doubt regarding working of base_local_planner and oscillations about the global plan

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Hi all,

I have a doubt regarding the working of the base_local_planner, specifically Trajectory Rollout planner. According to the above link, the local planner samples in the robot's control space, performs forward simulation, evaluates different trajectories and finally picks the highest scoring trajectory, My question is how does the local planner makes sure that the robot follows that exact trajectory? Does it use a PID Controller or something like that? The problem I am having is that robot does not follow the global plan accurately but oscillates about the global plan. I have tried tuning different parameters and followed http://answers.ros.org/question/73195/navigation-oscilation-on-local-planner/ which reduced the oscillations but its still not very good, the robot still oscillates about the global plan. So, I was wondering if it uses something like PID, how can I tune those parameters?

Update 1: One more thing, how does the base_local_planner uses odom (nav_msgs/Odometry) and gives a better estimate for /cmd_vel? There has to be some kind of a controller (maybe only P Control). Sorry If I am being really naive, but it would be great if someone can clear my doubt or point me in the right direction?

Any help will be appreciated.

Thanks a lot.
Naman Kumar