[Insight-developers] compose affine with header filter?

[Michael Stauffer (Circular Logic)]

Luis, thanks for the clarification. That's exactly what we were
suspecting.
 
I'm working now from some code from Hans that performs the operation. If
we run into trouble I'll take you up on your offer to help.
 
Cheers,
Michael


  _____  

From: Luis Ibanez [mailto:luis.ibanez at kitware.com] 
Sent: Wednesday, October 13, 2010 10:00 AM
To: Cory Quammen
Cc: Michael Stauffer (Circular Logic); Insight Developers
Subject: Re: [Insight-developers] compose affine with header filter?


Cory,

You are right,

The implicit transform that is stored in the itkImage
metadata can only describe a combination of:

1) Translation (via the origin)
2) Rotation / Reflection (via the Direction matrix)
3) Anisotropic scaling (via the spacing)


Combining these three modifications, it is not possible
to represent a generic Affine Transform.

In particular, as you pointed out, we can't represent
shearing (at least not for a generic case).


--


Michael:


The filter that you are describing will have to be
limited to composing the existing image grid with
only the following operations:


1) Translations
2) Rigid rotations & Reflections (flipping)
3) Anisotropic scaling parallel to the grid.


I'll be happy to have a phone /skype conversation
if you want to go about the details.

---

Also,

if you are writing your first ITK, you may find
useful to look at this presentation:
http://www.na-mic.org/Wiki/images/b/bc/Insight-Writing-a-New-Filter.ppt