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Ros2 Topic Pub Float32multiarray

8 min read Oct 01, 2024
Ros2 Topic Pub Float32multiarray

Publishing Float32MultiArray Messages in ROS 2

ROS 2, the next generation of the Robot Operating System, offers powerful tools for creating and using custom message types. One such message type, Float32MultiArray, is frequently used to represent data in multi-dimensional arrays. This article will guide you through the process of publishing Float32MultiArray messages in ROS 2.

Understanding Float32MultiArray

Float32MultiArray is a standard ROS 2 message type specifically designed to represent a multi-dimensional array of single-precision floating-point numbers (float32). This message type is particularly helpful when dealing with data like sensor readings, image data, or any other data that can be effectively represented as a multi-dimensional array.

Creating the ROS 2 Node

First, you'll need to create a ROS 2 node that publishes the Float32MultiArray messages. You can accomplish this using Python, C++, or any other supported language.

Here's a Python example:

import rclpy
from rclpy.node import Node
from std_msgs.msg import Float32MultiArray

class Float32MultiArrayPublisher(Node):

    def __init__(self):
        super().__init__('float32_multiarray_publisher')
        self.publisher_ = self.create_publisher(Float32MultiArray, 'my_topic', 10)
        self.timer_ = self.create_timer(0.5, self.publish_message)

    def publish_message(self):
        msg = Float32MultiArray()
        msg.data = [1.0, 2.0, 3.0, 4.0, 5.0]  # Example data
        self.publisher_.publish(msg)
        self.get_logger().info('Publishing: "%s"' % msg.data)

def main(args=None):
    rclpy.init(args=args)
    publisher = Float32MultiArrayPublisher()
    rclpy.spin(publisher)
    rclpy.shutdown()

if __name__ == '__main__':
    main()

Explanation:

  1. Imports: We import necessary libraries: rclpy for ROS 2 core functionality, Node to create a ROS 2 node, and Float32MultiArray for the message type.
  2. Node Class: The Float32MultiArrayPublisher class defines the node's functionality.
  3. Initialization:
    • We initialize the node with a name 'float32_multiarray_publisher'.
    • We create a publisher to send messages to the topic 'my_topic'. The queue size 10 specifies the maximum number of messages that can be queued if the subscriber is unavailable.
    • We create a timer that triggers the publish_message function every 0.5 seconds.
  4. Publishing Function:
    • The publish_message function generates a Float32MultiArray message.
    • We set the data attribute of the message with an example array: [1.0, 2.0, 3.0, 4.0, 5.0].
    • The message is published to the 'my_topic' topic.
    • A log message is printed with the published data.

Running the Node

Save the code as a Python file (e.g., float32_multiarray_publisher.py). Open a terminal and navigate to the directory where you saved the file. Run the node using the following command:

ros2 run your_package_name float32_multiarray_publisher.py

Replace your_package_name with the actual name of your ROS 2 package.

Subscribing to the Topic

To receive the published messages, you'll need another node subscribing to the 'my_topic' topic. This node can be built in any supported language as well.

Here's a simple Python subscriber example:

import rclpy
from rclpy.node import Node
from std_msgs.msg import Float32MultiArray

class Float32MultiArraySubscriber(Node):

    def __init__(self):
        super().__init__('float32_multiarray_subscriber')
        self.subscription_ = self.create_subscription(
            Float32MultiArray,
            'my_topic',
            self.listener_callback,
            10
        )
        self.subscription_  # prevent unused variable warning

    def listener_callback(self, msg):
        self.get_logger().info('Received: "%s"' % msg.data)

def main(args=None):
    rclpy.init(args=args)
    subscriber = Float32MultiArraySubscriber()
    rclpy.spin(subscriber)
    rclpy.shutdown()

if __name__ == '__main__':
    main()

Explanation:

  1. Imports: We import the required libraries.
  2. Node Class: The Float32MultiArraySubscriber class is defined.
  3. Initialization:
    • We initialize the node with a name 'float32_multiarray_subscriber'.
    • We create a subscriber to listen for messages on the 'my_topic' topic.
    • The listener_callback function is specified as the callback to be executed when a message is received. The queue size 10 controls the number of messages held in a buffer if the subscriber is unable to process them immediately.
  4. Callback Function:
    • The listener_callback function receives the Float32MultiArray message.
    • The data from the message is printed to the console.

Running the Subscriber

Create a new Python file (e.g., float32_multiarray_subscriber.py) with the subscriber code. In a separate terminal, navigate to the same directory and run the subscriber node:

ros2 run your_package_name float32_multiarray_subscriber.py

Once both the publisher and subscriber nodes are running, you should see the published data being received and logged by the subscriber node.

Important Notes

  • ROS 2 Workspace: Make sure you have set up a ROS 2 workspace and have the necessary packages installed (including std_msgs).
  • Topic Name: You can choose any topic name you like instead of 'my_topic'. Both the publisher and subscriber need to use the same topic name for communication.
  • Data Structure: Modify the msg.data array in the publish_message function to match the desired data structure and values you want to publish.
  • Frequency: Adjust the timer interval in the publisher node (the 0.5 value in the create_timer call) to control how frequently the messages are published.

Conclusion

This guide demonstrates how to publish Float32MultiArray messages in ROS 2, a fundamental task in robotics and other applications. By understanding how to create custom ROS 2 nodes and utilize message types like Float32MultiArray, you can effectively communicate data between different components in your ROS 2 systems. Remember to explore the vast array of available ROS 2 message types to choose the most suitable one for your specific data needs.

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