Factors That Hurt RTK Accuracy: Multipath, Satellite Geometry & Field Fixes

Table of Contents

• What is RTK? Basics of Real-Time Kinematic Positioning

• Effects of Multipath and Countermeasures

• Effects of Satellite Count and Geometry

• Effects of Field Environment

• Other Factors Affecting RTK Accuracy

• Simple Surveying with LRTK

• FAQ

What is RTK? Basics of Real-Time Kinematic Positioning

RTK positioning (Real-Time Kinematic) is a positioning technology that uses signals from GNSS satellites to obtain centimeter-level high-precision positions in real time on site. Conventional GPS (standalone positioning) can have errors of several meters, but RTK can reduce those errors to a few centimeters by applying correction data from a reference station (base station) to a rover (moving receiver). Because RTK can provide such high-precision position information immediately, it has been rapidly adopted across fields such as surveying, construction, and drone surveying.

The goal in RTK is to obtain the most accurate solution known as a “Fix” solution. A Fix solution is achieved by resolving carrier phase ambiguities as integer multiples of the wavelength, which keeps horizontal and vertical errors to within a few centimeters or less. Conversely, when conditions are insufficient to resolve integer biases, the result is a “Float” solution, with accuracy limited to several tens of centimeters. To realize RTK’s full performance, it is necessary to maintain a stable Fix solution as much as possible. However, in real fields, positioning accuracy can degrade and obtaining a stable Fix can become difficult due to various factors such as multipath (signal reflections), the number and geometry of satellites, and surrounding field conditions.

The next sections explain the three main factors affecting RTK accuracy—multipath, satellites, and field environment—and discuss their impacts on RTK positioning and possible countermeasures.

Effects of Multipath and Countermeasures

Multipath refers to the phenomenon where signals from satellites arrive at the receiver via multiple paths because they are reflected by surrounding buildings, the ground, or other objects. Reflected waves arrive slightly later than direct waves, causing the receiver to interpret the distance as longer than it actually is and introducing positioning errors. In RTK positioning, multipath-induced errors are a major factor that can prevent Fix solutions or degrade accuracy. Multipath is common in environments such as urban areas with high-rise buildings (often called “urban canyons”), near rock faces in mountainous areas, and close to large metal structures, so caution is required.

Basic multipath countermeasures focus on creating an environment that minimizes reflections. Specifically, pay attention to the following points:

• Choose open locations: Select measurement points where the sky is as open as possible and there are no nearby reflection sources such as buildings, rock faces, metal fences, or large vehicles.

• Install the antenna at a height: If measurement must be taken near buildings or obstacles, place the receiving antenna on as high a pole or rooftop as possible to reduce the influence of reflections from the ground and surroundings.

• Use a ground plane: If a metal plate or other ground plane can be attached to the antenna, use it to block reflections from below the antenna, reducing the influence of ground reflections.

• Exclude low-elevation satellites: Set an elevation mask (for example 15°–20°) on the receiver to exclude low-angle satellite signals that are more likely to be reflected by the ground or buildings. This helps filter out noisy signals and maintain positioning accuracy.

• Use high-quality equipment: If possible, use high-performance GNSS antennas and receivers with multipath mitigation features. However, significant improvement can often be achieved through the environmental measures above even without relying solely on equipment.

Thoroughly applying these countermeasures can greatly reduce multipath errors and lead to more stable Fix solution acquisition in RTK.

Effects of Satellite Count and Geometry

One major factor influencing RTK accuracy is the number of satellites available and their geometry. If the satellites used for positioning are biased toward one sector of the sky, the geometric configuration is weak and position uncertainty increases. This condition manifests as a higher DOP value (Dilution of Precision), and higher DOP values correspond to larger positioning errors and more difficulty in stably obtaining a Fix solution. Conversely, when satellites are evenly distributed across the sky, the geometry is strong, DOP values are low, and accuracy improves.

Generally, RTK initialization (resolving integer ambiguities) requires at least five satellites. Although position can be computed with four satellites, having a margin for error correction and reliability is preferable. In practice, being able to track seven to eight or more satellites simultaneously makes it easier to maintain a stable Fix solution. The required number of satellites, however, depends on satellite geometry, signal strength, and the reception environment. Modern GNSS receivers support multi-GNSS—GPS plus GLONASS, Galileo, BeiDou, and regional systems such as Japan’s QZSS (Michibiki)—and using multiple constellations increases the number of available satellites. With more satellites, even if some are blocked, others can compensate, which generally reduces DOP values and improves positioning accuracy and reliability. In environments with limited satellite visibility, such as urban areas, using a multi-GNSS receiver to secure satellite count is especially important.

