View source for Proposals:Decoupling ImageMetric from BSplineDeformableTransform

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= The Problem =

* The ImageToImageMetric knows too much
** It is aware of the 
*** BSplineDeformableTransform 
*** BSplineIntepolateImageFunction
** It performs dynamic_casting to discover the type of the Transform and Interpolator
** It caches several arrays for the BSplineDeformableTransform
*** The caching has the following problems
**** It is '''not optional''' (can't be turned off)
**** It is memory consuming (about 3 Gigabytes)
**** It break class encapsulation

= The Proposed Solution =

* Add a TransformCacher class
** A default cacher will not do anything
** A cacher for the BSplineDeformableTransform will take over the code that is currently in the ImageToImageMetric
** More sophisticated cachers could be added 
* The Transform class will use the default cacher
* The Metric will
** request the Transform for its cacher (at run time)
** use the cacher for passing a list of points to be mapped, and then map one by one using an index