[vtkusers] vtkParametricSpline and vtkParametricFunctionSource

[Anja Ende]

Hi Dean,

Thanks for the reply!

I had looked at it but had got a bit confused with the following lines:

x = (1.0 - u[0])*x0 + u[0]*x1;
y = (1.0 - u[0])*y0 + u[0]*y1;
z = (1.0 - u[0])*z0 + u[0]*z1;

But it is great to know that they can be used with any values. Perfect!

Thanks again.

Anja

On 10/11/06, Dean Inglis <dean.inglis at sympatico.ca> wrote:
>
> Anja,
>
> have a look at the code snippet taken from vtkSplineWidget below.
> Pass your screen coordinates as is (or any other type of points) to the
> vtkParametricSpline: these are your "handles" or control points: no need
> to normalize. You control how many points to generate along the spline
> with
> the
> Resolution term.  For a single line between control point pairs,
> set resolution to be numberOfControlPoints - 1.
>
> Dean
>
> Hi everyone,
>
> I have a question about the usage of vtkParametricSpline and
> vtkParametricSource. What I want to do is use Qt to draw a spline through
> some selected points on my image. I think the combination of
> vtkParametricSpline and vtkParametricFunctionSource can do what I want to
> achieve.
>
> Now, I acquire the control points coordinates through the mouse events and
> these are integers. What I would like to do is calculate the spline using
> these values. I noticed that the documentation for the vtkParametricSpline
> mentions:
> "This family of 1D splines is quaranteed to be parameterized in the
> interval
> [0,1]. Attempting to evaluate outside this interval will cause the
> parameter
> u to be clamped in the range [0,1]."
>
> I was wondering if I could pass the screen coordinates as input points to
> the spline or does everything has to be normalized between 0 and 1. I
> think
> working with integers would be faster and I would like to avoid the
> unnecessary conversions back and forth...
>
> Thanks and cheers,
>
> Anja
>
> vtkPoints* points = vtkPoints::New(VTK_DOUBLE);
>   points->SetNumberOfPoints(this->NumberOfHandles);
>
>   for ( i = 0; i < this->NumberOfHandles; ++i )
>     {
>     this->HandleGeometry[i] = vtkSphereSource::New();
>     this->HandleGeometry[i]->SetThetaResolution(16);
>     this->HandleGeometry[i]->SetPhiResolution(8);
>     vtkPolyDataMapper* handleMapper = vtkPolyDataMapper::New();
>     handleMapper->SetInput(this->HandleGeometry[i]->GetOutput());
>     this->Handle[i] = vtkActor::New();
>     this->Handle[i]->SetMapper(handleMapper);
>     handleMapper->Delete();
>     u[0] = (double)i / (double)(this->NumberOfHandles - 1.0);
>     x = (1.0 - u[0])*x0 + u[0]*x1;
>     y = (1.0 - u[0])*y0 + u[0]*y1;
>     z = (1.0 - u[0])*z0 + u[0]*z1;
>     points->SetPoint(i, x, y, z);
>     this->HandleGeometry[i]->SetCenter(x,y,z);
>     }
>
>   // vtkParametric spline acts as the interpolating engine
>   this->ParametricSpline = vtkParametricSpline::New();
>   this->ParametricSpline->Register(this);
>   this->ParametricSpline->SetPoints(points);
>   this->ParametricSpline->ParameterizeByLengthOff();
>   points->Delete();
>   this->ParametricSpline->Delete();
>
>   // Define the points and line segments representing the spline
>   this->Resolution = 499;
>
>   this->ParametricFunctionSource = vtkParametricFunctionSource::New();
>
>   this->ParametricFunctionSource->SetParametricFunction(this->ParametricSpli
> ne);
>   this->ParametricFunctionSource->SetScalarModeToNone();
>   this->ParametricFunctionSource->GenerateTextureCoordinatesOff();
>   this->ParametricFunctionSource->SetUResolution( this->Resolution );
>   this->ParametricFunctionSource->Update();
>
>   vtkPolyDataMapper* lineMapper = vtkPolyDataMapper::New();
>   lineMapper->SetInput( this->ParametricFunctionSource->GetOutput() ) ;
>   lineMapper->ImmediateModeRenderingOn();
>   lineMapper->SetResolveCoincidentTopologyToPolygonOffset();
>
>   this->LineActor = vtkActor::New();
>   this->LineActor->SetMapper( lineMapper );
>   lineMapper->Delete();
>
>


-- 
Cheers,

Anja
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