Global Navigation Satellite System (GNSS) is the collective name for satellite positioning systems — GPS, Galileo, GLONASS. The drone relies on GNSS for three critical functions: holding its position in the air, recording the home point, and the automatic Return to Home (RTH).
Signal degradation — urban canyons between tall buildings, interference or spoofing — weakens these functions silently, with no clear warning. So monitor the satellite count on your screen and be ready to fly in attitude mode, where only the pilot holds the position.