In GPS-denied unknown environment, the visual navigation and mapping for multi-rotor UAVs has become popular within the unmanned aircraft field. This paper gives an introduction to the technologies of UAV visual localization and mapping. First of all, the relative merits of two different autonomous flight control systems are analyzed and the difficulties and requirements of design are pointed out. Then, the different visual methods of UAV localization and mapping are investigated, the characteristics of some UAV visual methods are analyzed, and its present research development is summarized. Finally, the future research direction of UAV visual control is discussed.

multi-rotor UAV  /  flight control  /  visual localization  /  mapping