Explaining RTK GPS Accuracy: What Can You Actually Expect in the Field?

Table of Contents

• What is RTK?

• High accuracy achieved by RTK positioning

• Factors affecting RTK accuracy

• Applications and benefits of RTK

• Simple surveying with LRTK

• FAQ

In recent years, centimeter-level high-precision positioning has been increasingly demanded at construction and civil engineering sites, in surveying, disaster investigations, and infrastructure management. Position information obtained from car navigation systems or smartphone GPS can have errors of several meters, which is insufficient for tasks that require high accuracy. The technology drawing attention for this purpose is known as RTK positioning. Using RTK (Real Time Kinematic), it is possible to measure positions in the field with errors within a few centimeters. This article explains what RTK is, how it works and the principles behind its accuracy improvements, and what accuracy can realistically be expected in the field. It also introduces simple surveying using LRTK, a recent solution that makes RTK technology easily accessible to anyone.

What is RTK?

RTK stands for Real Time Kinematic, a high-precision positioning technique that corrects errors in GNSS satellite positioning, including GPS, in real time. In normal GPS measurement (standalone positioning), signals from satellites are processed by a single receiver. In that case, various error sources—such as satellite orbit and clock errors, signal delays in the ionosphere and troposphere (atmospheric errors), and reflections from buildings or the ground (multipath)—accumulate without correction, causing position errors of several meters. While such errors are often acceptable for everyday use, they are intolerable in construction management or precision surveying.

RTK positioning solves this problem by using relative positioning with two GNSS receivers. One is set up as a base station at a known accurate coordinate, and the other is a mobile unit (rover) used for measurement; both receivers observe the same satellite signals simultaneously. The base station calculates the difference between the position estimated from its received data and its known accurate position, and sends that correction information to the rover in real time via radio or the internet. The rover applies the received corrections to its satellite data to cancel out error sources and compute its own position. By observing two points simultaneously and canceling common errors, RTK achieves highly accurate positioning that standalone positioning cannot.

A key to RTK’s centimeter-level accuracy is the use of GNSS signal carrier phase. Because the carrier wavelength from satellites is relatively short—tens of centimeters—analyzing phase shifts allows distance measurement on the order of millimeters. However, integer-wavelength ambiguities must be resolved; only after successfully resolving these ambiguities does a high-precision solution known as a “fixed solution (Fix)” become available. Once a fixed solution is established, RTK can provide centimeter-level accuracy in real time. RTK requires a communication link between the base and rover, but recently network RTK solutions using mobile data (VRS and similar) have become widespread, allowing users to obtain correction information without providing their own base stations.

High accuracy achieved by RTK positioning

With RTK, positioning errors typically fall within a few centimeters horizontally and a few centimeters vertically. Under ideal conditions, various demonstrations have shown horizontal errors of about 2–3 cm (0.8–1.2 in) and vertical errors of about 3–4 cm (1.2–1.6 in). This is orders of magnitude more accurate than typical standalone GPS positioning (errors on the order of 5–10 m (16.4–32.8 ft)). In other words, positions that could previously only be narrowed down to several meters with conventional GPS can be pinpointed to a few centimeters with RTK. For example, in one experiment using a smartphone-mounted miniature RTK receiver, single measurements were within about 1.2 cm (0.5 in) of error, and averaging the measurements improved accuracy to about 0.8 cm (0.3 in) (8 mm (0.31 in)). Under favorable conditions, sub-1 cm accuracy is thus demonstrably achievable.

That said, obtaining such top-level accuracy requires good conditions. If satellite signals are interrupted or sufficient correction information is not received, RTK accuracy can degrade and temporary errors of tens of centimeters may occur. Vertical (height) errors also tend to be larger than horizontal errors, and in the field height-only errors of several centimeters or more can occur. However, for typical civil engineering surveying and construction management, centimeter-level accuracy in both horizontal and vertical directions is sufficient, and RTK meets that requirement. Compared with optical total station surveying, RTK’s horizontal accuracy in open outdoor environments is comparable, and when combined with the advantage of being able to measure many points in a short time, the value of introducing RTK is very high.

Factors affecting RTK accuracy

Although catalogs and theory advertise centimeter-level accuracy for RTK, obtaining that accuracy reliably in the field requires attention to several points. The main factors are as follows.

• Distance to the base station (baseline length): The longer the distance between the base and the rover, the greater the non-common errors (differences in ionospheric and tropospheric effects, etc.), leading to residual discrepancies that cannot be fully corrected. In general, for standalone RTK it is desirable to keep the baseline length within 10–20 km; beyond that, fixed-solution acquisition becomes unstable and accuracy tends to degrade by several centimeters or more. Note that vertical accuracy deterioration is particularly noticeable over long distances. When surveying a wide area, mitigating accuracy degradation due to long distances can be achieved by placing base stations as close as possible to the survey site or by using network RTK services that leverage multiple reference stations.

