Revision history [back]

I'd like to update this answer for some people, as ROS2 functionality has improved but the documentation has not yet caught up. (To be clear it is March 2021 and I am running ROS 2 Foxy)

If you have a URDF file (note that the syntax for URDF in ROS 2 is slightly different than ROS 1) in your package that you want to spawn into Gazebo, you have to do the following:

1) Launch gazebo (not the standard way, I will elaborate below)
2) Launch the robot state publisher with your URDF file
3) Run thespawn_entity node to spawn your robot into gazebo

Here is how you go about doing it (as individual steps)

1) Create a Launch File for for your robot state publisher, here is an example:

import os
from ament_index_python.packages import get_package_share_directory
from launch import LaunchDescription
from launch.actions import DeclareLaunchArgument
from launch.substitutions import LaunchConfiguration
from launch_ros.actions import Node

def generate_launch_description():

  use_sim_time = LaunchConfiguration('use_sim_time', default='false')
  urdf_file_name = 'urdf/camera_bot.xacro'

  print("urdf_file_name : {}".format(urdf_file_name))

  urdf = os.path.join(
      get_package_share_directory('ros2_sim_pkg'),
      urdf_file_name)

  return LaunchDescription([

        DeclareLaunchArgument(
            'use_sim_time',
            default_value='false',
            description='Use simulation (Gazebo) clock if true'),
        Node(
            package='robot_state_publisher',
            executable='robot_state_publisher',
            name='robot_state_publisher',
            output='screen',
            parameters=[{'use_sim_time': use_sim_time}],
            arguments=[urdf])
  ])

In this example I am launching the robot state publisher with a URDF file called camera_bot.xacro (I am using .xacro because I want to reference other XML files, but a standard .urdf or .xml will work all the same) from a package called ros2_sim_pkg. Change the URDF and package names to fit your project.

2) Build your workspace (colcon build)

3) Source your workspace in the terminals you open (source install/setup.bash)

4) Launch gazebo with ros2 launch gazebo_ros gazebo.launch.py

5) Launch the launch file you just created to configure your robot_state_publisher: ros2 launch ros2_sim_pkg cam_bot_world.launch. Make sure to change the package name and launch file name to match yours.

6) Run the URDF spawner node: ros2 run gazebo_ros spawn_entity.py -topic /robot_description -entity my_cam_bot`

The entity name will be the name of your model within gazebo, so feel free to change "my_cam_bot" to whatever you want. It will automatically spawn at the origin, so if you do not want this, you can check out the other parameters here: https://github.com/ros-simulation/gazebo_ros_pkgs/blob/foxy/gazebo_ros/scripts/spawn_entity.py#L51

And with that you should have gazebo running with your URDF spawned in at the origin. I do not have Karma points so I can not show you a picture of it working unfortunately.

You can feel free to combine all these steps into one big launch file for convenience, but I just wanted to illustrate the process order so it was more understandable.

Hope this helps.