A Must-Read for Beginners! Clear Explanation of Causes and Solutions When RTK Won't Fix

Table of Contents

• What is RTK positioning?

• Differences between Fix / Float / Single (no RTK)

• Main causes why RTK won't Fix

• Countermeasures when RTK won't Fix

• Simple surveying with LRTK

• FAQ

What is RTK positioning?

RTK positioning (real-time kinematic) is a technology that uses GNSS satellites to perform high-precision positioning in real time. Ordinary standalone positioning can have errors of several meters, but RTK corrects errors through relative positioning between a base station (reference station) and a rover, achieving centimeter-level accuracy (half-inch accuracy). In particular, when the state known as a Fix solution is achieved, positional reliability improves dramatically, greatly boosting efficiency in surveying and construction sites. RTK is also applied to drone surveying and autonomous vehicles for high-precision positioning, and is gaining attention as a foundational technology for obtaining accurate real-time location information.

However, beginners attempting RTK positioning often run into hurdles such as “it won't Fix” or “accuracy isn't achieved.” RTK is a delicate technology and is affected by various factors such as the surrounding environment and device settings. This article explains, from the basics and in an easy-to-understand way, the reasons why a Fix solution cannot be obtained with RTK and how to resolve them.

Differences between Fix / Float / Single (no RTK)

RTK positioning has several types of solutions depending on positioning accuracy. Here we explain the representative differences between Fix, Float, and Single positioning.

• Fix solution: This is the solution obtained by resolving the integer ambiguities from data with the base station. Simply put, it is the state where the number of satellite signal wavelengths can be decoded exactly as integers, and errors are suppressed to less than a few centimeters. This is the highest accuracy state that RTK aims for.

• Float solution: This is the provisional position computed while integer ambiguities remain unresolved. Compared to Fix, errors are larger, typically on the order of tens of centimeters to about 1 m (3.3 ft). Because the position is unstable and drifts over time, it is called a Float solution. This often occurs shortly after starting RTK or in poor environments.

• Single positioning (standalone positioning): This is normal GNSS positioning without corrections from a base station. It may simply be displayed as SINGLE or DGNSS. Accuracy is low, on the order of several meters, and RTK-level high-precision positioning is not being performed. If base station data cannot be received or the receiver is not in RTK mode, the receiver will be in Single positioning. For example, code-based positioning via wide-area satellite augmentation systems (SBAS) achieves at best about 1–3 m (3.3–9.8 ft) accuracy, which is orders of magnitude different from an RTK Fix solution.

Whether you are achieving a Fix solution is an important point for judging RTK quality. Always check displays such as “Fix,” “Float,” or “Single” on your surveying app or receiver status screen, and maintaining a Fix state as much as possible is the key to high-precision positioning.

Main causes why RTK won't Fix

When RTK positioning cannot obtain a Fix solution, several typical causes can be considered. Below are the main factors summarized.

• Insufficient number or poor geometry of satellites: If the number of available GNSS satellites is small or they are clustered in part of the sky, positioning accuracy degrades and it becomes difficult to obtain a Fix. Poor satellite geometry worsens geometric precision (DOP values), making it difficult to stably resolve integer ambiguities. High-precision 3D positioning generally requires stable tracking of five or more satellites, and when observed satellite count is low, the information needed for Fix is lacking.

• Obstructions and multipath: In environments where the sky view is blocked by buildings, trees, etc., satellite signals cannot be received sufficiently. Reflections from building façades or the ground cause multipath (signal reflection/interference) and are also a serious problem. When signals are degraded by these factors, the RTK engine cannot perform accurate calculations, preventing a Fix.

• Base station too far away: If you are too far from your own base station or from a network RTK service reference station, error factors between the two stations (such as ionospheric delay) can differ greatly and corrections become ineffective. In general, the longer the baseline length, the longer it takes to get a Fix and the less stable it becomes. (There are cases where Fix is achieved even when more than 50 km (31.1 miles) away, but stability is significantly reduced.)

• Correction data not being received: Correction data from the base station is the lifeline for RTK. If an NTRIP connection over the internet is cut or the base station data is no longer being broadcast, Fix will of course not be obtained. Even if data is being received, if the type of correction data doesn't match (e.g., using multi-frequency data with a single-frequency receiver) or the base station coordinate system doesn't match the rover's, the solution may not converge to a Fix.

