How to Check Whether You Are Receiving RTK Corrections

RTK (Real-Time Kinematic) surveying is a groundbreaking technique that enables centimeter-level (cm level accuracy (half-inch accuracy)) high-precision positioning in real time using satellite positioning. However, to achieve high precision with RTK, it is essential to continuously and actively receive error correction information (RTK correction data) from a reference station in real time. If this correction information is not arriving properly, you will never obtain the fixed solution known as "FIX." If RTK remains in a “float” state or degrades to standalone positioning accuracy, it is likely that the error correction data are not being correctly transmitted.

This article explains how to check whether you are receiving RTK correction data. After summarizing the correction information and reception methods that are central to RTK operation, it explains how to verify evidence that your GNSS is correctly receiving correction information. It also covers possible causes and countermeasures when RTK corrections do not arrive, so you can master the key points for reliably performing high-precision RTK surveying. At the end of the article we also introduce a new simplified surveying solution, LRTK.

Table of Contents

• What is RTK?

• Network RTK

• What is CLAS?

• How to check reception of RTK correction information

• Causes and countermeasures when RTK corrections cannot be received

• Recommendations for simplified surveying with LRTK

• FAQ

What is RTK?

RTK refers to a positioning method in which a reference station (a GNSS receiver with a precisely known position) and a rover (the GNSS used for RTK measurements at the survey point) simultaneously receive signals from multiple satellites and eliminate errors arising from carrier-phase and timing differences in succession. As a calculation method it is a type of relative positioning that uses the carrier-phase data of multiple GNSS satellites and performs error computations between the reference station and the rover generated every second. This allows position errors that were roughly 5–10 m (16.4–32.8 ft) when using standalone positioning to be drastically reduced to a few cm (a few in).

In RTK surveying, it is important that the rover can receive and integrate the error correction information ("correction data") actually sent from the reference station to the rover in real time. If communication is intermittent, corrections stop and the rover will revert from centimeter-level accuracy to levels comparable to standalone positioning or DGPS rather than maintaining the few-centimeter accuracy based on known positions. RTK has two solution states: float and fixed (FIX). The fixed solution is the high-precision solution achieved once corrections are fully integrated. If the system stays in a float solution, errors on the order of tens of cm (tens of in) can remain, which is often unacceptable in practice; therefore, obtaining the FIX solution as quickly as possible is key to RTK operation.

Historically (and still commonly), users would set up their own reference-station GNSS and use radio communications on site to send corrections in a “local reference station” setup, but increasingly alternatives such as network RTK that leverage reference-station networks and CLAS, the free high-precision augmentation service provided by Japan’s Quasi-Zenith Satellite System (QZSS), are becoming available. The following explains these representative RTK correction services: network RTK and CLAS.

Network RTK

Network RTK refers to obtaining RTK correction information over the Internet by using reference-station data from control networks operated by organizations such as the Geospatial Information Authority of Japan (GSI) or private companies. For example, services based on GSI’s nationwide GNSS reference network (GEONET) generate a virtual reference station (VRS) near the user and distribute correction data in that configuration. Users equip their rover with a mobile communication modem or SIM router and connect to the server with an Ntrip client to obtain correction data.

Using network RTK eliminates the need to install your own reference station and largely removes accuracy degradation due to distance from a reference station. Note that paid services typically charge annual or monthly fees, and service is unavailable in areas without cellular coverage, but where cellular connectivity is reliable, network RTK is a convenient way to obtain stable FIX solutions. To use it you must register with a specific RTK correction service, obtain Ntrip server information (caster name and ID/password), and enter those settings on the receiver’s configuration screen. Compared with local radio communication using VHF or UHF, network RTK also has the advantage of covering a much larger area.

What is CLAS?

CLAS is the centimeter-level (cm level accuracy (half-inch accuracy)) positioning augmentation service provided by Japan’s QZSS (Michibiki). Standalone GNSS positioning typically yields errors of about 5–10 m (16.4–32.8 ft), but receiving CLAS correction information can improve accuracy to a few centimeters (a few in). A major feature is that it achieves high precision without the traditional need to install a local reference station or use a communication line. CLAS signals are broadcast directly from the Michibiki satellites on the L6 band and can be received nationwide (and in mountainous or offshore locations provided sky visibility is available). CLAS is free of charge, and anyone with a CLAS-compatible GNSS receiver can immediately begin centimeter-level positioning.

CLAS employs a positioning method called PPP-RTK. It aggregates satellite orbit and clock error information observed at GSI’s reference network and local error components that vary with location due to the ionosphere and troposphere, and distributes these corrections via QZSS L6 signals so users can apply corrections locally. In simplified terms, global error components integrated from the nation’s established reference points (e.g., satellite orbit and clock errors) and local error components (ionospheric and tropospheric errors) are distributed concurrently; the receiver combines them to perform continuous real-time correction. In this way, users can achieve few-centimeter accuracy with only a single receiver, without installing a local reference station or obtaining corrections over the Internet.

