Basics of RTK GPS Surveying Every Surveyor Should Know: How High-Precision Positioning Works and How to Use It

Table of Contents

• What is RTK GPS?

• How RTK GPS Works

• Applications of RTK GPS

• How to Implement RTK Surveying

• Advantages and Points to Note for RTK Surveying

• Simple Surveying with LRTK

• FAQ

In surveying and construction sites, millimeter-level accuracy is sometimes required. Conventional GPS positioning can have errors of several meters, making it unsuitable for high-precision positioning. In recent years, RTK GPS has become essential knowledge for surveyors. RTK is a technology for performing high-precision positioning in real time, and when used properly it can determine positions with errors within a few centimeters. This article clearly explains the basics of RTK GPS, from how it works to how to use it in the field. At the end of the article, we also introduce the latest technology LRTK, which enables high-precision surveying easily for anyone.

What is RTK GPS?

RTK (Real Time Kinematic) GPS is a technology that measures positions with centimeter-level accuracy by correcting GNSS errors in real time. Standalone positioning (positioning performed with a single GPS receiver) typically has errors of about 5-10 m (16.4-32.8 ft), but RTK can reduce these errors to a few centimeters. RTK is a type of “relative positioning” that uses at least two receivers to receive satellite signals simultaneously and exchange data to correct positioning errors.

Specifically, one receiver is installed at a known coordinate as a base station, and another receiver is used as a mobile rover for measurements. The base station compares its known accurate position with the satellite-derived positioning data it receives, and calculates the errors contained in that data (such as satellite clock and orbit errors, and ionospheric and tropospheric effects). The base station then sends that error information to the rover in real time via radio or the Internet. The rover applies the received correction information to its own observations, cancelling out atmospheric and satellite-derived errors and obtaining high-precision coordinates immediately.

How RTK GPS Works

The key to understanding RTK is that “two receivers located close to each other are exposed to almost the same error factors.” If the base and rover are relatively close—on the order of a few kilometers to several tens of kilometers—the error factors affecting the satellite signals they receive (such as orbital deviations or signal delays) are largely common. By applying the corrections calculated by the base station to the rover, the common errors are cancelled out and relative high-precision positioning becomes possible. In this way, position accuracy that is normally at the meter level can be improved to the centimeter level in a single step. Typically, RTK-GNSS positioning achieves about 2-3 cm (0.8-1.2 in) horizontal accuracy and about 3-4 cm (1.2-1.6 in) vertical accuracy. This precision is sufficient for control point surveys and construction quality control.

A major feature of RTK positioning is that correction information is applied in real time, so measurement results are updated on-site continuously. Once the base and rover are set up, you can walk the site with the rover and measure arbitrary points, obtaining high-precision coordinates instantly. For example, in surveying sites the base station can be established while the rover successively observes multiple survey points, or a rover can be mounted on construction equipment to provide continuous real-time correction of operating position—operations that take advantage of RTK’s high precision and immediacy are becoming widespread. Also, a method called network RTK uses data from multiple base stations such as public control point networks to generate virtual reference stations (VRS) and distribute correction information over wide areas. This allows users to obtain correction information via the Internet without installing their own base station, making it increasingly easy to introduce RTK positioning.

Note that RTK is classified as relative positioning in its computation. The coordinates obtained by the rover are calculated relative to the base station, but if the base station’s position is set in advance to known public coordinates, the rover’s coordinates can also be obtained in the public coordinate system. Therefore, RTK makes it easy to directly compare points measured in the field with existing survey coordinate systems or map data.

Applications of RTK GPS

RTK GPS, which provides high-precision position information in real time, is being applied in many fields. It has become a standard technology in recent years, particularly in surveying and civil engineering, where it directly improves work efficiency and accuracy. Here are some representative applications.

