[vtkusers] vtkParametricSpline derivatives

[Karl Merkley]

OK, so I just should have gone and looked at the source first.  The  
Evaluate function for vtkParametricSpline doesn't even attempt to  
compute derivatives.  Looks like I do this myself.

    Karl

On Mar 21, 2008, at 8:01 AM, Karl Merkley wrote:

> I'm trying to compute the derivatives a a spline.  I can evaluate  
> points on the spline and get it to display but the derivative values  
> always come back as zeros.    I'm using the cvs version of VTK  
> updated earlier this week.   Any clues?
>
>  Thanks,
>       Karl
>
>    // create a spline interpolating all the points
>    vtkSmartPointer<vtkParametricSpline> spline =  
> vtkSmartPointer<vtkParametricSpline>::New();
>
>    spline->SetPoints(polydata->GetPoints());
>    spline->DerivativesAvailableOn();
>
>    double u[3] = {.5, .5, .5};
>    double pt[3];
>    double deriv[9];
>    spline->Evaluate(u, pt, deriv);
>    printf("point : %f %f %f\n", pt[0], pt[1], pt[2]);
>    printf("deriv: %f %f %f : %f %f %f : %f %f %f\n",   
> deriv[0],deriv[1],deriv[2],deriv[3],deriv[4],deriv[5],
>            deriv[6],deriv[7],deriv[8]);
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