Learning-ROS2

1 - Installation

I use ROS2 Humble: https://docs.ros.org/en/humble/Installation.html
Install terminator: sudo apt install terminator
Install python3-pip sudo apt install python3-pip
Install VS code IDE, and add extension of c++, python and cmake.

1-1 Setup environment for ROS2

We need to setup ROS2 evironmen in basrc to eable glabal running of ROS2 whenever we open terminal. To check setup.bash location, run the following in terminal;

cd /opt/ros   # locate ROS
ls

cd humble
ls

source setup.bash   # sourcing setup.bash

Setting up ROS2 evironment means that sourcing setup.bash. It is important to set up ROS2 environment for starting to use ROS2. We will add this initializing in bashrc to avoid sourcing this bash single time whenever we use ROS2. Open another terminal

source /opt/ros/humble/setup.bash   # test

gedit ~/.bashrc     # open barshrc file

Add this source /opt/ros/humble/setup.bash at the end of bashrc file and save it. Then we can start using ROS2 whenever opening terminal.

1-2 Launch a ROS2 prgram

Open terminator, split two vertical; In the first terminator;

ros2<space><tab><tab>
### >You will see action, launch, node, run

ros2 run demo_nodes_cpp talker      # run talker nodes

In the second terminator;

ros2 run demo_nodes_cpp listener      # run listener nodes

2 - Write ROS2 Program/Node

In this section, we will create ROS2 workspace in which ROS2 package would also be created. Then write the node inside the package, and then compile it and run it. To write ROS2 Program, it is needed to install ROS2 build tool (colcon) with sudo apt install python3-colcon-common-extensions. There is one more thing needed to do with colcon; it is to source the colcon bash in bashrc. Open terminal;

cd /usr/share/colcon_argcomplete/hook/
ls
### colcon-argcomplete.bash  colcon-argcomplete.zsh

gedit ~/.bashrc     # open the bashrc to source bash file

At the end line of bashrc, source bash by adding source /usr/share/colcon_argcomplete/hook/colcon-argcomplete.bash.

2.1 Create ROS2 workspace

To create ROS2 workspace, make directory of ROS2 worksapce under home; open terminator;

cd      # make sure home dir
ls

mkdir ros2_ws     # make ros2 workspace directory
ls

cd ros2_ws        
ls
mkdir src         # make src under ros2_ws
ls
### >src

build colcon    # build the ws using colcon
ls
### >build  install  log  src

cd install
ls
### >You will see some setup/bash files. It's important to care is local_setup.bash & setup.bash.

The difference between local_setup.bash and setup.bash is that sourcing local_setup source local_setup.bash means overlay and using whatever created under that workspace, but sourcing setup.bash means that using the created workspace plus underlay workspace which is global installed ROS2. So, it is highly recommended to source this setup.bash in bashrc. Open separate terminator;

gedit ~/.bashrc

### Add this and save->> source ~/ros2_ws/install/setup.bash

2.2 Create a Python & C++ Package

To create a ROS2 Node, we need a Package inside the created Workspace. Packages allow us to separate our code to reusable blocks. Packages are independent, i.e one package is for Camera, one package is for Motion Planning, and another is for Hardwar Control. To create a package, open terminator/terminal;

Python Package

cd ros2_ws/src    # cd to ros2_ws/src

ros2 pkg create my_py_pkg --build-type ament_python --dependencies rclpy      # Create ROS2 python package

ls    # check created package
### > my_py_pkg

After created Package, then compile the created package; Open Terminal;

cd ros2_ws/   # chage directory

colcon build      # compile if there is only one or all pkg

## OR ##

colcon build --packages-select my_py_pkg    # compile by selecting desired package

CPP Package

cd ros2_ws/src/     # cd to src
ls

ros2 pkg create my_cpp_pkg --build-type ament_cmake --dependencies rclcpp     # Create ROS2 C++ Package

ls
### > my_cpp_pkg  my_py_pkg