How to Check RTK Survey Accuracy? 6 Methods You Can Use on Site

RTK surveying is widely used across a range of sites—civil engineering, construction, infrastructure maintenance, construction quality control (as-built management), and as-built/topographic surveys—as a convenient method for obtaining high-precision coordinates in a short time. However, RTK does not automatically provide high accuracy simply by being used. Accuracy is affected by multiple factors, including satellite reception conditions, the stability of correction information, the surrounding environment, configuration settings, and observation procedures. What truly matters on site is not possessing RTK equipment, but being able to verify for yourself whether the positioning results can be trusted.

In practice, there are cases where people feel reassured simply because "Fix" is displayed on the screen and adopt the coordinates as they are. However, Fix is merely information indicating the state of the positioning solution, and it does not necessarily mean that the on-site required accuracy has been met. For example, errors in coordinate system settings, mistakes in entering antenna height, discrepancies with known control points, or temporary instability of correction information can cause non-negligible differences in measurements even when the solution shows Fix. In other words, accuracy checks should not be performed only at the end of the task; they need to be an operational routine carried out continuously before, during, and after the work.

This article organizes and explains six effective methods for practically verifying RTK surveying accuracy on-site. Rather than simply listing functions or terminology, it covers why those checks are necessary, in what situations they should be used, and what is容易に見落としやすいかまで含めて, all summarized in a form that can be used immediately in the field. We delve into this from a practical perspective to be useful both for those responsible for introducing RTK and for those already operating it but who are concerned about accuracy management.

Table of Contents

• Why accuracy verification is necessary in RTK surveying

• Method 1: Verify against known points

• Method 2 Repeatedly observe the same point

• Method 3: Check the Fix Status and Observation Status

• Method 4: Check the number of satellites and DOP

• Method 5 Observe the work environment and eliminate sources of error

• Method 6 Cross-check using alternative methods or under different conditions

• Summary

Why Accuracy Verification Is Necessary for RTK Surveying

RTK surveying is a technique that uses signals received from satellites and correction information to determine high-precision positions in real time. Compared with conventional standalone positioning, it is significantly more accurate and greatly contributes to improving the efficiency of surveying operations. However, that accuracy is heavily influenced by field conditions. In other words, the performance stated in equipment specifications and the accuracy actually obtained on site are not the same.

For example, in locations where the sky is sufficiently open, cm-level positioning (half-inch accuracy) can be obtained reliably, while the presence of reflective or blocking objects such as buildings, slopes, trees, heavy machinery, guardrails, and signs nearby can make positioning unstable. In urban or mountainous areas, satellite visibility itself tends to be biased, and even when correction information is being received the solution quality can deteriorate. Furthermore, errors caused by how equipment is used, which are easily overlooked in the field, also degrade accuracy significantly—operational factors such as the pole not being vertical, incorrect input of antenna height, mismatched coordinate systems, or correction service settings differing from expectations can all cause large accuracy degradation.

What’s important here is that checking RTK accuracy is not simply about verifying the numerical value of the error. Accuracy checks have three meanings: confirming whether the current value can be used, detecting early signs of anomalies, and ensuring you can explain the validity of the results after the work. Many cases of trouble on site do not become visible at the moment of measurement and only come to light when later processes fail to reconcile. To prevent such situations, it is necessary to have multiple decision-making indicators while positioning.

The basic principle of accuracy verification is not to base a judgment on a single piece of information. Combining multiple perspectives—such as the Fix indication, the number of satellites, the difference from known points, the variability of repeated observations, the surrounding environment, and cross-checks with other methods—to form a comprehensive judgment leads to reliable RTK operation in the field. Below, we will look at six specific methods for that purpose in order.

Method 1 Verify using known points

The most fundamental and most reliable method for verifying the accuracy of RTK surveying is to compare measurements with known points. A known point is a point whose correct coordinates are already established. Typical examples include public control points, control points managed within the project area, and known points established before construction. By observing those points with RTK and checking the differences from the known coordinates, you can directly determine how much confidence to place in the current positioning results.

An advantage of comparing with known points is that it can be evaluated by the difference in the coordinate values themselves—those that are ultimately required—rather than by on-screen displays or internal indicators. For example, even if the solution shows a Fix, if it is off from the known point by a few centimeters, that positioning result may not meet the site-required accuracy. Conversely, if agreement with known points is stable, it becomes easier to judge that the equipment status, correction status, and environmental conditions at that time are relatively good.

