Update ros2_launch_gazebo.md (#559)

Signed-off-by: David Dorf <[email protected]>

Author: david-dorf

harmonic/ros2_launch_gazebo.md

@@ -54,45 +54,48 @@ an option but not strictly necessary as you could decide to hardcode some of the
 values or not even use all the parameters.
 
 ### Python
-Python launch files provide more low-level customization and logic compared to XML launch files. 
-In the following example, the user can specify a world argument to launch an environment for
-the Moon, Mars, or Enceladus. It additionally sets the resource path environment variable and
-sets up empty arrays for topics to be bridged and remapped from Gazebo to ROS 2:
+Python launch files provide more low-level customization and logic compared to XML launch files. For example, you can set environment variables and include Python specific functions and logic.
+In the following example, the user can replace the example package, world, and bridged topic with their own. This is intended as a scaffolding more than something that can be run on its own.
+
 ```python
-from ament_index_python.packages import get_package_share_directory
 from launch import LaunchDescription
-from launch.actions import (DeclareLaunchArgument, SetEnvironmentVariable, 
-                            IncludeLaunchDescription, SetLaunchConfiguration)
-from launch.substitutions import PathJoinSubstitution, LaunchConfiguration, TextSubstitution
 from launch_ros.actions import Node
+from launch.actions import SetEnvironmentVariable, IncludeLaunchDescription
 from launch.launch_description_sources import PythonLaunchDescriptionSource
+from launch.substitutions import PathJoinSubstitution
+from launch_ros.substitutions import FindPackageShare
 
 
 def generate_launch_description():
-    pkg_ros_gz_sim = get_package_share_directory('ros_gz_sim')
-    pkg_spaceros_gz_sim = get_package_share_directory('spaceros_gz_sim')
+    ros_gz_sim_pkg_path = get_package_share_directory('ros_gz_sim')
+    example_pkg_path = FindPackageShare('example_package')  # Replace with your own package name
     gz_launch_path = PathJoinSubstitution([pkg_ros_gz_sim, 'launch', 'gz_sim.launch.py'])
-    gz_model_path = PathJoinSubstitution([pkg_spaceros_gz_sim, 'models'])
 
     return LaunchDescription([
-        DeclareLaunchArgument(
-            'world',
-            default_value='moon',
-            choices=['moon', 'mars', 'enceladus'],
-            description='World to load into Gazebo'
+        SetEnvironmentVariable(
+            'GZ_SIM_RESOURCE_PATH',
+            PathJoinSubstitution([example_pkg_path, 'models'])
+        ),
+        SetEnvironmentVariable(
+            'GZ_SIM_PLUGIN_PATH',
+            PathJoinSubstitution([example_pkg_path, 'plugins'])
         ),
-        SetLaunchConfiguration(name='world_file', 
-                               value=[LaunchConfiguration('world'), 
-                                      TextSubstitution(text='.sdf')]),
-        SetEnvironmentVariable('GZ_SIM_RESOURCE_PATH', gz_model_path),
         IncludeLaunchDescription(
             PythonLaunchDescriptionSource(gz_launch_path),
             launch_arguments={
-                'gz_args': [PathJoinSubstitution([pkg_spaceros_gz_sim, 'worlds',
-                                                  LaunchConfiguration('world_file')])],
+                'gz_args': [PathJoinSubstitution([example_pkg_path, 'worlds/example_world.sdf'])],  # Replace with your own world file
                 'on_exit_shutdown': 'True'
             }.items(),
         ),
+
+        # Bridging and remapping Gazebo topics to ROS 2 (replace with your own topics)
+        Node(
+            package='ros_gz_bridge',
+            executable='parameter_bridge',
+            arguments=['/example_imu_topic@sensor_msgs/msg/[email protected]',],
+            remappings=[('/remapped_imu_topic'),],
+            output='screen'
+        ),
     ])
 ```