<?xml version="1.0" ?>
<sdf version='1.7'>
  <world name="world_frame_relative_to">

    <frame name="world_frame"/>                 <!-- VALID: Directly relative_to implicit world frame. -->
    <frame name="F0">
      <pose relative_to="">1 0 0 0 0 0</pose>   <!-- VALID: Directly relative_to implicit world frame by default. -->
    </frame>
    <frame name="F1">
      <pose relative_to="F0">2 0 0 0 0 0</pose> <!-- VALID: Indirectly relative_to implicit world frame via frame F0. -->
    </frame>
    <frame name="F1a" attached_to="F1">
      <pose relative_to="world">4 0 0 0 0 0</pose> <!-- VALID: Directly relative_to implicit world frame. -->
    </frame>

    <model name="M1">
      <link name="L"/>
      <frame name="F0">
        <pose relative_to="L">0 3 0 0 0 0</pose>  <!-- VALID: Directly relative_to link L. -->
      </frame>
    </model>

    <frame name="F2">
      <pose relative_to="M1">3 0 0 0 0 0</pose>   <!-- VALID: Indirectly relative to canonical link L of model M1. -->
    </frame>

    <model name="M2">
      <pose relative_to="">0 0 4 0 0 0</pose>
      <link name="L"/>
    </model>

    <model name="M3">
      <pose relative_to="M2">0 0 5 0 0 0</pose>
      <link name="L"/>
    </model>

    <model name="M4">
      <pose relative_to="F1">0 0 6 0 0 0</pose>
      <link name="L"/>
    </model>

  </world>
</sdf>
