What are the causes of RTK errors? 8 explanations including multipath countermeasures

Table of Contents

• Basic concepts of how errors occur in RTK

• Error factor 1 Effects of reflected waves caused by multipath

• Error factor 2 Decreased accuracy due to poor satellite geometry

• Error Factor 3: Reception instability due to overhead obstruction

• Error factor 4: Disruption of correction information due to communication failure

• Error factor 5: Error amplification due to differences in reference station conditions

• Error factor 6: Equipment configuration errors and initialization failures

• Error factor 7 Mistaking coordinate systems and correction conditions

• Error factor 8: Variations in on-site operations and human error

• Summary

Basic Concept of How Errors Occur in RTK

RTK is a type of GNSS positioning that determines position based on signals received from satellites, and by using correction information sent from a base station it can achieve high accuracy. Compared with standalone positioning it is markedly more accurate, but that does not mean it will always produce the same level of accuracy. In the field, even when you think you are measuring the same spot, measurements can differ by a few cm (a few in), and under poor conditions the difference can be larger.

In such cases, the important thing is not to attribute RTK errors to a single cause. In practice, it is often not simply that multipath is to blame or that communications are to blame; multiple factors commonly combine to degrade accuracy. For example, measuring near buildings can increase reflected signals, at the same time reduce sky visibility, and also make communications unstable — such situations are not uncommon.

Also, with RTK, even if it appears on the surface that measurements are being obtained, the system may still be in an unstable state internally. There are many points easily overlooked on site, such as an unstable positioning status, an insufficient number of satellites, delayed updates of correction information, or incorrect coordinate system settings. If you proceed with work without understanding these factors, it can lead to problems such as mismatched coordinates later, discrepancies in as-built inspections, or the need for re-surveying.

Therefore, for RTK error mitigation, what you check on site is just as important as knowing the causes. By clarifying where to look for signs of errors, under which conditions work should be stopped, and which settings should be inspected every time, positioning quality becomes significantly more stable.

From here, we will explain the eight representative error factors commonly seen in RTK. While organizing topics such as multipath, communications, satellite geometry, obstructions, base station conditions, equipment settings, coordinate systems, and operational differences, we will also introduce practical points to check in the field.

Error Factor 1: Effects of Reflected Waves Caused by Multipath

One of the primary error sources in RTK to be aware of is multipath. Multipath refers to the phenomenon in which signals from satellites are reflected off building facades, metal fences, vehicles, signs, water surfaces, heavy machinery, and similar objects, and reach the receiver delayed in addition to the direct signal. Normally, the receiver calculates distance on the assumption that the satellite signal arrives straight, but when reflected waves mix in, the signal’s time of arrival shifts and errors are introduced into the position calculation.

What makes multipath troublesome is that it’s hard to notice by appearance. Even if a reasonable number of satellites is available, coordinates can become unstable when the surrounding reflection conditions are poor. Extra caution is needed especially in urban areas, around structures, near warehouse exterior walls, under bridges or beside elevated roads, and in material yards with a lot of steel. If it’s a clear day and communications are working but the errors are large, you should first suspect multipath.

What you need to check on site is whether there are any reflective surfaces around the measurement point. If metal or glass surfaces are very close by, the reception environment can deteriorate rapidly. Not only the receiver at the tip of the pole, but also the operator’s standing position and nearby vehicles can be sources of interference. Reception at lower positions is particularly susceptible to surrounding objects.

A practical countermeasure is first to check whether you can move the survey point slightly. In some cases, simply moving it tens of centimeters to several meters (tens of cm (several inches) to several m (several ft)) away can greatly improve reflection conditions. Next, it is important to choose a location with as open a sky and surroundings as possible. Rather than right next to a structure, measuring from a slightly separated location, if possible, will make readings more stable. Also, when positioning values are unstable, refrain from making an immediate decision in a short time; observing for a certain period to see the scatter of the coordinates can also be effective.

Furthermore, taking multiple measurements at the same point is also effective in the field. Rather than judging based on a single value, wait some time and reobserve; by checking whether the differences are large, you can more easily notice the influence of multipath. If there are fixed points or known points, it is also a good method to first confirm positioning stability at those points. If the difference from a known point is large, you can conclude that the reception environment at that location is likely problematic.

