Fig. 7. The structure of node
When more than one obstacle exists between the start point and the target destination, the algorithm produces a waypoint tree for each contact point of the obstacle. Fig. 8 is a marine chart of such case, and the waypoint tree is shown in Fig. 9. With the waypoint tree, one can extract the obstacles that actually affect navigation of the vehicle from all the static obstacles existing between start point S to destination point G. Information of the left and right paths for avoiding the obstacles will be stored in the waypoint tree. The waypoint tree will have the minimum required information for producing all the paths from start point S to destination point G.
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