[Insight-users] coordinate conversion

[Petr Jilkine]

Hello,

I have 2 images fixed and moving. I apply some linear transform to moving
image
to bring it to physical space of fixed image using ResampleImageFilter (see
metacode)

  typedef typename itk::ResampleImageFilter< InputImageType,
OutputImageType > ResampleFilterType;
  ResampleFilterType::Pointer resample = ResampleFilterType::New();

  resample->SetInput( moving );
  resample->SetTransform( transform );
  resample->SetSize( fixed->GetLargestPossibleRegion().GetSize() );
  resample->SetOutputOrigin(  fixed->GetOrigin() );
  resample->SetOutputSpacing( fixed->GetSpacing() );
  resample->SetOutputDirection( fixed->GetDirection() );
  resample->SetDefaultPixelValue( zeroValue );

I also have 2 point sets, one in fixed, another in moving image.
I would like to resample moving point set in a similar way.
For this I use (metacode)

  typedef itk::TransformMeshFilter< MeshType, MeshType, TransformType >
TransformMeshType;

  TransformMeshType::Pointer movingTransformMesh = TransformMeshType::New();
  movingTransformMesh->SetInput(movingMesh);
  movingTransformMesh->SetTransform(transform);
  movingTransformMesh->Update();
Probably I need to use an inverse transform instead.
I guess if the points in point sets had world coordinates if would work.
But coordinates of the points are wrt the center of corresponding image.
Now I need to convert these local coordinates to world coordinates taking
into account origin, spacing and direction matrix of the corresponding
image.
TransformMeshFilter seems a good candidate to do the job, but it is not
clear
how to pass origin, spacing and direction matrix to the filter.

Coordinates conversion like this seems a standard problem and
I guess there is a standard way to do it in ITK. However, so far
I couldn’t find an appropriate ITK class/function.

Any advice on this matter is really appreciated.

Thanks,
Peter Jilkine
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