[Insight-developers] The {Binary|Ternary}FunctorImageFilter problem.

[Williams, Norman K]

I feel like I saw I way to implement what Hans was asking for, and
foolishly I thought that adding the functionality near the base of the
inheritance hierarchy was actually a win -- it added new functionality to
a whole family of classes, without changing their behavior for existing
cases.

It has turned into a big mess. Partly that was my fault, because I was
doing something that was a bit tricky internally.  I also pushed it up to
Master based on limited feedback and without much testing on compilers
aside from gcc.

So I guess what Luis is proposing is this:

1. Back out the changes I made. That means reversing this patch:
   http://review.source.kitware.com/#change,1725

2. Add space checking to the existing functions, at the
   {Binary|Ternary}FunctorImageFilter level. Throw exception
   if spaces don't match to a tolerance.

3. Start a new, parallel tree of functor filters.  Probably needs to be
   in its own, new module?  What is it called?

Forgive me, Luis if I'm mis-representing what you've said.

I also think Hans is right, in that the existing system behaves in
surprising, incorrect ways for medical imaging. Here at Iowa we have a lot
of experience with using and teaching ITK at the undergraduate, graduate
and professional levels. Part of the steepness of the learning curve is
avoiding pitfalls that arise from the pitfalls associated with physical vs
image space.

But I want to be done with this controversy.  I can implement whatever
consensus solution is decided on.



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