Start Gazebo and PX4 SITL separately

• Terminal 1

make posix_sitl_default gazebo no_sim=1

• Terminal 2

# PX4 gazebo plugins
export GAZEBO_PLUGIN_PATH=${GAZEBO_PLUGIN_PATH}:/home/user/px4/Firmware/build/posix_sitl_default/build_gazebo
export GAZEBO_MODEL_PATH=${GAZEBO_MODEL_PATH}:/home/user/px4/Firmware/Tools/sitl_gazebo/models

# add iris model into warehouse world
#run
gazebo --verbose /home/user/px4/Firmware/Tools/sitl_gazebo/worlds/warehouse.world

Add iris into warehouse.world

<?xml version="1.0" ?>
<sdf version="1.5">
  <world name="default">
    <!-- A global light source -->
    <include>
      <uri>model://sun</uri>
    </include>
    <!-- A ground plane -->
    <include>
      <uri>model://ground_plane</uri>
    </include>
    <include>
      <uri>model://asphalt_plane</uri>
    </include>
    <!--add iris model for example -->
    <include>
      <uri>model://iris</uri>
      <pose>1.01 0.98 0.83 0 0 1.14</pose>
    </include>

Note

Try to add model with gz command, the model add into the world model list but not visible

gz model --spawn-file=iris.sdf --model-name=iaaa -p 1.01 0.98 0.83 0 0 1.14