Path-following of Underactuated Ships Using Polar Coordinates
This chapter is devoted to a different path-following approach from the preceding chapter. The approach is motivated by the practical experience of steering a ship in the sense that when traveling in open sea the helmsman first looks at the weather map, then generates way-points to avoid the vessel moving into bad weather areas. A continuous reference path curve is then generated so that it goes via (almost) all of the way-points. It is then practical to steer a vessel so that it is in a tube of nonzero adjustable diameter centered on the reference path, and moves along the path with the desired speed. In comparison with the approach in the preceding chapter, the control system developed in this chapter allows the ship to be far away from the desired path at the initial time, and covers situations of practical importance such as parking and point-to-point navigation.
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