To optimize satellite geometry, choose the time of day for surveying. By using GNSS planning tools to predict satellite geometry and check satellite elevations and DOP trends in advance, you can schedule work during periods of low DOP for improved accuracy. Also, be careful not to set the elevation mask angle too high in receiver settings; an excessively high mask reduces the number of satellites and weakens geometry. Low-elevation satellites up to about 15° are generally useful, and balancing satellite count and signal quality is key. If satellite visibility is extremely poor at a site, consider revising the surveying plan (wait until satellite geometry improves, observe from a different location), or use a network RTK with multiple base stations to compensate geometry.

Effects of Field Environment

The surrounding environment of the survey site greatly affects RTK accuracy. Basically, the more open the sky, the better the satellite signals can be received, which is favorable for high-precision positioning. Conversely, in urban areas with many tall buildings, within forests where trees are dense, or in mountain valleys, satellite signals can be blocked or attenuated, resulting in insufficient usable satellites and difficulty obtaining a Fix solution or significant accuracy degradation.

For example, in a forest with dense foliage, GNSS signals can be blocked by leaves, causing reduced signal strength and frequent cycle slips (signal loss) that drop the solution to Float. Also, in tunnels or under elevated structures, satellites are mostly not visible, making RTK positioning practically impossible. Because RTK accuracy and availability depend heavily on location, measurements should be taken where visibility is good whenever possible; in areas with many obstructions, change the time of day for measurements or move the antenna away from obstructions.

Additionally, non-GNSS factors at the site can also affect reception. For example, near high-voltage power lines or TV towers, or in environments with many construction radios or Wi‑Fi access points, strong radio noise can interfere with GNSS reception. Keeping distance from such interference sources is another key point for ensuring accuracy on site. In Japan, satellites like QZSS (Michibiki) can supplement signals from near the zenith, but fundamentally, measuring in a location where the sky is visible is the quickest path to stable RTK accuracy.

Other Factors Affecting RTK Accuracy

Besides the above, several other factors affect RTK accuracy and the stability of Fix solutions. Representative ones include:

• Distance to the base station (baseline length): RTK achieves high precision through relative positioning between a base station and a rover, so accuracy decreases as the distance between them becomes too large. Even when both receive signals from the same satellites, larger distance between base and rover increases differential delays from the ionosphere and troposphere, making corrections less effective. Typically, a baseline length within 10 km is desirable; beyond that, initializing a Fix can take longer and errors may expand to several centimeters or more. For wide-area positioning, using network RTK (e.g., VRS) to create a virtual base station nearby reduces the effective baseline length and is an effective approach.

• Atmospheric effects: GNSS signals are affected by the Earth’s atmosphere (ionospheric and tropospheric delays), which influences accuracy. RTK cancels much of these errors by receiving the same satellite signals at the same time, but if atmospheric differences between base and rover are large or solar activity is high, residual errors can degrade positioning accuracy. Modern RTK systems use dual- or triple-frequency receivers to remove ionospheric errors and apply advanced tropospheric models, but extreme weather or ionospheric disturbances can still pose challenges for accuracy maintenance.

• Communication and configuration factors: Because RTK requires real-time corrections, a stable communication link to receive base station corrections is important. Communication delays or interruptions prevent applying corrections and can cause the solution to revert to Float. Human errors such as incorrect base station coordinates or mismatched reference frames also affect output coordinates. To prevent these issues, choose appropriate correction formats and services, continuously monitor communication status, and correctly set known base station coordinates and the coordinate system in use.

Simple Surveying with LRTK

As discussed up to this point, performing stable, high-precision RTK positioning requires attention to device settings and environmental conditions. However, recently solutions have emerged that reduce that burden and make RTK surveying easy for anyone. A representative example is the LRTK series. LRTK is a product consisting of compact high-precision GNSS receivers provided by our company and a smartphone app, enabling centimeter-level positioning on site even without expert knowledge. Its appeal can be summed up in three words: “small and lightweight,” “easy to operate,” and “high accuracy.”

