[launch_ros] add ability to pass parameters to Node actions

[wjwwood]

Currently you can pass remapping arguments to Node as a dict, but to set parameters in a node from a launch file you need to pass a normal argument which points to an existing .yaml file.

To pass parameters via the launch file (without predefining them in an external .yaml file) will ultimately require the ability to pass parameters via the command line one at a time, which as of right now is not implemented yet.

In the meantime, individually specified parameters in a launch file for a node could be written into a temporary .yaml file by launch and then passed to the node, deleting the file after the node exits. However, I think this would step on a user specified parameter .yaml file unless the node can take more than one right now (it was discussed, but I don't know off-hand if it was implemented). In either case, if launch also lets you specify one or more .yaml files to be used as parameters (in addition to, and at the same time as, individually specified parameters for a node), then launch could just combine all of the yaml files and parameter kay-value pairs into a single .yaml file, cascading them in order (overwriting keys that appear more than once, with last wins).

It might look something like this:

launch_ros.actions.Node(...,
  parameters=[
    '/path/to/first_parameter_file.yaml',
    launch_ros.actions.node.NodeParameters({
      'foo': '1',
      // can have substitutions
      [LaunchConfiguration('ros_namespace'), '.my_node.executable_location']:
        [ExecutableInPackage('my_node', 'my_package')],
      ...,
    },
    [PackageShareDir('my_package'), Dir('config') / 'my_config_file.yaml'],
  ],
)

[sloretz]

In the meantime, individually specified parameters in a launch file for a node could be written into a temporary .yaml file by launch and then passed to the node, deleting the file after the node exits. However, I think this would step on a user specified parameter .yaml file unless the node can take more than one right now (it was discussed, but I don't know off-hand if it was implemented).

Multiple yaml files can be given on the command line. If two files specify a value for the same parameter then the value from the later file is used.

ros2 run demo_nodes_cpp talker __params:=generic-default-values.yaml __params:=more-specific-values.yaml

[wjwwood]

Cool thanks!

[sloretz]

Is this ticket complete now that #135 has been merged?

[dhood]

nah, it didn't include passing parameters as dicts

[dhood]

(which I'm working on now)

[poonam1120]

Hi,
I want to set value of use_sim_time as true when I am launching node via .launch.py file but I am not able to do this.
Node is getting launched with yaml file but not sure how to set value for use_sim_time here.
/my code snippet/
launch_ros.actions.Node(
package='test', node_executable='test_node', node_name='test_node',
output='screen',
parameters=[
parameters_file_path,
str('/home/root-pc/test.yaml'),
[EnvironmentVariable(name='FILE_PATH'), os.sep, 'test.yaml'],
],
),

****/
Any help would be appreciated.

Thanks.

[sloretz]

Hi @poonam1120,

I think this question would be a better fit for https://answers.ros.org/questions/ . Many more people watch that site, so you're likely to get an answer quicker. Comments on closed issues often don't get responses because closed issues on github aren't very visible.