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roslaunch - namespace substitution within group tags

asked 2016-03-16 00:13:14 -0500

BSBingham gravatar image

I'm working on a multiple robot application and am trying to develop a clean launch file. I have multiple blocks of XML in my launch file that look like...

<group ns="r1">
  <include file="$(find mypack)/launch/robot.launch">
    <arg name="namespace" value="r1" /> 

I need to pass the namespace to the robot.launch file explicitly (long story). I don't like it that I have to input the "r1" value twice. It would be more pleasing if I could use substitution to assign a value to the namespace argument so that I only had to define the "r1" value once. Something like...

<group ns="r1">
  <include file="$(find mypack)/launch/robot.launch">
    <arg name="namespace" value="$(arg ns)" /> 

I tried to have an argument before the group tag that I reassigned each time, but that caused errors. Evidently I can't reassign arguments.

Any creative thoughts much appreciated.

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answered 2016-03-16 01:54:36 -0500

mgruhler gravatar image

Well, what should work is the following:

  • have your robot.launch as it is
  • a robot_ns.launch with the following in it:

    <arg name="my_ns"/>
    <group ns="$(arg my_ns)">
        <include file="$(find mypack)/launch/robot.launch">
            <arg name="namespace" value="$(arg my_ns)" /> 
  • and then, in the top-level launch file, do the following:

    <include file="$(find mypack)/launch/robot_ns.launch">
        <arg name="my_ns" value="r1" /> 
    <include file="$(find mypack)/launch/robot_ns.launch">
        <arg name="my_ns" value="r2" /> 

You then don't reassign arguments (which you actually cannot) and you only have to write the namespaces out once.

I guess you could also have this in just one launch file, if your robot.launch could handle an empty namespace argument with the group tags correctly.

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Asked: 2016-03-16 00:13:14 -0500

Seen: 11,895 times

Last updated: Mar 16 '16