Multipath mitigation depends more on choosing the right location than on any special procedure. RTK accuracy is not determined solely by equipment performance; where and how you receive signals will affect the results. In areas with many reflections, first suspect the environment. Adopting this viewpoint is the first step toward reducing errors.

Error factor 2: Accuracy degradation due to poor satellite geometry

RTK accuracy is heavily influenced not only by the number of satellites being received but also by how those satellites are distributed across the sky. This is the problem of satellite geometry. Even if many satellites are being received, if they are clustered toward similar directions, position calculations can become unstable and the errors can grow.

An important aspect of understanding this concept is the indicator that shows the quality of satellite geometry. Generally, the more evenly satellites are distributed across the sky, the more favorable the position calculation becomes. Conversely, if they are biased toward a single low-elevation direction or the available satellites are limited, coordinate variability is more likely to occur. In the field, you need to be aware not only of whether there are enough satellites, but also of the quality of their arrangement.

Satellite geometry is more likely to degrade when the time of day and local conditions align. Nearby obstructions restrict the directions of usable satellites. Also, in mountainous or urban areas, only part of the sky may be visible, which tends to skew the satellite geometry. This is why, even at the same site, measurements can be easier in the morning than in the afternoon.

What you should check on site is not only the number of satellites displayed on the positioning screen, but also whether indicators of positioning quality are deteriorating. If the values are worse than usual, it takes longer to get a Fix, or the values do not stabilize even after a Fix, the satellite geometry may be unfavorable. Forcing work to proceed under such conditions makes it more likely that poor-quality data will remain, even if measurements appear to be successful.

As countermeasures, first consider reviewing the work time window. Rather than insisting on the same time every time, simply choosing time periods when satellite conditions are relatively stable can improve positioning repeatability. Next, ensure sky visibility. Although you cannot change the satellite geometry itself, moving to a location with fewer obstructions can improve the combination of satellites available.

Furthermore, for critical survey points, it is important not to stop at a single positioning but to perform multiple checks. Re-measuring at different times makes the influence of satellite geometry more likely to appear. If coordinates become unstable only during certain time periods, it is highly likely they are being affected by the satellite geometry conditions. At sites where you want to stabilize accuracy, you should not assume you can measure at any time; instead, adopt the approach of choosing conditions that make measurement easier.

Error factor 3: Reception instability due to overhead obstruction

In RTK, how open the sky above is is extremely important. If buildings, trees, slopes, mountains, bridges, or elevated structures block the sky, not only does the number of satellites that can be received decrease, but signal quality also tends to deteriorate. This is the error caused by sky obstruction. In particular, in locations where you are surrounded not only from above but on all sides, problems such as being unable to maintain a Fix, position jumps, and low repeatability are likely to occur.

The reason signal blockage becomes a problem is simple: RTK needs to continuously receive stable signals from multiple satellites. In situations where the sky appears restricted, the available satellites are limited and the conditions required for position calculation are easily compromised. Also, obstructed environments tend to promote multipath, so degradation in accuracy is often caused by more than one factor.

For example, beneath street trees, on narrow roads in densely populated residential areas, immediately next to retaining walls, at the lower parts of cut slopes, or near bridges, only part of the sky may be visible. In such locations, even if a sufficient number of satellites are in view, the actual quality may not be stable. When the visible sky is limited, the directions of usable satellites become biased, resulting in increased errors.

What you should check on site is not just directly above the survey point, but how the sky appears around it. Simply looking up on site before starting work and checking how open it is in all directions can make a big difference. Trees require particular attention: in seasons when leaves are dense, reception conditions can be worse than in winter. At some sites, you should anticipate that positioning performance may change with the seasons, even at the same point.

As a countermeasure, the basic approach is to first be creative about how you collect control points. If reception is poor at the exact position you want to measure, consider setting up auxiliary points and linking the position from there. Rather than forcing direct measurements under adverse conditions, it can be easier to manage accuracy overall by taking stable observations in an open area and then deploying to the required position by other means.