• Satellite visibility (measurement environment): RTK requires stable reception of satellite signals from the sky. In environments with tall buildings nearby or heavy tree cover, direct visibility to satellites is obstructed, reducing the number of satellites received and allowing multipath signals to enter, which destabilizes positioning. Choosing a site with a clear view of the sky is a basic requirement for achieving RTK’s high accuracy. Urban canyons and forests are environments in which RTK performs poorly; fixed solutions may not be obtained and accuracy may fall. Select measurement points with as few obstructions as possible.

• Communication environment (reception of correction information): Real-time corrections are essential to RTK, so stable data communication from the base station to the rover is important. If communication to the rover is interrupted, correction information will not arrive and the solution may revert to float (with errors on the order of tens of centimeters). Network RTK commonly uses cellular networks, but in mountainous areas where mobile coverage is lacking, RTK may not function. In such locations, using private short-range radio or UHF radios to connect the base and rover, or utilizing satellite-based correction systems such as Japan’s Quasi-Zenith Satellite System “Michibiki” CLAS (Centimeter Level Augmentation Service), which allows direct reception of correction signals from satellites, can be effective.

Considering the above points, the key to maximizing RTK accuracy is to keep the baseline short, choose a location with a clear view of the sky, and use a stable communication method for corrections. Recent high-performance GNSS receivers support multiple frequencies and multiple satellite constellations (not just GPS but also GLONASS, Galileo, Michibiki, etc.), which improves ionospheric error mitigation and increases the number of satellites tracked, making fixed-solution acquisition easier even under challenging conditions. With proper equipment selection and operational practices, it is possible to maintain centimeter-level positioning reliably in the field.

Applications and benefits of RTK

High-precision RTK positioning is utilized across many fields and uses that benefit from its accuracy. Here are the main application areas and the advantages of adopting RTK.

• Surveying and civil engineering: RTK is effective for topographic and land surveying where many ground features need to be measured across a wide area in a short time. Unlike total stations, it does not require line-of-sight, and a single person can walk with a GNSS rover and record point coordinates sequentially. Since coordinates can be obtained with centimeter-level accuracy in both plan and elevation, the collected point data can be used directly for high-precision plans and terrain models. RTK significantly reduces labor and increases efficiency in surveying, and the ability to verify results in real time is another benefit.

• Construction site layout and control (stakeout and marking): On construction and civil engineering sites, tasks such as stakeout and marking determine the exact positions and elevations of structures according to design plans. Traditionally, skilled technicians worked in pairs to set up batter boards or used surveying instruments to measure angles and distances for marking. With RTK-capable GNSS equipment, a single person can mark specified coordinates on site. A worker carrying a GNSS rover can follow guidance on a navigation app (e.g., “move 5 cm east”) to position themselves accurately without relying on experience. Accurate initial positioning reduces rework and prevents construction errors.

• Infrastructure inspection and maintenance: RTK’s accuracy is valuable for infrastructure maintenance of roads, railways, and bridges. For example, when monitoring road settlement or rail track deformation, repeated RTK observations at the same point allow detection of changes over time with centimeter precision. Also, locating installations on highways or buried utilities becomes easier when high-precision coordinates are pre-measured, improving inspection efficiency.

• Disaster investigation: RTK positioning is used for rapid situational assessment at disaster sites such as landslides or ground subsidence. Quickly surveying devastated terrain to create accurate maps and 3D models, or precisely measuring surface displacement before and after a landslide, is possible with RTK. In the immediate aftermath of a disaster, conventional survey benchmarks may be lost, but network RTK allows remote reception of corrections and immediate positioning in global coordinates, enabling high-precision surveying without local reference points. This speeds up recovery planning and quantitative damage assessment.

• UAV surveying (drone aerial photogrammetry): Increasingly, drones for photogrammetry are equipped with RTK. If the drone’s position during image capture is recorded with centimeter-level accuracy, the ground points visible in those images also gain improved positional accuracy. As a result, high-precision orthophotos and 3D point clouds can be created with fewer ground control points (GCPs), improving the accuracy and efficiency of volume calculations and as-built verification. While traditional aerial surveys required multiple known ground points for image georeferencing, RTK-equipped drones can gather survey-grade positional data during flight, making aerial site measurement more practical.

Thus, RTK’s high-precision positioning is useful across surveying, construction, infrastructure maintenance, and disaster response. Where centimeter-level positioning once required expensive equipment and specialist operators, miniaturization and cost reductions in receivers have made it possible for field technicians and workers to directly operate RTK devices. The spread of RTK is bringing high-precision positioning to more people and transforming field workflows.

Simple surveying with LRTK

As RTK demand has expanded, products that make traditional RTK equipment even easier to use have emerged. A representative example is the small RTK-GNSS system series called LRTK. Traditional RTK setups often required a stationary base station plus a pole-mounted rover, radio units, external batteries, and other cumbersome equipment. Initial costs were also high, posing a barrier for small and medium-sized businesses. LRTK aims to “make RTK available anytime, anywhere, to anyone,” and technological innovations have significantly improved those pain points.

