RTK vs GNSS: Clarifying Terminology Confusion

Table of Contents

• What is GNSS?

• What is RTK?

• Differences between GNSS and RTK (accuracy, applications, system composition)

• Why RTK is chosen in the field (surveying, construction, agriculture, disaster response)

• Evolution of RTK technology: What is LRTK?

• Simple surveying with a smartphone: LRTK usage procedure

• Effects of LRTK and the future

• FAQ

What is GNSS?

GNSS stands for *Global Navigation Satellite System*. Simply put, it is a general term for satellite positioning systems represented by GPS; it measures positions on Earth by using radio signals from artificial satellites. GNSS includes the U.S. GPS, Russia’s GLONASS, Europe’s Galileo, China’s BeiDou, and regional systems such as Japan’s Quasi-Zenith Satellite System (QZSS, nicknamed “Michibiki”). In everyday use the term “GPS” is widespread, but GPS is the name of the U.S. system; the collective term GNSS is used when including other countries’ satellite positioning systems as well.

A GNSS receiver receives time-stamped signals from multiple satellites and calculates the distance to each satellite to determine its own position (latitude, longitude, altitude). Normally, if signals from four or more satellites can be received, a three-dimensional position can be computed. For example, the GPS receivers built into our smartphones and car navigation systems are a type of GNSS and are used to display the current location on map apps or provide route guidance.

However, GNSS standalone positioning (the method of positioning with only one receiver) typically results in errors on the order of several meters to tens of meters. Positioning accuracy degrades due to various factors such as ionospheric and tropospheric signal delays, satellite and receiver clock errors, and radio reflections (multipath). In practice, smartphone and car GPS locations are said to have errors of roughly 5–10 m. This level of accuracy is acceptable for everyday navigation and location-based services, but it is insufficient for tasks that require very precise measurements, such as accurately determining property boundaries or precisely controlling heavy machinery.

What is RTK?

RTK stands for *Real Time Kinematic*, a technique that achieves high-precision satellite positioning. RTK positioning operates two GNSS receivers simultaneously: a “base station” and a “rover.” The base station computes error information (correction data) and sends it in real time to the rover, which applies the corrections to its positioning solution. Practically, the base station receiver is installed at a point with known accurate coordinates (a known point) and also receives GNSS satellite signals. The base station calculates the error components from the difference between its known location and the GNSS-derived position and transmits that correction information to the rover via radio or the Internet. The rover (the receiver at the point to be measured) applies the received correction information to its solution, allowing it to obtain centimeter-level accurate positions.

In other words, RTK cancels out residual errors in GNSS standalone positioning by making a relative comparison with another receiver. RTK also uses the phase of the carrier wave—a very short-wavelength component of the satellite signal—for measurement. By resolving the integer cycles of this carrier phase (the so-called integer wavelengths), millimeter-order accuracy is achievable. RTK positioning can provide horizontal accuracy on the order of about 2–3 cm (0.8–1.2 in), and vertical accuracy on the order of a few centimeters. Furthermore, averaging RTK measurement results over a certain period (for example, several tens of seconds to a few minutes) can further improve accuracy to the millimeter level.

RTK requires a communication link between the base station and the rover, but in recent years “network RTK” using the Internet has become widespread. For example, users can obtain correction data from private correction data distribution services that use data from the Geospatial Information Authority of Japan’s approximately 1,300 Continuously Operating Reference Stations (CORS), or use the centimeter-level augmentation service (CLAS) provided by Japan’s QZSS (Michibiki), so users do not need to set up their own base stations. As a result, a rover receiver alone can perform real-time centimeter-level positioning. Note that in single-base RTK, the correction effectiveness and accuracy decrease as the distance between the base and rover increases, but network RTK methods (such as VRS) that compute virtual reference stations from multiple reference points can provide stable centimeter-level positioning over wider areas.

Of course, to achieve the best accuracy, it is necessary to receive a sufficient number of satellites in an open-sky environment. Conversely, in places with poor satellite reception—such as inside tunnels or between high-rise buildings—even RTK may fail to provide high-precision positioning or may not be able to obtain a solution at all. RTK is extremely high-precision, but its performance depends on receiving GNSS signals in good conditions.

Differences between GNSS and RTK (accuracy, applications, system composition)

Now let’s compare GNSS standalone positioning and RTK positioning from several perspectives.

• Accuracy differences: GNSS standalone positioning typically produces errors on the order of several meters to tens of meters, whereas RTK-GNSS can keep errors within a few centimeters. For example, a typical smartphone GPS has accuracy of roughly 5–10 m, while RTK can be expected to deliver about 2–3 cm (0.8–1.2 in) accuracy. High-precision RTK positioning enables centimeter-level positioning that was previously impossible.

• Differences in main applications: Situations where GNSS standalone accuracy is sufficient include everyday uses such as current location display on car navigation or smartphone map apps and tracking logistics vehicles. In contrast, applications that require RTK’s high precision include civil surveying for establishing control points and cadastral surveys, machine guidance for construction equipment, autonomous tractor guidance in agriculture, precision aerial surveying with drones, and monitoring ground deformation. In applications where a few centimeters of positional difference affect outcomes, RTK positioning is indispensable.

