RTK (real-time kinematic)

Real-Time Kinematic (RTK) is a satellite-based navigation technique used for precise positioning and real-time monitoring. It is a differential GPS (Global Positioning System) method that provides centimeter-level accuracy for positioning applications.

To understand RTK, let's break it down into its key components:

1. GPS: The GPS system consists of a network of satellites orbiting the Earth, transmitting signals that can be received by GPS receivers on the ground. These signals contain information about the satellite's position and time.
2. Differential GPS (DGPS): DGPS is a technique used to improve the accuracy of GPS positioning. It involves comparing the measurements from a stationary GPS receiver at a known location (the reference station) with the measurements from a GPS receiver at an unknown location (the roving station). The difference between the two measurements, caused by errors in the GPS signals, is calculated and used to correct the position of the roving station.
3. RTK: RTK takes the concept of DGPS further by providing real-time corrections to achieve highly precise positioning. It requires two GPS receivers: a base station and a roving station. The base station receiver is set up at a known location, and its position is accurately determined. The roving station receiver is carried by the user or mounted on a moving vehicle, and its position needs to be determined accurately in real-time.

The RTK process involves the following steps:

1. Base Station Setup: The base station receiver is set up at a known location with a precisely known position. It typically has a stable mount and a clear view of the sky to receive satellite signals. The base station receives signals from multiple GPS satellites and calculates the difference between the measured positions and the known position.
2. Data Transmission: The base station transmits the correction data to the roving station in real-time. This can be done using various communication methods such as radio links, cellular networks, or the internet. It's important that the transmission is fast and reliable to ensure real-time positioning.
3. Roving Station Positioning: The roving station receiver receives the GPS signals from multiple satellites, just like any GPS receiver. However, in RTK, it also receives the correction data from the base station. Using this data, the roving station can calculate highly accurate positions in real-time.
4. Ambiguity Resolution: RTK involves a process called ambiguity resolution. The roving station receiver measures the carrier phase of the GPS signals, which is much more precise than the code-based measurements used in standard GPS. However, the carrier phase measurements contain integer ambiguities that need to be resolved to achieve centimeter-level accuracy. This is done by comparing the carrier phase measurements with the known baseline (distance) between the base station and the roving station.
5. Position Calculation: Once the integer ambiguities are resolved, the roving station calculates its precise position using the corrected carrier phase measurements. The resulting position is typically accurate to within a few centimeters, providing real-time and high-precision positioning.

Applications of RTK include land surveying, precision agriculture, machine guidance, construction, and navigation for autonomous vehicles. It enables precise positioning in real-time, allowing for increased efficiency, improved accuracy, and better decision-making in various industries.