ROS2 Tutorial

ROS Tutorial

Introduction

The Robot Operating System (ROS) is a set of software libraries and tools for building robot applications. ROS2 has different packages for setting up programmes. Usually in ROS you can create packages in CPP and Python. Here we are focused in creating in packages in Python. A python package contain different files like package.xml - which contains the meta-information, setup.py - which contains the instruction set for the package to how to compile it, </package_name – which contains all the python scripts and this directory have always the same name as the package.

For creating a ROS package, it is necessary to operate in a specific workspace called ROS2 workspace. The directory on your hard drive where your ROS2 packages are stored and accessible by ROS2 is known as the ROS2 workspace. The ROS2 workspace directory is typically referred to as ros2_ws.

For create a package, you need to work specifically in ROS2^workspace. The directory on your hard drive where your ROS2 packages are stored and accessible by ROS2 is known as the ROS2 workspace. The ROS2 workspace directory is typically referred to as ros2_ws

When you need to compile a package for it make to work. The command which can be used by ROS2 to compile is the following:

> colcon build <

This command, which must be executed in the ros2 ws directory for it to function, will compile your whole src directory.

ROS2 Nodes

Each node in ROS2 should be in charge of a specific module, such as one node for managing wheel motors, another for managing a laser rangefinder, etc. Different channels are available for each node's communication with other nodes

Abb.11 Communication between nodes

Source: here

In essence, ROS nodes are ROS programs. Use the ROS2 command to get a list of all the nodes active on a system:

> ros2 node list <

ROS client libraries enable communication between nodes created in different programming languages. Various ROS APIs require standard functionality, which is implemented by a core ROS client library (RCL). Writing client libraries for different languages is now simpler.