use parameters from python launch file in node

Question

I am trying to use parameters specified in my .launch.py file, but a ParameterNotDeclaredException is thrown when accessing any parameter. Does anyone know why? I try to access the parameters like this from within my Node:

self.get_parameter('buffer_size')

Here is the launch file. I'm using Foxy and Python

from launch import LaunchDescription
from launch_ros.actions import Node
def generate_launch_description():
    return LaunchDescription([
        Node(
            package='blackfly_calibration',
            executable='broadcaster',
            parameters=[
                {"capture_frequency": 20.0},
                {"buffer_size": 10},
                {"image_topic": "/camera/image_raw"}
            ],
        )
    ])

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Originally posted by rosnoob145 on ROS Answers with karma: 13 on 2021-08-15

Post score: 0

Answer 1

Before calling get_parameter, you had need to call;

self.declare_parameter(“buffer_size”,0)

Here you initialize buffer_size with a default value of 0, you can set a desired default parameter.

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Originally posted by Fetullah Atas with karma: 819 on 2021-08-16

This answer was ACCEPTED on the original site

Post score: 1

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Original comments

Comment by rosnoob145 on 2021-08-16:
thank you so much!