Bridge communication between ROS and Gazebo

This package provides a network bridge which enables the exchange of messages between ROS and Gazebo Transport.

The following message types can be bridged for topics:

And the following for services:

Run ros2 run ros_gz_bridge parameter_bridge -h for instructions.

Example 1a: Gazebo Transport talker and ROS 2 listener

Start the parameter bridge which will watch the specified topics.

# Shell A:
. ~/bridge_ws/install/setup.bash
ros2 run ros_gz_bridge parameter_bridge /chatter@std_msgs/msg/String@ignition.msgs.StringMsg

Now we start the ROS listener.

# Shell B:
. /opt/ros/humble/setup.bash
ros2 topic echo /chatter

Now we start the Gazebo Transport talker.

# Shell C:
ign topic -t /chatter -m ignition.msgs.StringMsg -p 'data:"Hello"'

Example 1b: ROS 2 talker and Gazebo Transport listener

Start the parameter bridge which will watch the specified topics.

# Shell A:
. ~/bridge_ws/install/setup.bash
ros2 run ros_gz_bridge parameter_bridge /chatter@std_msgs/msg/String@ignition.msgs.StringMsg

Now we start the Gazebo Transport listener.

# Shell B:
ign topic -e -t /chatter

Now we start the ROS talker.

# Shell C:
. /opt/ros/humble/setup.bash
ros2 topic pub /chatter std_msgs/msg/String "data: 'Hi'" --once

Example 2: Run the bridge and exchange images

In this example, we're going to generate Gazebo Transport images using Gazebo Sim, that will be converted into ROS images, and visualized with rqt_image_viewer.

First we start Gazebo Sim (don't forget to hit play, or Gazebo Sim won't generate any images).

# Shell A:
ign gazebo sensors_demo.sdf

Let's see the topic where camera images are published.

# Shell B:
ign topic -l | grep image
/rgbd_camera/depth_image
/rgbd_camera/image

Then we start the parameter bridge with the previous topic.

# Shell B:
. ~/bridge_ws/install/setup.bash
ros2 run ros_gz_bridge parameter_bridge /rgbd_camera/image@sensor_msgs/msg/Image@ignition.msgs.Image

Now we start the ROS GUI:

# Shell C:
. /opt/ros/humble/setup.bash
ros2 run rqt_image_view rqt_image_view /rgbd_camera/image

You should see the current images in rqt_image_view which are coming from Gazebo (published as Gazebo Msgs over Gazebo Transport).

The screenshot shows all the shell windows and their expected content (it was taken using ROS 2 Galactic and Gazebo Fortress):

Example 3: Static bridge

In this example, we're going to run an executable that starts a bidirectional bridge for a specific topic and message type. We'll use the static_bridge executable that is installed with the bridge.

The example's code can be found under ros_gz_bridge/src/static_bridge.cpp. In the code, it's possible to see how the bridge is hardcoded to bridge string messages published on the /chatter topic.

Let's give it a try, starting with Gazebo -> ROS 2.

On terminal A, start the bridge:

ros2 run ros_gz_bridge static_bridge

On terminal B, we start a ROS 2 listener:

ros2 topic echo /chatter std_msgs/msg/String

And terminal C, publish an Gazebo message:

ign topic -t /chatter -m ignition.msgs.StringMsg -p 'data:"Hello"'

At this point, you should see the ROS 2 listener echoing the message.

Now let's try the other way around, ROS 2 -> Gazebo.

On terminal D, start an Igntion listener:

ign topic -e -t /chatter

And on terminal E, publish a ROS 2 message:

ros2 topic pub /chatter std_msgs/msg/String 'data: "Hello"' -1

You should see the Gazebo listener echoing the message.

Example 4: Service bridge

It's possible to make ROS service requests into Gazebo. Let's try unpausing the simulation.

