Mahmoud Abas, Full-Stack Software Engineer & AI

ROS (Robot Operating System) - Structure of a ROS Package

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Structure of a ROS Package

Understanding how ROS organizes code, messages, and configuration

What Is a ROS Package?

text

my_ros_package/
├── CMakeLists.txt
├── package.xml
├── launch/
├── src/
├── include/
├── msg/
├── srv/
├── scripts/
└── config/

The package is the most basic unit of software organization in ROS
Contains everything needed to run part of a robot system: nodes, libraries, scripts, config, and launch files
The package layout determines how code and resources integrate into the ROS ecosystem

Build Files: `CMakeLists.txt` and `package.xml`

CMakeLists.txt: The build configuration file for CMake, ROS's build system. It defines how to compile and link code, which dependencies to include, and how to generate messages and services.

package.xml: Describes package metadata: name, version, dependencies, and author. Essential for package management and dependency resolution.

Source Code Layout: `src/`, `include/`, `scripts/`

cpp

#include <ros/ros.h>
int main(int argc, char **argv) {
  ros::init(argc, argv, "my_node");
  ros::NodeHandle nh;
  ROS_INFO("Node is running");
  ros::spin();
  return 0;
}

src/: Holds the node source code, typically C++ or Python.

include/: Stores header files, used mainly for larger C++ projects.

scripts/: Holds executable Python scripts and tools.

Communication Types: `msg/` and `srv/`

msg/: Contains custom message definitions used by nodes to communicate over topics. A message definition is just a list of typed fields, for example one int32 field named data.

srv/: Contains service definitions for two-way request and response communication. A service file lists request fields, then response fields, as two sections in the same definition.

Launch and Config: `launch/` and `config/`

launch/: Contains launch files that start multiple nodes at once, usually with configuration. Launch files are written in XML and help manage large, multi-node robot systems.

config/: Stores configuration files, typically YAML, used to pass parameters to nodes.

Creating and Building a Package

bash

catkin_create_pkg my_ros_package roscpp rospy std_msgs
cd ~/catkin_ws
catkin_make
rosrun my_ros_package my_node
roslaunch my_ros_package my_robot.launch

`catkin_create_pkg` scaffolds a new package with the given name and dependencies
`catkin_make` builds every package inside the workspace
`rosrun` launches a single node directly from its package
`roslaunch` starts one or more nodes together using a launch file

Hands-On Workspace Walkthrough

bash

mkdir ros_ws && cd ros_ws && mkdir src
catkin_make
cd src && catkin_create_pkg helloworld_pkg roscpp rospy std_msgs
source devel/setup.bash
rosrun helloworld_pkg publisher_node
rosrun helloworld_pkg subscriber_node

Set up a catkin workspace with a src/ folder, then build it once with catkin_make
Create a new package inside src/ with catkin_create_pkg
Add publisher and subscriber nodes, then rebuild with catkin_make
Sourcing devel/setup.bash after every build is critical, skip it and new packages won't be found
Run the publisher and subscriber nodes with rosrun to see them communicate

Key Takeaways

A ROS package bundles nodes, libraries, messages, services, scripts, and config into one organized unit
CMakeLists.txt and package.xml define how a package builds and what it depends on
msg/ and srv/ define custom communication types for topics and services
launch/ files start multiple nodes together; config/ holds their YAML parameters
catkin_create_pkg, catkin_make, and rosrun/roslaunch form the core package workflow

Open this lesson

Mahmoud AbasStructure of a ROS Package

mkdir ros_ws && cd ros_ws && mkdir src catkin_make cd src && catkin_create_pkg helloworld_pkg roscpp rospy std_msgs source devel/setup.bash rosrun helloworld_pkg publisher_node rosrun helloworld_pkg subscriber_node

Structure of a ROS Package

What Is a ROS Package?

Build Files: CMakeLists.txt and package.xml

Source Code Layout: src/, include/, scripts/

Communication Types: msg/ and srv/

Launch and Config: launch/ and config/

Creating and Building a Package

Hands-On Workspace Walkthrough

Key Takeaways

Open this lesson

Structure of a ROS Package

What Is a ROS Package?

Build Files: CMakeLists.txt and package.xml

Source Code Layout: src/, include/, scripts/

Communication Types: msg/ and srv/

Launch and Config: launch/ and config/

Creating and Building a Package

Hands-On Workspace Walkthrough

Key Takeaways

Open this lesson

Build Files: `CMakeLists.txt` and `package.xml`

Source Code Layout: `src/`, `include/`, `scripts/`

Communication Types: `msg/` and `srv/`

Launch and Config: `launch/` and `config/`

Build Files: `CMakeLists.txt` and `package.xml`

Source Code Layout: `src/`, `include/`, `scripts/`

Communication Types: `msg/` and `srv/`

Launch and Config: `launch/` and `config/`