Also, even at the same site, reception conditions can change depending on where you stand and how you set the pole. Simply avoiding the effects of tree branches or eaves can sometimes improve reception. If it is difficult to get a fix, or if a fix is obtained but is quickly lost, moving your position slightly is more effective than spending more time at the same spot. RTK’s performance is strongly dependent on the location, and you should understand that there are limits in environments where the sky is not open.

Error Factor 4: Disruption of Correction Information Due to Communication Failures

RTK assumes that correction information from the base station is received reliably. Therefore, poor communication quality directly becomes a source of error. If communications are interrupted, correction updates are delayed, or connections become intermittent, the Fix may not be maintainable and positioning can become unstable. In particular, for network-based operations, communication quality forms the foundation that supports accuracy.

On-site, attention tends to focus primarily on satellite reception, but in fact it is not uncommon for poor communications to be the cause of degraded accuracy. In mountainous areas, near underground structures, deep within development sites, or on sites with many temporary structures, communication quality may be unstable. Furthermore, even if communication is not completely lost, high latency alone can negatively affect positioning quality.

Communication-derived errors appear as symptoms such as failing to obtain a Fix, a Fix that does not persist, sudden jumps in values, or a change in position after reconnection. If you suspect only the satellite environment in such cases, you may misidentify the cause. In particular, when instability occurs in an open area, you should also suspect the correction information provider and the communication line.

What you should check on site are signal strength, the reception status of correction information, the update interval, and the continuity of the connection. Don’t be reassured just because it connected once before work; it’s important to verify whether you can still receive signals stably while walking around. On sites where communication conditions change at each measurement point, checking the entire work route can reduce problems.

As countermeasures, first identify in advance areas with weak communication. If you can grasp tendencies such as being connected at the edges of the site but weak in the center, or stable on the road side but prone to drop under the slope, it becomes easier to adjust the observation order and how you select measurement points. Next, do not force measurements when corrections are unstable. You should not rely only on the Fix indication; confirm that correction reception is being maintained before making observations.

Also, at sites with weak connectivity, procedures such as first verifying critical points in an open area or checking the differences at known points before commencing the main observations are effective. Communication issues are hard to see yet can have a major impact on results. To operate RTK reliably, it is essential to be as attentive to the communication environment as to the satellite environment.

Error Factor 5: Error Amplification Due to Differences in Reference Station Conditions

RTK accuracy is affected not only by the rover but also by the conditions at the base station. A prerequisite for RTK is that the base station is located on a stable, known point and is generating appropriate correction information. If this condition is compromised, no matter how carefully measurements are taken at the rover, the results are likely to retain errors.

What is particularly important for reference station conditions are the accuracy of the reference station coordinates, the distance to the rover, and the suitability of the correction method. If the reference station’s position information itself is not accurate, that offset will be reflected in the correction results. Also, if the distance between the reference station and the rover is too great, it becomes difficult to adequately compensate for differential effects such as the atmosphere, the ionosphere, and the troposphere, and errors tend to increase. In some field situations, the same RTK setup can show differences in accuracy depending on its relationship to the reference station.

When installing a standalone reference station, the reliability of the reference point is critically important. If you begin work with a station placed only at a provisional position, it may seem relatively consistent on site, but discrepancies will surface once it is tied into coordinates from other systems. This is a typical example that can easily lead to significant rework in later stages.

You cannot be completely confident even when using a network-based system. If the delivered correction method or area conditions are not suitable for the site, the expected accuracy may not be achieved. In locations with large environmental changes, such as mountainous or coastal areas, conditions can differ more than in flat urban areas. Therefore, it is important not to assume high accuracy simply because you are using a correction service.

What you should check on site are the type of reference station, the correction method being used, consistency with known control points, and on-site reproducibility. If known points exist, you should always verify them at the start of operations and confirm there are no issues with the reference-station conditions. If the discrepancy with the known points is large, you must consider not only the rover but also the reference-station conditions as potential causes.

As a countermeasure, first clarify the coordinate basis for the reference station. Do not place a reference station while the quality of known points is ambiguous; if using a temporary reference station, reconfirm it on another day. Operational procedures are needed to ensure the reliability of the reference system. Also, when distance conditions are unfavorable, review observation methods as necessary and consider verifying only critical points with an alternative method. RTK is not automatically reliable just because corrections are applied; accuracy can only be discussed after examining which corrections are used and under what conditions.

