roslaunch group ns doesn't work

edit

Hello,

As far as I know, there is two ways to change topics in the launch file:

• using group ns (<group ns="t1"> <node ..... > </group>)
• using remapping for node

I have tried both methods. But the first method is not always working. For example, I’ve tried to run the turtlebot3_teleop_key node within a group namespace. But still, it publishes to /cmd_vel topic. But when I use remapping, it works (publishes /t1/cmd_vel).

I want to know why sometimes using does not work, or what are the requirements?

this is my launch file (in noetic):

<launch>
  <arg name="model" default="$(env TURTLEBOT3_MODEL)"/>
  <arg name="name_space" default="t1"/>

  <group ns = "$(arg name_space)">
    <param name="model" value="$(arg model)"/>
    <node pkg="turtlebot3_teleop" type="turtlebot3_teleop_key" name="turtlebot3_teleop"  output="screen">
      <!--remap from="/cmd_vel" to="/$(arg name_space)/cmd_vel"/-->
    </node>
  </group>

</launch>

If I comment remap part, it still publishes /cmd_vel topic, not /t1/cmd_vel