what's difference between RTGoalHandle and RTGoalHandleFollow?

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The JointTrajectoryActionController supports three ways to command trajectories:

• Using the raw trajectory_msgs::JointTrajectory topic interface
• Using the pr2_controllers_msgs::JointTrajectoryAction action interface
• Using the control_msgs::FollowJointTrajectoryAction action interface.

It is my understanding that FollowJointTrajectoryAction superceeds the JointTrajectoryAction interface. The main difference between the two is that FollowJointTrajectoryAction allows you to specify path and goal tolerances in the action goal. These tolerances are optional, and if unspecified defaults specified in the parameter server are used. The older JointTrajectoryAction only used tolerances from the parameter server.

As to the RTGoalHandle*, they are convenience instances that allow a realtime controller to implement an actionlib server.