When you import an Alias file, any mirrored geometry it contains is imported. The mirrored nodes appear in the Autodesk Showcase scene and have names ending with "MIRRORED". For example, if the original node has the name "front_door", its mirrored counterpart (visible in the Organizer) has the name "front_door-MIRRORED".
This functionality is available using Autodesk DirectConnect (shipped and installed with Autodesk Showcase).
Symmetrical geometry is not supported on import.
