Factors Affecting RTK Accuracy and Countermeasures: How to Maintain High Accuracy on Site

Table of Contents

• Factor 1: Errors in base station coordinates or geodetic datum settings

• Factor 2: Correction data not applied (Float / Single positioning)

• Factor 3: Degraded satellite reception environment (obstruction / multipath)

• Factor 4: Accuracy degradation due to long baselines and atmospheric errors

• Factor 5: Equipment handling mistakes and vertical error factors

• What is simple surveying with LRTK

• FAQ

RTK (Real Time Kinematic) positioning is a technology that achieves much higher accuracy (centimeter-level) than standalone GPS by applying correction information from a GNSS base station in real time. Its use has rapidly expanded in recent years in civil engineering surveying and construction sites, greatly contributing to efficiency in tasks such as setting batter boards and managing as-built shapes. However, even though RTK can provide high accuracy, on-site issues such as position mismatches or errors of several centimeters can still occur. For example, surveyors sometimes report that "coordinates measured by RTK did not match a known point" or "there was a height discrepancy of several centimeters, which caused trouble."

Why do such errors and position shifts occur in RTK positioning? This article addresses the main factors that affect RTK accuracy and explains the causes and countermeasures to take on site. By correctly understanding the sources of error and responding appropriately, you can keep RTK positioning consistently stable and highly accurate. At the end of the article, we also introduce simple surveying using LRTK, which fundamentally resolves such issues and enables centimeter-class positioning easily for anyone.

Factor 1: Errors in base station coordinates or geodetic datum settings

In RTK surveying, it is fundamental to set accurate known coordinates at the base station. However, if the coordinate settings at the base station are incorrect, the resulting coordinates will be shifted no matter how accurate the positioning itself is. For example, entering a wrong digit for a known point's coordinate value or selecting the wrong coordinate system can produce positioning results that are far from the true location. When using Japan’s plane rectangular coordinate system, choosing the wrong zone number can cause the entire positioning result to be off by tens of meters, leading to a critical mistake. When surveying abroad, you will be using a different geodetic datum than in Japan, so substantial discrepancies can arise due to differences in the reference coordinate system. If you perform RTK positioning without aligning the datum, even if the relative positioning accuracy between rovers is centimeter-level, you may end up with position differences of several meters when compared to maps or drawings.

You also need to pay attention to differences in height reference. The height calculated by an RTK receiver is usually the ellipsoidal height (height relative to the reference ellipsoid used by GPS), whereas the elevations used in civil engineering practice are heights relative to mean sea level (geoid-based orthometric heights). The difference between them can be tens of meters depending on the region; within Japan, ellipsoidal heights are typically about +35–40 m ( +114.8–131.2 ft) higher than orthometric heights. Therefore, directly comparing the ellipsoidal height obtained from RTK with on-site elevations can lead to situations where "the heights do not match as expected."

• Countermeasures: Always double-check the coordinate values and geodetic datum settings that you enter for the base station in advance to prevent input errors or selecting the wrong system.

• When using known points, unify the geodetic datum and avoid mixing global datums (JGD2011/2022) with old datums. If necessary, perform localization (local coordinate transformation) to match the site’s coordinates.

• For heights, use a geoid model (geoid height) to correct the ellipsoidal height to orthometric height. Be sure to obtain the regional geoid heights in advance and apply them to the positioning data to align with the reference vertical datum.

• After surveying, make it a habit to compare the coordinates obtained by RTK with known control points on site to check for any discrepancies. Detecting errors early can prevent rework.

• To prevent human errors when setting coordinates, prepare work procedures and checklists and have multiple people verify entries so that one person’s input mistakes can be caught by another.

Factor 2: Correction data not applied (Float / Single positioning)

High-accuracy RTK positioning assumes that the rover is continuously receiving correction information from the base station. However, if correction data do not reach the rover due to communication issues or configuration errors, positioning will proceed without corrections. As a result, you may continue working with the solution status as Float or Single, recording positions that contain larger errors than expected. A Float solution means that correction data are being received but integer ambiguity resolution (fixing the integer carrier-phase ambiguities) has not yet been achieved; its accuracy is roughly ±0.5–1 m (±1.6–3.3 ft). In contrast, a Single solution (standalone GNSS without corrections) may produce errors of several meters or more. If you overlook the receiver or controller display on site and assume "it’s probably fine" and record points while still in Float, you risk having to remeasure or redo work later.