In practice, it is effective to avoid ending with a single check of known points at the start of work and instead recheck them during the work and at the end. Even if there are no problems first thing in the morning, it is not uncommon for accuracy to change in the afternoon due to changes in communication conditions or satellite geometry. If you check at least three times—at the start, mid-point, and end—you will find it easier to grasp the day’s variations in positioning quality. This habit is particularly important for long-duration tasks or work that moves across multiple areas.

However, there are some precautions for known-point verification. First, you must confirm that the known point itself is truly reliable. Using points based on old survey results or points that may have been moved by construction can make the comparison itself meaningless. Second, you must always confirm that the coordinate systems match. If the plane rectangular coordinate system’s zone number or the height datum differs, the differences will be due to mismatched settings rather than measurement errors. Third, it is important to keep the observation method consistent. If pole height, observation time, and setup vary each time, interpreting the comparison results becomes difficult.

When verifying known points, it is desirable to check the horizontal and height components separately rather than simply looking at the difference once. In RTK the vertical direction is generally more prone to instability, so even if the horizontal plane matches, the height alone may show a large discrepancy. For tasks with strict height requirements, it is important not to judge that there is no problem just because the horizontal plane matches. Checking at known points is the starting point for accuracy verification and can be considered the most practical method to return to when in doubt.

Method 2 Repeatedly observe the same point

The second method is to repeatedly observe the same point at different times and examine the variability of the results. This is a verification of reproducibility and is very effective in practical RTK surveying. Whether the value obtained when observing a single point is correct can be difficult to judge from that one observation alone. However, if reobservations under the same conditions, or after a short interval, yield similar values, it becomes easier to consider that position measurement reliable.

For example, if you observe the same point three times in succession and get nearly the same values in one case but slightly different values each time in another, the latter is less stable. In particular, signs such as the elevation varying greatly on each measurement or the horizontal position drifting in a consistent direction may indicate problems with satellite geometry, multipath, correction status, or the way the pole is set up. Repeated observations are a simple check to assess stability even when there are no obvious errors.

In practical work, not only continuous observations but also re-observations made after time intervals are effective. For example, if you check once before work, return after measuring another point and check again, and then check once more before finishing work, you can see trends in positioning variation at the same point. If the difference between morning and evening is large, you should suspect changes in satellite geometry, communication conditions, or variations in the field environment. Instabilities that were not apparent in single observations can become clear through time-separated observations.

The advantage of this method is that it is easy to carry out even in locations without known points. Even at sites where known-point matching is not possible, re-observing the same point can be done on the spot. Of course, high repeatability does not imply high absolute accuracy. It is possible that similarly biased values are being produced repeatedly. Nevertheless, it is at least useful for determining whether the positioning state is stable. In that sense, when combined with known-point matching it becomes a very strong method of verification.

When conducting repeated observations, it is important to make the observation conditions as consistent as possible. If the pole’s installation position differs even slightly, the values will of course change. You need to carefully align and then compare factors such as the pole’s verticality, ground contact position, posture during observation, observation time, and the equipment’s fixation state. Also, do not judge measurement results based only on impressions at the site; it is important to record them, even briefly. Keeping numerical records allows you to review trends later and helps analyze the causes of days with anomalies.

Method 3 Check the Fix Status and Observation Status

One of the most commonly checked items in RTK surveying is confirmation of the Fix status. This is certainly important, but it is insufficient to end the assessment solely based on whether it is Fix or not. What should really be examined for accuracy verification is not the Fix indication itself, but the overall quality: the states leading up to Fix, whether the Fix is being maintained, and whether it is consistent with other observation statuses.

Generally, RTK solutions can be in states such as Fix, Float, or standalone positioning. Fix is treated as the state in which the carrier-phase integer ambiguities have been resolved, yielding a high-precision solution. Conversely, Float means the integer values have not yet been resolved, and the accuracy is not as stable as with Fix. Therefore, for surveying, Fix is the default. However, on site it is sometimes adopted immediately after the display switches to Fix, and caution is needed here as well. Immediately after Fix, the solution may not yet be stable, so it can be advisable to wait for the values to settle for a few to around a dozen seconds.

Another important factor is the continuity of the Fix. Even if a Fix is obtained temporarily, if it immediately reverts to Float afterward, or if it keeps switching between Fix and Float, it cannot be considered stable positioning. In continuous measurements or mobile observations, even if the reading is Fix at the instant of measurement, the reliability of the results may decrease if the situation before and after is unstable. Therefore, during operations you should also check the Fix rate and duration, whether any warnings are displayed, and the status of correction reception.

