What is Optical flow

In this chapter, the authors address main issues of Navigation, Guidance, and Control (NGC) and vision system of Autonomous Surface Vessels (ASV). These issues compose research problems and related research findings in recent years. Related research results are reviewed first; then the hardware and subsystem of ASVs is introduced. For the typical rudder-propeller, three degrees of freedom horizontal underactuated model is presented. Visual ASV is applied more and more in complex and unknown environment with increasing demand of obstacles avoidance. Two examples of visual applications are demonstrated. One is riverbank identification using color segmentation and Hough Transform; the other is bridge detection using optical flow.