ros2 access current LaunchConfiguration

ros2

asked 2019-05-07 06:36:29 -0500

bergercookie
257 ●13 ●21 ●24

updated 2019-05-08 16:42:32 -0500

William

17335 ●101 ●182 ●262 http://wjwwood.io/

I'm in the middle of migrating a ROS1 app of mine to ROS2 and I'm currently trying to convert a .launch file to a python script.

I want to be able to pass a command line argument to the script and then get its value in the generate_launch_description call.

This is how I currently pass extra arguments to the LaunchDescription:

run_rqt_arg = DeclareLaunchArgument(name="run_rqt",
                                    default_value="True",
                                    description="Launch RQT?")
run_rviz_arg = DeclareLaunchArgument(name="run_rviz",
                                     default_value="True",
                                     description="Launch RVIZ?")

if run_rqt:
    rqt = Node(...)
    l.append(rqt)
if run_rviz:
    rviz = Node(...)
    l.append(rviz)

return LaunchDescription(l, run_rqt, run_rviz)

I'm running the launch script via ros2 launch ...

Is the passing of extra arguments handled correctly? How do I fetch the values of these cli args at runtime?

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2

answered 2019-05-08 16:53:57 -0500

William

17335 ●101 ●182 ●262 http://wjwwood.io/

The launch argument's value is stored in the "Launch Configurations", and those can be accessed using a substitution called launch.substitution.LaunchConfiguration(name) -> string.

If you want to do something conditionally based on this, I'd recommend using a launch.Condition which may be passed to any launch.Action, e.g.:

def generate_launch_description():
    run_rqt_arg = DeclareLaunchArgument(
        name="run_rqt",
        default_value="True",
        description="Launch RQT?")
    run_rviz_arg = DeclareLaunchArgument(
        name="run_rviz",
        default_value="True",
        description="Launch RVIZ?")

    rqt = Node(...,
        condition=launch.conditions.IfCondition(launch.LaunchConfiguration("run_rqt")))
    rviz = Node(...,
        condition=launch.conditions.IfCondition(launch.LaunchConfiguration("run_rviz")))

    return launch.LaunchDescription([run_rqt_arg, run_rviz_arg, run_rqt, run_rviz])

Comments

Hi William, is this feature (launch.substitution.LaunchConfiguration(name) -> string) still supported in the current dashing version? I have been trying to use launch.substitutions.LaunchConfiguration to access my arguments but it does not return a string. Any ideas on that?

I have also opened a question for this: https://answers.ros.org/question/3407...

relffok ( 2019-12-26 13:16:28 -0500 )edit

This is not supported anymore indeed.

achille ( 2021-03-23 18:32:28 -0500 )edit

So this answer is now out-of-date?

M@t ( 2021-07-05 18:52:27 -0500 )edit

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9

answered 2020-08-10 19:04:50 -0500

jrgnicho

486 ●3 ●12 ●14 http://rosindustrial.org/

I was able to evaluate launch arguments in a custom function outside of the LaunchDescription by using the OpaqueFunction launch action feature, see this link:

https://github.com/jrgnicho/collabora...

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1

I had the same issue of evaluating launch arguments. After a bit of struggle, the OpaqueFunction worked better than expected. My code is so much cleaner. Thank you for this!

ROS2 launch package definitely needs some documentation. It is a complete mystery right now. If anyone has questions on how I managed to use OpaqueFunction, I can help you out.