[vtkusers] smoothing errors

[Berk Geveci]

>I use vtkSmoothPolyDataFilter, to smooth a surface. It smoots the surface. 
>But, at the end of the smoothing process, I want to display smoothing 
>errors. For this purpose I use the   functions GenerateErrorScalars, and 
>GrenerateErrorScalarsOn. When I use these functions, in the render window, 
>smoothed surface is drawn with various colors. I think, these colors 
>correspond to different error values. Here I have the following questions:
>
>1- How is the smoothing error computed? (i.e, what is the error 
>measure?Laplacian smoothing is used but error measure?)

Here is the piece of code which calculates the errors

    for (i=0; i<numPts; i++)
      {
      // inPts are the points from the input
      // newPts are the output points
      // the error measure is simply ||x2 - x1||
      inPts->GetPoint(i,x1);
      newPts->GetPoint(i,x2);
      newScalars->SetComponent(i,0,
			       sqrt(vtkMath::Distance2BetweenPoints(x1,x2)));
      }

If you don't like the error measure, it should be very easy to change it.
just replace
newScalars->SetComponent(i,0,sqrt(vtkMath::Distance2BetweenPoints(x1,x2)));
with your prefered measure.


>2- How can I obtain the numerical values of these errors?

  Just get the scalars from the output's point data, for example:
  vtkScalars* errors = 
smoothFilter->GetOutput()->GetPointData()->GetScalars();

  and to get the error at ith point, you can
  errors->GetScalar(i);

>3- How can I draw a graphic to legend these error values?

  Use vtkScalarBarActor. There are examples in the user's guide.

-Berk


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