[Insight-users] RigidTransform vs AffineTransform?

[Manuel David Tabas Calle]

 Ok, thank you very much Luis.


Date: Tue, 14 Jul 2009 12:43:23 -0400
Subject: Re: [Insight-users] RigidTransform vs AffineTransform?
From: luis.ibanez at kitware.com
To: manueldavid.tabas at hotmail.es
CC: insight-users at itk.org

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


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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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