One feature of the LRTK series is its small, lightweight design. For example, the smartphone-integrated device LRTK Phone achieves a pocket-sized form factor with the receiver body weighing only about 125 g and a thickness of 13 mm (0.51 in). Antenna, GNSS receiver, battery, and communication module are integrated in an all-in-one structure, enabling centimeter-level positioning with a single unit. Wireless pairing with a dedicated smartphone app eliminates cumbersome cable connections, greatly simplifying field handling. Users can view positioning results in real time on a smartphone screen, input point names and notes, and share data to the cloud with a single touch. The price is designed to be far more accessible than traditional survey-grade GNSS equipment, positioning LRTK as a field tool for the era of “one device per person.”

LRTK also incorporates cutting-edge GNSS technologies. Its high-performance receivers, compatible with triple-frequency signals, are more resistant to multipath and ionospheric errors and can obtain fixed solutions more stably than older equipment. In addition, LRTK supports Japan’s Michibiki CLAS, enabling continued high-precision positioning from satellite-based correction signals even in mountainous or maritime areas outside mobile coverage. This means that even where network RTK VRS corrections are unavailable, RTK-equivalent accuracy can be maintained. By balancing field mobility and positioning accuracy, LRTK has evolved into a practical RTK terminal for real-world field use.

Although RTK equipment was once thought to be usable only by surveyors with specialized knowledge, LRTK has made positioning tasks far simpler. As RTK-GNSS that site technicians can operate with smartphone-like ease, LRTK’s use cases are expected to expand. LRTK’s democratization of high-precision surveying is bringing previously difficult centimeter-grade positioning into everyday reach. Leveraging such easy surveying tools is expected to accelerate ICT adoption in construction (i-Construction) and DX in the infrastructure sector, contributing significantly to productivity improvement and quality assurance on site. LRTK is heralding the arrival of a new era in which anyone, anywhere can perform centimeter-accurate positioning.

FAQ

Q: What is the difference between RTK positioning and normal GPS positioning? A. Normal GPS (standalone positioning) uses a single receiver to receive satellite signals and compute position, leaving various errors uncorrected and resulting in accuracy on the order of several meters. RTK positioning uses two receivers—a base and a rover—to perform differential corrections, canceling error sources and achieving centimeter-level accuracy. In short, the major difference is that “measuring with two receivers instead of one dramatically improves accuracy.”

Q: Can RTK really achieve 1 centimeter accuracy? A. Under good conditions, yes. Horizontal errors of about 1–2 cm and vertical errors within a few centimeters are realistically achievable with RTK. In open environments where a fixed solution is maintained, measurements with errors under 1 cm have been reported. However, this represents ideal conditions; environments with many surrounding buildings or obstacles can increase errors or prevent fixed solutions. Generally, horizontal accuracy of about 2–3 cm (0.8–1.2 in) is considered very good. To realize RTK’s centimeter accuracy, satellites must be well tracked and correction data must be stably received.

Q: What do I need to start RTK positioning? A. Basically, you need an RTK-capable GNSS receiver and a base station (or a service that provides correction information). Traditionally, users had to install a receiver as a base station and set up radio communication between the base and rover. However, today you can receive correction data without providing your own base by using the Geospatial Information Authority’s reference stations or network RTK services offered by carriers. In that case, a single rover receiver and an internet connection for communication are sufficient to perform RTK. In Japan, satellite-based correction services such as Michibiki’s CLAS also allow centimeter-class positioning without a base station if you have a compatible receiver.

Q: How far from the base station can I be while maintaining RTK accuracy? A. With a standalone base station, a rule of thumb is within 20 km. As baseline length increases, atmospheric errors differ by location and become harder to correct, so fixed-solution acquisition becomes unstable and errors tend to increase when baseline lengths exceed several tens of kilometers. However, using network RTK services can suppress accuracy degradation over wide areas. VRS systems, which create a virtual base station near the user, can provide corrections as if a nearby base existed even when the nearest physical reference station is far away, allowing near-equivalent accuracy in areas tens of kilometers away. Using nationwide CLAS correction signals also enables uniform high-precision positioning across Japan. Nevertheless, being closer to a base station generally yields more stable high accuracy, so when operating standalone RTK, try to place the base station as close to the site as possible.

Q: Can RTK be used in mountainous or out-of-coverage areas? A. There are several ways to use RTK where cellular coverage is not available. One is to use private radio communications; for example, using low-power radio or UHF radio can allow direct communication with a base station over a line-of-sight range of a few km. Another is to use satellite-based correction like CLAS, which provides correction signals from satellites and enables centimeter-class positioning in mountainous areas without internet. In practice, CLAS-capable receivers such as those in the LRTK family can continue high-precision positioning by receiving corrections from satellites even in remote mountains or on remote islands. However, in dense forests or deep valleys where satellite signals themselves cannot be received, satellite-based positioning is difficult regardless of RTK. In such cases, consider moving the measurement point to a more open location or temporarily combining other surveying methods (total station, terrestrial laser scanning, etc.).