• Countermeasures: During surveying, always check the receiver or app status and make sure the solution is definitely FIX before recording points or marking locations.

• If Float or Single is displayed during surveying, stop work calmly and wait for FIX to be restored before resuming. Try moving the antenna to a more open location, reconnecting to the base station, or adjusting environment and settings.

• Check radio and NTRIP service connection settings. Verify that server information for receiving corrections (address, port, mountpoint, login) is correct and that the correction service subscription has not expired. Monitor the communication status at both base and rover; if correction data are not arriving, promptly identify and address the cause.

• To avoid "it slipped into Float without me noticing," cultivate the habit of frequently checking the status screen. Always aim to be in FIX and be ready to notice anomalies immediately.

• Immediately after starting positioning, satellite acquisition and stable reception of corrections may take several tens of seconds. Before recording the first point, remain stationary and wait until FIX is achieved. Especially when surveying while moving, obtain FIX before starting movement to avoid recording unstable Float-period data.

Factor 3: Degraded satellite reception environment (obstruction / multipath)

RTK positioning uses radio signals from GNSS satellites, so the satellite signal reception environment strongly affects accuracy. When tall buildings surround the site or it is enclosed by forest, the sky is obstructed and the number of visible satellites decreases, degrading the satellite geometry for positioning. Also, when satellite signals reflect off concrete walls or metal surfaces, multipath occurs, introducing biases and noise into the positioning results. For example, in urban canyons, under elevated structures, or under trees, even if correction information is available, the satellite signals themselves can be unstable, making it difficult to obtain a FIX or causing degraded accuracy.

Strong radio interference from surrounding sources is another hidden factor. Near high-voltage power lines, strong electromagnetic noise can affect GNSS reception; construction radios, pocket Wi-Fi, or cellular base stations nearby can cause the receiver to pick up noise and reduce positioning accuracy. Such radio-noise environments can make RTK solutions unstable.

• Countermeasures: Install the antenna in as open a location as possible to ensure a clear view of the sky in all directions (360°). For base station antennas, mount them on building roofs or sufficiently high poles so nothing obstructs the sky above.

• When observing with the rover, choose locations with as much open sky as possible. Avoid measuring directly under trees, in building valleys, or any place where the sky is largely obscured, as satellite count may be extremely low and accuracy will suffer. If measurement in such locations is unavoidable, consider temporarily moving to a better location for observation.

• Avoid surveying near strong reflectors such as metal structures, large vehicles, or reflective water surfaces. If unavoidable, remove or move obstructions as much as possible before measurement, or install a ground plane (a metal plate to mitigate reflections) on the antenna to physically reduce multipath.

• Use a multi-GNSS receiver capable of GPS, GLONASS, Galileo, and QZSS (Michibiki) where possible. Tracking multiple constellations helps secure sufficient satellites even in challenging environments, improving the chance of maintaining accuracy. Also review the receiver’s elevation mask settings. Low-elevation satellites are more prone to reflection; generally set the mask to use satellites down to about 15–20° and exclude lower ones to reduce noise.

• In areas with suspected strong radio interference, move away from interference sources for surveying. Avoid being directly under high-voltage lines or close to TV/radio transmitters, and use any available noise filters for the receiver. Also disable unnecessary wireless communications on the receiver (turn off unused Bluetooth or Wi‑Fi) and keep other electronic devices at a distance to reduce interference. Choosing an electrically cleaner environment is the quickest route to obtaining a stable FIX.

Factor 4: Accuracy degradation due to long baselines and atmospheric errors

RTK achieves high accuracy by relative positioning between the base station and the rover. Therefore, as the distance (baseline length) between them increases, accuracy tends to degrade. This is because errors contained in the satellite signals received at the base and rover (ionospheric delays, tropospheric delays, satellite clock errors, etc.) vary with distance and cannot be completely canceled by differencing corrections. Even high-performance RTK-GNSS equipment commonly specifies positioning accuracy limits on the order of ±(8 mm + 1 ppm) (horizontal). The "1 ppm" means about 1 mm of additional error per 1 km of baseline. In other words, being 10 km from the base station theoretically adds about 1 cm (0.4 in) of error, and being 20 km away adds about 2 cm (0.8 in). In particular, differences in the troposphere can produce bias errors in the vertical component, so long-distance RTK is known to have degraded vertical accuracy. In practice, Japan’s public surveying manual stipulates allowable RTK errors of "within 15 mm (0.59 in) horizontally and within 50 mm (1.97 in) vertically," and the vertical allowance is looser than horizontal, which reflects that vertical errors tend to be larger at long baselines.