Moreover, as part of the observation status, it is also important to check whether correction information is being received normally, whether the connection with the reference station is being maintained, and whether solution updates have stopped. Even if a position appears to be displayed, the latest corrections may not actually have arrived, the update rate may have dropped, or communications may be intermittent. In such conditions it is difficult to notice anomalies by looking only at the numbers on the screen, so routinely checking the status screen helps with accuracy management.

In practice, do not take the Fix indication as the final judgment; it is important to compare it with known-point checks and re-observation results. If the Fix agrees with known points, that is reassuring, but if the Fix does not agree with known points there may be an operational problem somewhere. Conversely, even if it takes time to obtain a Fix, if it stabilizes afterwards and matches known points, it can be acceptable in practice. In other words, the Fix is an important piece of information, but it is not everything for accuracy verification. On site, you should use the Fix as an entry point and adopt an approach that assesses overall positioning quality.

Method 4 Check the number of satellites and DOP

The quality of RTK surveying is largely determined by which satellites are being received and how they are arranged. For this reason, checking the number of satellites and the DOP is a highly valuable accuracy verification method that can be performed easily on-site. DOP is an indicator that shows the geometric quality of the satellite configuration, and generally a smaller value is more favorable. Even with a large number of satellites, positioning quality can deteriorate if the configuration is biased, whereas if the number is sufficient and the configuration is good, it is more likely to lead to stable positioning.

What matters here is not to be reassured by the number of satellites alone. Modern GNSS receivers support multiple constellations, so the displayed satellite count can be quite high. However, a large number does not necessarily mean you are operating under good conditions. If many satellites are at low elevation angles, signals can be more susceptible to reflections (multipath), and if reception is biased toward a particular direction the geometric conditions can worsen. Therefore, treat satellite count as one indicator, and also evaluate DOP and the sky view.

On-site, what you should pay particular attention to are changes due to time of day and movement between locations. Because satellite geometry is not fixed, conditions can change between morning and afternoon. Also, even within the same site, signal reception can vary greatly at slope edges, forest edges, beside buildings, and near heavy equipment storage areas. When observing while moving, it is important to check as needed whether the satellite conditions at your current location are good, and if you feel the conditions are poor, be flexible and change your position slightly to recheck.

How DOP values are treated varies somewhat depending on the equipment and operational policy, but at the very least you should be cautious when values are clearly worse than usual. In the field, a practical approach is not to rely solely on absolute values but to compare them with values during normal operations to check for abnormalities. For example, if at a site that usually measures without problems you see high DOP today, fewer satellites, or poor solution stability, you should be more careful when verifying accuracy that day.

Checking the number of satellites and DOP is also useful for fault isolation during troubleshooting. When measurements do not match a known point, you first need to consider whether the satellite conditions are poor or whether there is a problem with settings or correction information. If the number of satellites and DOP are clearly poor, the likelihood of environmental factors is higher. Conversely, if satellite conditions are good but the measurements still do not agree, you are more likely to suspect other factors such as coordinate system settings or antenna height input. For these reasons, checking satellites and DOP should not be treated as mere reference display but used as fundamental information for on-site decision-making.

Method 5 Observe the work environment and eliminate sources of error

When checking the accuracy of RTK surveying, attention tends to focus on on‑screen numbers and coordinate differences, but in reality observing the field environment is what matters most. This is because many sources of error originate in the local environment, and their signs are often visible before they appear in the numbers. Conditions such as a restricted view of the sky, numerous nearby reflective surfaces, frequently moving machinery or vehicles, or terrain that tends to cause unstable communications all directly affect RTK accuracy.

For example, near metal fences, close to building walls, under bridges, in areas with dense trees, directly below slopes, or at positions where the arm of heavy equipment crosses overhead, satellite signal reflections or blockage are likely to occur. In such locations, even if it appears to be Fix, the positioning values may not be stable. On site, it is important to make a habit of checking the surroundings for reflective or obstructing objects as well as monitoring the device display. Especially when the values vary more than usual, it is more practical to suspect the environment first before assuming equipment failure.

