Real-Time Kinematic (RTK) and GNSS corrections

In today’s world, industries such as precision agriculture, construction, and geospatial mapping depend on highly accurate geolocation data. Standard GNSS positioning provides accuracy within meters, which is insufficient for these applications. Real-Time Kinematic (RTK) and Network RTK (NRTK) correction services offer centimeter-level precision, enabling greater efficiency, automation, and reliability in these industries.

In all GNSS positioning solutions, the position is computed based on the distance between the receiver and GNSS satellites. This distance is calculated by multiplying the speed of light times the time it takes for a signal to reach a GNSS receiver. It is a simple calculation, but the signal’s perceived propagation time is affected by several error sources, including satellite orbit and clock errors, as well as ionospheric and tropospheric effects. Combined, all these error sources contribute to inaccurate positioning. 

How RTK Differs from Traditional GNSS Positioning

RTK and standard GNSS positioning measure distance to satellites differently. Traditional GNSS uses code-based ranging, which measures the time it takes for signals to travel from satellites to the receiver. In contrast, RTK uses carrier-based ranging, which relies on the phase of the signal’s carrier wave.

Carrier-based ranging provides much greater accuracy because the wavelength of the L1 signal is 19 cm, whereas in traditional GNSS, the length of the code frequency corresponds to a wavelength of about 300m. However, carrier signals do not contain time stamps, making it challenging to determine the number of full wavelengths between the satellite and receiver. To resolve this, RTK employs Integer Ambiguity Resolution (IAR), a process that accurately calculates these wavelengths, enabling centimeter-level positioning.

To ensure successful IAR, RTK systems require correction data. This data is provided by a nearby reference station with a precisely known position, or through a network of reference stations in the case of Network RTK. Network RTK enhances positioning accuracy over wider areas by modeling signal errors more effectively.

What is RTK and How Does It Work?  

Single station RTK

In its simplest form, single station RTK, an RTK solution makes use of a single reference station near the GNSS receiver. As the reference station is in a surveyed position, it can estimate the errors for each received GNSS signal. After error corrections have been communicated to the user receiver, IAR takes place. A single reference station is sufficient, if the distance between the user and the reference station is reasonably short. When the distance between the user and the reference station grows too large (typically more than 25km), the atmospheric conditions at the two positions can differ. This may result in unsuccessful IAR. 

Network RTK (NRTK)

Network RTK (nRTK) goes a step further by leveraging multiple reference stations instead of a single base station. This results in more precise error modeling, improves accuracy over larger areas, and minimizes reliance on a single reference station. When using a network of reference stations, the coverage area of the RTK solution increases significantly without affecting accuracy.  

With a network of reference stations, it is possible to model distance-dependent errors more precisely. Based on such modelling, the dependence on the distance to the closest reference station decreases substantially. In an nRTK correction service, the rover connects to the correction source provided by the network processor, and from which the reference stations are typically abstracted. This method provides better corrections over the whole service area, allowing for a less dense network of reference stations. It also provides better reliability as it is less dependent on individual reference stations.  

Applications of RTK and Network RTK 

RTK and NRTK technology play a crucial role in various industries, including:

• Construction and mining: Providing accurate site measurements and improving machine control for efficiency.
• Precision Agriculture: Enabling automated farming equipment to optimize planting, irrigation, and harvesting.
• Geospatial Mapping: Enhancing the accuracy of land surveys, topographical mapping, and infrastructure development. 

u-blox’s High-Precision Positioning Solution 

u-blox’s PointPerfect Live provides the highest accuracy in real time on a regional scale via IP-based, RTK corrections. It works on open standards with any GNSS RTK hardware. It is ideal for applications seeking to achieve the highest performance and lowest latency in areas with network coverage.  

u-blox also offers the PointPerfect correction service, which provides fast, cm-level positioning across continents, using IP-based PPP-RTK corrections. PointPerfect also works with any GNSS RTK hardware, regardless of brand. Attain flexibility via open-standards and usage-based pricing that fit your budget and business.

RTK and Network RTK technology provide a crucial advantage in industries where highly precise, real-time positioning is essential. With u-blox’s cutting-edge solutions, you can enhance accuracy, efficiency, and automation in your operations. Explore how PointPerfect Live Network RTK and u-blox GNSS RTK modules can elevate your projects with reliable centimeter-level positioning.