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Understaning tf2 demo launch file

asked 2018-06-19 22:24:14 -0600

viveksudani gravatar image

I have one more question regarding the same on this page Writing a tf2 broadcaster (Python)(section 3 Running the broadcaster).

Why we need to initiate two different node named turtle1_tf2_broadcaster & turtle2_tf2_broadcaster. Can anyone explain whole code inside start_demo.launch which is here:

 <launch>
      <node pkg="turtlesim" type="turtlesim_node" name="sim"/>
      <node pkg="turtlesim" type="turtle_teleop_key" name="teleop" output="screen"/>

    <node name="turtle1_tf2_broadcaster" pkg="learning_tf2" type="turtle_tf2_broadcaster.py" respawn="false" output="screen" >
      <param name="turtle" type="string" value="turtle1" />
    </node>
    <node name="turtle2_tf2_broadcaster" pkg="learning_tf2" type="turtle_tf2_broadcaster.py" respawn="false" output="screen" >
      <param name="turtle" type="string" value="turtle2" /> 
    </node>

  </launch>
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answered 2018-06-20 04:47:48 -0600

destogl gravatar image

In ROS launch files are used to start multiple nodes with one command. In the above example one starts the same node multiple times but using different parameters. So basically following will happens:

  1. one starts turtle sim node with a name sim
  2. teleoperation node for turtlesim node is started
  3. node with a name turtle1_tf2_broadcaster is started and listens on a topic /turtle1/pose
  4. node with a name turtle2_tf2_broadcaster is started and listens on a topic /turtle2/pose

So basically the two broadcasters will broadcast different stuff depending on subscribed topic.

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@destogl, Thanks for reply. your explanation is well understood. But why we need two broadcasters. since we are running only one turtlesim node. I mean can't we run only one broadcaster instead of two?

viveksudani gravatar imageviveksudani ( 2018-06-24 01:00:33 -0600 )edit

If you read carefully the explanation on the end of the page you will see that second broadcaster is needed in the next tutorial. And here is just added for teaching purposes. See: Checking the results part

destogl gravatar imagedestogl ( 2018-06-24 15:51:26 -0600 )edit

Yay! I missed that lines😅. By the way thank you so much.😇 Now i m clear that second broadcaster has no role to play yet.

viveksudani gravatar imageviveksudani ( 2018-06-24 20:52:10 -0600 )edit

You are welcome! If you are happy with answer please mark it as answered.

destogl gravatar imagedestogl ( 2018-06-24 23:12:29 -0600 )edit
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answered 2018-06-20 04:16:19 -0600

sorry , maybe your answer is too big , in a word , launch file is a tool to launch some node (executable file) random

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Asked: 2018-06-19 22:24:14 -0600

Seen: 77 times

Last updated: Jun 20 '18