RTK GPS System
What is RTK, and how does it work?
RTK (Real-Time Kinematic) is a positioning technique to achieve more accurate GPS solutions, typically on the order of centimeters. The RTK system has three main components: 1) base station, 2) rover, and 3) radio. The GNSS (Global Navigation Satellite System) orbits at approximately 20,000 km above the Earth, its signals travel through space and the atmosphere developing small errors. The base station listens to the GNSS signals and has algorithms to detect these small errors to calculate Real-Time Correction Messages (RTCM). The base then sends the RTCM packets over the radio to the rover. The rover uses the RTCM packets and adjusts its solution to get a more accurate geo-location.
Do I need a more accurate GPS location?
Before commercial drones, aerial imagery was collected from satellites and manned aircraft, and resolution was limited by distance to the target. With pixel GSD (ground sample distance) on the order of tens of centimeters to meters, standard GPS accuracies of 2-3 meters were more than adequate to identify a data point and survey a mapped area. With the introduction of low altitude drones, image resolution is now limited by how close to the ground you want to fly. We are now capable of collecting imagery with pixel GSD on the order of millimeters.
Some examples of smaller area analysis are individual trees in an orchard and individual plots in a trial. In these cases, data placement matters because the areas we want to analyze are 2-3 meters in size or smaller.