ROS Topics

• ROS 2 Topics allow unidirectional communication between ROS 2 Nodes.

• When using ROS 2 Topics, a ROS Node can act as a publisher, subscriber, or both.

• A ROS Node acting as a publisher can publish data on a ROS Topic, and a subscriber ROS Node can subscribe to a ROS Topic.

• Publisher and Subscriber Nodes will exchange ROS Messages over a ROS Topic.

• A ROS Message is a simple data structure comprising typed fields (integers, floating point numbers, booleans, etc.), so a ROS Message can hold data of various types.

Consider this analogy

• Let’s say you are subscribed to a newspaper called The Galactic, published by a publishing house called OSRF.

• Every morning your paperboy, Jon Doe, will deliver this newspaper to you.

OSRF <--> ROS 2 Publisher Node

• OSRF, acting as the Publisher Node, is publishing the newspaper.

You <--> ROS 2 Subscriber Node

• You, along with your neighbors who are subscribed to the newspaper, are the Subscriber Nodes.

Jon Doe <--> ROS 2 Topic

• Jon Doe, the paperboy delivering the newspaper from the publisher to its subscribers, acts as the ROS 2 Topic.

The Galactic Newspaper <--> ROS 2 Message

• The physical newspaper represents the ROS 2 Message.

Sports and Technology Sections of The Galactic <--> Data Fields in ROS 2 Message

• The sections of the newspaper are equivalent to the Data Fields defined in the ROS 2 Message.