How to Use the COGAR Example Package

This section explains how to use the example_pkg ROS package. The package contains two nodes: talker and listener, which can be used to communicate via ROS topics.

Running the Talker Node

The talker node publishes messages to a topic called chatter. To run the node, use the following command in your catkin workspace:

rosrun example_pkg talker.py

This will start the talker node, and it will begin publishing messages to the chatter topic.

Running the Listener Node

The listener node subscribes to the chatter topic and prints the messages received. To run the node, use the following command in your catkin workspace:

rosrun example_pkg listener.py

Once the listener node is running, it will print the messages that the talker node is publishing.

Using the Launch File

You can also use a launch file to start both the talker and listener nodes simultaneously. The launch file simplifies the process of starting multiple nodes with a single command.

To launch both nodes at once, use the following command:

roslaunch example_pkg example.launch

This will start both the talker and listener nodes and automatically connect them through the chatter topic. Then you should see the following output in your terminal:



This video demonstrates how the result should look when the nodes are running successfully.

Viewing the Topic

You can check if the nodes are communicating properly by echoing the chatter topic:

rostopic echo /chatter

This will display the messages being published by the talker node and received by the listener node.

Troubleshooting

If you encounter issues, make sure that:

  1. ROS is properly installed and sourced.

  2. The nodes are correctly built and no errors appear when running the talker or listener.

  3. Ensure that the correct ROS master URI is set (e.g., ROS_MASTER_URI=http://localhost:11311).

For further help, refer to the installation instructions.