px4-firmware/launch/posix_sitl.launch

<launch>
    <!-- Posix SITL environment launch script -->

    <arg name="headless" default="false"/>
    <arg name="gui" default="true"/>
    <arg name="ns" default="/"/>
    <arg name="world" default="iris"/>
    <arg name="build" default="posix_sitl_default"/>

    <node pkg="px4" type="sitl_run.sh" name="simulator" args="posix-configs/SITL/init/rcS none gazebo $(arg world) $(find px4)/build_$(arg build)">
        <env name="no_sim" value="1" />
    </node>

    <include file="$(find gazebo_ros)/launch/empty_world.launch">
        <arg name="headless" value="$(arg headless)"/>
        <arg name="gui" value="$(arg gui)"/>
        <arg name="world_name" value="$(find px4)/Tools/sitl_gazebo/worlds/$(arg world).world" />
    </include>
</launch>