Difference between revisions of "ROS HOWTO"

Revision as of 13:16, 18 April 2012

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ROS (Robot Operating System) is an open-source framework for the creation of software for robots. It is a very interesting tool, since it promises to take care of many lower-level issues that make realizing the software for autonomous robots so difficult and time-consuming. By leaving such issues (e.g., communication among modules) to ROS, the programmer can focus on the more interesting high-level issues (e.g., perception or reasoning). More precisely, in the words of its creators:

"ROS provides libraries and tools to help software developers create robot applications. It provides hardware abstraction, device drivers, libraries, visualizers, message-passing, package management, and more."

Though striving to be as easy-to-use as possible, ROS is a very complex tool. This is unavoidable, as autonomous robots themselves are extremely complex systems. Before you can start building your own software based on ROS, you have to devote a fair amount of time to studying how it works and how to use it. This part of the wiki is dedicated to helping you getting to grips with ROS as quickly as possible.

The ROS website itself includes a good deal of information and tutorials, and you are invited to use them. However, not all of them are very clear, nor all topics are equally covered. Here we'll try to complement what's provided by ROS with additional information, instead of saying the same things in another way.

Nodes

The basic element of a ROS-based software system is the node. A node is a module of the system, which communicates with other modules using ROS. Communications take the form of messages that are published on

In practice, a node is a single executable file: if you use C++, you will write a .cpp file including a main block (along with anything else it needs) and then compile it to produce such executable. A node can perform several types of activities, including:

• publish messages to a ROS topic
• request a service from ROS servers as a ROS client
• act as a ROS server, providing a service to ROS clients
• execute a task whenever a message is published on a ROS topic
• manage a timeout and execute a task whenever it expires
• execute a task periodically

By using this basic ROS node template and uncommenting the parts that you need, you can quickly set up the structure of the .cpp file of a node.

(with ROS, at present, you will use C++ or Python)