On terminal A, start the service bridge:

ros2 run ros_gz_bridge parameter_bridge /world/shapes/control@ros_gz_interfaces/srv/ControlWorld

On terminal B, start Gazebo, it will be paused by default:

ign gazebo shapes.sdf

On terminal C, make a ROS request to unpause simulation:

ros2 service call /world/<world_name>/control ros_gz_interfaces/srv/ControlWorld "{world_control: {pause: false}}"

Example 5: Configuring the Bridge via YAML

When configuring many topics, it is easier to use a file-based configuration in a markup language. In this case, the ros_gz bridge supports using a YAML file to configure the various parameters.

The configuration file must be a YAML array of maps. An example configuration for 5 bridges is below, showing the various ways that a bridge may be specified:

 # Set just topic name, applies to both
- topic_name: "chatter"
  ros_type_name: "std_msgs/msg/String"
  gz_type_name: "ignition.msgs.StringMsg"

# Set just ROS topic name, applies to both
- ros_topic_name: "chatter_ros"
  ros_type_name: "std_msgs/msg/String"
  gz_type_name: "ignition.msgs.StringMsg"

# Set just GZ topic name, applies to both
- gz_topic_name: "chatter_ign"
  ros_type_name: "std_msgs/msg/String"
  gz_type_name: "ignition.msgs.StringMsg"

# Set each topic name explicitly
- ros_topic_name: "chatter_both_ros"
  gz_topic_name: "chatter_both_ign"
  ros_type_name: "std_msgs/msg/String"
  gz_type_name: "ignition.msgs.StringMsg"

# Full set of configurations
- ros_topic_name: "ros_chatter"
  gz_topic_name: "ign_chatter"
  ros_type_name: "std_msgs/msg/String"
  gz_type_name: "ignition.msgs.StringMsg"
  subscriber_queue: 5       # Default 10
  publisher_queue: 6        # Default 10
  lazy: true                # Default "false"
  direction: BIDIRECTIONAL  # Default "BIDIRECTIONAL" - Bridge both directions
                            # "GZ_TO_ROS" - Bridge Ignition topic to ROS
                            # "ROS_TO_GZ" - Bridge ROS topic to Ignition

To run the bridge node with the above configuration:

ros2 run ros_gz_bridge parameter_bridge --ros-args -p config_file:=$WORKSPACE/ros_gz/ros_gz_bridge/test/config/full.yaml

Example 6: Using ROS namespace with the Bridge

When spawning multiple robots inside the same ROS environment, it is convenient to use namespaces to avoid overlapping topic names. There are three main types of namespaces: relative, global (/) and private (~/). For more information, refer to ROS documentation. Namespaces are applied to Gazebo topic both when specified as topic_name as well as gz_topic_name.

By default, the Bridge will not apply ROS namespace on the Gazebo topics. To enable this feature, use parameter expand_gz_topic_names. Let's test our topic with namespace:

# Shell A:
. ~/bridge_ws/install/setup.bash
ros2 run ros_gz_bridge parameter_bridge chatter@std_msgs/msg/String@ignition.msgs.StringMsg \
  --ros-args -p expand_gz_topic_names:=true -r __ns:=/demo

Now we start the Gazebo Transport listener.

# Shell B:
ign topic -e -t /demo/chatter

Now we start the ROS talker.

# Shell C:
. /opt/ros/humble/setup.bash
ros2 topic pub /demo/chatter std_msgs/msg/String "data: 'Hi from inside of a namespace'" --once

By changing chatter to /chatter or ~/chatter you can obtain different results.

API

ROS 2 Parameters:

• subscription_heartbeat - Period at which the node checks for new subscribers for lazy bridges.
• config_file - YAML file to be loaded as the bridge configuration
• expand_gz_topic_names - Enable or disable ROS namespace applied on GZ topics.

Changelog for package ros_gz_bridge

0.244.14 (2024-04-08)

• Added conversion for Detection3D and Detection3DArray (#523) (#526) Co-authored-by: wittenator <9154515+wittenator@users.noreply.github.com>
• Add ROS namespaces to GZ topics (#512) Co-authored-by: Alejandro Hern