Using CLAS brings many advantages. Compared with standalone positioning, time to solution is fast and consistent accuracy can be maintained. CLAS is not limited by the radio range of local reference stations, and there are no service fees. However, you need a CLAS-capable GNSS receiver. Recently, compact RTK devices that fully support CLAS and smartphone app integration have appeared. Using the LRTK series equipped with CLAS sensors, for example, makes it easy to perform RTK surveying even at sites outside cellular coverage.

GSI indicates that CLAS horizontal static positioning accuracy is within about 6 cm (about 2.4 in) with 95% probability (vertical within about 12 cm (about 4.7 in)). Even during kinematic positioning the horizontal error remains around 10 cm (around 3.9 in), demonstrating accuracy far superior to traditional meter-level GNSS positioning. That said, in some cases CLAS may produce slightly larger errors than local-reference-station RTK (e.g., where short-baseline RTK would achieve 2–3 cm, CLAS may be around 5–6 cm). Nevertheless, for typical surveying and construction management tasks this level is generally acceptable.

How to check reception of RTK correction information

When operating RTK, make sure your rover is properly receiving and processing correction information. Below are the main checkpoints to determine whether RTK correction data are being received.

• Reception indicator check: Some GNSS receivers and software provide icons that indicate reception status of RTK correction information. For example, in an Ntrip client’s settings screen a connection indicator lighting green typically means data are being received normally. If your GNSS receiver or connection software has such a reception indicator, check it regularly.

• Positioning mode check: Check the positioning mode output by the GNSS receiver. If corrections are being received properly, the receiver will switch from standalone positioning to RTK mode. Survey controllers and configuration software may display mode names such as “FIX” or “FLOAT.” If “FIX” is displayed, correction signals are being received and an integer solution is resolved—the highest-precision state. “FLOAT” means that while corrections are arriving, not all ambiguities have been resolved yet (errors on the order of tens of cm). If the display remains “Standalone” or “DGPS” for a long time, corrections are likely not being applied for some reason.

• Correction data age check: Many high-precision GNSS receivers provide an “Age” value indicating how old the received RTK correction data are. If the Age is shown as a few seconds, corrections are being received and used. If Age exceeds 10 seconds or shows zero, correction communication may have stopped.

• Reference station information check: Some RTK receivers or software list the ID and distance of the connected reference station. For example, when using a VRS service, a virtual reference-station distance such as 5 km may be displayed. The presence of these figures is proof that reference-station data are being received from the server. Without transmitted data such values will not be displayed.

• Coordinate stability check: When RTK corrections are applied correctly, if the rover is held stationary at one point on the ground and observations are taken, the reported coordinates will scatter only within a few cm (a few in). Reflection-rich environments or immediately after FIX acquisition may degrade quality slightly, but you should not see drift by several meters (several ft) as in the absence of corrections. Stopping at the same position for a while and observing how much the processed position moves is one way to confirm that corrections have not been lost.

• CLAS reception status check: If you are using CLAS for RTK surveying, check CLAS-specific status indicators. For example, CLAS-capable GNSS receivers may display states such as “PPP-RTK FIX,” indicating CLAS signals are being received and corrections applied. On L6-capable devices you can also check the number of QZSS satellites being tracked and the C/N0 values of those signals to verify correct L6 reception.

Causes and countermeasures when RTK corrections cannot be received

If you have completed the checks above but still do not receive RTK correction information, the following causes are possible. Below are recommended countermeasures for each.

• Radio communication out of range: For standalone RTK using radio, recheck that the reference and rover radio settings match exactly. If frequency, channel, or ID differ between sender and receiver, communication will fail. On large sites confirm you are not exceeding the practical communication distance of low-power radios (on the order of several km). If you are outside radio range, corrections will not arrive. Line-of-sight obstructions or environments such as tunnels that block radio waves also cause communication dropouts. Countermeasures include repositioning to secure observation lines, mounting the reference-station antenna higher to extend range, and using repeaters or relays as needed to enlarge the radio coverage area.

• Cellular network out of service: For network RTK using SIM cards or smartphones, check cellular reception at the site first. Verify whether nearby cellphones can connect and whether data speeds are sufficient. If reception is weak, connecting a high-gain mobile router or Wi‑Fi router with an external antenna can improve sensitivity. Having multiple carrier SIMs available allows switching to the stronger network when reliability of a single SIM is a concern.

• Correction service or configuration issues: Problems on the RTK service side or misconfiguration can also prevent reception. For example, the Ntrip server itself may be down, or incorrect ID/password may prevent connection. Selecting the wrong mount point (virtual reference station) can result in data in a format the receiver cannot process. Prepare alternative mount points or interfaces to try if necessary. Verify that the reference station is outputting RTCM messages and that the receiver is configured to accept those message types; reviewing correction formats and reception settings often resolves issues.

• GNSS equipment misconfiguration: A basic but common error is running the reference station GNSS in rover mode or leaving the rover device in fixed/base mode, preventing correct application of corrections. Also be careful not to select the wrong geodetic datum or coordinate system. Typically both RTK units should be set to the same datum; if coordinate values are abnormally offset, recheck the reference station’s coordinate system.