Observing the communication environment is also essential. When using network-based correction information, the stability of the cellular network affects positioning quality. In mountainous areas, roads in cut sections, around structures that are close to or below ground level, and deep within material yards, communications can become unstable. If corrections become intermittent, maintaining a Fix becomes difficult, which can result in reduced accuracy. Therefore, before observation you should assess the site including the communication status, and, if necessary, adjust measurement locations and the sequence of work.

The advantage of environmental observation is that it’s easy for workers who are not familiar with equipment to carry out. Whether the sky above is open, whether there are large reflective objects nearby, whether communications are likely to be interrupted, or whether the ground is unstable and the pole could easily wobble — these points can be judged in a short time with experience. “Accuracy verification” may sound difficult, but in practice the first step is to determine on-site whether “it is really appropriate to measure at this location.”

Even more important is the judgment not to force measurements in environments that appear problematic. RTK is convenient, but it is not universally applicable to every location. Deciding whether you really need to measure on the spot, whether moving a short distance would improve conditions, or whether it would be better to use an alternative method is also part of accuracy checks. By not only verifying numerical values but also adopting an attitude of eliminating environmental factors, you can create conditions in which errors are less likely to occur in the first place.

Method 6 Cross-check using alternative methods or under different conditions

The sixth method is to cross-check RTK results by other means or under different conditions. This is the most time-consuming method, but it is correspondingly more reliable for verifying accuracy. Whether a cross-check is performed can greatly affect the level of confidence, especially at critical points, in processes that are difficult to reverse, or in situations where an explanation of the results is required.

There are several methods for cross-checking. For example: re-observing the same point at a different time, observing with a different receiver, verifying positional relationships using other techniques such as a total station, or checking relationships with multiple known points. These approaches make it easier to detect errors that depend on specific equipment or temporary satellite conditions. Problems that are not visible from values obtained only with the same equipment at the same moment can surface when conditions are changed and the results are compared.

An approach that is easy to implement on site is to recheck only the critical points at a different time. For example, pile-driving positions, reference control points, and points in as-built management that affect subsequent processes should not be measured just once on the spot; simply checking them again at the end of the work can be meaningful. If there is a large discrepancy between the initial check and the recheck, it provides an opportunity to review the day’s overall results. Conversely, if the difference is sufficiently small, it increases confidence in the outcomes.

Comparing RTK with other methods is also useful for understanding its characteristics. RTK excels at quickly surveying large areas, but in obstructed environments or for elevation control, other methods can be more advantageous. Through cross-checking, the field accumulates knowledge about the conditions in which RTK is strong and those that require caution. This not only provides one-off verifications but also contributes to improving operational quality at the organizational level.

Furthermore, cross-checking is important from an accountability standpoint. When asked on site, "Is this coordinate really correct?", simply saying it was a Fix or that many satellites were used can be a weak explanation. However, if there are multiple pieces of evidence—such as consistency with known control points, small differences on re-observation, and matching relative positions using different methods—it becomes easier to justify the validity of the results. Accuracy verification is not only for reassuring yourself but also for creating the basis to convince others.

There is no need to perform cross-checks at every point. Balancing against available work hours, it is practical to carry them out starting with high-priority targets such as important points, locations with poor conditions, observations that cause concern, and sites being visited for the first time. Rather than doing them strictly for every point, an approach that reliably checks key locations is the most sustainable and effective method in the field.

Summary

Checking the accuracy of RTK surveying does not end with simply looking at the device screen’s Fix display. To obtain reliable positioning results, you need to verify multiple aspects: the validity of the coordinates themselves, the reproducibility of the observations, the status of the satellites and corrections, the surrounding environment, and agreement under different conditions. In the field especially, it is important not to over-rely on any single indicator.

Of the six methods introduced this time, the most fundamental is verification against a known point. Here you check whether the current positioning is significantly off, then assess stability by repeated observations of the same point. On top of that, comprehensively check the Fix status, the continuity of receiving corrections, the number of satellites and DOP, and the site conditions, and cross-check under different conditions as necessary. If you make this routine habitual, you can greatly reduce RTK accuracy issues.

What matters in practice is operations that notice anomalies exceptionally early, rather than perfect theory. Simply repeating the basics—morning checks of known points, re‑observing critical points, visual inspection of the environment, and checks before finishing work—can greatly change the reliability of results. RTK is an extremely powerful tool, but its true value is realized only when paired with proper accuracy verification. The shortcut to stable RTK use is to embed six field‑usable methods into your company's operations and build a system that places as much emphasis on verifying as on measuring.