ROS 2 Integration#

In this tutorial we will learn how to Integrate ROS 2 with Ignition. We will establish communication between them. This can help in many aspects; we can receive data or commands from ROS and apply it to Ignition and vice versa.

ros_gz_bridge#

ros_gz_bridge provides a network bridge which enables the exchange of messages between ROS 2 and Ignition Transport. Its support is limited to only certain message types. Please, check this README to verify if your message type is supported by the bridge.

Example uses of the bridge can be found in ros_gz_sim_demos, including demo launch files with bridging of all major actuation and sensor types.

Requirements#

Please follow the Install Gazebo and ROS document before starting this tutorial. A working installation of ROS 2 and Gazebo is required to go further.

Bidirectional communication#

We can initialize a bidirectional bridge so we can have ROS as the publisher and Ignition as the subscriber or vice versa. The syntax is /TOPIC@ROS_MSG@IGN_MSG, such that TOPIC is the Ignition internal topic, ROS_MSG is the ROS message type for this topic, and IGN_MSG is the Ignition message type.

For example:

ros2 run ros_gz_bridge parameter_bridge /TOPIC@ROS_MSG@IGN_MSG

The ros2 run ros_gz_bridge parameter_bridge command simply runs the parameter_bridge code from the ros_gz_bridge package. Then, we specify our topic /TOPIC over which the messages will be sent. The first @ symbol delimits the topic name from the message types. Following the first @ symbol is the ROS message type.

The ROS message type is followed by an @, [, or ] symbol where:

@ is a bidirectional bridge.
[ is a bridge from Ignition to ROS.
] is a bridge from ROS to Ignition.

Have a look at these examples explaining how to make communication connections from ROS to Ignition and vice versa.

It is also possible to use ROS Launch with the ros_ign_bridge and represent the topics in yaml format to be given to the bridge at launch time.

- ros_topic_name: "scan"
  gz_topic_name: "/scan"
  ros_type_name: "sensor_msgs/msg/LaserScan"
  gz_type_name: "ignition.msgs.LaserScan"
  direction: IGN_TO_ROS  # BIDIRECTIONAL or ROS_TO_IGN

Publish key strokes to ROS#

Let’s send messages to ROS using the Key Publisher an Ignition plugin.

Note: Make sure to have all workspaces you need (ROS, Ignition and, ros_ign…) sourced.

First we will start a bridge between ROS and Ignition specifying the topic at which the Key Publisher plugin sends messages and also the type of the messages as follows:

ros2 run ros_gz_bridge parameter_bridge /keyboard/keypress@std_msgs/msg/Int32@ignition.msgs.Int32

We started a bridge on /keyboard/keypress topic with message of type Int32. For ROS it is std_msgs/msg/Int32 and for Ignition it is ignition.msgs.Int32

In another terminal launch an Gazebo Sim world, for example the empty.sdf world:

ign gazebo empty.sdf

Then add the Key Publisher plugin from the dropdown menu on the top right corner.

empty_world_with_KeyPublisher

In another terminal start the ROS listener:

ros2 topic echo /keyboard/keypress

This command listens to the messages sent over the /keyboard/keypress topic.

On the Ignition window, press on the keyboard keys and you should find data on the listener terminal. This is what the terminals should look like:

exchange_messages

Now it’s your turn! Try to send data from ROS to Ignition. You can also try different data types and different directions of communication.

Video walk-through#

A video walk-through of this tutorial is available from our YouTube channel: Ignition tutorials: ROS 2 Foxy integration.