About geometry_msgs/Twist

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Hi, These are just msgs in a structured way so that they can be published or subscribed by a node. They are just values. It depends on the node which actually uses them to manipulate robot. It depends on how you want to use it. For example in teleop_base package the teleop_base_keyboard.cpp takes the msgs from keyboard and uses them as m/sec. If your node takes this msgs as mm/sec then the node execution will be accordingly.

You can know the msg types by the following command.

rosmsg show geometry_msgs/Twist

whose output is

geometry_msgs/Vector3 linear
  float64 x
  float64 y
  float64 z
geometry_msgs/Vector3 angular
  float64 x
  float64 y
  float64 z

Hope this helps, Karthik