- What makes up a catkin Package?
- Packages in a catkin Workspace
- Creating a catkin Package
- Building a catkin workspace and sourcing the setup file
- package dependencies
- Customizing Your Package
What makes up a catkin Package?
For a package to be considered a catkin package it must meet a few requirements:
The package must contain a catkin compliant package.xml file.
- That package.xml file provides meta information about the package.
The package must contain a CMakeLists.txt which uses catkin.
If it is a catkin metapackage it must have the relevant boilerplate CMakeLists.txt file.
- Each package must have its own folder
- This means no nested packages nor multiple packages sharing the same directory.
The simplest possible package might have a structure which looks like this:
my_package/ CMakeLists.txt package.xml
Packages in a catkin Workspace
The recommended method of working with catkin packages is using a catkin workspace, but you can also build catkin packages standalone. A trivial workspace might look like this:
workspace_folder/ -- WORKSPACE src/ -- SOURCE SPACE CMakeLists.txt -- 'Toplevel' CMake file, provided by catkin package_1/ CMakeLists.txt -- CMakeLists.txt file for package_1 package.xml -- Package manifest for package_1 ... package_n/ CMakeLists.txt -- CMakeLists.txt file for package_n package.xml -- Package manifest for package_n
Before continuing with this tutorial create an empty catkin workspace by following the Creating a workspace for catkin tutorial.
Creating a catkin Package
This tutorial will demonstrate how to use the catkin_create_pkg script to create a new catkin package, and what you can do with it after it has been created.
First change to the source space directory of the catkin workspace you created in the Creating a Workspace for catkin tutorial:
# You should have created this in the Creating a Workspace Tutorial $ cd ~/catkin_ws/src
Now use the catkin_create_pkg script to create a new package called 'beginner_tutorials' which depends on std_msgs, roscpp, and rospy:
$ catkin_create_pkg beginner_tutorials std_msgs rospy roscpp
catkin_create_pkg requires that you give it a package_name and optionally a list of dependencies on which that package depends:
# This is an example, do not try to run this # catkin_create_pkg <package_name> [depend1] [depend2] [depend3]
catkin_create_pkg also has more advanced functionalities which are described in catkin/commands/catkin_create_pkg.
Building a catkin workspace and sourcing the setup file
Now you need to build the packages in the catkin workspace:
$ cd ~/catkin_ws $ catkin_make
After the workspace has been built it has created a similar structure in the devel subfolder as you usually find under /opt/ros/$ROSDISTRO_NAME.
To add the workspace to your ROS environment you need to source the generated setup file:
$ . ~/catkin_ws/devel/setup.bash
When using catkin_create_pkg earlier, a few package dependencies were provided. These first-order dependencies can now be reviewed with the rospack tool.
$ rospack depends1 beginner_tutorials
roscpp rospy std_msgs
As you can see, rospack lists the same dependencies that were used as arguments when running catkin_create_pkg. These dependencies for a package are stored in the package.xml file:
$ roscd beginner_tutorials $ cat package.xml
<package format="2"> ... <buildtool_depend>catkin</buildtool_depend> <build_depend>roscpp</build_depend> <build_depend>rospy</build_depend> <build_depend>std_msgs</build_depend> ... </package>
In many cases, a dependency will also have its own dependencies. For instance, rospy has other dependencies.
$ rospack depends1 rospy
genpy roscpp rosgraph rosgraph_msgs roslib std_msgs
A package can have quite a few indirect dependencies. Luckily rospack can recursively determine all nested dependencies.
$ rospack depends beginner_tutorials cpp_common rostime roscpp_traits roscpp_serialization catkin genmsg genpy message_runtime gencpp genlisp message_generation rosbuild rosconsole std_msgs rosgraph_msgs xmlrpcpp roscpp rosgraph rospack roslib rospy
Customizing Your Package
This part of the tutorial will look at each file generated by catkin_create_pkg and describe, line by line, each component of those files and how you can customize them for your package.
Customizing the package.xml
First update the description tag:
5 <description>The beginner_tutorials package</description>
Change the description to anything you like, but by convention the first sentence should be short while covering the scope of the package. If it is hard to describe the package in a single sentence then it might need to be broken up.
Next comes the maintainer tag:
This is a required and important tag for the package.xml because it lets others know who to contact about the package. At least one maintainer is required, but you can have many if you like. The name of the maintainer goes into the body of the tag, but there is also an email attribute that should be filled out:
7 <maintainer email="firstname.lastname@example.org">Your Name</maintainer>
Next is the license tag, which is also required:
You should choose a license and fill it in here. Some common open source licenses are BSD, MIT, Boost Software License, GPLv2, GPLv3, LGPLv2.1, and LGPLv3. You can read about several of these at the Open Source Initiative. For this tutorial we'll use the BSD license because the rest of the core ROS components use it already:
The next set of tags describe the dependencies of your package. The dependencies are split into build_depend, buildtool_depend, exec_depend, test_depend. For a more detailed explanation of these tags see the documentation about Catkin Dependencies. Since we passed std_msgs, roscpp, and rospy as arguments to catkin_create_pkg, the dependencies will look like this:
27 <!-- The *_depend tags are used to specify dependencies --> 28 <!-- Dependencies can be catkin packages or system dependencies --> 29 <!-- Examples: --> 30 <!-- Use build_depend for packages you need at compile time: --> 31 <!-- <build_depend>genmsg</build_depend> --> 32 <!-- Use buildtool_depend for build tool packages: --> 33 <!-- <buildtool_depend>catkin</buildtool_depend> --> 34 <!-- Use exec_depend for packages you need at runtime: --> 35 <!-- <exec_depend>python-yaml</exec_depend> --> 36 <!-- Use test_depend for packages you need only for testing: --> 37 <!-- <test_depend>gtest</test_depend> --> 38 <buildtool_depend>catkin</buildtool_depend> 39 <build_depend>roscpp</build_depend> 40 <build_depend>rospy</build_depend> 41 <build_depend>std_msgs</build_depend>
All of our listed dependencies have been added as a build_depend for us, in addition to the default buildtool_depend on catkin. In this case we want all of our specified dependencies to be available at build and run time, so we'll add a exec_depend tag for each of them as well:
As you can see the final package.xml, without comments and unused tags, is much more concise:
1 <?xml version="1.0"?> 2 <package format="2"> 3 <name>beginner_tutorials</name> 4 <version>0.1.0</version> 5 <description>The beginner_tutorials package</description> 6 7 <maintainer email="email@example.com">Your Name</maintainer> 8 <license>BSD</license> 9 <url type="website">http://wiki.ros.org/beginner_tutorials</url> 10 <author email="firstname.lastname@example.org">Jane Doe</author> 11 12 <buildtool_depend>catkin</buildtool_depend> 13 14 <build_depend>roscpp</build_depend> 15 <build_depend>rospy</build_depend> 16 <build_depend>std_msgs</build_depend> 17 18 <exec_depend>roscpp</exec_depend> 19 <exec_depend>rospy</exec_depend> 20 <exec_depend>std_msgs</exec_depend> 21 22 </package>
Customizing the CMakeLists.txt
Now that the package.xml, which contains meta information, has been tailored to your package, you are ready to move on in the tutorials. The CMakeLists.txt file created by catkin_create_pkg will be covered in the later tutorials about building ROS code.