Pls tell me the mechanism of TF outcomes of turtlebot [closed]

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Hi all, I have turtlebot2 and groovy. After roslaunching turltebot_bringup minimal.launch, and rosrunning tf tf_monitor, I can see the info of TF tree of different frames of joints and links. But I don't know by which way this happened, because in minimal.launch file and its sub-file(marked by include file...), I cannot find any broadcaster thing. I found "" and "<node pkg="robot_state_publisher" type="robot_state_publisher" name="robot_state_publisher">" in sub-file "_robot.launch". But I'm still confused in it. And I found turtlebot model files are located in turtlebot_description/urdf/graveyard/..., which are problematic after being converted to URDF and rvized. Thanks for your help!