To launch posix_sitl_default via ROS, follow instructions under "Launching Gazebo with ROS Wrappers" https://dev.px4.io/en/simulation/ros_interface.html
under ../Firmware/posix-configs/SITL/init/lpe edit iris (or whichever model) param set ATT_EXT_HDG_M 1 (1 for vision estimate, 2 for mocap estimate) param set LPE_FUSION 28 (default 145 for GPS. Explanation of bits in QGroundControl) *delete gpssim start