<?xml version="1.0"?><gz:world   xmlns:gz='http://playerstage.sourceforge.net/gazebo/xmlschema/#gz'  xmlns:model='http://playerstage.sourceforge.net/gazebo/xmlschema/#model'  xmlns:sensor='http://playerstage.sourceforge.net/gazebo/xmlschema/#sensor'  xmlns:window='http://playerstage.sourceforge.net/gazebo/xmlschema/#window'  xmlns:params='http://playerstage.sourceforge.net/gazebo/xmlschema/#params'>  <params:GlobalParams>    <gravity>0.0 0.0 -9.8</gravity>  </params:GlobalParams>  <model:ObserverCam>    <id>userCam0</id>    <xyz>0 0 20</xyz>    <rpy>0 30 0</rpy>    <imageSize>640 480</imageSize>  </model:ObserverCam>     <model:LightSource>    <id>0</id>    <xyz>0 0 40</xyz>  </model:LightSource> <model:GroundPlane>    <id>ground1</id>    <color>0.5 0.5 0.5</color>    <textureFile>grid.ppm</textureFile>  </model:GroundPlane>  <model:Factory>    <id>factory1</id>  </model:Factory></gz:world>