[vtkusers] vtkImageInterpolator -> gradient

[David Gobbi]

On Mon, Jun 13, 2016 at 4:17 AM, Martin Genet <
martin.genet at polytechnique.edu> wrote:
>
>
> I was wondering: has there been any progress on this side? It would quite
> useful. Any thought on the implementation? Thanks!
>

No progress, it's still just an idea.  When I wrote that wiki page, I was
thinking the gradient would be useful if these interpolators were used for
either isosurfacing or ray casting. What were you thinking of using the
gradient for?

The computation of derivatives for b-spline interpolation is currently
implemented in the vtkBSplineTransform class, which uses the derivatives to
provide the Jacobian matrix for the transformation:
https://gitlab.kitware.com/vtk/vtk/blob/master/Filters/Hybrid/vtkBSplineTransform.cxx#L202
Computing a gradient would be similar, but would need only three
derivatives instead of nine.

 - David
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