fix: avoid remote Gazebo model lookups

src/nav2_turtlebot_simulator/launch/simulator.launch.py

@@ -21,6 +21,18 @@ HOUSE_FURNITURE_BOXES = {
     'table_marble/': ('1.40 0.86 0.76', None),
 }
 
+LOCAL_GROUND_PLANE_MODEL = '''    <model name="ground_plane">
+      <static>1</static>
+      <link name="link">
+        <collision name="collision"><geometry><plane><normal>0 0 1</normal><size>100 100</size></plane></geometry></collision>
+        <visual name="visual"><cast_shadows>false</cast_shadows><geometry><plane><normal>0 0 1</normal><size>100 100</size></plane></geometry><material><ambient>0.24 0.27 0.32 1</ambient><diffuse>0.24 0.27 0.32 1</diffuse></material></visual>
+      </link>
+    </model>'''
+
+LOCAL_SUN_LIGHT = '''    <light type="directional" name="sun">
+      <cast_shadows>false</cast_shadows><pose>0 0 10 0 0 0</pose><diffuse>0.8 0.8 0.8 1</diffuse><specular>0.2 0.2 0.2 1</specular><direction>-0.5 0.1 -0.9</direction>
+    </light>'''
+
 
 def replace_house_visual_meshes_with_boxes(house_model):
     """Keep physical mesh collisions, but render furniture as inexpensive boxes."""
@@ -109,7 +121,14 @@ def create_flat_house_world(gazebo_dir):
         )
 
     with open(world_path, 'r', encoding='utf-8') as source:
-        flat_world = source.read().replace('model://turtlebot3_house', 'model://turtlebot3_house_flat')
+        flat_world = source.read()
+    flat_world = flat_world.replace(
+        '    <include>\n      <uri>model://ground_plane</uri>\n    </include>',
+        LOCAL_GROUND_PLANE_MODEL,
+    ).replace(
+        '    <include>\n      <uri>model://sun</uri>\n    </include>',
+        LOCAL_SUN_LIGHT,
+    ).replace('model://turtlebot3_house', 'model://turtlebot3_house_flat')
 
     flat_world_path = os.path.join(tempfile.gettempdir(), 'nav2_turtlebot3_house_flat.world')
     with open(flat_world_path, 'w', encoding='utf-8') as destination:
@@ -119,6 +138,7 @@ def create_flat_house_world(gazebo_dir):
     os.environ['GAZEBO_MODEL_PATH'] = os.pathsep.join(
         part for part in (flat_models_dir, existing_model_path) if part
     )
+    os.environ['GAZEBO_MODEL_DATABASE_URI'] = ''
     return flat_world_path