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ROS2 Parameters

ROS / ros world

Using ROS2 parameter file from cli and launch file Use multiple parameters files to demonstrate parameter override

parameter file

Demo:

Simple python Node with multiple parameters

Node 
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import rclpy
from rclpy.node import Node

PARAM1 = "param1"
PARAM2 = "param2"

class MyNode(Node):
    def __init__(self):
        node_name="minimal"
        super().__init__(node_name)
        p1 = self.declare_parameter(PARAM1, 1)
        p2 = self.declare_parameter(PARAM2, 2)
        self.get_logger().info(f"P1: {p1.value}")
        self.get_logger().info(f"P1: {p2.value}")

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

if __name__ == '__main__':
    main()

Param files

params1.yaml
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minimal:
  ros__parameters:
    param1: 10
    param2: 20
params2.yaml
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/**:
  ros__parameters:
    param1: 100
    param2: 200

wildcard

The params2.yaml use wildcard as node name matching

usage

wildcard

Wildcards can be used for node names and namespaces.
- * matches a single token delimited by slashes (/). - ** matches zero or more tokens delimited by slashes. - Partial matches are not allowed (e.g. foo*).

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/**:
    ros__parameters:
        wildcard_full: "Full wildcard for any namespaces and any node names"

/**/parameter_blackboard:
    ros__parameters:
        wildcard_namespace: "Wildcard for a specific node name under any namespace"

/*:
    ros__parameters:
        wildcard_nodename_root_namespace: "Wildcard for any node names, but only in root namespace"
use default params value declare in code
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# run node without load any parameter file
ros2 run ros_py param_demo.py 
[INFO] [1740517785.377374134] [minimal]: P1: 1
[INFO] [1740517785.377601145] [minimal]: P1: 2
load params from file
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# Run node with parameter file
ros2 run ros_py param_demo.py --ros-args --params-file params1.yaml
[INFO] [1740517874.809880531] [minimal]: P1: 10
[INFO] [1740517874.810112715] [minimal]: P1: 20
load multiple params file

wildcard matching

params2.yaml has global match /**

load params from multiple files
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ros2 run ros_py param_demo.py \
--ros-args \
--params-file params1.yaml \
--params-file params2.yaml
[INFO] [1740518709.532923265] [minimal]: P1: 100
[INFO] [1740518709.533163666] [minimal]: P1: 200

Load multi parameter file from launch file

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from launch import LaunchDescription
from launch_ros.actions import Node
from ament_index_python.packages import get_package_share_directory
from pathlib import Path

def generate_launch_description():

    param_file = Path(get_package_share_directory('ros_py')).joinpath('config', 'param_demo.yaml')
    param_file_arm = Path(get_package_share_directory('ros_py')).joinpath('config', 'param_demo.arm.yaml')

    param_files = [param_file, param_file_arm]

    return LaunchDescription([
        Node(
            package='ros_py',
            executable='param_demo.py',
            name='param_demo',
            parameters=param_files,
        )
    ])

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from launch import LaunchDescription
from launch_ros.actions import Node
from ament_index_python.packages import get_package_share_directory
from pathlib import Path
import os

def generate_launch_description():

    use_arm_config = os.environ.get('USE_ARM_CONFIG', 'false').lower() == 'true'
    param_file = Path(get_package_share_directory('ros_py')).joinpath('config', 'param_demo.yaml')
    param_file_arm = Path(get_package_share_directory('ros_py')).joinpath('config', 'param_demo.arm.yaml')

    param_files = [param_file]
    if use_arm_config:
        param_files.append(param_file_arm)

    return LaunchDescription([
        Node(
            package='ros_py',
            executable='param_demo.py',
            name='param_demo',
            parameters=param_files,
        )
    ])
usage
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USE_ARM_CONFIG=true ros2 launch ros_py param_demo_simple.launch.py
USE_ARM_CONFIG=false ros2 launch ros_py param_demo_simple.launch.py

# or using export

Reference