• Strong radio interference or noise: If there are powerful radio sources nearby, such as directly under high-voltage lines or near radio stations, GNSS reception can be interfered with. If noise contaminates the signal, positioning accuracy can worsen drastically and the solution may remain Float. For example, construction radios or Wi-Fi routers operating nearby can introduce such noise.

• Incorrect device settings or hardware faults: If GNSS receiver or software settings are incorrect, RTK processing will not be performed properly. For example, if the rover is not set to RTK mode or the base station coordinates are misconfigured, a Fix will not be obtained. Also suspect hardware issues such as broken antenna cables or poor connections that weaken the signal.

• Problems in measurement procedures: Operational procedures matter. For example, if you start moving while the solution is still Float right after starting positioning, you may not transition to Fix. Not allowing sufficient stationary time, or continuing measurement after Fix is lost without taking action, can result in collecting data without Fix.

Countermeasures when RTK won't Fix

If any of the above causes ring true, the following countermeasures can increase the chance of obtaining a Fix solution.

• Improve satellite visibility and geometry: Choose an environment and time when as many satellites as possible are visible. It is recommended to check satellite geometry in advance with a GNSS planner and perform positioning during times with many satellites and good DOP values. If possible, use multi-GNSS-capable equipment that supports not only GPS but also GLONASS, Galileo, and QZSS (Michibiki) to increase the number of usable satellites and improve stability. Also avoid setting the elevation mask too high in receiver settings (an elevation mask around 15° is a good balance).

• Avoid obstructions and mitigate multipath: Choose measurement spots with as much open sky as possible and ensure a clear view of the sky. Simply moving away from buildings, trees, or large vehicles that obstruct the view can increase the number of visible satellites and make Fix easier. Placing a metal ground plane under the antenna to reduce reflections from the ground or mounting the antenna higher to reduce the effect of surrounding reflections are effective measures. Some high-quality GNSS antennas and receivers have multipath mitigation features, but fundamentally the key is to create an environment that avoids reflections. If multipath is severe, moving the site by just a few meters can sometimes improve the situation.

• Keep baseline length short: If you can install your own base station, place it as close as possible to the survey area. If using a network RTK service, check whether the base station providing the corrections is too far away. Switch to a nearer reference station or a VRS (virtual reference station) service if available to effectively shorten the baseline length. A shorter baseline reduces differential errors such as ionospheric effects, shortening the time to Fix and improving stability.

• Check correction data reception: Monitor whether correction data such as via NTRIP is being received correctly. If using a mobile connection, place the device in an area with good reception and check for disconnections or delays. Confirm via the receiver or app RTK status screen that the “Age of Diff (age of differential data)” and the number of received messages indicate corrections are arriving in real time. If the correction data has a lag of tens of seconds or more, it is difficult to maintain a Fix, so aim to receive corrections as close to real-time as possible. If no data is coming, reconfigure the connection or try restarting the mobile router. Use the correction format appropriate for your receiver type (e.g., MSM4 for single-frequency receivers, MSM7 for multi-frequency receivers). For private base stations, recheck that the configured base station coordinates are correct and update them to precise known coordinates if necessary.

• Avoid radio interference: During positioning, keep away from strong transmitters and other RF sources. Avoid places directly under high-voltage transmission lines, near large radars, or near radio towers where GNSS signals are likely to be noisy. If you must work in such environments, use high-performance antennas, noise filters, and keep distance from other devices to minimize impact. Also turn off internal Bluetooth or other wireless modules in the receiver if they are not in use to avoid emitting unnecessary radio signals.

• Review and reset device settings: Recheck RTK configuration parameters. Verify the rover is in the correct RTK mode, base station information (coordinates and mount point) is accurate, and unused radios are turned off. Performing a reset, such as switching back to single positioning mode and then back to RTK, or restarting the receiver or app, can be effective. Check antenna and cable connections for looseness or corrosion and reseat them if necessary.

• Enforce correct measurement procedures: In the field, do not rush—get into the habit of starting measurements only after the Fix has stabilized. After powering on and starting positioning, remain stationary for several tens of seconds and wait for the first Fix. If you start moving before a Fix is achieved, stop and wait for the receiver to re-establish Fix. If Fix breaks to Float while surveying a moving object, stop at important points and wait to regain Fix before recording positions. If you cannot obtain a Fix, restarting positioning (receiver or correction data) can be effective. If that still fails, try moving to a location with a clearer sky view—sometimes Fix is achieved almost miraculously just by relocating. Always be conscious of whether you are recording in Fix, and avoid collecting data when quality cannot be guaranteed.

