Understanding ROS Topics

This tutorial introduces ROS topics as well as using the rostopic commandline tools.

Before we move forward, let's start by making sure that we have roscore running, in a new terminal:

$ roscore
If you left roscore running from the last tutorial, you may get the error message:

roscore cannot run as another roscore/master is already running.
Please kill other roscore/master processes before relaunching
This is fine. Only one roscore needs to be running.

ROS Topics

The rostopic tool allows you to get information about ROS topics.

You can use the help option to get the available sub-commands for rostopic

root@erlerobot:~# rostopic -h
rostopic is a command-line tool for printing information about ROS Topics.

    rostopic bw    display bandwidth used by topic
    rostopic echo    print messages to screen
    rostopic find    find topics by type
    rostopic hz    display publishing rate of topic
    rostopic info    print information about active topic
    rostopic list    list active topics
    rostopic pub    publish data to topic
    rostopic type    print topic type

Type rostopic <command> -h for more detailed usage, e.g. 'rostopic echo -h'

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