• Hardware failure or power loss: Faulty GNSS antennas, damaged cables, or drained batteries will stop correction reception. If a cable is broken, the satellite signal itself may not be received and RTK will not achieve FIX. Before heading to the field, verify all equipment including power is functioning. For long RTK sessions, ensure spare batteries for both reference and rover. If corrections cannot be received on-site, consider not insisting on RTK and instead collect data for later PPK processing.

• Insufficient satellite reception environment: In theory RTK can resolve a FIX with five or more satellites, but if the satellite geometry is poor or data quality is low, a FIX may be hard even with five satellites in view. Perform observations in places with clear sky, use multiple GNSS constellations such as GPS, GLONASS, and QZSS to ensure enough satellites are available, which improves FIX acquisition rates. If RTK is unstable due to environmental factors, consider changing the time of day or measurement location.

Recommendations for simplified surveying with LRTK

So far we have explained how to check reception of RTK correction information and the possible causes and countermeasures when reception fails. Successfully performing RTK surveying requires many checks of the surrounding environment, communications, and device settings, and calls for considerable knowledge and experience. One promising solution that addresses these challenges and makes centimeter accuracy accessible to anyone is LRTK.

LRTK is a new surveying system designed to make high-precision positioning easy using smartphones and dedicated compact devices. By combining multiple satellite positioning technologies and cloud services, it removes many of the complexities that traditionally accompany RTK operations. For example, without worrying about reference-station installation, communication links, or coordinate system adjustments, LRTK can automatically achieve millimeter-level positioning simply by setting the device on site. In actual operation LRTK leverages QZSS augmentation signals, enabling stable positioning even in mountainous areas without cellular coverage.

Some of the benefits of using LRTK:

• Ease of use: Intuitive smartphone app-centric operation means users without specialized GNSS expertise can operate it. No complicated configuration or on-site adjustments are required; a short training period is sufficient.

• High accuracy: By combining observations from multiple points and advanced cloud correction techniques, LRTK achieves roughly 1–2 cm (0.4–0.8 in) positioning accuracy horizontally and vertically. Using a dedicated monopod enables stable single-operator measurements, and averaging over dozens of samples can approach sub-millimeter precision.

• Reliability: LRTK substantially reduces risks of communication dropouts and configuration errors common with traditional RTK. Data are automatically saved to the cloud in real time, so measurement logs remain even in the event of device failure.

• Efficiency: The portability and one-touch start of measurements improve surveying productivity compared with conventional workflows. Because post-processing is reduced, you can obtain results on site and move on to the next task.

Introducing LRTK, which uses the latest technologies, can free you from common RTK concerns like “won’t fix” or “insufficient accuracy.” If interested, check LRTK’s detailed information. Free service brochures are currently available, so consider requesting materials.

FAQ

Q: What is the difference between GPS standalone positioning and RTK positioning? A: Standalone GPS (GNSS) positioning typically has position errors of about 5–10 m (16.4–32.8 ft) due to various complex factors. RTK positioning receives error correction data from a reference station and applies those corrections to the rover’s GNSS measurements, canceling errors to achieve centimeter-level accuracy. In other words, standalone GNSS gives “raw” positioning values, while RTK provides “corrected” positioning. However, RTK requires additional procedures such as reference-station setup, communication lines, and registration with RTK services.

Q: Is RTK positioning possible in places without cellular coverage? A: Yes. One option is to use CLAS broadcast by Japan’s QZSS to achieve centimeter-level positioning without network access. Alternatively, in areas without network coverage you can install a local reference station on site and use post-processing methods like PPK. LRTK devices equipped with QZSS CLAS can obtain a FIX solution even outside cellular coverage.

Q: Is there a cost to use RTK correction information? A: Costs vary by the method used. Setting up your own reference station involves no particular service fees, but network RTK services typically charge monthly or annual fees. CLAS is provided free by the government. LRTK combines CLAS and cloud-based RTK correction infrastructure into a comprehensive service; fees depend on the subscription plan, but users generally do not need to be concerned about usage fees during operation.

Q: Does using multi-GNSS or dual-frequency receivers improve RTK accuracy? A: Yes, significantly. Receivers that support multiple constellations can see many more satellites, making it easier to secure the required satellites even in poor sky-view conditions. Dual-frequency receivers (e.g., L1/L2) greatly improve ionospheric error correction and permit faster ambiguity resolution than single-frequency units. The result is shorter time to initial FIX and much better post-FIX maintenance. For stable high accuracy, using multi-GNSS and multi-frequency receivers where possible is advantageous.

Q: What is LRTK? A: LRTK is a new high-precision positioning service that replaces conventional RTK workflows. Combining a smartphone with a dedicated receiver and a cloud-based correction platform, LRTK lets anyone perform centimeter-level positioning without specialized procedures. There is no need for tedious reference-station setup or coordinate transformations; go to the site with the device, press a button, and surveying is complete. Communication and configuration troubles are minimized, and data are automatically saved to the cloud for safe, reliable results. For details, please refer to LRTK’s official information.