RTK vs GPS: The Difference in “Practical Accuracy” That Matters on Site

Table of Contents

• Accuracy and limitations of ordinary GPS positioning

• What is RTK positioning? How it achieves high accuracy

• Practical accuracy differences between RTK and GPS

• Benefits of RTK use in surveying and construction sites

• RTK use in agriculture

• Other use cases (infrastructure inspection, drone surveying, etc.)

• Smartphone RTK “LRTK”: simple surveying anyone can do

• Frequently Asked Questions (FAQ)

Accuracy and limitations of ordinary GPS positioning

The GPS in the smartphones and car navigation systems we use daily is convenient for showing your current location on a map and for navigation. However, the accuracy of position information from ordinary GPS (GNSS standalone positioning) is generally an error on the order of several meters. When a signal from satellites is processed by only a single receiver, various error sources such as signal delays in the atmosphere, satellite clock offsets, and radio signal reflections (multipath) are not corrected and accumulate. As a result, the obtained position coordinates can be off by several meters.

For tasks like checking your location on a smartphone or following roads on a car navigation system, ordinary GPS accuracy is usually acceptable. Even with a few meters of error, you can be guided to the vicinity of your destination. However, for tasks that require precise position measurement—such as surveying or civil engineering construction—an error of several meters is unacceptable. For example, a 5 m (16.4 ft) error in boundary surveying would shift the site to a completely different location and be practically useless. Likewise, if height measurements on a construction site have errors of several meters, installation of structures and quality control of finished shapes would be impaired. In this way, the accuracy of general GPS often fails to meet the level required for actual field work.

What is RTK positioning? How it achieves high accuracy

That’s where RTK positioning comes in. RTK stands for Real Time Kinematic, and it is a method that realizes centimeter-level high accuracy by correcting satellite positioning errors in real time. While ordinary GPS positions using a single receiver, RTK performs relative positioning using two GNSS receivers (a base station and a rover) simultaneously. One is set up as a base station at a point whose accurate coordinates are known in advance, and the other is operated as a rover at the point to be measured.

The base station computes error components (correction information) from the difference between its known position and the position measured by GNSS, and transmits that correction information to the rover via radio or the Internet. The rover applies the received corrections to its own positioning solution, canceling out the errors and calculating a high-accuracy position. Simply put, instead of measuring with a single receiver, measuring with two receivers at the same time to cancel errors dramatically improves accuracy.

By this RTK principle, positioning can typically be confined to errors of about 2–3 cm (0.8–1.2 in) horizontally and about 3–5 cm (1.2–2.0 in) vertically. This is an improvement by orders of magnitude compared to conventional errors on the meter scale. RTK also uses the phase of the carrier wave of GPS signals, which has a short wavelength (tens of centimeters), and by averaging measurements over a certain time it can achieve precision approaching the millimeter level. In other words, RTK delivers practically sufficient accuracy in real time on site that ordinary GPS cannot achieve.

To perform RTK positioning, a communication means to receive correction information from the base station is required. Traditionally, you needed to prepare your own radio equipment to connect the base station and rover by radio. Recently, however, network RTK—where correction data can be obtained via the Internet from services such as the Geospatial Information Authority of Japan’s Continuously Operating Reference Stations or paid correction services provided by carriers—has become widespread. In Japan, the Quasi-Zenith Satellite System “Michibiki” has also introduced a centimeter-class augmentation service (CLAS), making high-precision positioning possible without users having to install their own base station. As a result, an era has arrived in which you can easily perform real-time centimeter-precision positioning with just a single GNSS receiver acting as the rover.

Practical accuracy differences between RTK and GPS

There is a significant gap in practical accuracy obtainable in the field between RTK and ordinary GPS (standalone positioning). With RTK, in open areas you can stably achieve errors of a few centimeters both horizontally and vertically. By contrast, ordinary GPS can have horizontal errors of around 5–10 m (16.4–32.8 ft), and in some cases errors of more than 10 m (more than 32.8 ft) may occur. In other words, RTK can be said to be roughly 100 times more accurate than GPS, and the reliability of positioning is markedly different. The differences can be summarized as follows.

• Positioning method: GPS measures satellite signals with a single receiver (standalone). RTK uses two receivers (base station + rover) for relative positioning.

• Positional accuracy: GPS errors are on the order of several meters to over ten meters. RTK errors are on the order of a few centimeters (horizontal 2–3 cm (0.8–1.2 in), vertical 3–5 cm (1.2–2.0 in) as a guideline).

• Required equipment: GPS requires only a standalone receiver. RTK requires a receiver plus base station data (your own base station or a distribution service) and a communications environment.

• Practical use cases: GPS is suitable for rough location awareness and navigation. RTK is used where high accuracy is required, such as surveying, construction management, and precision agriculture.

• Usage notes: GPS is simple but has large errors and is unsuitable for precise positioning. RTK is highly accurate but requires acquisition of correction data and ensuring satellite visibility.

