Creating Node.md

Steps to create a ROS Node

In this section we will learn how to create a ROS Node inside pkg_ros_basics ROS Package which we created in the previous section.

1. Navigate to pkg_ros_basics.

cd ~/catkin_ws/src/pkg_ros_basics

OR

roscd pkg_ros_basics

NOTE: roscd will work only if you have sourced setup.bash of your catkin workspace.

2. Create a scripts folder for your Python scripts and navigate into the folder.

mkdir scripts
cd scripts

3. Create a Python script called node_hello_ros.py.

touch node_hello_ros.py

4. Open the script in any text editor and start editing.

gedit node_hello_ros.py

or if you have any code editor like vsCode or vim you can use that too.

5. The First line of all your Python ROS scripts should be the following shebang:

#!/usr/bin/env python3

The #! shebang is used to tell the kernel which interpreter should be used to run the commands present in the file.

6. Now write a ROS Node to print Hello World! on the console.

#!/usr/bin/env python3

import rospy

def main():    
    
    rospy.init_node('node_hello_ros', anonymous=True)
    rospy.loginfo("Hello World!")
    rospy.spin()

if __name__ == '__main__':
    try:
        main()
    except rospy.ROSInterruptException:
        pass

7. Now you have to make this script executable.

chmod +x node_hello_ros.py

8. Now in order to run your ROS Node,

Open up a terminal and run ROS Master.

roscore

9. Once the roscore is up running, open a new termminal and run the ROS Node.

rosrun pkg_ros_basics node_hello_ros.py

NOTE: This command will work only if you have sourced setup.bash of your catkin workspace either manually or using .bashrc.

You should get some output like this,

[INFO] [1601277063.968749]: Hello World!

To create an executable python file

After creating a package, make a new scripts folder to store all the python files.

cd ~/catkin_ws/src/<package>
mkdir scripts

To create a python script, first, navigate inside the scripts folder using the cd command, and then create the script using the touch command.

cd scripts
touch filename.py

Now you can edit your python file.

Before running a new python file, you have to make it executable by running the following command-

cd ~/catkin_ws/src/<package>/scripts
chmod +x filename.py

To create an executable cpp file

After creating a package, create a src folder to store all the cpp files in that folder.

cd ~/catkin_ws/src/<package>
mkdir src

To create a cpp file, first, navigate inside the src folder using the cd command, and then create the file using the touch command.

cd src
touch filename.cpp

Now you can edit your cpp file, but for making it executable we have to edit the CMakeLists.txt file which is present in the package.

Add these lines at the bottom of CMakeLists.txt file,

add_executable(filename src/filename.cpp)
target_link_libraries(filename ${catkin_LIBRARIES})

Then run this command,

cd ~/catkin_ws
catkin build