world.launch.py

from launch_ros.actions import Node
from launch_ros.substitutions import FindPackageShare
from launch import LaunchDescription
from launch.actions import IncludeLaunchDescription, DeclareLaunchArgument
from launch.launch_description_sources import PythonLaunchDescriptionSource
from launch.substitutions import PathJoinSubstitution, LaunchConfiguration
import os
import xacro
from ament_index_python.packages import get_package_share_directory


def generate_launch_description():
    pkg_ros_gz_sim = get_package_share_directory('ros_gz_sim')
    share_dir = get_package_share_directory('diff_bot_description')

    use_sim_time_cmd = DeclareLaunchArgument(
        name='use_sim_time',
        default_value='True',
        description='use simulation clock if set to true'
    )

    gz_launcher = IncludeLaunchDescription(
        PythonLaunchDescriptionSource(
            os.path.join(pkg_ros_gz_sim, 'launch', 'gz_sim.launch.py')),
        launch_arguments={'gz_args': PathJoinSubstitution([
            share_dir,
            'worlds',
            f'custom_warehouse3.sdf -r' 
        ])}.items(),
    )

    return LaunchDescription([
        use_sim_time_cmd,
        gz_launcher     
    ])