[ros-users] Robot model display in Rviz

hi

I have created an urdf package for my robot refering the urdf tutorials and
its working as expected.I have included a visual tag to the top link of my
robot so that i can visualize it on rviz.I tried creating a launch file
using following set of instruction

<launch>
<param name="robot_description" command="cat $(find packagename)/model.xml" />

</launch>

but when i try to launch this file i get invalid parameter tag error

Invalid <param> tag: Cannot load command parameter [my_urdf.xml]:
command [cat $learning_urdf/my_urdf.xml] returned with code [1].

Param xml is <param command="cat $learning_urdf/my_urdf.xml"
name="my_urdf.xml"/>

Actually I am not quite sure what give as a parameter name.

so if any one can suggest it would be a great help.

Regards,
Shayan Sengupta