RTK (Real-Time Kinematic) surveying is a groundbreaking technology that enables centimeter-level positioning in real time by satellite positioning. However, in actual fieldwork one often hears that "RTK won't easily FIX (an integer-fixed solution cannot be obtained)." If the solution remains float, positional errors can reach several tens of centimeters, potentially causing rework or re-measurement due to insufficient accuracy.

This article takes up five representative factors that are considered the main causes of RTK not fixing, and provides a thorough explanation of each. We cover common causes such as satellite reception environment issues, troubles receiving correction data, and mistakes in reference point coordinates, and introduce key points to prevent accuracy degradation and work interruptions. Survey professionals should find this useful. At the end of the article we also introduce a new easy surveying solution, LRTK, that solves these challenges.

Table of Contents

• Poor satellite reception environment

• Unable to receive correction information

• Reference point / coordinate setting errors

• GNSS equipment misconfiguration or malfunction

• Baseline distance and atmospheric error effects

• Recommendation for easy surveying with LRTK

• FAQ

1. Poor satellite reception environment

For RTK positioning, being able to stably receive signals from multiple GNSS satellites such as GPS and GLONASS is an essential prerequisite for obtaining a FIX solution. However, if the field's satellite reception environment is poor, the number of observed satellites may be insufficient or the data quality required for positioning may not be ensured, and a fixed solution may never be obtained. For example, in urban areas surrounded by high-rise buildings or inside forests, the sky view is often blocked and the number of usable satellites tends to decrease. Multipath, where satellite signals reflect off concrete walls, metal surfaces, or water surfaces, is also a serious problem. When reflected waves cause measurement distance errors, the RTK ambiguity (integer solution) analysis becomes disturbed and FIX is less likely to be achieved.

Moreover, if strong radio-emitting equipment such as high-voltage power lines or radar is nearby, noise or interference can be added to GNSS signals and reception strength may decrease. Bad weather cannot be ignored either. During heavy rain or thunderstorms, ionospheric effects and signal attenuation increase and RTK can become unstable. Under such adverse satellite reception environment conditions, there is a higher risk that the RTK solution will remain float and not reach FIX.

Countermeasures: When performing positioning, choose a location with as wide an open sky as possible. Place base station antennas at clear vantage points with an unobstructed 360° view, and remove nearby obstacles around the rover measurement point in advance if feasible. It is also wise to avoid observing near large reflective objects. If avoidance is difficult, attaching a ground plane (ground plate) to the antenna or using a high-performance choke-ring antenna to reduce multipath is effective. Additionally, modern GNSS receivers increasingly support multi-GNSS (tracking multiple satellite systems) and dual-frequency reception. By using these features, you can increase the number of usable satellites even in poor-visibility environments and mitigate ionospheric errors, improving FIX rates. If RTK is unstable due to environmental factors, consider changing the time of day (measuring when satellite geometry is better) or complementing with other methods like a total station rather than forcing it.

2. Unable to receive correction information

In RTK, centimeter-level accuracy is obtained only by continuously receiving real-time correction data sent from a base station (reference point). Therefore, if communication between the base station and the rover is interrupted and correction information is not delivered, no matter how long you wait you will not obtain a FIX solution. When corrections stop, RTK reverts to standalone positioning or DGPS-level accuracy, and the solution remains float.

Causes for not receiving correction information include communication environment and equipment configuration issues. In radio-type RTK, if the frequency or channel settings of the base and rover radios do not match, or if the rover goes beyond line-of-sight range, correction data will be cut off. In cases using low-power or simple radios, the practical communication distance is limited to a few kilometers, so in wide-area sites you can easily move out of range. Radio shielding environments such as tunnels or building shadows also cause communication loss. On the other hand, in network RTK relying on mobile Internet like NTRIP, corrections may not be received if the site is out of cellular coverage or mobile data is unstable, or if the base station service has an outage.

Countermeasures: First, check base and rover communication settings in advance. When using radios, verify that transmission frequencies and group IDs match on both ends, and inspect antenna connections for looseness or breaks. Install the base station antenna as high as possible for line-of-sight distance and consider relay antennas to expand coverage. When using a network connection, prepare SIM cards from multiple carriers on site so you can use the one with the best signal, and if necessary use an external antenna or mobile Wi‑Fi router to improve reception. Also, battery depletion during long surveys is a common cause of lost corrections. Confirm sufficient battery levels for both base and rover beforehand and carry spare power. If you absolutely cannot obtain real-time corrections, consider recording raw data in static mode and performing PPK (post-processing kinematic) later.