• Surveying and construction: RTK is used in a wide range of civil surveying tasks such as control point surveys, land boundary measurement, construction quality control, and installation of control points. Because one person can carry a GNSS receiver and measure multiple points, work efficiency improves dramatically compared to conventional optical methods like total stations that require repeated setups. In addition, machine guidance and machine control—where RTK rovers are mounted on heavy machinery (bulldozers, excavators, etc.) for automated control of construction positions—are becoming widespread. Real-time correction of machine position and elevation enables precise construction without relying on the operator’s experience.

• Drones and aerial surveying: Mounting RTK receivers on drones improves automatic navigation accuracy and the precision of aerial photogrammetry. Standard GPS can produce drift and positioning errors that lead to meter-level offsets in terrain models derived from aerial images. RTK-capable drones can apply position corrections during flight, accurately follow preplanned routes, and acquire aerial imagery with precise positioning data. This improves the positional accuracy of orthoimages and 3D point clouds, reducing the need for additional adjustments in mapping and quality control.

• Agriculture: RTK is used in precision agriculture (smart farming). Increasing examples include mounting RTK-GNSS on tractors and combines for automatic steering to maintain accurate straight paths and for section-based seeding and fertilization. With centimeter-level positional accuracy, machinery can traverse fields without overlap or missed areas, improving productivity. RTK is also used on pesticide-spraying drones to precisely control altitude and spray lines, minimizing impact on surrounding areas while ensuring accurate application.

• Other fields: High-precision RTK positioning is expected in various situations requiring improved positional accuracy, such as autonomous vehicle and robot navigation, infrastructure maintenance, and structural monitoring using positioning sensors. For example, RTK-equipped sensors can continuously monitor displacements of bridges and roads in traffic infrastructure inspections, and small RTK units worn by athletes can enable motion analysis in sports tracking. RTK technology is becoming a foundational technology that supports the digital transformation of many industries.

How to Implement RTK Surveying

What preparations are needed to perform RTK surveying on-site? Fundamentally, RTK requires a high-precision GNSS receiver and a way to obtain correction information. There are two main implementation methods.

• Establish your own base station: The user prepares a GNSS receiver for the base station and installs it at a known point (a point whose coordinates are known). To transmit correction information from the base to the rover, specialized radios or modems in the UHF band are commonly used. The rover also needs a GNSS receiver and a radio receiver to receive base data in real time on-site. This method requires purchasing two units of equipment initially, but it provides the advantage of independent operation without relying on communications infrastructure. It is suitable for large sites or areas outside cellular coverage.

• Use a network RTK service: You can perform RTK positioning by connecting to existing correction data distribution services without installing your own base station. For example, you can use publicly installed reference stations operated nationwide by the Geospatial Information Authority or private control station networks, obtaining correction data for a virtual reference station (VRS) near the rover via the Internet. The rover receives correction information via a protocol called NTRIP** over mobile data (cellular) or Wi‑Fi and applies it to real-time positioning. This method typically requires only one GNSS receiver for the rover, since base station data is provided by the service, reducing equipment and operational burden. Service fees and communication are required, but this is a convenient way to balance ease of use and accuracy.

In either method, the GNSS receiver used as the rover must support RTK solution algorithms and be a high-precision model. A controller (a dedicated field device, tablet, etc.) is also required to display and record the rover’s positioning results. Recently, tablet-style devices that integrate the receiver and control software, and systems that manage positioning data by linking with smartphones, have appeared, improving field operability.

Advantages and Points to Note for RTK Surveying

RTK surveying offers many benefits, but there are also points to be aware of in operation. Below are the main advantages and cautions.

Main advantages of RTK surveying:

• High-precision positioning: You can obtain positions in real time with errors of only a few centimeters, making RTK suitable for tasks requiring precision such as control point establishment and detailed quality checks. Vertical accuracy also improves to a few centimeters, enabling onsite management of elevation differences and volume calculations previously difficult to do in the field.

• Improved work efficiency: One person can carry the receiver and measure without requiring line-of-sight, and there is greater freedom of movement between points. There is no need for repeated setups like with total stations, allowing rapid observation of many points over large sites. This can reduce personnel and shorten working time.

