• middleware, i.e. inter-process communication
• hardware abstraction for robots
• message definitions (for RPC)
• package management system, tailored towards development
• collection of open-source software packages
• multi language: C++, Python, Java
• multi platform: (Ubuntu Linux), Windows 10, OSX

• topics (publish - subscribe)
• services (remote procedure calls)
• actions (preemptable, long-running tasks)
• nodes: logical computing components, several per process possible
• remapping: renaming of nodes, topics, etc.
• node parameters

• ROS2 packages use ament, a series of build helpers that hook into or extend existing build tools (like cmake or python's setuptools) to facilitate building and package management
• colcon is a meta build tool that crawls your workspace for packages and builds them
• hierarchical stacking of workspaces:

  /opt/ros/<distro>
    ⮤ /homes/juser/ros
  

  activate environment with: source <workspace dir>/setup.bash
• workspace structure
  • src/
  • build/
  • install/
    • setup.bash

# create your ROS workspace
mkdir -p ~/ros/src
cd ~/ros/src

# clone lecture repository from github
git clone https://github.com/rhaschke/lecture

# install colcon-top-level-workspace to allow building from any folder in your workspace
pip install git+https://github.com/rhaschke/colcon-top-level-workspace

# source your parent ROS environment
source /opt/ros/<distro>/setup.bash

# once build in your workspace's root folder
cd ~/ros
colcon build

• package.xml
  • defines folder as a ROS package
  • defines dependencies: build, test, run
  • author, license, package information
• CMakeLists.txt

source /opt/ros/<distro>/setup.bash
ros2 topic pub chatter std_msgs/msg/String 'data: "Hello World"' &
ros2 topic echo chatter

Inspect ROS universe:

ros2 node list
ros2 topic list
ros2 service list
ros2 interface list

rqt_graph