3. Reference point / coordinate setting errors

In RTK surveying, it is essential that the coordinates of the reference points used and the geodetic/coordinate system settings are accurate. If these are mistaken, even if RTK FIXes, the resulting coordinates will be shifted and can cause large errors. For example, entering a known point coordinate for the base station with one digit off, or selecting the wrong zone number in Japan’s plane rectangular coordinate system, can result in positioning tens of meters off. There are actual cases where "I entered a known point coordinate with a one-digit mistake and later the data didn't match—panic ensued," so coordinate setting errors are a serious problem not to be laughed off.

Particular care is required when using geodetic or survey coordinate systems different from those in Japan. If you are using the Japan Geodetic Datum (JGD2011/2022) versus the old Tokyo datum, or employing a unique local coordinate system, unless you perform coordinate transformations correctly the resulting coordinates will not match the project's reference. In the vertical direction, forgetting to apply geoid height corrections will make the obtained heights deviate significantly from the site’s elevation.

Countermeasures: Before starting surveying, be sure to confirm the coordinates of the reference points to be used and the geodetic/coordinate system. Refer to contract documents or known-point sheets and set the correct reference coordinate system in the equipment (e.g., JGD2011, prefecture/zone designations). When setting up the base station, double-check that the entered known-point coordinates are correct. If possible, observe one known point before work begins to verify that the device returns the expected coordinates. When surveying in a local custom coordinate system, perform site calibration using multiple known points to align the device coordinates with the local survey coordinates. If you discover a setting error later, it may be possible to salvage recorded raw data by converting it to the correct coordinate system afterward. However, conversion work is laborious, so preventing setting mistakes from the start is crucial.

4. GNSS equipment misconfiguration or malfunction

System or equipment misconfiguration and malfunctions can also cause RTK not to fix. A basic example is incorrect mode settings between base and rover. If a receiver that should operate as a base is left in rover mode, or conversely a rover is set to fixed mode, corrections will not be correctly generated or applied and positioning will fail. Also, when using RTK network services, selecting the wrong mount point (virtual reference point for corrections) can result in incompatible data formats and no solution.

Equipment-specific problems such as faulty GNSS antennas or cables are also significant. If an antenna connector is loose or a cable is broken, the receiver may not receive satellite signals or correction data properly and RTK will not FIX. Pay attention to field terminals (controllers) and software settings as well. If the geodetic or projected coordinate system settings are wrong, as mentioned earlier the results will be shifted; if the RTK solution mode is incorrectly set (e.g., a mobile receiver is set to base), you will not get the correct solution. Firmware or application bugs and freezes can also occur occasionally. Especially for GNSS receivers controlled by tablets or smartphones, there have been cases where an app was force-closed and correction reception stopped.

Countermeasures: Preventing equipment trouble requires pre-field checks. Inspect the GNSS receiver, antenna, and radio equipment connections, and confirm power and battery levels. For new sites, simulate and verify surveying software settings (geodetic system, projected coordinate system, antenna height input, communications settings, etc.) from the initial setup. Keep receiver firmware and control apps updated to the latest stable versions and monitor release notes for fixes. During work, if you notice abnormal behavior, pause measurements, reboot, and verify with another known point to isolate the cause as early as possible. Basic measures like checking the bubble on the survey pole to ensure plumbness and avoiding antenna height input errors are also important to prevent human errors.

5. Baseline distance and atmospheric error effects

When RTK does not FIX, RTK-specific constraints such as the baseline length between base and rover and atmospheric errors should be considered. Generally, the farther the distance from the base station, the larger the differential ionospheric and tropospheric errors between the two stations, and the greater the residuals that cannot be canceled by corrections, making it harder to obtain an integer-fixed solution. Even high-precision RTK receivers have specifications like "horizontal accuracy 8 mm + 1 ppm," meaning about 1 mm of additional error per kilometer. Thus, if the rover is tens of kilometers from the base, the observation precision required for resolving integer ambiguities cannot be maintained and the solution becomes unstable. Single-frequency (L1-only) equipment in particular cannot sufficiently correct ionospheric errors, so long baselines may take very long to go from float to FIX, or may never FIX.

Also, ionospheric disturbances such as solar flares and times of unfavorable satellite geometry reduce FIX rates. Even with no nearby obstructions, if the satellite geometry overhead is skewed and PDOP is high, RTK initialization can take a long time. Conversely, if multi-GNSS tracking can maintain 10 or more satellites, you can usually obtain a stable FIX even with some atmospheric errors.

