Create packages

Create a package:

# catkin_create_pkg <package_name> [depend1] [depend2] [depend3]
$ catkin_create_pkg pkg_name std_msgs rospy roscpp

Package dependencies are stored in package.xml Navigate to the package directory:

# roscd <package_name>
$ roscd pkg_name

Copy files from other package:

$ roscp [package_name] [file_to_copy_path] [copy_from_this_path]

Publishing and subscribing

Publish using command line

$ rostopic pub <name of the topic> <type of the topic> [args...]
# press TAB after rostopic pub <name of the topic> <type of the topic>, it auto fills the information needed

Publisher, subscriber and other examples in python are available. Download as follows:

$ wget https://raw.github.com/ros/ros_tutorials/kinetic-devel/rospy_tutorials/001_talker_listener/talker.py
$ chmod +x talker.py
$ wget https://raw.github.com/ros/ros_tutorials/kinetic-devel/rospy_tutorials/001_talker_listener/listener.py
$ chmod +x listener.py

For the Service and Client samples in the tutorial, I got error: “ImportError: No module named beginner_tutorials.srv” when trying to run it, found this link helpful.

Build workspace

Build the workspace:

$ cd ~/catkin_ws
$ catkin_make # need to do this everytime after changing the folder structure

# to build only one package
$ catkin_make [--only-pkg-with-deps]() <target_package>

Run node

After starting ROS with roscore in a terminal, Run your node in another terminal:

# rosrun <package_name> <file_name>
$ rosrun beginner_tutorials talker.py

Checking information from command line

# show all ros topic
$ rostopic list
# to check specific topic
$ rostopic list | grep <topic_name>
# show message type, subscriber, publisher
$ rostopic info <name of the topic>
# to measure the frequency of the image topic
$ rostopic hz <topic_name>
# show what is included in a topic
$ rosmsg show <a topic type>
# to display an image
$ rqt_image_view <topic_name>

# check ros launch logs (especially when there is an error), this shows the directory
$ roslaunch-logs
# to open the directory in GUI
$ nautilus <directory>

Launch file

<group>: launch a group of nodes. Use ns attribute to push nodes into a separate namespace.

<param>: <rosparam command="load" file="FILENAME" /> to load a YAML file. <if="" name="" value="">, change a parameter to some value if a condition is meet.