How Accurate Is RTK? Real-World Conditions, Limits & What to Expect

Table of Contents

• What is RTK?

• How accurate is RTK?

• Conditions for achieving centimeter accuracy

• Limits and cautions of RTK positioning accuracy

• Simple surveying with LRTK

• Frequently asked questions (FAQ)

In recent years, there has been a growing need for high-precision positioning at the centimeter level in fields such as surveying and construction. However, ordinary standalone positioning (positioning with a single GNSS receiver) leaves position errors of several meters to about 10 m (33 ft) because satellite and radio error sources are not corrected. In fact, it is common for smartphone GPS to have horizontal position errors of about 3–10 m (9.8–32.8 ft), which is insufficient for construction management or control-point surveying that require high accuracy.

This is where RTK (Real Time Kinematic) positioning comes in. RTK uses two receivers simultaneously—a base station (a receiver installed at a known point) and a rover (the receiver to be positioned)—and the base station sends measured error information to the rover for correction, enabling high-precision real-time positioning that cannot be achieved with standalone positioning. Simply put, by observing simultaneously with two receivers instead of one, common errors can be canceled out, greatly reducing satellite positioning errors. With RTK positioning, it is possible to achieve “centimeter-class accuracy,” keeping positional errors within a few centimeters.

That said, many people may wonder, “Can it really achieve several-centimeter accuracy?” or “How reliable is it under different conditions?” In this article, we explain in detail—with the latest knowledge—how accurate RTK positioning actually is, the conditions required to achieve centimeter accuracy, and its limits and cautions.

What is RTK?

RTK stands for Real Time Kinematic, a high-precision positioning technique that corrects errors by simultaneous observation at two locations. In normal GPS/GNSS standalone positioning, errors accumulate due to satellite orbit and clock errors, signal delays in the atmosphere, and radio reflections (multipath) from terrain and buildings, causing meter-level position offsets. In contrast, RTK positioning receives the same satellite signals simultaneously at a base station (a receiver with known coordinates) and a rover (the receiver to be positioned), and the base station sends error correction information to the rover in real time. Because the rover applies these corrections in its calculations, common error sources are canceled out and positioning accuracy improves dramatically.

RTK positioning also uses GNSS carrier phase (the phase of the carrier wave) to achieve centimeter-order accuracy. By resolving the carrier wavelength (about 20 cm (7.9 in) or less) in integer-cycle units—known as integer ambiguity resolution—millisecond-level measurement errors can be reduced and highly accurate relative positions can be computed. However, resolving integer ambiguities requires multi-frequency observations and high-quality data, and the calculations are performed by advanced algorithms. RTK’s distinguishing feature is that these techniques make real-time centimeter-class positioning possible.

How accurate is RTK?

So, how accurate is RTK positioning in practice? In short, under good conditions, RTK-GNSS typically achieves horizontal errors of about 1–2 cm (0.4–0.8 in) and vertical errors of about 2–3 cm (0.8–1.2 in). “Centimeter-class” generally refers to such errors within a few centimeters, which is orders of magnitude more precise than conventional GPS standalone positioning (meter-level errors).

Official standards give examples: for RTK systems using Japan’s Continuously Operating Reference Stations, a guideline is “horizontal error: 1 cm (0.4 in) + 2 ppm × baseline length; vertical error: 2 cm (0.8 in) + 2 ppm × baseline length.” This means that the error slightly increases as the distance (baseline length) between the base and rover grows. Concretely, with a baseline of about 10 km (6.2 mi) the horizontal error guideline is about 3 cm (1.2 in), and at 20 km (12.4 mi) it is about 5 cm (2.0 in). Recently, GNSS receivers have improved, and some manufacturers specify even tighter figures such as “horizontal: 8 mm (0.31 in) + 1 ppm × D,” so in practice, accuracies of 2–3 cm are often reported even at 10 km (6.2 mi).

