[Insight-developers] itk::ImageBase::TransformIndexToPhysicalPoint/TransformPointToContinuousIndex ignores spacing?

[Bill Lorensen]

I believe they do take spacing into account.

On Tue, Mar 17, 2009 at 8:56 AM, kent williams
<norman-k-williams at uiowa.edu> wrote:
> It looks like I'm going to have to roll my own functions to go between
> indices and points for the WarpImageFilter because this doesn't work:
>
> while( !outputIt.IsAtEnd() )
>  {
>  // get the output image index
>  index = outputIt.GetIndex();
>  outputPtr->TransformIndexToPhysicalPoint( index, point );
>
>  typename DeformationFieldInterpolatorType::ContinuousIndexType defIndex;
>  fieldPtr->TransformPhysicalPointToContinuousIndex(point,defIndex);
>  if(!m_DeformationFieldInterpolator->IsInsideBuffer(defIndex))
>    {
>    itkExceptionMacro(<< "Output location outsde DeformationField"
>                      " Buffer" << point);
>    }
>    // get the required displacement
>    displacement =
>    m_DeformationFieldInterpolator->EvaluateAtContinuousIndex(defIndex);
>    // stuff removed
>  }
>
> What I thought would happen (and what the function names seem to imply) is
> that given an IJK index into an image volume, you could get a world
> coordinate system point corresponding to that index.
>
> And conversely, given a point in the WCS, you can retrieve a corresponding
> continuous index.
>
> The problem? These functions don't take spacing into account; so the names
> of the functions are false advertising.  So calling
> TransformPhysicalPointToContinuousIndex with physical point in the output
> image doesn't return a continuous index inside the Deformation Field.
>
> In the particular test I'm working on, the output image has a size of
> 16x16x16 and spacing of 1MM, the deformation field has a size of 8x8x8 and
> spacing of 2MM.
>
> Since this behavior has been written in stone for years I don't imagine it
> will be changed.  But it's a bit disappointing to me.
>
> Is there a way to use the existing ITK physical point/index stuff that takes
> spacing into account?
>
>
>
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