• Real-time deliverables: Since coordinates are obtained on-site immediately, there is no need to bring data back to the office for post-processing. You can confirm results in the field, quickly detect mistakes or omissions, and reduce the risk of re-surveying.

• Integration with other systems: GNSS positioning results are obtained in absolute coordinates such as latitude/longitude or plane rectangular coordinates, making them easy to integrate with GIS, CAD drawings, and other survey deliverables. If the base station is tied to public coordinates, acquired data can be placed directly in official survey coordinate systems.

Points and constraints of RTK surveying:

• Dependence on measurement environment: GNSS positioning requires reception of satellite signals from the sky, so accuracy degrades in urban canyons surrounded by tall buildings or in forests where satellite visibility is blocked. RTK cannot be used where satellite signals do not reach, such as inside tunnels or buildings. In such environments you must switch to conventional total station surveying or static GNSS surveying (long-duration observations with post-processing). In these cases, alternative methods should be used.

• Distance to the base station: If you use your own base station, accuracy decreases if the rover is too far from the base. Generally, it is desirable to keep the baseline (distance between base and rover) within 20-30 km. Beyond that, differences in atmospheric errors become significant, solutions may become unstable, and errors can expand beyond several centimeters.

• Dependence on communications: Communication means for sending and receiving correction information in real time are essential. Using radios limits you to their range, and using cellular networks means services are unavailable outside coverage areas. If communication is interrupted, correction information will not be received and accuracy cannot be maintained, so in mountainous areas consider installing repeaters or choosing carriers carefully.

• Initialization and satellite loss: Achieving centimeter-level accuracy with RTK requires an initialization calculation called integer ambiguity resolution of carrier phase biases. Typically, a high-precision fixed solution (FIX) is obtained within a few seconds to a few minutes after startup, but if satellite signals are lost or the environment changes drastically, reinitialization may be necessary. During that time accuracy can temporarily degrade (a FLOAT solution with errors on the order of tens of centimeters), so when observing important points it is important practice to confirm a FIX solution before recording.

• Equipment cost and operation: RTK-capable GNSS receivers and communication equipment are expensive and involve initial investment. In addition, using commercial correction services incurs service fees. However, lower-cost receivers and inexpensive services have appeared in recent years, lowering the barrier to entry. You also need to be familiar with equipment management, power supply, and software operation. If you operate a radio station yourself, licensing and technical conformity procedures under radio law are also required.

As described above, while RTK surveying is a revolutionary high-precision technology, it is important to understand environmental and operational conditions and use it appropriately. With proper preparation considering these points, RTK becomes a powerful tool for surveyors.

Simple Surveying with LRTK

One of the latest solutions making RTK technology even easier to use is LRTK. LRTK is a smartphone-based high-precision positioning system designed to make centimeter-level positioning—previously requiring specialized surveying equipment—accessible to anyone. Conventional RTK required expensive GNSS receivers and radio equipment, but LRTK enables RTK positioning with minimal gear using smartphone attachments and apps.

A feature of LRTK is that it can achieve sub-1 cm accuracy, which is impossible with standalone smartphone positioning. By combining a smartphone with a monopod (pole) to use it like a surveying instrument, positioning with accuracy comparable to professional equipment becomes possible. For example, by averaging data for several tens of seconds when measuring a point, advanced algorithms can reduce errors to the millimeter level, shrinking standalone GPS errors of about 5-10 m (16.4-32.8 ft) down to a few millimeters to a few centimeters. Support for multi-frequency and multi-GNSS observations, together with high-precision processing performed in the cloud, allows automatic high-precision solutions without specialized knowledge.

Moreover, LRTK is revolutionary in that it can perform not only point positioning but also 3D scanning by integrating smartphone cameras and LiDAR functions. By simply walking around the site with the smartphone held out, you can acquire point cloud data of surrounding terrain and structures and attach absolute coordinates to that point cloud. The acquired data can be uploaded to the cloud and used immediately to measure distances, areas, and volumes. In other words, with LRTK, surveying tasks that previously required multiple instruments and personnel can be completed by a single person with a smartphone in hand.

