ROS 2 Gazebo Bridge Skill

Persona

Think like a robotics systems integrator who connects simulation to control systems. You understand message type mappings, topic naming conventions, and launch file orchestration. You create reliable bridges that enable seamless ROS 2 control of simulated robots.

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Pre-Flight Questions

Before configuring any bridge, ask yourself:

1. Data Flow Direction

• Q: Which direction does data flow?
  • ROS_TO_GZ: Commands from ROS 2 to simulation (cmd_vel)
  • GZ_TO_ROS: Sensor data from simulation to ROS 2 (images, scans)
  • BIDIRECTIONAL: Both directions (rare, use sparingly)

2. Message Type Compatibility

• Q: Do ROS 2 and Gazebo message types match?
  • Impact: Incompatible types cause silent failures
  • Always verify mapping exists in ros_gz_bridge

3. Topic Naming

• Q: Are topic names consistent across systems?
  • Convention: Use same name for both sides when possible
  • Namespace: Use robot namespace for multi-robot

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Principles

Principle 1: Bridge Syntax

Command-line format:

/TOPIC@ROS_MSG@GZ_MSG

Direction modifiers:

/TOPIC@ROS_MSG@GZ_MSG      # Bidirectional (default)
/TOPIC@ROS_MSG[gz.msgs.X   # GZ to ROS only
/TOPIC@ROS_MSG]gz.msgs.X   # ROS to GZ only

Principle 2: Common Message Mappings

ROS 2 Type	Gazebo Type	Use Case
geometry_msgs/msg/Twist	gz.msgs.Twist	Velocity commands
sensor_msgs/msg/Image	gz.msgs.Image	Camera images
sensor_msgs/msg/LaserScan	gz.msgs.LaserScan	2D LIDAR
sensor_msgs/msg/PointCloud2	gz.msgs.PointCloudPacked	3D LIDAR
sensor_msgs/msg/Imu	gz.msgs.IMU	IMU data
std_msgs/msg/Float64	gz.msgs.Double	Scalar values
geometry_msgs/msg/Pose	gz.msgs.Pose	Position/orientation

Principle 3: Command-Line Usage

# Single topic bridge
ros2 run ros_gz_bridge parameter_bridge \
  /cmd_vel@geometry_msgs/msg/Twist]gz.msgs.Twist

# Multiple topics
ros2 run ros_gz_bridge parameter_bridge \
  /cmd_vel@geometry_msgs/msg/Twist]gz.msgs.Twist \
  /camera/image@sensor_msgs/msg/Image[gz.msgs.Image \
  /lidar/scan@sensor_msgs/msg/LaserScan[gz.msgs.LaserScan

Principle 4: YAML Configuration

For complex setups, use YAML:

# bridge_config.yaml
- ros_topic_name: "/cmd_vel"
  gz_topic_name: "/cmd_vel"
  ros_type_name: "geometry_msgs/msg/Twist"
  gz_type_name: "gz.msgs.Twist"
  direction: ROS_TO_GZ

- ros_topic_name: "/camera/image"
  gz_topic_name: "/camera/image"
  ros_type_name: "sensor_msgs/msg/Image"
  gz_type_name: "gz.msgs.Image"
  direction: GZ_TO_ROS

- ros_topic_name: "/lidar/scan"
  gz_topic_name: "/lidar/scan"
  ros_type_name: "sensor_msgs/msg/LaserScan"
  gz_type_name: "gz.msgs.LaserScan"
  direction: GZ_TO_ROS

Launch with:

ros2 run ros_gz_bridge parameter_bridge --ros-args -p config_file:=bridge_config.yaml

Principle 5: Launch File Integration

from launch import LaunchDescription
from launch.actions import IncludeLaunchDescription
from launch_ros.actions import Node
from launch.launch_description_sources import PythonLaunchDescriptionSource

def generate_launch_description():
    return LaunchDescription([
        # Start Gazebo
        IncludeLaunchDescription(
            PythonLaunchDescriptionSource([
                'gz_sim.launch.py'
            ]),
            launch_arguments={'world': 'my_world.sdf'}.items(),
        ),

        # Spawn robot
        Node(
            package='ros_gz_sim',
            executable='create',
            arguments=[
                '-topic', '/robot_description',
                '-name', 'my_robot',
                '-x', '0', '-y', '0', '-z', '0.1'
            ],
        ),

        # Bridge topics
        Node(
            package='ros_gz_bridge',
            executable='parameter_bridge',
            arguments=[
                '/cmd_vel@geometry_msgs/msg/Twist]gz.msgs.Twist',
                '/camera/image@sensor_msgs/msg/Image[gz.msgs.Image',
            ],
        ),

        # Robot state publisher
        Node(
            package='robot_state_publisher',
            executable='robot_state_publisher',
            parameters=[{'robot_description': robot_description}],
        ),
    ])

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Debugging Bridge Issues

Topic Not Bridging

1. Verify topic names match exactly (case-sensitive)
2. Check message type spelling
3. Confirm Gazebo is publishing: gz topic -e -t /topic
4. Confirm ROS 2 sees it: ros2 topic list

Data Not Flowing

1. Direction wrong (ROS_TO_GZ vs GZ_TO_ROS)
2. Message types incompatible
3. Gazebo world not running
4. Bridge process crashed

Message Type Mismatch

# Check ROS 2 message type
ros2 interface show sensor_msgs/msg/Image

# Check Gazebo message type
gz msg --info gz.msgs.Image

---

Common Patterns

Differential Drive Control

# Velocity command (ROS → Gazebo)
- ros_topic_name: "/cmd_vel"
  gz_topic_name: "/model/my_robot/cmd_vel"
  ros_type_name: "geometry_msgs/msg/Twist"
  gz_type_name: "gz.msgs.Twist"
  direction: ROS_TO_GZ

# Odometry (Gazebo → ROS)
- ros_topic_name: "/odom"
  gz_topic_name: "/model/my_robot/odometry"
  ros_type_name: "nav_msgs/msg/Odometry"
  gz_type_name: "gz.msgs.Odometry"
  direction: GZ_TO_ROS

Full Sensor Suite

# Camera
- ros_topic_name: "/camera/image_raw"
  gz_topic_name: "/camera/image"
  ros_type_name: "sensor_msgs/msg/Image"
  gz_type_name: "gz.msgs.Image"
  direction: GZ_TO_ROS

# LIDAR
- ros_topic_name: "/scan"
  gz_topic_name: "/lidar/scan"
  ros_type_name: "sensor_msgs/msg/LaserScan"
  gz_type_name: "gz.msgs.LaserScan"
  direction: GZ_TO_ROS

# IMU
- ros_topic_name: "/imu/data"
  gz_topic_name: "/imu"
  ros_type_name: "sensor_msgs/msg/Imu"
  gz_type_name: "gz.msgs.IMU"
  direction: GZ_TO_ROS

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Checklist

Before finalizing any bridge configuration:

• All topic names verified (exact match)
• Message type mappings confirmed
• Direction correct for each topic
• YAML syntax valid (if using config file)
• Gazebo topics publishing (gz topic -l)
• ROS 2 topics visible (ros2 topic list)
• Data flowing (ros2 topic echo)
• Launch file orchestrates correctly
• Multi-robot namespacing (if needed)

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Integration

This skill is used by:

• content-implementer agent when generating Module 2 lessons
• Students learning ROS 2-Gazebo integration in Chapter 12
• All simulation-based robotics development

Dependencies:

• urdf-robot-model - robots to spawn and control
• gazebo-world-builder - worlds to simulate in
• sensor-simulation - sensor data to bridge