In practical use, if the base station is within a few kilometers and satellites are well visible, RTK almost always positions with errors around 1–3 cm (0.4–1.2 in). For example, in tests using multi-GNSS RTK receivers in open areas, the mean horizontal error was about 2 cm (0.8 in) and the elevation error about 3.5 cm (1.4 in), with maximum offsets contained within about 5–7 cm (2.0–2.8 in). In urban tests surrounded by high-rise buildings, mean errors were around 5 cm (2.0 in), but occasional errors exceeding 10 cm (3.9 in) were observed due to signal reflection and blockage. Thus, while RTK accuracy varies with environment, under good conditions it delivers a few centimeters and under poor conditions it generally remains within tens of centimeters.

Also note that RTK solutions come in two types. One is the fixed solution (Fix), where integer ambiguity has been correctly resolved; when fixed, RTK positioning errors are indeed within a few centimeters. The other is the float solution (Float), where integer ambiguities are not fully resolved and are computed as floating values. Float solutions are less accurate than fixed ones, and errors can be on the order of tens of centimeters to about 1 m (3.3 ft). In actual surveying, to maximize the benefits of RTK, check the rover software or receiver display and record measurements only after a fixed solution (FIX) has been obtained.

Conditions for achieving centimeter accuracy

To reliably obtain centimeter accuracy with RTK, several conditions and points should be met. The main conditions are listed below.

• Good satellite reception environment: It is essential to operate in an open sky area. If overhead visibility is obstructed, the number of usable satellites decreases, causing reduced accuracy and solution instability. In building canyons or forests, satellite signals are easily blocked or subject to multipath, so observe in as unobstructed an environment as possible. Also, using a modern multi-GNSS receiver that can receive not only GPS but also GLONASS, Galileo, and QZSS (Michibiki) increases the number of visible satellites and helps maintain accuracy.

• Keep the base station close: The closer the base station (the source of corrections) is to the rover, the more similar are their common error sources and the higher the accuracy. Generally, centimeter accuracy is easier to maintain within a few kilometers, and errors tend to grow gradually beyond 10 km (6.2 mi). If you can deploy your own portable base station, placing it near the work area will improve accuracy. If you cannot set up a base, you can use national Continuously Operating Reference Stations or network RTK correction services provided by carriers (e.g., NTT DOCOMO’s ichimill). Using network services such as VRS and real-time correction networks allows centimeter accuracy over wide areas even with a single rover.

• High-performance GNSS equipment and settings: RTK requires a high-precision GNSS receiver and antenna that support dual-frequency or better. Multi-frequency receivers (L1/L2/L5, etc.) correct ionospheric delays and resolve integer ambiguities faster and more stably than single-frequency receivers, resulting in much better accuracy. Use a high-sensitivity, low-multipath survey antenna and secure it firmly. Placing a simple ground plane metal plate under the antenna can reduce reflections from the ground or nearby structures. On the receiver side, enable multi-GNSS, set an appropriate mask angle (minimum satellite elevation), and select the appropriate rover mode (static or kinematic); these tunings also contribute to improved accuracy.

• Stable communications and data updates: The communication link that delivers correction data from the base to the rover is also important. If radio or internet connections are unstable and corrections are lost, the RTK solution can revert to float or degrade. Use dedicated radio modems or cellular networks (4G/5G) to ensure low-latency, stable communication. A higher correction data update rate (e.g., 1 Hz or 5 Hz) also helps maintain accuracy, especially during kinematic surveys.

• Initialization and observation time: Obtaining a fixed solution in RTK requires a certain initialization time after starting positioning. Usually, fixed solution is reached within a few seconds to several tens of seconds, but in unfavorable satellite geometry it can take several minutes or more. To ensure centimeter accuracy, allow enough observation time until a fixed solution is obtained. In kinematic surveys, data immediately after starting may be float, so be careful. Even in static surveys, averaging coordinates over several seconds to several tens of seconds smooths transient errors and stabilizes accuracy.

