official guide: https://docs.ros.org/en/humble/Tutorials/Beginner-Client-Libraries/Colcon-Tutorial.html

So far we have made multiple files and our folder is getting messy.

Let’s structure our project by using ROS Packages.

What are ROS Packages?

ROS Packages are, as the name implies, packages of code that are highly sharable between ROS developers.

They consist of a folder, package.xml file, and source code

        cpp_package_1/
		      ... imagine much code files here ..
          package.xml

First, we need to create a ROS workspace.

We do this by making 2 folders one inside another. I am calling my workspace ros_ws and the folder inside it src

image.png

Then inside this src folder is where we put all of our packages.

  ros_ws/
    src/
      cpp_package_1/
		      ...
          package.xml

      py_package_1/
		      ...
          package.xml

      ...
      cpp_package_n/
		      ...
          package.xml
package types

packages can be either C++ or python.

the intern file structure is different for each but for this guide we will stick to creating python packages

Creating a package

Let’s go to the src folder to create the package

  cd ros2_ws/src

to create a package we use this command:

  ros2 pkg create --build-type ament_python --license Apache-2.0 --node-name my_node my_package

a bunch of text should have been printed out but the result should look something like this:

image.png

What’s inside a python package

  • package.xml file containing meta-information about the package
  • resource/<package_name> marker file for the package
  • setup.cfg is required when a package has executables, so ros2 run can find them
  • setup.py containing instructions for how to install the package
  • my_package - a folder with the same name as your package, used by ROS 2 tools to find your package, contains __init__.py
  • my_node.py an example node file (how nice of them)

Let’s move all of our code into the my_package/my_package folder (this is next to the my_node.py file)

image.png

To register all the new files we added open setup.py and put in the following:

image.png

Now back in the command line make sure you are in the ros_ws folder!!!

let’s build our package with colcon build --symlink-install

image.png

what is building?

if you are a CS major at Rose-Hulman you will learn the answer to this in CSSE132

but TLDR; is it combines all the code files into one program that can be run easily

Then in a new terminal go into the ros_ws folder with cd ros_ws and run source install/setup.sh.

From now on whenever you open a new terminal you must run source install/setup.sh in the workspace folder. This lets you run the ROS command

Then to run say our publisher.py file we do ros2 run <package name> <file_name>

image.png

remember to run source install/setup.sh for the subscriber!!!

image.png

and congrats you have successfully setup your own ROS package.

Sidenote:

running colcon build --symlink-install has created other folder build, install, and log

for the most part, these can be ignored.

Exercise!!!! ( ik u love them )

  • try running the server and client setup but with in the enviroment
  • Create a new package called server_client_pkg and copy the server.py and client.py files in there. Then build and run the two files.