LRTK significantly lowers the barrier to high-precision positioning and is changing how surveying is done. It is designed to be compatible with conventional RTK, so not only professional surveyors but also field technicians and facility managers can take advantage of high-precision positioning. For those who want to start high-precision positioning, easy systems like LRTK are a reassuring option.

FAQ

Q: What is the difference between RTK and ordinary GPS positioning? A: The accuracy of the results is vastly different. Standalone GPS positioning typically has errors of about 5-10 m (16.4-32.8 ft), whereas RTK positioning reduces errors to a few centimeters by using corrections from a base station. RTK is also a type of relative positioning that corrects errors by exchanging data between two receivers, which is a major difference from standalone GPS. In short, RTK is a positioning method that achieves high accuracy by using a base station to cancel out GPS errors.

Q: What accuracy can be achieved with RTK GPS? A: Under good conditions, horizontal accuracy of about 1-3 cm (0.4-1.2 in) and vertical accuracy of a few centimeters can be achieved. In typical operation, horizontal/planar accuracy of 2-3 cm (0.8-1.2 in) and vertical accuracy of 3-5 cm (1.2-2.0 in) are commonly cited. This level of accuracy is comparable to conventional surveying instruments and is sufficient for control point surveys and construction management. However, accuracy depends on factors such as the distance between the base and rover and the surrounding environment (satellite reception conditions), so errors larger than a few centimeters can occur in some situations. Under ideal conditions errors below 1 cm (0.4 in) may occur, but it is safer to estimate accuracy as several centimeters in usual practice.

Q: What is needed to start RTK surveying? A: Basically, you need a high-precision GNSS receiver (RTK-capable) and a means to receive correction data from a base station. Specifically, prepare the following:

• GNSS receiver for the base station (only needed if you install your own base station; it is set up at a known point to generate corrections)

• GNSS receiver for the rover (carried to points to be measured; a high-precision unit with RTK solution algorithms)

• Communication equipment (radios to link base and rover, or a mobile router/SIM-equipped device to receive corrections over a network)

• Survey controller (a device to connect to the receiver to obtain corrections and to display/save coordinates—dedicated field controllers, tablets, PCs, or smartphones)

• Power supplies and poles (tripods, poles, batteries, and other accessories for field measurements)

For the above, a base station is unnecessary when using a network RTK service; you can operate with just a rover. Also check mobile network coverage for stable outdoor communication and any radio licensing procedures if you plan to operate your own radio system.

Q: Are radio licenses or special qualifications required for RTK positioning? A: No qualification is required simply to perform RTK positioning, but there are operational considerations. If you transmit correction information from your own base station using dedicated radio (e.g., UHF), you must obtain a license from the Ministry of Internal Affairs and Communications in Japan to establish that radio station. However, many GNSS surveying devices are equipped with technically certified radio modems that can be used with simplified licensing procedures and are explained at the time of purchase. If you use a network RTK service over cellular networks, radio licenses are not required (you only need a contract with a communications provider). Regarding surveyor qualifications, if RTK survey data are to be submitted as public survey results, the work should be performed under the supervision of a licensed surveyor; but operating RTK as a technology does not require a specific license to use. Nevertheless, if the results are to be treated as official survey deliverables, it is preferable that a qualified surveyor (at least an assistant surveyor) be responsible.

Q: Are there environments or situations where RTK cannot be used? A: Yes. Typical examples are environments where satellite signals cannot reach. RTK cannot be used in tunnels, indoors, or underwater because GNSS signals cannot be received. In urban canyons with dense high-rise buildings or in dense forests, satellite visibility is reduced and positioning becomes unstable; in some cases positioning may be impossible. In such places, you may need to set up temporary base points in open areas and use alternative methods, supplement with a total station, or perform static GNSS surveys in advance to establish control points and then use conventional methods in difficult areas. Also, temporary degradations such as heavy rain or solar flares can worsen GNSS reception and reduce accuracy, so check satellite geometry and ionospheric forecasts and choose times with better conditions when possible.