[ns] How to create DEMfiles?

[Rafiq Shaikh]

Hi All,

I am trying to create a multi-hop wireless topology. I plan to use DEMfiles
to create a topology. I looked at the NS manual but could not find much details 
on how to create DEMfile. 
Is there any document or any information on how to create a DEM file?
Any help or pointers would be of great help to me.

Thanks in advance.

Regards,
-Rafiq.