[Insight-users] Quaternion does not equal Versor

[Matt McCormick]

Hi Anja,

A versor is a normalized quaternion -- a quaternion changes both the
orientation and length of a vector, but a versor changes only the
orientation, so the values may not be the same.

See

  http://en.wikipedia.org/wiki/Quaternion
  http://www.itk.org/CourseWare/Training/QuaternionsI.pdf

HTH,
Matt



On Wed, Jul 17, 2013 at 10:55 AM, Groch, Anja
<a.groch at dkfz-heidelberg.de> wrote:
> Hi,
>
>
>
> I’m not so familiar with the difference of a versor and a quaternion, but I
> thought, the 4 representing values should be the same in both structures.
>
>
>
> If so, then there might be a bug, when converting a
> itkVersorRigid3DTransform into a vnl_quaternion (or I’m just doing the
> conversion in a wrong way).
>
>
>
> I’m doing the conversion of a itk::VersorRigid3DTransform<double>::Pointer
> transform as follows:
>
>
>
> vnl_quaternion<double>(transform->GetMatrix().GetVnlMatrix());
>
>
>
> The resulting quaternion does not equal the versor, for example read out
> with ->GetVersor(). From the few examples I tried, it looks as if only the
> direction of the rotation changes, but rotation axis and angle are the same.
>
>
>
> Thanks a lot in advance for your help!
>
> Best
>
> Anja
>
>
>
> --------------
>
> Dipl.-Inform. Anja Groch
>
> German Cancer Research Center (DKFZ)
>
> Div. Medical and Biological Informatics
>
> Junior Group: Computer-assisted Interventions (E131)
>
> Im Neuenheimer Feld 280
>
> 69120 Heidelberg, Germany
>
>
>
> Email:  a.groch at dkfz.de
>
> Phone:  (+49) 6221/42-3548
>
> Fax:    (+49) 6221/42-2345
>
> http://www.dkfz-heidelberg.de/de/mbi/people/Anja_Groch.html
>
>
>
>
>
>
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