As shown, there is a clear difference between RTK and GPS in terms of accuracy and usability. Especially on surveying and construction sites, whether the error is several meters or several centimeters can determine the success or failure of the work. RTK pinpoints positions with accuracy orders of magnitude better than GPS, enabling advanced tasks that were previously impossible with GPS.

That said, RTK is not always perfect; field conditions require attention. If satellite signal reception conditions are poor, RTK accuracy can also degrade. For example, in urban areas surrounded by high-rise buildings or in forests, satellites may be blocked or signals reflected, and a fixed solution may not be obtained (the solution becomes unstable). Temporary errors exceeding 10 cm (3.9 in) can also occur. Even so, in open-sky conditions RTK can stably maintain centimeter-level accuracy, and the difference compared with GPS is dramatic. In short, to fully realize RTK performance it is important to operate in locations with as clear a sky view as possible and to continuously receive stable correction information.

Benefits of RTK use in surveying and construction sites

Centimeter-level accuracy enabled by RTK brings revolutionary benefits to surveying and construction sites. Traditionally, field surveying involved two-person teams using optical instruments such as total stations, and staking out and marking during construction often relied on skilled workers’ experience for careful positioning. By introducing RTK-capable GNSS surveying instruments, one person can walk with a GNSS rover and quickly measure many points in a short time. Because you can obtain geodetic coordinates (latitude, longitude, height) in real time and point data in the plane rectangular coordinate system, on-site checking against drawings and additional measurements are easy. Survey productivity dramatically increases, leading to reduced labor costs and shorter construction periods.

RTK is also powerful for quality control during construction and for staking-out operations. For example, in road works and land development sites where you need to finish the ground to design heights and slopes, using RTK allows you to monitor the blade height accurately from a machine and perform grading work while seated in the machine. In increasingly common ICT construction methods, GNSS receivers are mounted on construction machines such as bulldozers and excavators to provide real-time guidance for blade height and position—machine guidance / machine control (MG/MC)—where RTK centimeter accuracy is indispensable. Machine operators can work guided by in-cab monitors that indicate “X cm to design surface,” preventing over-excavation and improving efficiency. This reduces human error and rework, significantly enhancing quality control and work efficiency.

RTK is also used for pile driving and installation of structures on construction sites. Without relying on experience, a guidance app from a GNSS rover can give real-time directions like “move 5 cm east,” enabling anyone to perform accurate positioning. This allows for precise staking and marking from the first try, reducing re-measurement and rework. Furthermore, with the spread of RTK positioning, positioning work that previously required a surveyor is increasingly being carried out by construction managers and workers themselves. Site personnel can measure site elevations with a tablet and immediately reflect them in construction for rapid quality control. In this way, RTK delivers centimeter-level accuracy across construction and civil engineering workflows, contributing to both improved quality and labor savings.

RTK use in agriculture

Centimeter accuracy from RTK is also valuable in agriculture and smart farming. Autonomous steering tractors have become more common in recent years, and many of them use RTK for high-precision positioning. By installing a GNSS antenna on a tractor and knowing the vehicle position to the centimeter to automate steering, even large fields can be plowed and seeded straight and uniformly without manual labor. RTK guidance minimizes overlap and skips with adjacent passes, reducing redundant work and shortening working time. Precision straight driving that was difficult even for veterans becomes achievable by anyone, contributing to increased yields through uniform seeding and fertilization.

For example, introducing RTK automatic-steering tractors has been reported to reduce working time by about 5–10% in some cases. Accurate straight-line driving also reduces the risk of trampling unwanted areas, protecting crops from damage. In one demonstration, RTK introduction led to approximately a 10% increase in crop yield. Thus, in precision agriculture, RTK positioning contributes not only to labor-saving and reduced material costs but also to increased yields and reliable autonomous operation. Moreover, driving data obtained with RTK can be visualized and analyzed in the cloud to inform cultivation planning, enabling data-driven farming. With centimeter-level high-precision data, agriculture is shifting toward scientific approaches that do not rely solely on experience and intuition.

Other use cases (infrastructure inspection, drone surveying, etc.)

The benefits of centimeter-level positioning extend beyond construction and agriculture. For infrastructure maintenance, associating high-accuracy position information with photos or sensor measurements taken during regular inspections of bridges and tunnels makes it easy to record exact locations of deterioration and monitor changes over time. Marking the position of buried pipes identified by ground-penetrating radar with RTK reduces the risk of damaging pipes in later excavation work. In large plants and railway maintenance sites, RTK receivers mounted on work vehicles can monitor their positions to check in real time for position deviations relative to restricted areas. These are examples of RTK helping prevent human error.

RTK also plays an important role in the growing fields of drone surveying and equipment inspection. RTK-capable drones can record their own position with high accuracy during flight, so orthophotos and 3D point cloud models created from aerial photographs exhibit minimal positional offsets. Traditionally, precise drone surveying required placing many ground control points (known-coordinate targets) and correcting data, but RTK drones can reduce the number of required control points, greatly streamlining the surveying workflow. The high-accuracy maps and point clouds obtained are powerful tools for road and river maintenance, disaster damage mapping, and more. Combining real-time high-accuracy positioning with digital twin implementations of sites will lead to higher-quality planning and improved preventive maintenance.