• Countermeasures: Keep the distance between base and rover as short as possible. If you can set up your own base station, place it as close to the survey area (for example near the center of the worksite) as possible.

• If self-installation of a base station is difficult, consider network RTK services such as electronic reference points from the Geospatial Information Authority of Japan or commercial VRS (Virtual Reference Station) services. VRS via NTRIP can create a virtual base station near the user, effectively reducing the baseline to a few kilometers or less.

• Use dual-frequency (L1/L2 or higher) high-precision GNSS receivers if possible. Observing on two frequency bands cancels much of the ionospheric error, making it easier to maintain FIX solutions over longer distances than with single-frequency units. Recent models also use L5 and other frequencies for improved stability.

• If accuracy is unstable due to baseline effects even when satellite count is sufficient, try restarting the receiver or switching to alternative augmentation methods. For example in Japan, equipment that can receive the QZSS (Michibiki) CLAS signal can obtain corrections directly from satellites, mitigating long-baseline issues even outside of communication coverage. Consider such measures as appropriate to the situation.

Factor 5: Equipment handling mistakes and vertical error factors

While RTK can provide high accuracy, small human errors or operational mistakes can cause unexpected position shifts. For example, if the rover pole is slightly tilted even though you think it is vertical, the measured point coordinates will shift accordingly. A 2 m (6.6 ft) surveying pole tilted by 1° causes the horizontal position to shift by about 3 cm (1.2 in). Poles should be kept strictly vertical using a bubble level, but on-site conditions sometimes make perfect verticality difficult. Inputting the wrong antenna height (instrument height) is another common error: an incorrect height from the pole tip to the antenna reference point results in the same error being inserted into the computed elevation. Also, poor calibration of the receiver or its built-in IMU can cause tilt compensation functions to work improperly and degrade accuracy.

Additionally, RTK positioning generally has poorer vertical accuracy than horizontal accuracy. Because satellites are primarily overhead, vertical positioning geometry is inevitably weaker than horizontal geometry. As a result, slight error sources can easily cause height offsets of several centimeters. As noted earlier, official standards set looser tolerances for vertical accuracy. In practical work, however, a 5 cm (2.0 in) height difference can be problematic for batter board layout or as-built control, so it cannot be ignored.

• Countermeasures: When observing points, carefully check pole verticality with the bubble level and ensure you do not measure with a tilted pole. Remember that even slight tilt can cause several centimeters of error.

• Using RTK receivers with built-in IMU for tilt compensation is one option. They can automatically correct for some pole tilt and compute accurate coordinates even when the pole is slightly inclined, which is useful in confined spaces where it is difficult to stand the pole perfectly vertical. However, do not over-rely on this; still make every effort to keep the pole vertical.

• Verify the antenna height (instrument height) setting for each site to avoid input errors. When installing your own base station, calibrate it on a known point in advance to ensure correct height and coordinates. Regularly calibrate receivers and tilt sensors to keep them in proper working condition.

• Always perform check surveys during work. Observe several known control points or batter board positions on site with known accurate coordinates using RTK and confirm the magnitude of any errors. If you find deviations of several centimeters or more, immediately investigate and resolve the cause before continuing main surveying. If the check survey shows no anomalies, you can proceed with confidence.

What is simple surveying with LRTK

So far we have reviewed the main factors affecting RTK accuracy and their countermeasures. However, on real sites you may still face issues such as "there is a confined location where the antenna cannot be positioned freely," "the base station inevitably ends up far away," or "we are uneasy about performing complex settings or adjustments in the field." In such cases, our company’s LRTK simple surveying solution can help.

LRTK consists of a compact, high-performance RTK-GNSS receiver and a smartphone app, developed to make high-accuracy positioning on site easier and more reliable than ever. Several features that distinguish it from conventional equipment cover the error sources mentioned above through both hardware and software.

• Stable positioning with multi-GNSS and dual-frequency support: LRTK receivers can use GPS as well as GLONASS, Galileo, and QZSS (Michibiki) simultaneously, and operate on dual-frequency bands (L1/L2). They can reliably acquire enough satellites even in urban or near-forest environments, and dual-frequency observation improves ionospheric error mitigation. This helps prevent satellite shortage and accuracy degradation over long baselines, enabling quicker and more stable acquisition of FIX solutions.

