The intention of this collection is to give you a very quick overview of ROS and act a 'cheatsheet'. For a more through analysis of ROS and its packages, refer to the ROS wiki.
Note:
Commands followed by a ✶ will take over an instance of your terminal. As a result, to run each instance of these commands, you will need a new terminal (having a terminal emulator that can be tabbed will go a long way in preventing clutter). Don't forget to pay attention to the output of these programs as they are used for warnings and errors. To end a program while keeping the terminal window open, press Ctrl-C . Additionally, be careful to not accidentally close these terminals as they will end the program they are running.
$ roscore$ rosrun package-name executable-name arg-name:=arg-value:= assignment.
Keep in mind that rosrun starts only one node. For more nodes, you need more terminals and other instances of rosrun.
$ roslaunch package-name launch-file-name$ rosnode list /rosout node which is started by roscore at all times.
$ rosnode info node-name$ rostopic list$ rostopic echo topic-name$ rostopic info topic-name$ rosmsg show message-type-name$ rostopic pub --rate=x topic-name message-type msg$ rosbag record -O filename.bag topic-names-a records on every topic. -j compresses the recording. -x "regex" excludes a topic that matches the regex from the recording. Some topics (e.g. /camera/rgb/image_raw) will take a lot of space in a bag file. In such scenarios, this flag is handy. $ rosbag info filename.bag$ rosbag play filename.bag$ rosrun rviz rviz$ rviz$ roslaunch turtlebot3_gazebo turtlebot3_gazebo_rviz.launch✶ Launches an RViz instance that automatically connects to the gazebo simulator and sets up the RViz based on the waffle_pi robots.
The ROS software is provided in packages. These packages include nodes, libraries, datasets, or anything that constitutes something useful. A package is usually maintained in a folder with the same name and has a number of files and folders. The relevant files and folders for this course are,
msg/: Folder containing Message (msg) types.scripts/: Executable scripts.launch/: Package launch files.worlds/: Folder containing the world files.CMakeLists.txt: CMake build file.package.xml: An XML file that holds information about the package (packages name, authors, dependencies, etc.) and is required to have the package be compliant with the ROS ecosystem.To create a ROS package, you need to first navigate to the source directory in your catkin workspace,
$ cd ~/catkin_ws/src/Then we can use catkin_create_pkg to create a package,
$ catkin_create_pkg package_name [dependency1] [dependency2] [dependency3] ...Here is an example package with some basic dependencies,
$ catkin_create_pkg intro_robo_sample_pkg std_msgs rospy roscppRunning the above command will create a folder with the name intro_robo_sample_pkg, which includes some basic files and folders. For further information on creating ROS packages, refer to this tutorial.
Run the following command to build your new package,
$ cd ~/catkin_ws && catkin_make
$ source devel/setup.bash msg files are simple text files that describe the fields of a ROS message. msgs are simply text files with with a field type and a field name per line. Here is the Vector3 msg as an example,
float64 x
float64 y
float64 z
In the above example, we can see that the Vector3 msg has three 64bit float fields named x,y, and z. In a ROS msg file, the field types always come on the left are immediately followed by a name that will refer to that name. The following filed types are allowed,
Attention: Although we will be using Python (which is dynamically typed), you should pay close attention to the filed types of the msg you are using. If you assign an inappropriate value to a filed, python will not complain, but ROS will refuse to publish your msg.
If you have included a msg file in your package, you should be able to easily reference it in your scripts. For more information, refer to this tutorial
source your-neotic-directory/devel/setup.bash . chmod u+x script_name .