Smartphone RTK “LRTK”: simple surveying anyone can do

Although RTK is highly accurate and convenient, it used to require expensive dedicated GNSS surveying instruments and skilled operators, making adoption difficult. Now, however, an era is arriving in which anyone can easily achieve centimeter-level positioning using a smartphone. A representative solution is “LRTK.” LRTK is a smartphone-integrated compact RTK-GNSS receiver that transforms an iPhone or iPad into a pocket-sized all-purpose surveying instrument simply by attaching it. By attaching a device weighing only approximately 125 g to your smartphone and launching a dedicated app, you can obtain correction data from network RTK services or Japan’s Michibiki (CLAS) and immediately achieve centimeter-level positioning.

Using LRTK greatly simplifies surveying and positioning tasks. For example, you can hold the device over the point to be measured and tap a button on the smartphone screen to record the latitude, longitude, and height of that point. Recorded location data are automatically saved to the cloud, so you can check site measurement data from the office in real time. The app also automatically converts to the plane rectangular coordinate system and applies geoid height corrections, allowing you to obtain accurate coordinates without specialized knowledge. LRTK supports not only single-point measurements but also continuous positioning; you can plot up to 10 points per second while walking to measure terrain cross-sections, for example.

LRTK is also useful for staking and marking on site. Combined with GNSS guidance apps, the system can display on the smartphone the deviation from a preset target coordinate, guiding you to the correct position. Intuitive guidance without complex equipment operations enables even inexperienced users to perform accurate positioning. In addition, some apps can overlay design lines or buried-object locations on the smartphone camera view in AR, making it easy to visually confirm the position of underground infrastructure or design lines on the actual scene, which contributes to improved safety during excavation.

RTK equipment that once required investments of several million yen can now be introduced at surprisingly affordable prices with LRTK. Compact and inexpensive enough for one person to carry one device to the site, it enables non-specialists to make measurements themselves when needed. Field reports from sites that introduced LRTK include comments such as “We can now handle small measurements ourselves that we used to request from the surveying team, and productivity has dramatically improved.” The latest smartphone RTK devices like LRTK are opening a new era in which anyone can easily handle centimeter-precision positioning.

Frequently Asked Questions (FAQ)

Q: Can RTK positioning really achieve accuracy of a few centimeters? A: Yes. Using RTK, horizontal errors are generally confined to about 2–3 cm (0.8–1.2 in), and vertical errors to about 3–5 cm (1.2–2.0 in). In ideal environments—where the sky view is wide and many satellites can be tracked—even sub-centimeter errors are achievable. However, in urban areas with tall buildings or inside forests, accuracy can temporarily degrade and offsets of 10 cm (3.9 in) or more may occur. To stably obtain centimeter-level accuracy, it is desirable to perform positioning where satellite visibility is good.

Q: What do I need to start RTK positioning? A: The basics are an RTK-compatible GNSS receiver (rover) and a base station (or correction service) that provides error correction information. A standalone GPS receiver is insufficient to achieve centimeter-level accuracy, so you need either a nearby base station with known coordinates or access to base station data via the Internet. In Japan, correction information can be obtained from the Geospatial Information Authority’s Continuously Operating Reference Stations or paid VRS services provided by communications companies. You also need a communication link between the receiver and the base station (radio modem or mobile network). Recently, Internet distribution systems such as Ntrip have become widespread, and receivers that support them can operate RTK without dedicated radio equipment.

Q: Is RTK surveying possible with a smartphone? A: Yes. The GPS built into a smartphone alone is limited to several meters of accuracy, but by connecting an external RTK-capable receiver to the smartphone you can achieve centimeter-level positioning. Using a smartphone-compatible compact device like LRTK, your everyday smartphone becomes a high-precision GNSS surveying instrument. If you receive correction information with a dedicated app while positioning, you can perform point surveying and staking at accuracies comparable to professional surveying equipment. The smartphone screen shows current positions and point coordinates in real time, making operation intuitive for beginners. RTK surveying, which used to be expensive and specialized, has become significantly easier and more affordable thanks to smartphones.

Q: What factors affect RTK positioning accuracy? A: The main factors are satellite signal reception conditions and the quality of correction information. High accuracy is obtained when satellites are well visible (wide open sky), whereas in areas shadowed by buildings or trees, signal blocking and multipath increase errors. Correction accuracy also decreases with distance from the base station, so single-base-station RTK is generally recommended to be operated within a few kilometers of the base (network RTK extends the coverage somewhat by using virtual reference points). In addition, when using mobile communications, communication delays or disconnections that interrupt correction data will degrade accuracy. Therefore, to stably operate RTK, ensure a clear sky view as much as possible and secure stable delivery of correction data.