roslaunch - namespace substitution within group tags

Question

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" /> 
  </include>
</group>

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)" /> 
  </include>
</group>

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.

---

Originally posted by BSBingham on ROS Answers with karma: 108 on 2016-03-16

Post score: 3

Answer 1

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)" /> 
        </include>
    </group>
  

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

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.

---

Originally posted by mgruhler with karma: 12390 on 2016-03-16

This answer was ACCEPTED on the original site

Post score: 1