[Insight-users] RigidTransform vs AffineTransform?

[Luis Ibanez]

David,

Yes, there are differences between the Similarity and Affine Transforms.

The Similarity Transform does:   Translation, Rotation and Uniform Scaling

The Similarity Transform does *not* do Shearing, and it can not do
non Uniform scaling (e.g. scale X by 5 and scale Y by 7 ).


     Luis


--------------------------------------------------------------------------------------------------
On Tue, Jul 14, 2009 at 12:33 PM, Manuel David Tabas Calle <
manueldavid.tabas at hotmail.es> wrote:

>
> and what about Similarity2dTransform and AffineTransform??
>
> what are teh differences??
>
> Thanks!
>
> ------------------------------
> Date: Tue, 14 Jul 2009 12:02:21 -0400
> From: luis.ibanez at kitware.com
> To: mort.motes at gmail.com
> CC: insight-users at itk.org
> Subject: Re: [Insight-users] RigidTransform vs AffineTransform?
>
>
>
>
> 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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