ROS2_pubsub/README.md

# pubsub - Publisher & Subscriber Package
Minimal Publisher & Subscriber Template for ROS2.  
```
Created for ROS Workshop 2020  
Course Roverentwicklung für Explorationsaufgaben  
Institute for Space Systems  
University of Stuttgart.
```  
Class Code created by [Patrick Winterhalder](https://www.irs.uni-stuttgart.de/en/institute/team/Winterhalder/),  
[IRS](https://www.irs.uni-stuttgart.de), University of Stuttgart.  
  
  
## Workshop Prerequisites
In order to run ROS2 you must install **Ubuntu 20.04 LTS** on a capable machine (preferrably desktop/laptop).  
* Install [Ubuntu 20.04](https://help.ubuntu.com/lts/installation-guide/index.html)

For a successful workshop you must conduct [this installation on your desktop machine](https://egit.irs.uni-stuttgart.de/RoverLehre/ROS2_pubsub/src/branch/master/non-ros-files/workshopinstall.sh) or [this installation on your Raspberry Pi](https://egit.irs.uni-stuttgart.de/RoverLehre/ROS2_pubsub/src/branch/master/non-ros-files/rpi_install.bash). Go through the commands of these *.bash file line by line and check if every commands finishes without errors! Following these .bash files should do the following:  

* Install Visual Studio Code using the [Ubuntu Software Installer](https://wiki.ubuntuusers.de/Ubuntu_Software/)
* Install [Git](https://linuxconfig.org/how-to-install-git-on-ubuntu-20-04-lts-focal-fossa-linux) (no account required yet)
* Install [ROS2](https://index.ros.org/doc/ros2/Installation/Foxy/Linux-Install-Debians/) (choose "desktop" on PC or "base" on Raspberry Pi, this eliminates all GUI tools from the installation, e.g. rviz and rqt).
  * Also install _argcomplete_
  * No need for _ROS 1 bridge_ or _RMW implementations_
  * Install and update _rosdep_

After successfully installing ROS2 you should get to know it by working through the ["Beginner: CLI Tools"](https://index.ros.org/doc/ros2/Tutorials/) tutorial. This will teach you how to [configure your ROS 2 environment](https://index.ros.org/doc/ros2/Tutorials/Configuring-ROS2-Environment/) and you will learn about:  

* Source setup files (understand **Underlay** & **Overlay**)
* How to configure the .bashrc file (shell startup script), a good example is [here](https://egit.irs.uni-stuttgart.de/RoverLehre/ROS2_pubsub/src/branch/master/non-ros-files/bashrc_overlay.bash))
* Add all _colcon_ workspaces to the shell startup script
* Check environment variables (check for correct installation)
* Configure *ROS_DOMAIN_ID* (DDS Network Number)
* Work through the tutorials covering _turtlesim, rqt, topics, services, actions_

## Install Instructions
The following steps describe how you can create a local copy of this repository containing ROS2 publisher and subscriber class templates.
* Move to your colcon workspace `cd <workspace_path>` (eg. `cd ~/colcon_ws`)
* Clone this repository: `git clone https://egit.irs.uni-stuttgart.de/RoverLehre/ROS2_pubsub.git .` (include `.` at the end of the command in oder to copy everything to this locations!)
* Build workspace: `colcon build` , __Note:__ Only the files inside _/src/_ are of importance.
* Remember to run `source ~/<workspace_path>/install/local_setup.sh` after every build.  
In order to avoid this repetitive command, add line 23-27 from [_.bashrc_](https://egit.irs.uni-stuttgart.de/RoverLehre/ROS2_pubsub/src/branch/master/non-ros-files/bashrc_overlay.bash) to your shell startup script for every overlay you want to source. This script runs everytime you start a new console, thus loading your overlays automatically. This is very handy if you are working with multiple _colcon_ workspaces (overlays) simultaneously.


## Workshop Content
In this workshop you will:
* Create a new _colcon_ workspace
* Create a new package inside your newly created _colcon_ workspace
  * `ros2 pkg create --build-type [ament_cmake, ament-python] <package_name>`
* Build your _colcon_ workspace, this means making it a functional ROS2 workspace from which you can start nodes: 
  * First move to your workspace root: `cd ~/<workspace_path>`
  * Run `colcon build --symlink-install`
* Add your workspace overlay to the shell startup script for sourcing everytime you open a new console:
  * Add [this](https://egit.irs.uni-stuttgart.de/RoverLehre/ROS2_pubsub/src/branch/master/non-ros-files/bashrc_overlay.bash) to the end of .bashrc (`sudo nano .bashrc`)
  * In [this template](https://egit.irs.uni-stuttgart.de/RoverLehre/ROS2_pubsub/src/branch/master/non-ros-files/bashrc_overlay.bash) find all instances of "`~/ws_overlay_foxy`" and replace it with the path to your own _colcon_ workspace (replace `~/` with `$HOME` for representing the home directory variable in bash scripts)
* Create a custom ROS message (*.msg) in order to define custom topics to exchange information between nodes by following [these instructions](https://egit.irs.uni-stuttgart.de/RoverLehre/ROS2_pubsub/src/branch/master/non-ros-files/instructions_custom_topics.md).

## Rules and Standard
In order for your code to work and to prevent major problems please read through [this document](https://egit.irs.uni-stuttgart.de/RoverLehre/ROS2_pubsub/src/branch/master/non-ros-files/Programming_Rules.md). This will give you a brief oversight over how to develop a ROS2 package using Python.

## Presentation
The workshop's content is covered in [this presentation](https://egit.irs.uni-stuttgart.de/RoverLehre/ROS2_pubsub/src/branch/master/non-ros-files/ws-05-ros-workshop%20%281%29.pdf).