TF and robot state publisher

I am unable to understand the robot state publisher . please help me!!!


The robot state pulisher what it does is based on the robot_description ( which is a URDF file or XACRO ), publishes into the TF topic the Axis of coordines of each of the physical elements that comprise the robot. Lets say if we have a two wheel robot, this robot state publisher will publish the frames and its position/orientation of the chassis in the world. The wheels position however will be a combination of the position described in the URDF and the motor angle to give the exact position and orientation in reference to the chasis.