Countermeasures: Keep the distance between the base station and the survey point as short as possible. If you can install your own base station, place it close to the site; if that's difficult, use national continuously operating reference stations (e.g., GSI reference stations) or VRS (Virtual Reference Station) services to effectively shorten the baseline. Also plan to avoid times when satellite availability or geometry is poor by checking satellite operation in advance—for example, consult services that predict GNSS satellite visibility and PDOP values provided by the Geospatial Information Authority of Japan. On days with large ionospheric disturbances, refrain from high-precision positioning or record short-duration observation data for later precise processing (PPK or PPP). Not insisting on RTK's real-time nature and flexibly using other surveying methods as appropriate will ultimately help minimize rework.

Recommendation for easy surveying with LRTK

So far we have reviewed typical causes and countermeasures for RTK failing to FIX. Successful high-precision RTK surveying requires attention to many points such as environmental checks and equipment settings, and demands specialized knowledge and experience. One solution to spotlight is LRTK, a new surveying system that addresses these challenges and makes centimeter-level positioning easy for anyone.

LRTK is a newly designed surveying system that allows high-precision positioning easily using a smartphone or dedicated compact device. By combining multiple satellite positioning technologies with cloud services, it removes the complexities that traditionally accompany RTK operations. For example, without having to worry about advanced tasks such as base station setup, communication assurance, or coordinate system adjustments, LRTK can automatically achieve millimeter- to centimeter-level positioning simply by setting up the device on site. In operation, LRTK also utilizes the augmentation signals of the Michibiki satellites (QZSS), enabling stable positioning even in mountainous areas where cellular reception is poor.

Below are some of the benefits of using LRTK:

• Ease of use: Intuitive smartphone-app-centered operation makes it usable without specialized GNSS knowledge. Complicated settings and field adjustments are unnecessary, and it can be used after a short training.

• High accuracy: By combining observations from multiple points and advanced cloud correction techniques, LRTK achieves approximately 1–2 cm positioning in both horizontal and vertical. Using a dedicated monopod allows a single operator to obtain stable measurements, and averaging dozens of measurements can approach sub-millimeter precision.

• Reliability: Risks of communication loss and configuration mistakes common in traditional RTK are greatly reduced. Data are automatically saved to the cloud in real time, so measurement logs remain even if equipment fails.

• Efficiency: Because equipment can be carried in a pouch and positioning started with one touch, surveying productivity improves over conventional methods. Post-processing is also reduced, enabling immediate results on site and faster progression to subsequent tasks.

By introducing LRTK, you can be freed from worries such as "won't FIX" or "cannot get accuracy" associated with RTK surveying. If interested, check the LRTK details. Free service introduction materials are currently available, so please consider requesting documentation.

FAQ

Q: If an RTK survey remains in a float solution and cannot be fixed, what should I do? A: First, check in order whether any of the five factors introduced here (satellite reception environment, correction information, coordinate settings, equipment settings, baseline length) are causing the problem. Inspect whether you can move to a more open sky location, whether base station radio signals reach the rover, and whether there are configuration mistakes. If FIX still does not occur, pause measurements and wait for satellite geometry to improve. If you absolutely cannot obtain a real-time FIX, consider stopping RTK and recording static observations for later PPK processing.

Q: How many satellites must be visible for RTK to FIX at minimum? A: Generally, it is desirable to observe five or more satellites simultaneously to obtain an RTK fixed solution (roughly four for pseudo-range differences plus one for interference error correction). However, if satellite geometry is poor or data quality is degraded by multipath, even with five satellites FIX may be difficult. Practically, it is ideal to consistently track seven to eight or more satellites. Multi-GNSS receivers that use GPS/GLONASS/Michibiki/Galileo, etc., can more easily secure around ten satellites even in urban areas, which improves FIX rates.

Q: Does using a multi-GNSS, dual-frequency receiver increase FIX rates? A: Yes, it does. Multi-GNSS-capable receivers significantly increase the number of available satellites, making it easier to secure the necessary positioning satellites even when sky view is poor. Dual-frequency receivers (e.g., L1/L2) greatly improve ionospheric delay correction accuracy compared with single-frequency units, enabling faster ambiguity resolution. As a result, time to initial FIX and FIX retention (maintaining a FIX after it is obtained) are greatly improved. For stable high-precision results, using multi-GNSS and multi-frequency receivers where possible is advantageous.

Q: What kind of service is LRTK? A: LRTK is a new high-precision positioning service that serves as an alternative to conventional RTK operations. By combining a smartphone with a dedicated receiver and linking to a cloud correction platform, it enables centimeter-level positioning without specialized procedures. It eliminates troublesome base station setup and coordinate transformation work—just go to the site with the device and press a button to complete surveying. It also avoids communication and configuration issues, and measurement data are automatically saved to the cloud, ensuring safe and reliable results. For more details, refer to official LRTK information.