Catkin Packages#

What you will need

  • New ROS DTProject as described here

What you will get

  • Learn how to create a new catkin package inside a DTProject

ROS uses the catkin build system to organize and build its software. If you are not familiar with the catkin build system, you can learn about it by following the official tutorials.

In a nutshell, catkin organizes entire projects in the so-called catkin workspaces. A catkin workspace is nothing more than a directory containing a bunch of software modules called catkin packages. Each software module can contain a set of executables (e.g., binaries, script files) called ROS nodes. ROS nodes interact with one another using two of the most common communication patterns, called publish-subscribe and request-reply.

ROS implements the publish-subscribe pattern using ROS Publishers and ROS Subscribers, and the request-reply pattern using ROS Services. More on these later.

Let us now take a step back and review catkin workspaces, packages, and nodes more in details.

Catkin workspace#

The directory packages/ you find at the root of a DTProject is a catkin workspace.

Advanced: the real story behind the packages directory

In reality, packages/ is more of a sub-workspace, as it is internally joined with other packages/ directories from other projects (the ancestor projects) to form a full catkin workspace.

Create a new Catkin package#

Open a terminal at the root of the DTProject my-ros-project created earlier. Again, Catkin packages are directories inside the directory packages/ of my-ros-project. Let us go ahead and create a new directory called my_package inside packages/.

mkdir -p ./packages/my_package

A Catkin package (also known as a ROS package) is simply a directory containing two special files, package.xml and CMakeLists.txt. So, let us turn the my_package folder into a ROS package by creating these two files.

Create the file package.xml inside my_package using your favorite text editor and place/adjust the following content inside it:

<package>
  <name>my_package</name>
  <version>0.0.1</version>
  <description>
  My first Catkin package in Duckietown.
  </description>
  <maintainer email="[email protected]">YOUR_FULL_NAME</maintainer>
  <license>None</license>

  <buildtool_depend>catkin</buildtool_depend>
</package>

Replace YOUR_FULL_NAME with your first and last name and [email protected] with your email address.

Now, create the file CMakeLists.txt inside my_package using your favorite text editor and place/adjust the following content inside it:

cmake_minimum_required(VERSION 2.8.3)
project(my_package)

find_package(catkin REQUIRED COMPONENTS
  rospy
)

catkin_package()

We now have a catkin package inside a catkin workspace in a ROS-capable DTProject. We will now add our code by adding ROS nodes to our catkin package.