simulation-expert

name	simulation-expert
description	Expert in simulating autonomous robots with ROS 2 and Gazebo Sim (Ignition). Handles asset preparation, sensor integration, bridging, and launch configuration.

Simulation Expert Skill

This skill provides detailed instructions for setting up and managing Gazebo Sim environments for ROS 2.

1. Asset Preparation (URDF & Plugins)

Plugin Namespace Difference

• Gazebo Fortress (Humble): ignition::gazebo::systems::... | filename: ignition-gazebo-...
• Gazebo Harmonic (Jazzy): gz::sim::systems::... | filename: gz-sim-...

Diff Drive Plugin Example (Harmonic/Jazzy)

<gazebo>
  <plugin filename="gz-sim-diff-drive-system" name="gz::sim::systems::DiffDrive">
    <left_joint>left_wheel_joint</left_joint>
    <right_joint>right_wheel_joint</right_joint>
    <wheel_separation>1.25</wheel_separation>
    <wheel_radius>0.3</wheel_radius>
    <topic>cmd_vel</topic>
    <odom_topic>odom</odom_topic>
    <tf_topic>tf</tf_topic>
    <frame_id>odom</frame_id>
    <child_frame_id>base_link</child_frame_id>
    <odom_publisher_frequency>50</odom_publisher_frequency>
  </plugin>
  
  <plugin filename="gz-sim-joint-state-publisher-system" name="gz::sim::systems::JointStatePublisher">
    <topic>joint_states</topic>
  </plugin>
</gazebo>

2. Sensor Integration

CRITICAL: You MUST add the gz::sim::systems::Sensors plugin to the <world> or <robot> (via <gazebo> tag) for sensors to work.

Lidar Example

<gazebo reference="lidar_link">
  <sensor name="lidar" type="gpu_lidar">
    <topic>scan</topic>
    <update_rate>10</update_rate>
    <lidar>
      <scan>
        <horizontal>
          <samples>360</samples>
          <resolution>1</resolution>
          <min_angle>-3.14</min_angle>
          <max_angle>3.14</max_angle>
        </horizontal>
      </scan>
      <range>
        <min>0.10</min>
        <max>10.0</max>
      </range>
    </lidar>
    <visualize>true</visualize>
  </sensor>
</gazebo>

3. Bridge Configuration (ros_gz_bridge)

Create a bridge.yaml file in config/ directory.

Mapping Matrix

Data Type	ROS 2 Type	Gazebo Type (Harmonic)
Twist	geometry_msgs/msg/Twist	gz.msgs.Twist
LaserScan	sensor_msgs/msg/LaserScan	gz.msgs.LaserScan
Image	sensor_msgs/msg/Image	gz.msgs.Image
Odom	nav_msgs/msg/Odometry	gz.msgs.Odometry
Clock	rosgraph_msgs/msg/Clock	gz.msgs.Clock
TF	tf2_msgs/msg/TFMessage	gz.msgs.Pose_V

YAML Example

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

- ros_topic_name: "/clock"
  gz_topic_name: "/clock"
  ros_type_name: "rosgraph_msgs/msg/Clock"
  gz_type_name: "gz.msgs.Clock"
  direction: GZ_TO_ROS

4. Launch File Workflow

Template

import os
from ament_index_python.packages import get_package_share_directory
from launch import LaunchDescription
from launch.actions import IncludeLaunchDescription, SetEnvironmentVariable
from launch.launch_description_sources import PythonLaunchDescriptionSource
from launch_ros.actions import Node

def generate_launch_description():
    pkg_ros_gz_sim = get_package_share_directory('ros_gz_sim')
    pkg_my_bot = get_package_share_directory('my_bot_description')

    # KEY STEP: Set Resource Path
    gz_resource_path = SetEnvironmentVariable(
        name='GZ_SIM_RESOURCE_PATH',
        value=os.path.join(pkg_my_bot, '..')
    )

    # 1. Start Gazebo
    gz_sim = IncludeLaunchDescription(
        PythonLaunchDescriptionSource(
            os.path.join(pkg_ros_gz_sim, 'launch', 'gz_sim.launch.py')
        ),
        launch_arguments={'gz_args': '-r empty.sdf'}.items(),
    )

    # 2. Spawn Robot
    spawn = Node(
        package='ros_gz_sim', 
        executable='create',
        arguments=['-topic', 'robot_description'], 
        output='screen'
    )

    # 3. Bridge
    bridge = Node(
        package='ros_gz_bridge',
        executable='parameter_bridge',
        parameters=[{
            'config_file': os.path.join(pkg_my_bot, 'config', 'bridge.yaml'),
            'qos_overrides./tf_static.publisher.durability': 'transient_local',
        }],
        output='screen'
    )

    return LaunchDescription([gz_resource_path, gz_sim, spawn, bridge])