Creating a ROS Package

This tutorial covers using roscreate-pkg or catkin to create a new package, and rospack to list package dependencies. The package that will be created through this tutorial is available here.

Table of Content

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. This package.xml file provides meta information about the package.
  • The package must contain a CMakeLists.txt which uses catkin. Catkin metapackages must have a boilerplate CMakeLists.txt file.
  • There can be no more than one package in each folder. This means no nested packages nor multiple packages sharing the same directory

The simplest possible package might look 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/         -- CATKIN WORKSPACE
  src/                    -- SOURCE SPACE
    CMakeLists.txt        -- The 'toplevel' CMake file
    package_1/
      CMakeLists.txt
      package.xml
      ...
    package_n/
      CMakeLists.txt
      package.xml
      ...
  build/                  -- BUILD SPACE
    CATKIN_IGNORE         -- Keeps catkin from walking this directory
  devel/                  -- DEVELOPMENT SPACE (set by CATKIN_DEVEL_PREFIX)
    bin/
    etc/
    include/
    lib/
    share/
    .catkin
    env.bash
    setup.bash
    setup.sh
    ...
  install/                -- INSTALL SPACE (set by CMAKE_INSTALL_PREFIX)
    bin/
    etc/
    include/
    lib/
    share/
    .catkin
    env.bash
    setup.bash
    setup.sh
    ...

At the Erle-board, the catkin workspace is at /root/catkin_ws.

If you wish to create another catkin workspace, follow the Creating a workspace for catkin tutorial.

Creating a catkin Package

This section 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 'erle_beginner_tutorials' which depends on std_msgs, roscpp, and rospy:

root@erlerobot:~/catkin_ws/src# catkin_create_pkg erle_beginner_tutorials std_msgs rospy roscpp
Created file erle_beginner_tutorials/package.xml
Created file erle_beginner_tutorials/CMakeLists.txt
Created folder erle_beginner_tutorials/include
Created folder erle_beginner_tutorials/src
Successfully created files in /root/catkin_ws/src/erle_beginner_tutorials. Please adjust the values in package.xml.

This will create a erle_beginner_tutorials folder which contains a package.xml and a CMakeLists.txt, which have been partially filled out with the information you gave catkin_create_pkg.

root@erlerobot:~/catkin_ws/src# tree erle_beginner_tutorials/
erle_beginner_tutorials/
├── CMakeLists.txt
├── include
├── package.xml
└── src

2 directories, 2 files

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 is described in catkin/commands/catkin_create_pkg.

Package dependencies

First-order dependencies

When using catkin_create_pkg earlier, a few package dependencies were provided. These first-order dependencies can now be reviewed with the rospack tool.

root@erlerobot:~# rospack depends1 erle_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:

root@erlerobot:~# roscd erle_beginner_tutorials/
root@erlerobot:~/catkin_ws/src/erle_beginner_tutorials# cat package.xml

<?xml version="1.0"?>
<package>
  <name>erle_beginner_tutorials</name>
  <version>0.0.0</version>
  <description>The erle_beginner_tutorials package</description>

  <!-- One maintainer tag required, multiple allowed, one person per tag -->
  <!-- Example:  -->
  <!-- <maintainer email="[email protected]">Jane Doe</maintainer> -->
  <maintainer email="[email protected]">root</maintainer>


  <!-- One license tag required, multiple allowed, one license per tag -->
  <!-- Commonly used license strings: -->
  <!--   BSD, MIT, Boost Software License, GPLv2, GPLv3, LGPLv2.1, LGPLv3 -->
  <license>TODO</license>


  <!-- Url tags are optional, but mutiple are allowed, one per tag -->
  <!-- Optional attribute type can be: website, bugtracker, or repository -->
  <!-- Example: -->
  <!-- <url type="website">http://ros.org/wiki/erle_beginner_tutorials</url> -->


  <!-- Author tags are optional, mutiple are allowed, one per tag -->
  <!-- Authors do not have to be maintianers, but could be -->
  <!-- Example: -->
  <!-- <author email="[email protected]">Jane Doe</author> -->


