Passing parameters to Node() and LaunchDescription()

Question

I am lost :) Here is the problem (ROS2). Say, I have

params_file = LaunchConfiguration('params_file')
declare_params_file_cmd = DeclareLaunchArgument(
    'params_file',
    default_value=def_nav2_params_path 
        if robots[0]['name']=='' else def_nav2_params_path_multi,
    description='Full path to the ROS2 parameters file to use for all launched nodes')

Now I have access to this command line parameter in some node:

params_file = LaunchConfiguration('params_file')

So far so good.

But let's say I want to modify the file in a "calling" code:

namespaced_params = ReplaceString(
    source_file=params_file, replacements={
        "namespace"  :  (namespace),                # /robot1
        "robot_name" :  (robot['name']),            # robot1                
    }
)

Now I want the node to use that modified file:

robot_localization_node = Node(
    package='robot_localization',
    executable='ekf_node',
    name='ekf_filter_node',
    namespace=namespace,
    output='screen',
    parameters=[namespaced_params, {'use_sim_time': use_sim_time }]
) 

It works fine. However, we also have LaunchDescriptions, so I can call one launch file from another:

IncludeLaunchDescription(
    PythonLaunchDescriptionSource(os.path.join(def_launch_dir, 'bringup_launch.py')),
    condition=LaunchConfigurationNotEquals('mode', 'simple'),
    launch_arguments={
        'namespace': namespace,
        'use_namespace': 'True',
        'slam': slam,
        'map': map_yaml_file,
        'keepout_mask': keepout_mask,
        'use_sim_time': use_sim_time,
        'params_file': namespaced_params,
        'default_bt_xml_filename': default_bt_xml_filename,
        'autostart': 'True' }.items()),
])

Here, I have passed namespaced_params to launch file, but I have no idea how to use it! Because in that launch file I see the already familiar

params_file = LaunchConfiguration('params_file')

which reads a command line argument, so I assume, it will get an initial, non-modifier params file. So how can I access namespaced_params?

Thank you.

=================

I'll try to rephrase it shorter: if in a "main" launch file I have

params_file = LaunchConfiguration('params_file')
declare_params_file_cmd = DeclareLaunchArgument(
    'params_file',
    default_value=def_nav2_params_path 
        if robots[0]['name']=='' else def_nav2_params_path_multi,
    description='Full path to the ROS2 parameters file to use for all launched nodes')

and then I do this:

namespaced_params = ReplaceString(
    source_file=params_file, replacements={
        "namespace"  :  (namespace),                # /robot1
        "robot_name" :  (robot['name']),            # robot1                
    }
)

and pass namespaced_params as one of launch_arguments:

IncludeLaunchDescription(
    PythonLaunchDescriptionSource(os.path.join(def_launch_dir, 'bringup_launch.py')),
    condition=LaunchConfigurationNotEquals('mode', 'simple'),
    launch_arguments={
        'namespace': namespace,
        'use_namespace': 'True',
        'slam': slam,
        'map': map_yaml_file,
        'keepout_mask': keepout_mask,
        'use_sim_time': use_sim_time,
        'params_file': namespaced_params,
        'default_bt_xml_filename': default_bt_xml_filename,
        'autostart': 'True' }.items()),
])

Then which of the two will I get inside bringup_launch.py, when I issue params_file = LaunchConfiguration('params_file') ?

In other words, how can I access launch_arguments that I passed to bringup_launch.py?

Answer 1

I have figured it all out. A fully functional example at https://robotics.snowcron.com, in the "multiple robots" section.