PX4 Fixed Wing Control Without GPS


I would like to use PX4 SITL with gazebo and fly a fixed-wing vehicle. However there are some constrains. I do not have any kind of positioning system. In my vehicle, I only have a laser range finder for altitute measurement. I need to control this aircraft just by setting airspeed and some kind of heading (like yaw in quadcopters). Any help would be appreciated.