[vtkusers] pipeline update

[Adrian Albert]

Hi

Thanks! It"s clear now:)

On Tue, Apr 22, 2008 at 7:40 PM, Amy Squillacote <ahs at cfdrc.com> wrote:

> Hi Adrian,
>
> A call to Update() in VTK does propagate back to earlier filters in the
> pipeline. However, the pipeline checks whether the a filter is up-to-date
> before calling Update() on it, so as long as you don't make any changes to
> the instance of vtkImageGradientMagnitude between calling Update() on it and
> calling Update() on the instance of vtkImageGradient, each filter should
> perform its computation only once.
>
> - Amy
>
> Adrian Albert wrote:
>
> >
> > 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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>
> --
> Amy Squillacote                    Phone: (256) 726-4839
> Computer Scientist                 Fax: (256) 726-4806
> CFD Research Corporation           Web: http://www.cfdrc.com
> 215 Wynn Drive, Suite 501
> Huntsville, AL  35805
>
>
>


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