  <!-- The *_depend tags are used to specify dependencies -->
  <!-- Dependencies can be catkin packages or system dependencies -->
  <!-- Examples: -->
  <!-- Use build_depend for packages you need at compile time: -->
  <!--   <build_depend>message_generation</build_depend> -->
  <!-- Use buildtool_depend for build tool packages: -->
  <!--   <buildtool_depend>catkin</buildtool_depend> -->
  <!-- Use run_depend for packages you need at runtime: -->
  <!--   <run_depend>message_runtime</run_depend> -->
  <!-- Use test_depend for packages you need only for testing: -->
  <!--   <test_depend>gtest</test_depend> -->
  <buildtool_depend>catkin</buildtool_depend>
  <build_depend>roscpp</build_depend>
  <build_depend>rospy</build_depend>
  <build_depend>std_msgs</build_depend>
  <run_depend>roscpp</run_depend>
  <run_depend>rospy</run_depend>
  <run_depend>std_msgs</run_depend>


  <!-- The export tag contains other, unspecified, tags -->
  <export>
    <!-- You can specify that this package is a metapackage here: -->
    <!-- <metapackage/> -->

    <!-- Other tools can request additional information be placed here -->

  </export>
</package>

Indirect dependencies

In many cases, a dependency will also have its own dependencies. For instance, rospy has other dependencies:

root@erlerobot:~/catkin_ws/src/erle_beginner_tutorials# rospack depends1 rospy
genpy
rosgraph
rosgraph_msgs
roslib
std_msgs

A package can have quite a few indirect dependencies. Luckily rospack can recursively determine all nested dependencies.

root@erlerobot:~/catkin_ws/src/erle_beginner_tutorials# rospack depends erle_beginner_tutorials
cpp_common
rostime
roscpp_traits
roscpp_serialization
genmsg
genpy
message_runtime
rosconsole
std_msgs
rosgraph_msgs
xmlrpcpp
roscpp
rosgraph
catkin
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

The generated package.xml should be in your new package. Now lets go through the new package.xml and touch up any elements that need your attention.

description tag

First update the description tag:

  <description>The erle_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.

maintainer tags

Next comes the maintainer tag:

  <!-- One maintainer tag required, multiple allowed, one person per tag -->
  <maintainer email="[email protected]">vmayoral</maintainer>

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:

license tags

Next is the license tag, which is also required:

  <!-- One license tag required, multiple allowed, one license per tag -->
  <!-- Commonly used license strings: -->
  <!--   BSD, MIT, Boost Software License, GPLv2, GPLv3, LGPLv2.1, LGPLv3 -->
  <license>BSD</license>

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:

We strongly recommend to share your code under an Open Source Initiative license

The Open Source Initiative (OSI) is a non-profit corporation with global scope formed to educate about and advocate for the benefits of open source and to build bridges among different constituencies in the open source community.

dependencies tags

The next set of tags describe the dependencies of your package. The dependencies are split into build_depend, buildtool_depend, run_depend, test_depend. For a more detailed explination 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:

  <!-- The *_depend tags are used to specify dependencies -->
  <!-- Dependencies can be catkin packages or system dependencies -->
  <!-- Examples: -->
  <!-- Use build_depend for packages you need at compile time: -->
  <!--   <build_depend>message_generation</build_depend> -->
  <!-- Use buildtool_depend for build tool packages: -->
  <!--   <buildtool_depend>catkin</buildtool_depend> -->
  <!-- Use run_depend for packages you need at runtime: -->
  <!--   <run_depend>message_runtime</run_depend> -->
  <!-- Use test_depend for packages you need only for testing: -->
  <!--   <test_depend>gtest</test_depend> -->
  <buildtool_depend>catkin</buildtool_depend>
  <build_depend>roscpp</build_depend>
  <build_depend>rospy</build_depend>
  <build_depend>std_msgs</build_depend>
  <run_depend>roscpp</run_depend>
  <run_depend>rospy</run_depend>
  <run_depend>std_msgs</run_depend>

Final package.xml

As you can see the final package.xml, without comments and unused tags, is much more concise:

<?xml version="1.0"?>
<package>
  <name>erle_beginner_tutorials</name>
  <version>0.0.1</version>
  <description>The erle_beginner_tutorials package</description>

  <maintainer email="[email protected]">vmayoral</maintainer>

  <license>BSD</license>

  <buildtool_depend>catkin</buildtool_depend>
  <build_depend>roscpp</build_depend>
  <build_depend>rospy</build_depend>
  <build_depend>std_msgs</build_depend>
  <run_depend>roscpp</run_depend>
  <run_depend>rospy</run_depend>
  <run_depend>std_msgs</run_depend>

  <export>
  </export>
</package>

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