The following are some common ROS1 and ROS2 CLI commands: ROS1 ROS2 Function rosrun ros2 run Running a node rosnode ros2 node Information about node rostopic ros2 topic Command for ROS topic roslaunch ros2 launch Command to launch a launch file rosservice ros2 service Command for ROS servide rospack ros2 pkg Information about package

Step 1: Create the service (.srv) file, namely ServiceName.srv, inside an “srv” folder. Step 2: Modify setup.py. Step 3: Modify package.xml. Step 4: Write the service_server node in the package subfolder inside the package folder. There are two ways to write a service_server node in Python: 1) old-school approach, and 2) member-function approach. The following …

Step 1: Create the service (.srv) file, namely ServiceName.srv, inside an “srv” folder.

Step 2: Modify CMakeLists.txt.

Add the following:

find_package(builtin_interfaces REQUIRED)
find_package(rosidl_default_generators REQUIRED)

# and put below before ament_package():
rosidl_generate_interfaces(ros2_exercise_cpp
  "srv/ServiceName.srv"
  DEPENDENCIES builtin_interfaces
)

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There are three ways to to write a Python publisher in ROS2, namely:

• Old-school approach
• Object-oriented (member-function) approach
• Local function (lambda) approach

Below is an example of each approach to write a Python node listening to “Hello World” stream. The code is taken from here: https://github.com/ros2/examples/tree/foxy/rclpy/topics/minimal_subscriber/examples_rclpy_minimal_subscriber

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There are three ways to to write a Python publisher in ROS2, namely:

• Old-school approach
• Object-oriented (member-function) approach
• Local function approach

Below is an example of each approach to write a Python node publishing “Hello World”. The code is taken from here: https://github.com/ros2/examples/tree/foxy/rclpy/topics/minimal_publisher/examples_rclpy_minimal_publisher

(more…)

There are three ways to to write a C++ publisher in ROS2, namely:

• Old-school approach
• Object-oriented (member-function) approach
• Local function (lambda) approach

Below is an example of each approach to write a C++ node listening to “Hello World” stream. The code is taken from here: https://github.com/ros2/examples/tree/foxy/rclcpp/topics/minimal_subscriber

(more…)

There are three ways to to write a C++ publisher in ROS2, namely:

• Old-school approach
• Object-oriented (member-function) approach
• Local function (lambda) approach

Below is an example of each approach to write a C++ node publishing “Hello World”. The code is taken from here: https://github.com/ros2/examples/tree/foxy/rclcpp/topics/minimal_publisher

(more…)

Creating a C++ package

Step 1: Create the package using the following CLI command:

cd ~/ros2_ws/src
ros2 pkg create [PACKAGE_NAME] --build-type ament_cmake --dependencies rclcpp std_msgs [OTHER_DEPENDENCY_PACKAGES] 

Step 2: Modify package.xml file for package dependencies of the created node(s).

Step 3: Modify CMakeLists.txt.

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ROS2 build system is colcon. In ROS1, the build system is catkin. What is the difference between ROS1 and ROS2 packages? In ROS1, you can mix C++ and Python nodes in a single package. In ROS2, as a standard practice, you either make a C++ package or a Python package. [Although as a non-standard practice, …

In ROS1, the structure of an overlay workspace, called the catkin workspace, looks like this: workspace_folder: |–src |–CMakeLists.txt |–package_1_folder |– |–package_n_folder |–devel |–build |–install The catkin workspace is built by running “catkin_make” command. To rebuild a catkin workspace, simply delete all the folders inside the workspace but the “src” folder and subsequently run the “catkin_make” …