Navigation planning system and navigation planning method

A navigation planning system, comprising:

• a processing circuitry configured to:
• acquire a planned route for a movable body on a water;
• acquire movable body information including a position, a moving direction, and a speed of the movable body;
• acquire obstacle information including a position, a moving direction, and a speed of an obstacle located in a surrounding area of the movable body;
• generate a plurality of potential evasion routes, different from the planned route, each comprising a starting point located on the planned route and a return point located on the planned route;
• select an evasion route from among the plurality of potential evasion routes;
• calculate a collision risk indicating a risk level of collision between the movable body and the obstacle based on the movable body information and obstacle information;
• obtain a maximum evasion route collision risk when the movable body travels on the evasion route, and a maximum planned route collision risk when the movable body travels on the planned route;
• compare the maximum evasion route collision risk with the maximum planned route collision risk;
• and
• output a navigation route change signal to cause the movable body to change the planned route to the evasion route when the maximum evasion route collision risk is less than the maximum planned route collision risk,
• wherein the processing circuitry further configured to:
• calculate a planned route distance travelled by the movable body for a predetermined time on the planned route and an evasion route distance travelled by the movable body for a predetermined time on the evasion route respectively;
• determine whether to output the navigation route change signal based on the maximum evasion route collision risk and the maximum planned route collision risk, and the planned route distance and the evasion route distance;
• and
• output the navigation route change signal when one of a difference between the evasion route distance and the planned route distance is within a predetermined value, and a distance ratio between the evasion route distance and the planned route distance is equal to or less than a predetermined value.