I took this info from another site:
“D-RTK is a high precision navigation and positioning system specially designed for DJI
A3 series flight controllers. Using dynamic differential technology, it provides ultra-accurate, centimeter-level 3D positioning. This enhanced accuracy over typical barometer, compass and GPS systems makes D-RTK essential for commercial, industrial and scientific applications where accuracy is imperative.”
"Real Time Kinematic (RTK) satellite navigation is a technique used to enhance the precision of position data derived from satellite-based positioning systems (global navigation satellite systems, GNSS) such as GPS, GLONASS, Galileo, and BeiDou. It uses measurements of the phase of the signal’s carrier wave, rather than the information content of the signal, and relies on a single reference station or interpolated virtual station to provide real-time corrections, providing up to centimeter-level accuracy. With reference to GPS in particular, the system is commonly referred to as Carrier-Phase Enhancement or CPGPS.[1] It has applications in land survey, hydrographic survey, and in consumer unmanned aerial vehicle navigation."