How can I change the default global path planning algorithm (A* and dijkstra) into my custom path planner (RRT)?

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Hi, I'm new to ROS. I want change the path planning in global_planner package. The default path planning algorithms are Astar (A*) and Dijkstra. I want to use the RRT (Rapidly-exploring random tree) algorithm for path planning but I don't know where to start. The code in Navigation stack is huge and there is only a few comment to explain the code.

Please show me the way to do it. Thank you!