make simulation use specific world file and have skybox

the sdf file isn't hand-crafted. I ran the launch file, then saved it from gazebo, then modified the scene tag to add a sky tag, then pasted that over my file, then removed the added robot model.

description/example_gazebo.xacro

@@ -87,7 +87,7 @@
     <!-- Note that although visualise is set to true, it won't actually visualise the depth camera in gazebo. To see the preview, 
             try swapping "depth" to "camera"-->
     <gazebo reference="camera_link">
-        <sensor type="depth" name="my_camera">
+        <sensor type="camera" name="my_camera">
             <update_rate>20</update_rate>
             <visualize>true</visualize>
             <camera name="cam">
@@ -99,7 +99,6 @@
                 </image>
                 <clip>
                     <near>0.02</near>
-                    <far>300</far>
                 </clip>
                 <noise>
                     <type>gaussian</type>

launch/example.launch.py

@@ -0,0 +1,85 @@
+# Author: Addison Sears-Collins
+# Date: September 19, 2021
+# Description: Load a world file into Gazebo.
+# https://automaticaddison.com
+# https://automaticaddison.com/how-to-load-a-world-file-into-gazebo-ros-2/
+
+import os
+from launch import LaunchDescription
+from launch.actions import DeclareLaunchArgument, IncludeLaunchDescription
+from launch.conditions import IfCondition, UnlessCondition
+from launch.launch_description_sources import PythonLaunchDescriptionSource
+from launch.substitutions import Command, LaunchConfiguration, PythonExpression
+from launch_ros.actions import Node
+from launch_ros.substitutions import FindPackageShare
+
+def generate_launch_description():
+
+  # Set the path to the Gazebo ROS package
+  pkg_gazebo_ros = FindPackageShare(package='gazebo_ros').find('gazebo_ros')   
+
+  # Set the path to this package.
+  pkg_share = FindPackageShare(package='two_wheeled_robot').find('two_wheeled_robot')
+
+  # Set the path to the world file
+  world_file_name = 'cafe.world'
+  world_path = os.path.join(pkg_share, 'worlds', world_file_name)
+
+  # Set the path to the SDF model files.
+  gazebo_models_path = os.path.join(pkg_share, 'models')
+  os.environ["GAZEBO_MODEL_PATH"] = gazebo_models_path
+
+  ########### YOU DO NOT NEED TO CHANGE ANYTHING BELOW THIS LINE ##############  
+  # Launch configuration variables specific to simulation
+  headless = LaunchConfiguration('headless')
+  use_sim_time = LaunchConfiguration('use_sim_time')
+  use_simulator = LaunchConfiguration('use_simulator')
+  world = LaunchConfiguration('world')
+
+  declare_simulator_cmd = DeclareLaunchArgument(
+    name='headless',
+    default_value='False',
+    description='Whether to execute gzclient')
+
+  declare_use_sim_time_cmd = DeclareLaunchArgument(
+    name='use_sim_time',
+    default_value='true',
+    description='Use simulation (Gazebo) clock if true')
+
+  declare_use_simulator_cmd = DeclareLaunchArgument(
+    name='use_simulator',
+    default_value='True',
+    description='Whether to start the simulator')
+
+  declare_world_cmd = DeclareLaunchArgument(
+    name='world',
+    default_value=world_path,
+    description='Full path to the world model file to load')
+
+  # Specify the actions
+
+  # Start Gazebo server
+  start_gazebo_server_cmd = IncludeLaunchDescription(
+    PythonLaunchDescriptionSource(os.path.join(pkg_gazebo_ros, 'launch', 'gzserver.launch.py')),
+    condition=IfCondition(use_simulator),
+    launch_arguments={'world': world}.items())
+
+  # Start Gazebo client    
+  start_gazebo_client_cmd = IncludeLaunchDescription(
+    PythonLaunchDescriptionSource(os.path.join(pkg_gazebo_ros, 'launch', 'gzclient.launch.py')),
+    condition=IfCondition(PythonExpression([use_simulator, ' and not ', headless])))
+
+  # Create the launch description and populate
+  ld = LaunchDescription()
+
+  # Declare the launch options
+  ld.add_action(declare_simulator_cmd)
+  ld.add_action(declare_use_sim_time_cmd)
+  ld.add_action(declare_use_simulator_cmd)
+  ld.add_action(declare_world_cmd)
+
+  # Add any actions
+  ld.add_action(start_gazebo_server_cmd)
+  ld.add_action(start_gazebo_client_cmd)
+
+  return ld

launch/rsp_sim.launch.py

@@ -1,9 +1,10 @@
 import os
 from ament_index_python.packages import get_package_share_directory
 from launch import LaunchDescription
-from launch.actions import IncludeLaunchDescription
+from launch.actions import IncludeLaunchDescription, DeclareLaunchArgument
 from launch.launch_description_sources import PythonLaunchDescriptionSource
 
+from launch_ros.substitutions import FindPackageShare
 
 from launch_ros.actions import Node
 import xacro
@@ -30,7 +31,14 @@ def generate_launch_description():
         'use_sim_time': True}] # add other parameters here if required
     )
 
+    pkg_share = FindPackageShare(package=pkg_name).find(pkg_name)
+    world_file_name = 'gz_world.sdf'
+    world_path = os.path.join(pkg_share, 'worlds', world_file_name)
 
+    declare_world_cmd = DeclareLaunchArgument(
+        name='world',
+        default_value=world_path,
+        description='Full path to the world model file to load')
 
     gazebo = IncludeLaunchDescription(
         PythonLaunchDescriptionSource([os.path.join(
@@ -50,6 +58,7 @@ def generate_launch_description():
 
     # Run the node
     return LaunchDescription([
+        declare_world_cmd,
         gazebo,
         node_robot_state_publisher,
         spawn_entity