rviz collision detection (fuerte)

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I'm trying to enable collision detection in RVIZ (debian/AMD64).

I built a xacro description of my robot, using basic collision tags.

Example:

    <link name="${prefix}_AX1" >
 <visual> 
  <origin xyz="0 0 0" rpy="${pi/2} 0 ${pi/2}" />
 <geometry>
    <box size="${AX_length}  ${AX_width} ${AX_height}"/>
  </geometry>
  <material name="black">
    <color rgba="0 0 0 1.0"/>
  </material>
</visual>
<collision>
    <geometry>
        <box size="${AX_length}  ${AX_width} ${AX_height}"/> 
    </geometry>
  <inertial>
    <mass value=".055"/>
    <inertia ixx="1.0" ixy="0.0" ixz="0.0" iyy="1.0" iyz="0.0" izz="1.0"/>
  </inertial>
</collision>
    </link>

The robot has 2 forelegs in the (x,y) plan, parallel to y. I allow them to rotate about z-axis from -pi/2 to pi/2. I thought that the checkbox collision-enabled would prevent them from crossing.

Do I have to use gazebo ?