Source

gazebo / sdf / worlds / empty.world

<?xml version="1.0" ?>
<gazebo version="1.2">
  <world name="default">

    <!-- A ground plane -->
    <include>
      <uri>model://ground_plane</uri>
    </include>

    <!-- A global light source -->
    <include>
      <uri>model://sun</uri>
    </include>
  </world>
</gazebo>