Examples

Example #1: ROS 2 Node to Get and Set Parameters

Aim

To write a ROS 2 Node that reads parameters from a config.yaml file, prints them on the console, and modifies the phone number.

Code

node_param_get_set.py

#!/usr/bin/env python3
import rclpy
from rclpy.node import Node

class ParamNode(Node):
    def __init__(self):
        super().__init__('node_param_get_set')

        # 1. Read from Parameter Server
        self.get_logger().info("Reading from Parameter Server.")

        # Get all the parameters inside 'details'
        # Store the parameters in variables
        param_config_my = self.get_parameters_by_prefix('details')
        first_name = param_config_my['name.first'].value
        last_name = param_config_my['name.last'].value
        address = param_config_my['contact.address'].value
        phone = param_config_my['contact.phone'].value

        # Print the parameters
        self.get_logger().info(f">> First Name: {first_name}")
        self.get_logger().info(f">> Last Name: {last_name}")
        self.get_logger().info(f">> Address: {address}")
        self.get_logger().info(f">> Phone: {phone}")

        # 2. Modify the Phone Number
        self.set_parameters([rclpy.parameter.Parameter('details.contact.phone', rclpy.Parameter.Type.INTEGER, 55555)])
        new_phone = self.get_parameter('details.contact.phone').value
        self.get_logger().info(f">> New Phone: {new_phone}")

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

if __name__ == '__main__':
    main()

Explanation

• This ROS 2 node reads parameters from the parameter server, prints them, and modifies the phone number.

• It utilizes the ROS 2 rclpy library and leverages the get_parameters_by_prefix() function to access nested parameters.

• The parameters include first name, last name, address, and phone number. The node prints these values and updates the phone number to 55555.