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ROS2, set parameters from file and directly?

asked 2021-01-03 12:51:46 -0500

mschratter gravatar image

I have one parameter which is defined inside the python launch file (multiple nodes use this parameter), and the other parameters should be loaded from a parameter file.

Is it possible to use a parameter file and to set parameters directly in a python launch file at the same time? In the documentation, I did not find a way to handle this. It looks like, it is only possible to set a parameter file or to define the parameters directly.

    trajectory_visualization_param = get_param_file('arg_trajectory_visualization, 'arg_trajectory_visualization.param.yaml')

    trajectory_source = "p3"

    trajectory_visualization_velocity_planner_node = Node(
              parameters=[{"trajectory_source": trajectory_source}],

I do not want to have something like a global parameter server.

Is there a way to handle this nicely, or how would you handle this?

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1 Answer

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answered 2021-01-06 13:04:03 -0500

jacobperron gravatar image

updated 2021-01-06 13:06:54 -0500

This can be done as of ROS Foxy.

To set a single parameter on all nodes in the same scope of a launch file, you can use the SetParameter action. The parameter will be set on all nodes launched after the SetParameter action, also applying to any included launch files.

For example, to set the ROS parameter use_sim_time for all nodes in a launch file, you can something like

import launch
import launch_ros.actions

def generate_launch_description():
    return launch.LaunchDescription([
        launch_ros.actions.SetParameter(name='use_sim_time', value=True),
        # 'use_sim_time' will be set on all nodes following the line above

This is also supported in front-end launch files, for example XML:

  <set_parameter name="use_sim_time" value="true" />
  <!-- 'use_sim_time' will be set on all nodes following the line above -->

Note, you can use a launch "group" to scope the SetParameter action. In the following example, the talker node does not have the use_sim_time parameter set, but the listener node does:

    <set_parameter name="use_sim_time" value="true" />
    <node name="listener" pkg="demo_nodes_cpp" exec="listener" output="screen" />
  <node name="talker" pkg="demo_nodes_cpp" exec="talker" output="screen" />

I'll add that it's currently not possible to set parameters from a parameters file in a similar way, though it would be interesting to add such a feature.

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Have you tried using "double-star" syntax in a YAML file?

    use_sim_time: true
Josh Whitley gravatar image Josh Whitley  ( 2021-04-21 12:31:33 -0500 )edit

The issue is that the YAML file must be passed to each Node action in the launch file. It would be nice to have an option to set a parameters YAML file with a global action in launch, such that it will be automatically passed to all nodes. I'm not sure it is straight-forward to implement such a launch action though.

jacobperron gravatar image jacobperron  ( 2021-04-22 15:48:18 -0500 )edit

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Asked: 2021-01-03 12:51:46 -0500

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Last updated: Jan 06 '21