Hi<br><br>Thanks! It"s clear now:)<br><br><div class="gmail_quote">On Tue, Apr 22, 2008 at 7:40 PM, Amy Squillacote <<a href="mailto:ahs@cfdrc.com">ahs@cfdrc.com</a>> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
Hi Adrian,<br>
<br>
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.<br>
<br>
- Amy<br>
<br>
Adrian Albert wrote:<br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><div><div></div><div class="Wj3C7c">
<br>
Dear All,<br>
<br>
<br>
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?<br>
For example, this code should calculate the gradient of the gradient magnitude (a measure of a second order derivative):<br>
<br>
// Gradient magnitude<br>
vtkImageGradientMagnitude* grad = vtkImageGradientMagnitude::New();<br>
grad->SetDimensionality( 3 );<br>
grad->SetInput (this->GetMultivariateField (whichField)); grad->Update ();<br>
<br>
// Gradient of gradient magnitude<br>
vtkImageGradient* gradGrad = vtkImageGradient::New();<br>
gradGrad->SetDimensionality( 3 );<br>
gradGrad->SetInput (grad->GetOutput ());<br>
gradGrad->Update ();<br>
Specifically, would I cause two computations of the gradient magnitude (first 4 lines of code) by calling Update twice?<br>
<br>
Thanks!<br>
Adrian<br>
<br>
-- <br>
---------------------------------------------------<br>
Adrian Albert<br>
School of Engineering and Science<br>
Jacobs University Bremen<br>
Germany<br>
Tel.: 00494212003258<br></div></div>
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</div></blockquote><font color="#888888">
<br>
-- <br>
Amy Squillacote Phone: (256) 726-4839<br>
Computer Scientist Fax: (256) 726-4806<br>
CFD Research Corporation Web: <a href="http://www.cfdrc.com" target="_blank">http://www.cfdrc.com</a><br>
215 Wynn Drive, Suite 501<br>
Huntsville, AL 35805<br>
<br>
<br>
</font></blockquote></div><br><br clear="all"><br>-- <br>---------------------------------------------------<br>Adrian Albert<br>School of Engineering and Science<br>Jacobs University Bremen<br>Germany<br>Tel.: 00494212003258