By meeting the above conditions, you can maximize RTK performance and determine positions almost always at centimeter-class accuracy.

Limits and cautions of RTK positioning accuracy

RTK can provide very high-precision positioning, but it is not perfect and has several limits and cautions. Before taking centimeter accuracy at face value, understand the following points.

• Accuracy varies with environment: Even with RTK, poor environments cause degraded accuracy or loss of positioning. In urban canyons or forests, satellite blockage and multipath make it difficult to obtain fixed solutions, and errors can temporarily expand to tens of centimeters. In experiments, environments surrounded by high-rise buildings showed horizontal errors up to about 12 cm (4.7 in) and vertical errors around 18 cm (7.1 in). In open terrain, errors are almost always within a few centimeters. Keep in mind that RTK does not always guarantee absolute centimeter accuracy under all conditions.

• Vertical accuracy is worse than horizontal: Due to GNSS characteristics, height accuracy is generally lower than horizontal accuracy. Typically, RTK vertical errors can be about 1.5–2 times the horizontal errors, meaning vertical errors may range from several centimeters to tens of centimeters. For surveys where elevation accuracy is critical, it is recommended to verify with optical leveling in addition to RTK. However, for most civil engineering needs that require height accuracy of a few centimeters, RTK is usually sufficient.

• Base station accuracy and geodetic datum: RTK delivers high relative accuracy with respect to the base station. In other words, the rover’s position relative to the base station can be known to within a few centimeters, but if the base station’s coordinates are not precisely known, the absolute position in an external datum will be offset accordingly. For official surveying tied to national datums, ensure the base station’s known coordinates are accurately measured and set. Conversely, if you set up a base station at an arbitrary point, you can still perform relative centimeter-level surveys within the site, but converting results to a national coordinate system may require post-processing translations.

• Initialization errors and false fixes: There is a non-zero risk of incorrect integer solutions (false fixes) in RTK computations. Under strong multipath or ionospheric disturbances, an incorrect fixed solution may appear temporarily, producing coordinates with biases of tens of centimeters or more. Modern receivers and software include quality indicators (RTK ratio, covariance, etc.) to detect such errors, but on site it is prudent to measure important points multiple times or cross-check from different base points.

• Environments where GNSS cannot be used: As with GNSS in general, RTK cannot be used where satellite signals cannot reach—e.g., tunnels, indoors, or underground. Also, during times of very poor satellite geometry (high PDOP), fixed solutions may be temporarily unobtainable. Therefore, choose survey times with favorable satellite geometry (low PDOP) when possible.

With these points in mind, you can use RTK without overtrusting centimeter accuracy by applying proper operation and checks. Conversely, if used correctly with an understanding of conditions, RTK provides reliable accuracy for most practical applications.

Simple surveying with LRTK

Although RTK is highly useful, traditionally it required expensive dedicated equipment and expertise, posing a barrier for many engineers. Recently, a more user-friendly RTK solution called LRTK has emerged. LRTK is a compact RTK-GNSS system provided by Refixia (Refixia Co., Ltd.), designed to work with smartphones so anyone can easily perform centimeter-class surveying.

For example, a product called LRTK Phone attaches a dedicated antenna to a smartphone for standalone positioning and uses LRTK Cloud correction services to achieve cm-class positioning without complex equipment setup. With the dedicated app’s one-tap averaging function, averaging of 60 measurements can record a point position with high accuracy of about 8 mm (0.31 in). Tasks that used to require two surveyors with a total station can be done by a single person using a smartphone and pole with LRTK.

