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Embedding a launch file with a parameter

asked 2013-05-16 23:34:48 -0600

markkre gravatar image

updated 2013-11-14 11:33:03 -0600

tfoote gravatar image

I have two ros launch files, A.launch and B.launch.

I want B.launch to be included in A.launch like that:

A.launch:

<launch>
    <node name="rosbridge" pkg="rosbridge" type="rosbridge.py" />
    <include file="$(find some_package_name)/launch/B.launch">
    </include>
    ...
</launch>

Works pretty nice. However, it becomes a problem, as soon as there is a parameter necessary in B.launch:

B.launch:

<launch>
    <node name="$(arg START_NODE_NAME)" pkg="some_package_name" type="some_type">
    </node>
</launch>

I tried to use the following tag in A.launch:

<launch>
    <node name="rosbridge" pkg="rosbridge" type="rosbridge.py" />
    <include file="$(find some_package_name)/launch/B.launch">
            <arg name="START_NODE_NAME" value="goal_server" />-->
    </include>
    ...
</launch>

but that didn't work out either.

Is that scenario just not possible?

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2 Answers

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answered 2013-05-17 01:19:19 -0600

dornhege gravatar image

You're on the right track. You only need to define the arg in B.launch, i.e. add

<arg name="START_NODE_NAME" />

to the top of B.launch.

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works, thanks!

markkre gravatar imagemarkkre ( 2013-05-23 02:06:55 -0600 )edit
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answered 2013-05-17 08:01:00 -0600

Thomas D gravatar image

The answer from @dornhege will work with no problems.

To go a bit further, I tend to treat launch files like a separate language, where each individual launch file is a function and the <arg> tags at the top of the launch file are the function parameters that have default values. To accomplish that I would put the following line just below the <launch> tag in both launch files:

<arg name="START_NODE_NAME" default="goal_server"/>

There are two benefits to this approach:

  1. In A.launch you can simply have the following line:

    <include file="$(find some_package_name)/launch/B.launch"/>
    

    and you will have B.launch use goal_server as the node name.

  2. You can remap arguments for your launch files when starting A.launch from the command line:

    roslaunch your_package A.launch START_NODE_NAME:=new_goal_server
    

    This is helpful when you want to try changing a few things without necessarily going into the actual files to modify values.

More tips can be found here for using roslaunch with large projects.

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Unfortunately this won't work. You still have to give the arg in 1., when you include B.launch and basically say: <arg name="START_NODE_NAME" value="$(arg START_NODE_NAME)"/>. If you don't, the default will always be used, even if you start as in 2! Changing this behavior is a proposed feature.

dornhege gravatar imagedornhege ( 2013-05-17 08:07:21 -0600 )edit

Thanks @dornhege. I thought this works for me, but I'll double-check it now. Do you know of an issue or ticket link for this where the discussion can continue?

Thomas D gravatar imageThomas D ( 2013-05-17 08:48:24 -0600 )edit

Proposed in http://www.ros.org/wiki/sig/roslaunch as "bubbling args".

dornhege gravatar imagedornhege ( 2013-05-17 09:36:44 -0600 )edit

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Asked: 2013-05-16 23:34:48 -0600

Seen: 696 times

Last updated: May 17 '13