[vtkusers] pipeline update

[Adrian Albert]

Dear All,


I have a question about the pipeline update mechanism in VTK: If I call
Update () on an algorithm that has as input the output of another algorithm,
does the Update command propagate down the pipeline and causes a
recomputation for all algorithms involved?
For example, this code should calculate the gradient of the gradient
magnitude (a measure of a second order derivative):

  // Gradient magnitude
  vtkImageGradientMagnitude* grad = vtkImageGradientMagnitude::New();
  grad->SetDimensionality( 3 );
  grad->SetInput (this->GetMultivariateField (whichField));
  grad->Update ();

  // Gradient of gradient magnitude
  vtkImageGradient* gradGrad = vtkImageGradient::New();
  gradGrad->SetDimensionality( 3 );
  gradGrad->SetInput (grad->GetOutput ());
  gradGrad->Update ();

Specifically, would I cause two computations of the gradient magnitude
(first 4 lines of code) by calling Update twice?

Thanks!
Adrian

-- 
---------------------------------------------------
Adrian Albert
School of Engineering and Science
Jacobs University Bremen
Germany
Tel.: 00494212003258
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