[Insight-users] RigidTransform vs AffineTransform?

[Luis Ibanez]

Hi Motes:


                    A Rigid Transforms is not
               just an Affine centered Transform.


1) A Rigid Transform supports:
       Translations and Rotations

2) An Affine Transform supports:
        Translations, Rotations, Scaling and Shearing.


In ITK, both the Rigid and Affine transforms are "centered".
Which means that you can specify what point of space should
be used as the center of rotations.


Yes, there is something unique that is accomplished by using
a Rigid Transform:


  Managing Translations and Rotations, by only optimizing
  in an space of Six dimensions, instead of the space of
  12 dimensions where you have to optimize an Affine Transform.
   (this for the case of 3D images).



     Regards,


           Luis


--------------------------------------------------------------------------------------------
On Sun, Jul 12, 2009 at 3:14 PM, motes motes <mort.motes at gmail.com> wrote:

> In the itkSoftwareGuide an examples is walked through using a
> RigidTransform. But is a RigidTransform not just a centered AffineTransform?
> I am a bit confused that a RigidTransform exists, as I understand rigid and
> non-rigid are concepts that includes transforms. Something like:
>
> Rigid:
>  - Translation
>  - Affine
>
> Non-Rigid
>  - BsplineDeformableTransform
>
>
> Or are there something unique about a RigidTransform that is not
> accomplished using eg. translation or Affine transforms?
>
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