Error Factor 6: Equipment Configuration Errors and Initialization Failures

RTK errors can easily occur not only because of the reception environment but also due to mistakes in device settings. In fact, in practice misconfigurations can be a bigger source of trouble than the difficulty of positioning technology. Even if the equipment itself is functioning correctly, if the settings do not match the field conditions, the result can be the acquisition of shifted coordinates.

A common example is an incorrect entry of the antenna height. If the pole length is not entered correctly, it is held at an angle, or the tip is not firmly grounded, the measured height and horizontal position tend to differ each time. For RTK, which requires accuracy on the order of a few centimeters, mistakes in entering the antenna height cannot be ignored. Although it seems simple, it is one of the most common mistakes made in the field.

Another common problem is insufficient checking of the positioning mode and initialization status. It is not uncommon for observers to assume they had achieved a Fix when observations were actually unstable, for settings to have changed after a reboot, or for the previous site’s settings to have remained. This is especially true when equipment is shared among multiple people, making handover errors more likely.

Furthermore, internal device settings — such as the selection of the satellite system, the correction reception method, and the format of the output coordinates — are more numerous than expected, and if even one of them is off, consistency will be lost. Even if the device's display makes it seem like measurements are being taken, if the settings are not consistent, discrepancies will become apparent when the data are later overlaid with other datasets.

The items to check on site are the initial settings list before starting work. By making a habit of checking antenna height, positioning status, correction reception status, the coordinate system in use, known-point verification, recording format, etc., in the same order every time, you can greatly reduce human error. It is especially important to recheck immediately after powering on the equipment and after moving on site. The status can change during movement or reconnection.

As a countermeasure, standardizing the inspection items is effective. Rather than relying on individual experience, running the same verification flow at each site makes it easier to prevent mistakes. Also, at critical points it is important to include checks of known points before and after observations and to verify by actual measurement that the settings are correct. Errors in instrument settings take time to trace back to their cause once they occur. That is why the approach of preventing them through pre-checks is the most important.

Error Factor 7: Mixing Up Coordinate Systems and Correction Conditions

A frequently overlooked source of error in RTK is mixing up coordinate systems or correction settings. Because this can occur even under good reception conditions, extra caution is required in the field. Even if positioning looks stable, if the coordinate system or transformation settings being used are incorrect, the entire result can be offset.

Coordinate system issues tend to arise not merely from simple configuration errors, but from inconsistencies in the assumptions used during on-site operations. For example, the coordinates used in the field may not match the design data, the zone number of the plane rectangular coordinate system may differ, elevations may be handled differently, or the assumptions for geoid corrections may not be aligned. In such cases, the measured values may appear plausible at first glance, but when overlaid with other drawings, point clouds, or as-built data, significant discrepancies emerge.

Also, at sites that use on-site localization or local coordinates, the method for creating transformation parameters is important. If the selection of reference points is biased or there are errors in corresponding points, the results may be correct in one area but deviate in another. This is more a problem of operational design than of instrument error.

What you need to confirm on site is which coordinates are being used and by which reference. You must check—not only the horizontal position but also how height is handled—that the assumptions are consistent across drawings, design, construction, and inspection. For example, if the height reference in the design drawings differs from the height reference used during surveying, the survey itself may be correct but the results will be wrong. RTK gives numbers immediately, so it’s easy to feel reassured on the spot, but unless you check the meaning of the coordinates, you cannot operate accurately.

As a countermeasure, it is important to put in writing, before construction or work begins, the coordinate system, elevation datum, and transformation rules to be used on site. If you ensure that measurements can be processed under the same assumptions regardless of who carries them out, it becomes easier to prevent discrepancies from being discovered later. Furthermore, performing checks against known points that include height as well as horizontal position will allow you to detect coordinate system mismatches earlier.

Coordinate system errors are not like multipath errors that fluctuate on the spot; they can shift the entire result in a consistent direction. That is why you must not be reassured by good reception alone and must always verify which coordinate system you are working with. RTK error mitigation requires more than just looking up at the sky on site; it is important to consider management that includes aligning the data's reference frames.

