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It's the same topic but different data comes from the different sources. The tf listener aggregates this data from different parts of the system that have knowledge about different transforms. For example the ekf knows about odometry, amcl knows about the localization in the map, and the robot state publisher knows about the joint positions. If you put that together you can know about the gripper position in the frame of the map. If you are missing any of those links you cannot get the aggregate transform but only incremental parts of that transform.