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I am migrating one of my ROS 1 launch files to ROS 2 launch.xml, and I need help implementing an if condition.
I want to implement a condition such as the following:
<param name="x" value="0.0" if="$(var condition)" />
But this is not working with ROS 2 launch.xml. The ROS 2 design documents mentions the eval expression, but there is no documentation on how to use it.
A workaround that can be used in the XML format is the tag <let>. This tag works in galactic with the argument "if". Your launchfile would then look like this:
<let name="x" value="true" if="$(var condition)"/>
<let name="x" value="false" unless="$(var condition)"/>
<node .......>
<param name="x" value="$(var x)"/>
</node>
It uses a little bit more lines but I think it's a useful method if you don't want to rewrite all of the file in Python
For others - there is a nice new tutorial about ROS 1/2 launch files, called rosetta_launch.
ROS1 - XML, ROS2 - Python.
It can be helpful with transition from XML to Python launchers.
I saw this yesterday, it's indeed a wonderful resource :)
It is currently not possible, there is an issue in the ros2 git repo: https://github.com/ros2/launch_ros/is...
Asked: 2022-08-14 12:23:03 -0600
Seen: 2,503 times
Last updated: Feb 07 '23
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A launch file in ROS 2 can be written in Python, XML, or YAML. So, a workaround is to rewrite your launch file in Python. Please read the documentation for more information.
Yep, that's what I eventually did.