system.launch.xml

<?xml version="1.0"?>
<launch>

    <arg name="spawn_only" default="false"/>
    <arg name="sim_only" default="false"/>
    <arg name="motion_tracking" default="true"/>
    <arg name="spawn_gimbal" default="$(env SPAWN_GIMBAL false)"/>

    <include unless="$(var spawn_only)" file="/ros_ws/launch/gzweb.launch.xml" >
        <arg name="world" value="flightarena.world" />
    </include>

    <!-- Spawn a specified vehicle -->
    <node unless="$(var sim_only)"
          pkg="gazebo_ros"
          exec="spawn_entity.py"
          args="-entity  $(env PX4_SIM_MODEL)_$(env PX4_SYSID)
                -file /tmp/$(env PX4_SIM_MODEL)_$(env PX4_SYSID).sdf
                -spawn_service_timeout 30.0
                -x $(env PX4_SIM_INIT_LOC_X)
                -y $(env PX4_SIM_INIT_LOC_Y)
                -z $(env PX4_SIM_INIT_LOC_Z)"
    />

    <!-- Spawn the gimbal from the local database-->
    <group if="$(var spawn_gimbal)">
        <node unless="$(var sim_only)"
            pkg="gazebo_ros"
            exec="spawn_entity.py"
            args="-entity gimbal_100
                    -database gimbal_tripod
                    -spawn_service_timeout 30.0
                    -x $(env GIMBAL_INIT_LOC_X -1.3)
                    -y $(env GIMBAL_INIT_LOC_Y 6)
                    -z $(env GIMBAL_INIT_LOC_Z 0)"
        />
    </group>

    <!-- Spawn Motion Tracking -->
    <node if="$(var motion_tracking)"
        pkg="motion_tracker_sim"
        exec="motion_tracker"
        output="screen"
        respawn="true"
    />

</launch>