Unmanned underwater vehilcles operate in a 3-dimensional environment and the vehicles do not have to consider static obstacles that are located below a certain depth. Global path planning for the autonomous navigation system adopts a new palnning algorithm (Kim, 2005) in which points of contact with the obstacles and waypoint trees are utilized to get the optimal path to the target destination. To get the global path, this algotithm computes the position of contact points between the start point and the static obstacle, and then connects the contact points to produce a waypoint tree. The waypoint tree is searched using a depth-first search algorithm to get the optimal path to the destination. The waypoints produced are delievered to the Virtual world, and will be used by other subsystems such as the collision avoidance system.
Fig. 6 shows an example of paths produced using the contact points when there is a static obstacle between the start point and the destination. First, it calculates the position of the left contact point Ls and the right contact point Rs between the start point S and the obstacle, then it calculates the position of the left contact point Lg and the right contact point Rg between the destination G and the obstacle. Then, the contact points between Ls and Lg and the contact points between Rs and Rg are calculated recursively. The produced paths and contact points are stored using the data structure shown in Fig. 7 where the coordinates of the points are the data of the node, and the pointers are directed to next nodes.
Fig. 6. Path planning
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