• Support for satellite augmentation signals (CLAS): Some LRTK models can directly receive CLAS, the centimeter-class augmentation service provided by Japan’s QZSS (Michibiki). This allows users to obtain corrections from satellites and achieve centimeter-level positioning even where an RTK base station cannot be set up. It is a major advantage for maintaining high accuracy in mountain areas or large sites without cellular coverage, eliminating concerns about communication loss or long baselines.

• Intuitive operation via smartphone linkage: A dedicated smartphone app allows anyone to easily manage base and rover setup and connection status. Satellite reception and correction status are visible at a glance, so even if FIX is not achieved you can quickly identify the cause. Complex NTRIP settings are preconfigured with common correction services, so you can connect by selecting from a list. LRTK’s user-friendly design enables even non-specialists to operate correctly without confusion.

• Cloud integration and tilt compensation: Positioning data can be synchronized to the cloud in real time, allowing immediate sharing and checking of on-site results with the office. LRTK receivers also include built-in tilt sensors that automatically compensate when the pole is slightly tilted, enabling accurate coordinate acquisition even when the pole cannot be set perfectly vertical in confined spaces. This prevents missing measurement points and greatly improves work efficiency.

LRTK is thus a next-generation simple surveying solution that balances RTK accuracy and usability. It is designed to significantly reduce common on-site troubles such as "positions do not match" or "cannot get FIX," making it possible for anyone to obtain stable high-accuracy positioning easily. If you are struggling with RTK discrepancies or complex settings in your current workflow, consider switching to LRTK. It can be a reliable partner under complicated conditions.

FAQ

Q1. What accuracy can be obtained with an RTK FIX solution? How large are the errors in Float or Single? A. Generally, when an RTK FIX solution is obtained, both horizontal and vertical errors are typically within a few centimeters. In contrast, a Float solution may have errors on the order of several tens of centimeters, and a Single (standalone, without corrections) may be off by several meters or more. For example, the LRTK system sets target accuracies roughly as: Single within 10 m (32.8 ft), Float within 1 m (3.3 ft), and FIX within 2 cm (0.8 in). For tasks requiring precise positioning, Float or Single are insufficient, so always obtain FIX before using measurement values.

Q2. How many satellites are required to obtain an RTK FIX solution? A. It depends on the algorithm, but generally it is said that both the base and rover need to simultaneously track five or more satellites. With GPS alone, four satellites are just enough for standalone positioning and are insufficient to obtain an RTK FIX. Modern multi-GNSS receivers can receive ten or more satellites at once, reducing cases where lack of satellites prevents FIX. However, satellite geometry is also important: even a large number of satellites clustered in one part of the sky may not produce good accuracy. Choosing a time when satellites are well distributed is also a shortcut to obtaining FIX sooner.

Q3. How long does it usually take from starting RTK positioning until FIX is obtained? A. Under good conditions, it often takes about 30 seconds to 2 minutes to reach FIX after starting positioning. If the sky is open and satellite signals are stable, FIX can be achieved within a minute after turning on the receiver. Conversely, in poor environments or with initial setup difficulties, you may remain in Float for more than 5 minutes. Once FIX is obtained, it is generally maintained as long as communication remains intact. If FIX does not occur after 5 minutes, review the factors discussed in this article and check settings and environment; sometimes restarting the receiver or changing the measurement location results in faster FIX.

Q4. Do weather or time of day affect RTK accuracy? A. Weather itself, such as rain or clouds, has little direct effect on GNSS radio waves, so RTK FIX is not greatly different between clear and bad weather. However, heavy rain can cause significant signal attenuation and may make FIX take longer than usual. Also, suspend surveying during thunderstorms for safety. On the other hand, time of day affects the satellite geometry (the relative positions in the sky), so RTK accuracy and ease of obtaining FIX can vary. Working during daytime when satellites are more evenly distributed is generally better than during late-night low-satellite-height periods. Additionally, periods of strong solar activity increase ionospheric disturbances and can adversely affect GNSS positioning. In extreme cases, large geomagnetic storms that cause visible auroras have been reported to destabilize RTK solutions, but this is not a common concern for everyday surveying.