Hello Sir,
I am not forcing you to add CAD in SH3D. But if you are planning to make it then here is some helpful links:
http://www.ibm.com/developerworks/library/os-autocad/
http://www.cadsofttools.com/pressreleases/dwgimportnet.htm
http://www.gnu.org/software/libredwg/
I think autocad DWG files can be read either svg or Obj- wireframe(wire/spline) mode.
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