• Differences in system composition: GNSS standalone positioning completes positioning with a single receiver that receives satellite signals. RTK positioning requires two receivers—a base and a rover—and a communication method linking them (or a connection to a correction information service that acts as the base). Traditionally, each site needed its own base station, expensive GNSS receivers, and radio modems. However, today it is possible to receive correction information from nationwide CORS networks or QZSS CLAS, and small, low-cost RTK-capable GNSS receivers are available, so RTK system composition has become much easier than before.

Why RTK is chosen in the field (surveying, construction, agriculture, disaster response)

How is high-precision RTK positioning practically useful in field operations? Here are representative application areas.

• Surveying (map creation and civil investigations): In surveying, where determining land boundaries and creating detailed topographic maps require high positional accuracy, RTK-GNSS surveying enables efficient observations with accuracy comparable to conventional optical surveying instruments (total stations). Recently, RTK GNSS surveying has begun to be used even for public surveys ordered by national and local governments. Unlike optical instruments, GNSS does not require line-of-sight between measured points, so surveying can proceed more easily with one person in hilly terrain or obstructed sites. A single surveyor carrying a handheld GNSS receiver can perform surveying, greatly improving efficiency and labor savings on site.

• Construction (construction management): On construction sites there are many tasks where centimeter-level deviations directly affect quality, such as automatic control of heavy machinery, stake driving, and layout marking. Using RTK’s high-precision position information for machine guidance and survey data improves construction accuracy and work efficiency. For example, importing design data into RTK-capable equipment makes it easy to accurately set stake positions on site. RTK-GNSS is also used for as-built verification (measuring and inspecting completed structures), enabling inspections with smaller errors than before. High-precision positioning brings major benefits to construction in terms of both quality control and productivity.

• Agriculture (smart agriculture): High-precision position information is indispensable in smart agriculture for autonomous tractors, rice transplanters, and pesticide-spraying drones. Introducing RTK-enabled GPS guidance systems allows agricultural machines to determine their position accurately and drive almost without error in straight lines or sow/fertilize at specified intervals. This reduces overlapping work and unevenness, contributing significantly to increased productivity and labor savings; consequently, many advanced farmers have introduced RTK-GNSS. RTK is an important foundation supporting the advancement of autonomous farming technologies and contributes to stable food production and labor reduction.

• Disaster prevention and response: At earthquake or landslide sites it is necessary to quickly understand terrain changes and damage. Combining drone aerial photography with RTK allows rapid creation of detailed maps and 3D models of affected areas. RTK is also powerful for accurately measuring damage sites or locating temporary works during disaster recovery. Some local governments in Japan have even introduced on-site measurement systems combining iPhones and RTK receivers to speed up and simplify disaster response. Surveying at disaster sites, which previously relied on experience and intuition, can now be conducted objectively and with high precision using RTK.

Evolution of RTK technology: What is LRTK?

As RTK technology has evolved, a recent innovation is the solution called LRTK. LRTK is a smartphone-compatible positioning device and cloud service designed to make high-precision RTK positioning easier; it can be considered an “evolved” form of high-precision RTK. It consists of a pocket-sized RTK-GNSS receiver (LRTK device) that can be attached to a smartphone, weighing approximately 150 g and with a thickness of about 1 cm (0.4 in), together with a dedicated positioning app and cloud service. The goal is to make centimeter-level positioning—which was once expensive and specialist-only—available to anyone. The pocket-sized device includes a high-performance antenna and battery, and its simplicity—requiring no complicated cable connections or large-scale equipment—is a major feature.

For example, attaching this dedicated small receiver to an iPhone and launching the LRTK app is sufficient to obtain centimeter-level position information in real time. The LRTK device can directly receive high-precision augmentation information such as the CLAS signal broadcast by Japan’s QZSS (Michibiki) and correction data from various network RTK services, so high-precision positioning is possible without preparing a dedicated base station. Moreover, even in mountainous areas or disaster sites where cellular signals do not reach, if the LRTK device can receive the satellite augmentation signal from Michibiki (CLAS) from above, it can continue high-precision positioning without Internet connection, improving on-site reliability. The acquired positioning data (latitude, longitude, height) are not only saved on the smartphone but are also synchronized to the cloud immediately. By accessing the dedicated cloud web page, you can view the measured points on a map and easily share data with other team members.