The accuracy of the LRTK system has been confirmed to be comparable to first-class GNSS survey instruments used by the Geospatial Information Authority of Japan. In tests, the coordinate difference between LRTK receivers and class-1 instruments was within 5 mm (0.20 in), showing results comparable to professional equipment. Because LRTK leverages consumer smartphones, it greatly reduces cost, making RTK adoption easier for companies and municipalities trying it for the first time. LRTK also supports network RTK and the quasi-zenith satellite QZSS’s centimeter-class augmentation service (CLAS), enabling immediate high-precision positioning on site without a dedicated base station.

Using LRTK for simple surveying can greatly improve efficiency and reduce labor. For example, in as-built checks at construction sites, workers can walk with a pole-mounted LRTK receiver and have points automatically recorded to the cloud. Results can be checked in real time and additional measurements taken as needed. The interface is intuitive so staff without specialized knowledge can operate it safely. Free trials and comprehensive support systems are available, making it much easier to introduce than traditional surveying methods. If you are considering bringing high-precision positioning into your fieldwork, consider trying simple surveying with LRTK.

Frequently asked questions (FAQ)

Q: Can RTK positioning really achieve centimeter accuracy? A: Yes. Under appropriate conditions, RTK can achieve accuracy within a few centimeters. In experiments, RTK positioning in open areas typically had mean errors of about 2–3 cm (0.8–1.2 in). However, in environments such as high-rise urban areas or forests, temporary deviations of more than 10 cm (3.9 in) can occur, so it cannot be said to be “always absolutely a few centimeters.” With good environment and equipment, RTK can reliably achieve centimeter accuracy.

Q: What is the difference between fixed (Fix) and float (Float) solutions? A: A fixed solution in RTK means the integer cycle ambiguities have been correctly resolved, yielding the highest accuracy (within a few centimeters). A float solution occurs when the integer part is unresolved and calculations use floating values, resulting in lower accuracy; errors may range from tens of centimeters to about 1 m (3.3 ft). When using RTK for surveying, wait until the receiver or software indicates “FIX” (fixed solution) before recording measurements.

Q: When is RTK accuracy hard to achieve? A: RTK accuracy is difficult in environments with poor satellite reception. For example, in narrow building canyons, forests, or mountainous areas where overhead visibility is limited, satellite signals may be blocked or reflected, making it harder to maintain fixed solutions. Accuracy also degrades when corrections from the base station cannot reach the rover (out of communication range or radio blockage) or during ionospheric disturbances such as solar flares. Choose open locations and times when possible, and ensure communication stability to maintain accuracy.

Q: How far from the base station can I position? A: RTK accuracy degrades as distance from the base station increases, but a practical guideline is that centimeter accuracy is maintained up to several tens of kilometers in many cases. Experimentally, errors of about 5 cm (2.0 in) have been observed even at 20 km (12.4 mi), but beyond 30 km (18.6 mi) fixed-solution stability becomes less certain. For wide-area RTK positioning, using network RTK (VRS) based on Continuously Operating Reference Stations effectively makes a nearby base available virtually, enabling centimeter accuracy over areas exceeding 50 km (31.1 mi).

Q: How accurate is height with RTK? A: Height accuracy is generally worse than horizontal. In theory, vertical error is about 1.5–2 times the horizontal error. Practically, where horizontal is ±2 cm (0.8 in), height is often ±3–4 cm (1.2–1.6 in). However, depending on satellite geometry and surroundings, vertical errors can exceed 10 cm (3.9 in). For critical elevation data, treat RTK heights as a guide and confirm with leveling as a secondary check. Still, for most civil engineering uses that require height accuracy of a few centimeters, RTK is usually adequate.

Q: Which is more accurate, RTK or a total station? A: It depends on measurement conditions. In open areas, RTK can achieve centimeter-level accuracy that matches the practical precision of optical total stations. For wide-area positioning, RTK is often more efficient than prism-based total stations. However, for millimeter-level precision or for indoor/underground surveys where satellites are not visible, total stations are superior. Choose the instrument according to the application. For typical control-point surveys and as-built checks, RTK now often provides sufficient accuracy with higher efficiency, so its use has become more widespread.