[Insight-users] VersorRigid3dTransform

[Martin Urschler]

Hi Karthik,

Thanks for your answer.
There is one minor thing that I still don't understand. Shouldn't the 
center of rotation have an effect on the translation parameters that are 
used in a registration? Using the code I posted in my last message, the 
registration would start at exactly the same point in the metric space 
in both cases, independent of a specified center of rotation or not, 
since the 6 parameter values areidentical. IMHO that can't be right. I 
see now, that the transform has to be treated carefully when putting it 
into the registration/optimization, however I think one will start at 
different locations of the metric function with and without rotation 
center... right?

thanks,
Martin

Karthik Krishnan wrote:
> Hi Martin,
> 
> Yes the transforms are indeed different.
> 
> transform->GetParameters() does not tell you the whole story though. It 
> prints out the translation components and the versor, but not the 
> center. You can try transform->Print(std::cout ) to see the center. In 
> fact, if you place the following line
> 
>  std::cout << transform->TransformPoint( point ) << std::endl;
> 
> before and after you set the center, you will see that the transformed 
> point is indeed different.
> 
> It does bring up one minor point concerning transforms like the 
> VersorRigidTransform and other transforms that contain the center (they 
> derive from the MatrixOffSetTransformBase). If you were to copy the 
> transform parameters over into another transform, you will also need to 
> explicitly copy the center otherwise your new transform will be 
> incorrect.  ie....
> 
>  TransformType::Pointer finalTransform = TransformType::New();
>  copiedTransform->SetCenter( originalTransform->GetCenter() );
>  copiedTransform->SetParameters( originalTransform->GetParameters() );
> 
> Maybe this info should be put in the Doxygen ...... ? ?
> 



-- 
Martin Urschler
TU Graz - Institute for Computer Graphics & Vision
EMail: martin at urschler.info  ICQ: 41586273
Web: http://www.urschler.info
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