For navigation, Dragon uses positional information that it receives from the ISS, along with GPS data it calculates itself. As it approaches the station, it uses imagery of the ISS and the relative size of the station to compute the distance to the station. Because it might well be in darkness, Dragon uses thermal imaging as the station is slightly warmer than the background.That's an impressive system. I never thought about the number of safety systems and fallbacks needed to ensure safety when navigating around the ISS.