Furthermore, LRTK systems provide various additional functions that utilize the obtained high-precision coordinates. They offer an all-in-one set of diverse surveying and measurement functions that previously required separate devices and software: 3D point-cloud scanning on the smartphone screen, AR (augmented reality) overlay of design data, and automatic calculation of distances, areas, and volumes between measured points. For example, if you import design coordinate data into the LRTK app, the AR function makes it easy to display those positions on the smartphone screen while performing stake-driving work. Despite having such high functionality, the equipment is compact, easy to handle, and priced much lower than traditional professional GNSS equipment, making it realistic for each field worker to carry and use a smartphone positioning device. In actual verifications, positioning accuracy obtained with LRTK has been reported to be comparable to conventional first-class GNSS surveying instruments, with results showing errors below 5 mm (0.20 in). LRTK is truly an innovative solution that could be called the democratization of RTK technology—high-precision positioning is no longer limited to specialist professionals and is becoming accessible to everyone.

Simple surveying with a smartphone: LRTK usage procedure

So how is smartphone surveying with LRTK performed? Here is an example of basic steps.

• Preparing the LRTK device and smartphone: Attach the LRTK device (a dedicated ultra-compact RTK-GNSS receiver) to your smartphone and turn on the device. Prepare in an outdoor location with good visibility to acquire satellites.

• Starting high-precision positioning: Launch the LRTK app on the smartphone and connect to the device via Bluetooth or similar. When you start receiving correction information in the app, positioning stabilizes in about 30–60 seconds and enters high-precision mode (Fix solution). At this point the smartphone can be used as a centimeter-grade surveying instrument.

• Measuring points: Move to the point you want to measure while carrying the LRTK device (if necessary, attach the device to the tip of a dedicated pole or monopod for measurement) and tap the “Measure” button in the smartphone app. The latitude, longitude, and height of that point are measured instantly and recorded in the smartphone along with the date/time and notes. You can also take photos for each measured point and save them linked to the position data if needed.

• Saving and sharing data: Recorded positioning data can be synchronized automatically to the cloud. Uploading the coordinates acquired on site to the cloud allows you to check results on a map and share information with other members without returning to the office. There is no need to record notes by hand in a paper field book, greatly reducing the workload of organizing data.

Effects of LRTK and the future

By utilizing LRTK, surveying work that once required specialized expensive equipment and advanced skills becomes remarkably simple. With only a smartphone, high-precision positioning and various measurements can be completed on site, so “field” work across many industries—not just civil engineering and construction—will change dramatically. The spread of LRTK, an evolved form of GNSS and RTK, means the era of efficient and advanced smartphone surveying is just around the corner. Wider adoption of high-precision GNSS technology will strongly support field DX (digital transformation) and is expected to lead to safer, more productive, and smarter on-site operations. In future surveying and construction management, solutions like RTK and LRTK will become new standards and continue to evolve as foundational technologies that support our lives and industries.

※For details on LRTK, please also refer to official websites and similar sources.

FAQ

Q: What is the difference between GNSS and GPS? A: GNSS is a collective term for satellite positioning systems including GPS. GPS is the name of the U.S. satellite positioning system, and GNSS refers to the whole set including Russia’s GLONASS, Japan’s Michibiki (QZSS), etc. In everyday language people often say “GPS,” but technically GPS is part of GNSS.

Q: What is the difference between RTK and GNSS? A: GNSS standalone positioning determines position using only satellite signals and thus has errors on the order of several meters, while RTK uses correction information from a base station to cancel those errors in real time and achieve centimeter-level accuracy. Simply put, GNSS is the base technology, and RTK is an advanced positioning method that dramatically improves GNSS accuracy.

Q: What is needed to use RTK? A: Traditional RTK positioning required two GNSS receivers—a base station at a known point and a rover at the measurement point—and a communication method linking them (radio modem or Internet-based Ntrip, etc.). Today, however, you can obtain correction data from networks such as the Geospatial Information Authority’s CORS, satellite augmentation (QZSS CLAS), or private correction services, so RTK can be performed as long as the rover receiver and a communication environment are available. It is also important to use the system in as open-sky an environment as possible to receive high-quality GNSS signals.

Q: How accurate is RTK positioning? A: Under typical conditions, RTK positioning provides high accuracy with horizontal errors within a few centimeters and vertical errors within several to a dozen centimeters. Even smartphone-based RTK can achieve accuracy comparable to dedicated surveying instruments if proper correction data are used. In practice, LRTK-only positioning often stays within about 1–2 cm (0.4–0.8 in), and averaging measurements over time can achieve sub-centimeter (less than 1 cm) accuracy.

Q: What is LRTK? A: LRTK is a next-generation high-precision positioning solution that combines a smartphone with a small RTK-GNSS receiver and a supporting app/cloud service. By attaching a small receiver to a smartphone, you can achieve real-time centimeter-level positioning and get an all-in-one solution that includes cloud data sharing and AR display. In short, LRTK makes high-precision surveying possible for anyone without specialist equipment.

Q: Can beginners in surveying use RTK? A: Yes. Traditional RTK surveying required setup and positioning knowledge and was challenging for beginners. However, solutions like LRTK allow users to perform positioning by following guidance in a smartphone app. They are designed to be usable without difficult settings or specialist knowledge, so non-experts can benefit from RTK. Going forward, RTK technology that is easy for beginners to use will continue to spread.