[Insight-developers] "itkSyNImageRegistrationMethod" cannot return its metric's transform properly

[Nicholas Tustison]

Hi Ali,

I don't think that there's a deficiency.  I just ran the itkSyNImageRegistrationTest
and added the following snippet to write the displacement field to disk starting
at line 275.

  typedef itk::ImageFileWriter<DisplacementFieldType> WriterType2;
  typename WriterType2::Pointer writer2 = WriterType2::New();
  writer2->SetFileName( "/Users/ntustison/Desktop/testDisplacementField.nii.gz" );
  writer2->SetInput( outputTransform->GetDisplacementField() );
  writer2->Update();

The result was a non-zero displacement field that looked reasonable based
on the parameters specified by the test.

Nick


On Dec 1, 2012, at 8:30 PM, "Ghayoor, Ali" <ali-ghayoor at uiowa.edu> wrote:

> Hello Developers,
> 
> In a registration framework, at each iteration, I get the current moving transform from the metric of the "itkSyNImageRegistrationMethod" filter; however, the returned moving transform has a displacement field with all zero values at every iteration. 
> 
> To inspect this deficiency in ITK, I used "itkSyNImageRegistrationTest.cxx", and made some modifications in the test code for this purpose.
> I added an iteration observer to the SyN registration stage:
> 
>     typedef CommandIterationUpdate<DisplacementFieldRegistrationType> DisplacementFieldCommandType; 
>     typename DisplacementFieldCommandType::Pointer DisplacementFieldObserver = DisplacementFieldCommandType::New(); 
>     displacementFieldRegistration->AddObserver( itk::IterationEvent(), DisplacementFieldObserver ); 
> 
> Then, inside the observer class, I asked for the parameters of the moving transform at the current iteration:
> 
>    std::cout << " parameters: " << const_cast<TFilter *>( filter )->GetMetric()->GetMovingTransform()->GetParameters() << std::endl; 
>    std::cout << " fixed parameters " << const_cast<TFilter *>( filter )->GetMetric()->GetMovingTransform()->GetFixedParameters() << std::endl;
> 
> However, the Parameters of the moving transform is an all zero valued displacement field at each iteration.
> Do you know why the registration filter does not return the right moving transform? Could you please help about this problem.
> 
> Thanks,
> Ali
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