[vtkusers] Is it possible to have a "bounding sphere" for an actor

[Elvis Dowson]

Hi,
        Is there some way to create a "bounding sphere" for an actor?  
Should I attempt to write my own vtkBoundingSphere class to support  
this?

Later on I would like to extend this to support creation of a user  
defined bounding area, which can be the result of an implicit  
function, to support bounding sphere intersection tests.

I will be grateful if someone can help point me in the right  
direction, so I can develop this functionality.

Best regards,

Elvis Dowson