Embedded Motion Control/Tutorials/Creating a ROS package

Description: This tutorial covers using roscreate-pkg or catkin to create a new package, and rospack to list package dependencies.

Using roscreate

Before we create a package, let's see how the roscreate-pkg command-line tool works. This creates a new ROS package. All ROS packages consist of the many similar files : manifests, CMakeLists.txt, mainpage.dox, and Makefiles. roscreate-pkg eliminates many tedious tasks of creating a new package by hand, and eliminates common errors caused by hand-typing build files and manifests.

To create a new package in the current directory:

roscreate-pkg [package_name]

You can also specify dependencies of that package:

roscreate-pkg [package_name] [depend1] [depend2] [depend3]

Creating a New ROS Package

Now we're going to go into your home or project directory and create our beginner_tutorials package. We are going to make it depend on std_msgs, roscpp, and rospy, which are common ROS packages.

Now go your EMC group directory:

cd ~/ros/emc/emc<YOUR_GROUP_NR>

We can now use roscreate-pkg to create our first ROS package. However, there is a small problem: every package in ROS must have a unique name. This means if you and your group members all use the same package name and share these packages using the SVN, ROS won't know which of the packages to use. Therefore, create a package with a unique name:

roscreate-pkg beginner_tutorials_<YOUR_NAME> std_msgs rospy roscpp

You will see something similar to:

Created package directory /home/sdries/ros/emc/emc01/beginner_tutorials_sjoerd
Created include directory /home/sdries/ros/emc/emc01/beginner_tutorials_sjoerd/include/beginner_tutorials_sjoerd
Created cpp source directory /home/sdries/ros/emc/emc01/beginner_tutorials_sjoerd/src
Created package file /home/sdries/ros/emc/emc01/beginner_tutorials_sjoerd/Makefile
Created package file /home/sdries/ros/emc/emc01/beginner_tutorials_sjoerd/manifest.xml
Created package file /home/sdries/ros/emc/emc01/beginner_tutorials_sjoerd/CMakeLists.txt
Created package file /home/sdries/ros/emc/emc01/beginner_tutorials_sjoerd/mainpage.dox

Please edit beginner_tutorials_sjoerd/manifest.xml and mainpage.dox to finish creating your package

You're going to want to spend some time looking at the manifest.xml file in your newly created package. Manifests play an important role in ROS as they define how packages are built, run, and documented.

Now lets make sure that ROS can find your new package. It is often useful to call rospack profile after making changes to your path so that new directories will be indexed:

rospack profile
rospack find beginner_tutorials_<YOUR_NAME>

Should result in:

~/ros/emc/emc<YOUR_GROUP_NR>/beginner_tutorials_<YOUR_NAME>

If this fails, it means ROS can't find your new package, which may be an issue with your ROS_PACKAGE_PATH. Make sure you correctly followed the steps in this previous tutorial .

Try moving to the directory for the package.

roscd beginner_tutorials 
pwd

Results in:

/home<YOUR_NAME>/ros/emc/emc<YOUR_GROUP_NR>/beginner_tutorials_<YOUR_NAME>

First-order package dependencies

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

rospack depends1 beginner_tutorials_<YOUR_NAME> 

Result in:

std_msgs
rospy
roscpp

As you can see, rospack lists the same dependencies that were used as arguments when running roscreate-pkg. These dependencies for a package are stored in the manifest file. Take a look at the manifest file.

roscd beginner_tutorials<YOUR_NAME>
cat manifest.xml

Gives:

<package>

...

  <depend package="std_msgs"/>
  <depend package="rospy"/>
  <depend package="roscpp"/>

</package>

Indirect package dependencies

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

rospack depends1 rospy

Results in:

roslib
roslang

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

rospack depends beginner_tutorials_<YOUR_NAME>

cpp_common
rostime
roscpp_traits
roscpp_serialization
genmsg
genpy
message_runtime
std_msgs
rosgraph
rosgraph_msgs
catkin
rospack
roslib
rospy
rosconsole
xmlrpcpp
roscpp

ROS Client Libraries

You may be wondering what rospy and roscpp dependencies are from the previous examples. rospy and roscpp are Client Libraries. The client libraries allow different programming languages to communicate through ROS. rospy is the client library for Python. roscpp is the client library for C++.

Review

Lets just list some of the commands we've used so far:

roscreate-pkg = ros+create-pkg : generates all the files needed to create a ROS package rospack = ros+pack(age) : provides information related to ROS packages rosstack = ros+stack : provides information related to ROS stacks

Now that you've made a new ROS package, let's build our ROS package.