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PathJoinSubstitution and parameter config file

Using PathJoinSubstitution to build path to parameter yaml file.

Project

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├── CMakeLists.txt
├── config
│   └── params.yaml
├── launch
│   └── param_yaml_demo.launch.py
├── launch_tutorial
│   ├── __init__.py
│   └── simple_node.py
├── package.xml
└── src
param.yaml
config/params.yaml
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/**:
  ros__parameters:
    arg1: "from param file"
param_yaml_demo.launch.py
launch/param_yaml_demo.launch
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import os

from ament_index_python.packages import get_package_share_directory
from launch import LaunchDescription
from launch.actions import DeclareLaunchArgument
from launch.substitutions import PathJoinSubstitution
from launch.launch_description_sources import PythonLaunchDescriptionSource
from launch.substitutions import LaunchConfiguration
from launch_ros.actions import Node


def generate_launch_description():
    ld = LaunchDescription()

    config_file = PathJoinSubstitution([
        get_package_share_directory('launch_tutorial'),
        'config',
        'params.yaml'
    ])

    node = Node(
        package='launch_tutorial',
        executable='simple_node.py',
        name='simple',
        output='screen',
        parameters=[config_file])

    ld.add_action(node)
    return ld
simple_node.py 
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#!/usr/bin/env python3

import rclpy
from rclpy.node import Node

class MyNode(Node):
    def __init__(self):
        node_name="minimal"
        super().__init__(node_name)
        self.declare_parameter('arg1', "hello default")
        self.get_logger().info("Hello ROS2")
        self.get_logger().info(self.get_parameter("arg1").value)

def main(args=None):
    rclpy.init(args=args)
    node = MyNode()
    rclpy.spin(node)
    node.destroy_node()
    rclpy.shutdown()

if __name__ == '__main__':
    main()

Demo: Launch gz ros bridge

Launch gz bridge with yaml file that set from argument using:

  • DeclareLaunchArgument
  • LaunchConfiguration
  • PathJoinSubstitution
  • ParameterValue

```python from ament_index_python.packages import get_package_share_directory from launch import LaunchDescription from launch_ros.actions import Node from launch.substitutions import PathJoinSubstitution from launch.actions import DeclareLaunchArgument from launch.substitutions import LaunchConfiguration from launch_ros.parameter_descriptions import ParameterValue

PKG_BRINGUP = 'ardupilot_bringup' BRIDGE_CONFIG = "bridge.yaml" CONFIG_FOLDER = "config"

def generate_launch_description(): ld = LaunchDescription()

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config_file_arg = DeclareLaunchArgument(
    'config_file',
    default_value=BRIDGE_CONFIG,
    description='Name of the bridge config file'
)


config_file = LaunchConfiguration('config_file')

bridge_file = PathJoinSubstitution([
    get_package_share_directory(PKG_BRINGUP),
    CONFIG_FOLDER,
    config_file
])

ros_gz_bridge = Node(
    package="ros_gz_bridge",
    executable="parameter_bridge",
    parameters=[
        {'use_sim_time': True},
        {'config_file': ParameterValue(bridge_file, value_type=str)}
    ],
)

ld.add_action(config_file_arg)
ld.add_action(ros_gz_bridge)


return ld
```