestimating the importance of the initialization location. Some begin measuring near the target point only to find many obstructions nearby and continue recording while the state is unstable. In such cases, it is often better to confirm a stable state at a slightly distant open location before approaching the target. The shortest route is not necessarily the fastest in high-precision positioning.

Failing to recheck also leads to errors. Even for single-point observations, getting the same point at a later time, checking for inconsistencies with nearby positions, or testing at a point near a known reference helps detect obvious mistakes early. Instead of trying to get it right in one go, inserting short checks often improves overall site efficiency.

Ignoring how the terminal is held or set up is another problem. Receiver orientation, how it is held, distance to surroundings, and the influence of the body or metal objects can all affect results. It is important to make results similar regardless of who uses the device on site, so standardizing simple usage rules is effective.

Another overlooked issue is overexpectation relative to operational goals. Just because CLAS can achieve high-precision positioning does not mean it can replace all surveying or construction management workflows. Depending on required accuracy, how evidence is recorded, internal rules, and submission requirements, another method or additional checks may be necessary. Viewing the method as a panacea without understanding its characteristics will lead to inconsistent evaluation on site.

To prevent failures, follow basic operational rules rather than complicated theory: start in an open sky location, confirm positioning state, perform short rechecks, keep records, and use the method according to the task. Enforcing these basics alone will greatly improve the usability of CLAS.

How to choose a positioning method that is easy to use on site

When choosing between CLAS and RTK, if you judge only by comparison table numbers, you are likely to be confused on site after introduction. In practice, who will use it, where, how often, and how it will be used are more important than theoretical maximum performance. When selecting a method, thinking about five elements—accuracy, communications, environment, operational structure, and recordkeeping—helps organize the decision.

First consider how much accuracy you need. Requirements differ depending on whether you only need a rough sense of location, whether you need to reliably locate the same place on revisits, or whether you need precise management of installation positions. Choosing a method without clarifying this can lead to unnecessarily heavy operations or insufficient accuracy.

Next, consider site communications. If communications are stable, you can leverage methods that use communications. If many sites have weak communications, methods that reduce communication dependency are more valuable. Ignoring site conditions when choosing a method makes it impractical in the field.

Third is the overhead environment. Whether skies are generally open or obstructions are common affects satellite reception. Not only communications, but satellite visibility is a key consideration in method selection. For high-precision positioning, reviewing site photos and terrain conditions alone makes decisions easier.

Fourth is operational structure. Whether skilled operators always use the system, whether it will be shared among many people, or whether you want quick training affects the choice of device and method. High performance that is difficult to operate or verify tends not to be adopted in practice. The perspective of whether anyone can use it without confusion is as important as accuracy.

Finally, consider how you will keep records. Whether you manage positioning results as coordinates only, save them with photos and notes, overlay them on drawings or point clouds later, or use them for internal sharing affects the choice of device and workflow. High-precision positioning only realizes its value when records are usable.

Viewed this way, method selection is not just a technical comparison but part of business design. CLAS is a very strong option because it is particularly effective for tasks that cannot rely on communications or that emphasize mobility. Conversely, trying to handle everything with a single method may be impractical. On site, choosing the best method per task is important.

Summary

CLAS is a method that uses augmentation information received from satellites to make high-precision position information easier to handle. In addition to aiming for higher accuracy than normal satellite positioning, it may be less affected by communication environment and is attracting attention for use in mountainous areas, suburbs, and wide-area inspection sites. However, it may struggle where sky visibility is poor and is not a universal solution for every site.

From a practical perspective, using CLAS involves preparing compatible equipment, stabilizing positioning in a place with an open sky, confirming status while recording target points, and saving results reproducibly. Even if the operations themselves are not complex, selecting an initialization location and implementing recheck procedures are important to avoid failures on site.

The difference from RTK lies in how correction information is received and which site conditions each method handles better. RTK is often strong where communications are stable, while CLAS becomes a suitable choice where communications are unstable. What is important is not which is superior, but which can be used stably for your operations.

If on your sites you want to confirm positions without being affected by communications, attach high-precision location data to photos and inspection results, or use high-precision positioning in a portable form, it is worth reviewing device selection and operation. In such practical contexts, using iPhone-mounted GNSS high-precision positioning devices such as LRTK can make on-site position recording, inspection, and simple surveying proceed more smoothly. Understanding the differences between positioning methods like CLAS and RTK and adopting high-precision positioning in a form that fits your site will help balance work quality and efficiency.