ROS 2 Topics

ROS 2 Topic Overview

In ROS 2, topics are the communication channels used for publish-subscribe messaging. They allow nodes to exchange data asynchronously without direct connections. Here's how it works:

1. Publishers: Nodes that send messages to a topic. For example, a sensor node might publish temperature readings to a /temperature topic.
2. Subscribers: Nodes that receive messages from a topic. For instance, a logging node might subscribe to the /temperature topic to record data.
3. Messages: The data structure exchanged over topics. These are predefined formats (like integers, strings, arrays, etc.) specified in .msg files.

Key Features:

• Decoupled Communication: Publishers and subscribers do not need to know about each other.
• Topic Names: Identified by strings (e.g., /robot/speed).
• Quality of Service (QoS): Configurations like reliability and durability to ensure robust communication in various environments.
• Tools:
  • Use ros2 topic list to view active topics.
  • Use ros2 topic echo to see the data published on a topic.
  • Use ros2 topic pub to manually publish data for testing.

This structure supports scalable and modular robotic applications.

Renaming a Topic at Runtime

Renaming a node at runtime is useful when their are two ROS packages with the same node name. This method will allow you to change the name of the node so that both packages can run with out interference.

The command to rename a topic is:

ros2 run {package_name} {node_name} --ros-args -r __{topic_old_name}:{topic_new_name}