Error Factor 8: Variations in On-site Operations and Human Error

The final major factor affecting RTK accuracy is variability in field operations and human error. Even when using the same equipment, results can vary from person to person. This is because RTK is not a system that automatically delivers high precision; it relies on a consistent level of operational quality.

For example, actions such as not keeping the pole vertical, poor contact between the survey point and the ground, observation times that are too short, recording immediately after obtaining a fix, or moving on to the next point without confirming stability all lead to errors. Especially on sites where work is rushed, the mere fact that numbers have been produced can be taken as reassurance, making it easy to skip quality checks.

Also, when multiple people work together, differences in verification criteria directly translate into variability in the results. One operator may wait to observe even a slight sway, while another records immediately, so data of inconsistent accuracy can become mixed even at the same site. Such variability is hard to detect during post-processing and tends to cause problems when integrating the outputs.

What needs to be checked on site is whether the judgment criteria for each operator are standardized. Deciding in advance which conditions are considered stable, how much variation warrants a re-measurement, and how frequently to perform known-point checks will reduce individual differences. RTK makes equipment operation look simple, so it is often assumed that differences in experience will have little effect, but in practice differences in operational rules directly translate into differences in results.

As a countermeasure, first standardize the observation procedures. By fixing the workflow—from post-power-on checks, known-point checks, and stability confirmation before the main observation, to re-measurement of critical points and end-of-work reconciliation—you can more easily reduce errors. Also, the more important a point is, the less it should be left to a single measurement; it is desirable to reconfirm from different directions and to perform observations separated in time.

Additionally, it is important to keep on-site records. If you know at what time, under what conditions, and in what state the observations were made, it becomes easier to trace the causes of errors later. Conversely, if no records are kept, when an error occurs it is difficult to tell whether it was due to communication, obstruction, or the coordinate system, making it hard to prevent recurrence.

RTK positioning errors are not just caused by the equipment. On-site practices, the thoroughness of checks, and the uniformity of procedures are directly reflected in accuracy. To reliably achieve high-precision positioning, you need not only technology but also a focus on managing operational quality.

Summary

Sources of RTK error cannot be adequately prevented by addressing only one factor. As representative examples, it is important to be aware of eight: multipath, satellite geometry, sky obstructions, communication failures, base station conditions, equipment settings, coordinate system mix-ups, and variability in field operations. Although these may appear independent, in actual fieldwork multiple factors often overlap simultaneously and degrade accuracy.

In particular, multipath is prone to occur in urban areas and around structures, and failing to account for the presence of reflective surfaces increases errors. Satellite geometry and sky obstruction directly affect how the sky is visible and thus determine positioning quality, so choosing the time of day and the locations of survey points is important. For communications, because stable reception of correction information is a prerequisite, you must check not only the reception quality but also the continuity of the connection.

Also, the reference station conditions, equipment settings, and handling of the coordinate system carry the risk of shifting the entire results even when measurements at the site appear to be normal. Entering the antenna height, selecting the positioning mode, checking against known points, and confirming the reference for horizontal position and height must be established as routine basic operations each time. Furthermore, to eliminate differences in judgment among operators, it is essential to standardize observation procedures and unify the rules for re-measurement and verification.

To reduce errors on site, the first thing to implement is to standardize the pre-task checklist. Simply verifying, in the same order each time, the sky openness, nearby reflective objects, communication status, consistency with known points, equipment settings, and the assumptions of the coordinate system can prevent many errors in advance. Additionally, for critical points, do not stop at a single observation; by re-observing or performing time-difference checks you can more easily detect incidental errors.

RTK is a very convenient and highly accurate method, but if you use it under poor conditions you will not obtain the expected results. Conversely, if you understand the sources of error and make a habit of checking the points that should be verified on site, accuracy will become much more stable. If you plan to use RTK in the field going forward, it is important to adopt the mindset of managing the four elements—environment, settings, reference, and operations—as an integrated whole, rather than relying solely on the performance of the equipment. Doing so will reduce re-surveys and rework and make it easier to achieve RTK operations that are usable in practical work.