[Insight-users] what is the valid region in BSplineDeformableTransform

[Zhiyong Xie]

I am not quite understand the valid region defined in 
BSplineDeformableTransform.
suppose I have a cubic B-spline curve with 4 control points (size=4), 
according to
the code in  SetGridRegion(), the size of ValidRegion will be
4-2*m_Offset = 4-2*2 = 0.

as my understanding, it should be 1.
can anybody explain this to me or tell me where I can find the stuff 
(book or paper)
based on which this calss is implemented?

Thanks

Sean