ROS Introduction

ROS: Robot Operating System

• 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

middleware concepts

• topics (publish - subscribe)
• services (remote procedure calls)
• nodes: logical computing components, several per process possible
• central naming service (roscore)
• remapping: renaming of nodes, topics, etc.
• central parameter storage

further reading

• http://wiki.ros.org
• Clearpath Tutorials

catkin build system

• extends cmake to facilitate package management dependencies, installation to standard locations
• catkin_make, catkin_make_isolated, catkin tools
• hierarchical stacking of workspaces:

  /opt/ros/<distro>
   ⮤ /vol/famula/stable/ros/<distro>
      ⮤ /homes/juser/ros
  

  load config with: source <workspace dir>/setup.bash
• workspace structure
  • src/
  • build/
  • devel/
    • setup.bash

catkin_make_isolated

# create your catkin workspace
mkdir -p ~/ros/src
cd ~/ros/src
source /opt/ros/*/setup.bash # source your underlay workspace
catkin_init_workspace

# clone lecture repository from github
git clone https://github.com/rhaschke/lecture
# catkin_make_isolated needs to run from root of your workspace
cd ..
catkin_make_isolated

catkin tools

# install catkin tools (if not yet available)
sudo apt install python3-catkin-tools python3-osrf-pycommon

# create your catkin workspace
mkdir ~/ros
cd ~/ros
# catkin tools can remember your underlay workspace:
catkin config --extend /opt/ros/<distro>
mkdir src
cd src

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

# catkin can build from any folder in your workspace
cd lecture
catkin build

For more details on catkin config and catkin create pkg follow the links.

package structure

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

example ros session

source ~/ros/devel/setup.bash
roscore &
rostopic pub -r 1 chatter std_msgs/String "Hello World" &
rostopic echo chatter

Inspect ros universe:

rosnode list
rostopic list
rosservice list
rosmsg list

rqt_graph

Remapping arguments

rosrun roscpp_tutorials talker chatter:=foobar
rosrun roscpp_tutorials listener chatter:=foobar