2_turtlebot_word.launch

<launch>
 
  <arg name="world_file"  default="$(env TURTLEBOT_GAZEBO_WORLD_FILE)"/>

  <arg name="base"      value="$(optenv TURTLEBOT_BASE kobuki)"/> <!-- create, roomba -->
  <arg name="battery"   value="$(optenv TURTLEBOT_BATTERY /proc/acpi/battery/BAT0)"/>  <!-- /proc/acpi/battery/BAT0 --> 
  <arg name="gui" default="true"/>
  <arg name="stacks"    value="$(optenv TURTLEBOT_STACKS hexagons)"/>  <!-- circles, hexagons --> 
  <arg name="3d_sensor" value="$(optenv TURTLEBOT_3D_SENSOR hokuyo)"/>  <!-- kinect, asus_xtion_pro --> 

  <include file="$(find gazebo_ros)/launch/empty_world.launch">
    <arg name="use_sim_time" value="true"/>
    <arg name="debug" value="false"/>
    <arg name="gui" value="$(arg gui)" />
    <arg name="world_name" value="$(arg world_file)"/>
  </include>
    <group ns="robot1">
<param name="/use_sim_time" value="true" />
    <param name="tf_prefix" value="robot1_tf" />
    <include file="$(find turtlebot_gazebo)/launch/includes/$(arg base).launch.xml">
    <arg name="base" value="$(arg base)"/>
    <arg name="stacks" value="$(arg stacks)"/>
    <arg name="3d_sensor" value="$(arg 3d_sensor)"/>
    <arg name="robot_name"  value="robot1" />
    <arg name="x" value="1.0"/>
    <arg name="y" value="1.0"/>
    <arg name="z" value="0.0"/>
     </include>
    </group>

 <group ns="robot2">
<param name="/use_sim_time" value="true" />
    <param name="tf_prefix" value="robot2_tf" />
    <include file="$(find turtlebot_gazebo)/launch/includes/$(arg base).launch.xml">
    <arg name="base" value="$(arg base)"/>
    <arg name="stacks" value="$(arg stacks)"/>
    <arg name="3d_sensor" value="$(arg 3d_sensor)"/>
    <arg name="robot_name"  value="robot2" />
    <arg name="x" value="-1.0"/>
    <arg name="y" value="1.0"/>
    <arg name="z" value="0.0"/>
     </include>
    </group>
   
  <!-- Fake laser -->
  
</launch>