joint_states_aggregator and joint_state_publisher

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Hello,

I'm working with NXT-ROS. I have created an application and when i was running the rxgraph I realized that there is a node i don't know: joint_state_publisher. I think it isn't part of the NXT software, but part of basic ROS. I don't really know what it does, I know it is subscribed to a topic called joint_state and that it publishes another topic called joint_states. In the wiki it just says that publishes a JointState type of message where all the joints are defined. I think it might be that it receives information from the node nxt_ros about each of the sensors and it publishes all in a single topic.

Related to this, I thought that this was what the node joint_states_aggregator did.