• Small and lightweight: Traditional survey RTK equipment was bulky with batteries and tripods, but LRTK series receivers are compact enough to fit in a pocket. For example, the smartphone-integrated model “LRTK Phone” weighs only about 125 g and has a thickness of about 13 mm (0.51 in), designed to attach to and be carried with a handheld smartphone. It is comfortable to carry on site and serves as a personal surveying tool ready for immediate use.

• Easy operation: LRTK pairs with a dedicated smartphone app and is designed for intuitive RTK operation. Connect the receiver to the smartphone via Bluetooth or Wi‑Fi, and perform correction settings, switch positioning modes, and record data with a single tap in the app. Turn on the power and launch the app to start positioning immediately; photo capture, position data recording, and point cloud scanning can be performed together. Because users do not need to be conscious of complex GNSS settings, non-specialists can handle it on site, greatly lowering the barrier to surveying.

• High accuracy: Despite being small and convenient, positioning accuracy is very high and can stably achieve centimeter-level Fix solutions. Higher-end models such as the “LRTK Pro2” support CLAS correction signals provided by Japan’s QZSS Michibiki, enabling high-precision positioning via satellite corrections even in mountainous areas without cellular coverage. Some models include tilt compensation (tilt sensors) that automatically correct the pole tip position when the pole is tilted, allowing accurate point coordinates to be obtained even when the antenna must be tilted to avoid obstructions, thereby improving site efficiency. Furthermore, by averaging positioning data in the app, single-point accuracy can be stabilized to a few millimeters to about 1 cm (0.4 in).

Centimeter-level positioning that traditionally required expert knowledge and bulky equipment can now be performed easily by anyone using LRTK. New surveying styles using LRTK have been demonstrated in many places, including infrastructure inspections in urban areas with high-rise buildings, surveying in mountainous areas outside cellular coverage, and as-built management at construction sites. For more information, please refer to the LRTK official site and case study pages.

FAQ

Q. What level of positioning accuracy can RTK achieve? A. Under optimal conditions, RTK positioning can achieve about 1–2 cm in horizontal position and about 2–3 cm in height. This assumes a sufficient number of visible satellites, minimal multipath, and stable reception of correction data. Under poor environmental conditions, errors of several centimeters or more may occur, and in some cases a Fix solution may not be obtainable.

Q. What are Fix and Float solutions? A. RTK results come in two types: a Fix solution and a Float solution. A Fix solution is the most accurate, achieved when integer ambiguities in the carrier phase between satellite and receiver are correctly resolved (errors are less than a few centimeters). A Float solution occurs when integer ambiguities cannot be resolved and remain as floating-point values, typically resulting in accuracy on the order of several tens of centimeters. The goal of RTK is to obtain a Fix solution; if only a Float solution is available, some error factors may be affecting the measurement.

Q. How many satellites are required for RTK? A. In general, about five satellites are said to be the minimum to initialize RTK (obtain an integer-fixed solution). Position computation itself is possible with four satellites, but it is safer to have some margin for error correction and reliability. In practice, being able to track seven to eight or more satellites simultaneously makes it easier to maintain a stable Fix solution. The required number depends on satellite geometry, signal quality, and reception conditions.

Q. How far from the base station can RTK be used? A. The shorter the baseline between the base station and rover, the better the accuracy; as a guideline, within 10 km is desirable. At distances of 20 km or more, differential effects of the ionosphere and troposphere can degrade accuracy and make maintaining a Fix more time-consuming. Recently, network RTK (correction data distribution services) can enable positioning tens of kilometers away, but errors tend to be larger. For high precision, it is practical to perform measurements within a range of a few to several tens of kilometers.

Q. Is high-precision RTK possible in urban canyons or forests? A. RTK tends to be unstable in urban areas with poor satellite visibility or within forests, but it can be possible depending on conditions. Use a multi-GNSS receiver to capture as many satellites as possible, plan work during times when satellite geometry is favorable, and improve satellite visibility by placing the antenna in open spots or using an extension pole to rise above the canopy. However, if conditions are extremely poor, maintaining a Fix may be difficult and periodic drops to Float are unavoidable. In some cases you may need to move the measurement point or supplement satellite positioning with other technologies (inertial navigation, post-processing, etc.).

Q. Is there an easy way to start RTK surveying? A. Yes. Recently there are simple RTK systems that can be used without specialist knowledge. One example is the LRTK series, which combines a smartphone with a compact GNSS receiver to enable anyone to perform centimeter-precision surveying easily. As introduced in this article, LRTK greatly reduces on-site setup and positioning work, making it recommended for those trying RTK for the first time.