Simple surveying with LRTK

Even with the above countermeasures, operating RTK stably in the field requires experience and know-how. For those attempting high-precision positioning for the first time, equipment settings and environmental adjustments can be a high hurdle. A solution called LRTK can help beginners achieve high-precision surveying easily.

The LRTK series are small RTK-GNSS receivers that attach to a smartphone and are designed to provide centimeter-level positioning without worrying about complex settings. Compared to conventional surveying GNSS equipment, they are compact and light enough to fit in a pocket, reducing the burden of carrying them to the field. With an intuitive dedicated smartphone app, you can set corrections and start positioning with a few taps after powering on. They are easy to use even without deep GNSS knowledge, making them suitable for surveying beginners.

Despite their simplicity, the positioning accuracy is very high and can stably achieve a Fix solution. Multi-GNSS support allows reliable satellite tracking even in urban or mountainous areas, and some models that support Japan's Quasi-Zenith Satellite System (CLAS) can maintain high accuracy even outside mobile network coverage. For example, if an LRTK device is kept stationary for a certain period and the data averaged, coordinates that would deviate by several meters with standalone positioning can be reduced to within a few centimeters. Without cumbersome manual adjustments or specialist tuning, LRTK enables you to start simple surveying immediately in the field. Furthermore, using LRTK allows on-site personnel to quickly measure and share data for tasks that used to be left to specialized surveying teams—such as setting batter boards or measuring as-built dimensions—improving efficiency and reducing labor.

Making high-precision location information easy for anyone to handle is the concept behind LRTK. Those troubled by causes that prevent RTK from Fixing can often solve issues smartly by leveraging these modern devices.

FAQ

Q. How long does it usually take for RTK to achieve a Fix? A. Under good conditions, it often takes from several tens of seconds up to about 1 minute after starting reception to obtain a Fix. With initial setup complete and no obstructions, a Fix is obtained relatively quickly after satellites are acquired. However, if satellite geometry is poor or radio conditions are bad, it may take several minutes or you may not achieve a Fix at all. If Fix is not obtained for a long time, review the environment and settings.

Q. Can positioning results be used while still in a Float solution? A. Float solutions have lower positional accuracy and can include errors of tens of centimeters to, in some cases, over 1 m (3.3 ft). They are basically insufficient for surveying or precision positioning. If coarse location information is acceptable for your purpose, Float may be usable, but for tasks requiring accuracy—such as dimensional control or boundary measurement—always obtain a Fix before using the data.

Q. Can a single-frequency GNSS receiver achieve a Fix? A. A single-frequency receiver (L1 only) can achieve a Fix, but compared to multi-frequency receivers it often takes longer to initialize and is more prone to instability due to ionospheric error effects. If possible, use a multi-frequency receiver; if using a single-frequency receiver, measure in open-sky environments and allow extra time. When using only a single-frequency receiver, operate more cautiously by selecting environments and times with fewer error factors.

Q. Can RTK be used at sites far from the reference station? A. The farther you are from the reference station, the more difficult it is to maintain RTK accuracy. It is generally desirable to be within about 10 km (6.2 miles); beyond that, Fix acquisition tends to be slower and less stable. When using RTK over long distances, obtain nearby reference station data from public CORS or commercial VRS services where possible. If you must operate tens of kilometers away, be aware that accuracy will decrease.

Q. Does bad weather (rain or snow) affect RTK positioning? A. RTK positioning is generally less affected by weather, and rain or light snow does not greatly affect accuracy. However, heavy rain or snow that wets or covers the antenna can reduce signal strength and make Fix more difficult. Extreme conditions such as thunderstorms accompanied by lightning can temporarily degrade reception. Considering safety, it is prudent to refrain from surveying in very severe weather.

Q. Can RTK be used indoors or inside tunnels? A. GNSS signals do not reach inside buildings or underground, so RTK positioning generally cannot be performed indoors or in tunnels. In environments where roofs or walls completely block satellite visibility, it is difficult to even acquire satellites, let alone obtain a Fix. If high-precision indoor positioning is necessary, consider alternatives such as total stations or local positioning systems instead of GNSS.

Q. Can a Fix be maintained while surveying on the move? A. If movement is slow and satellite visibility is maintained, continuous positioning with a maintained Fix is possible. RTK is used for high-precision tracking on drones and vehicles in practice. However, sudden attitude changes or high-speed movement that cause temporary satellite loss can break Fix and revert to Float. For moving surveys, consider stopping to regain Fix at necessary points or complementing GNSS data with an IMU (inertial measurement unit) as needed.