[vtkusers] vtkContourFilter issue

[Francois Bertel]

Hello,

Dimension is the number of points along an axis, not the number of cells.

Number of cells along an axis= (number of points along an axis)-1

numCells=dim-1

if the extent starts at 0 (ie point index 0), it stops at dim-1,
therefore it goes from 0 to numCells, not numCells-1

Fix that first and see how it goes.

On Wed, Dec 9, 2009 at 9:42 AM, David Doria <daviddoria+vtk at gmail.com> wrote:
> I create an ImageData:
>
> vtkSmartPointer<vtkImageData> grid = vtkSmartPointer<vtkImageData>::New();
> grid->SetOrigin(xmin, ymin, zmin);
> grid->SetExtent(0, this->NumberOfCellsX-1, 0, this->NumberOfCellsY-1,
> 0, this->NumberOfCellsZ-1); //same as grid->SetDimensions(10, 10, 10);
> grid->SetSpacing((xmax-xmin)/static_cast<double>(this->NumberOfCellsX),
> (ymax-ymin)/static_cast<double>(this->NumberOfCellsY),
> (zmax-zmin)/static_cast<double>(this->NumberOfCellsZ));
>
> Then I set a value at each point:
>
>  for (int z = 0; z < dims[2]; z++)
>    {
>    for (int y = 0; y < dims[1]; y++)
>      {
>      for (int x = 0; x < dims[0]; x++)
>        {
>       //compute d ....
>        grid->SetScalarComponentFromDouble(x,y,z,0,d);
>        }
>      }
>    }
>
> Then I want to extract the 0 isosurface of this scalar field.
>
> I tried to do:
>
> vtkSmartPointer<vtkContourFilter> contourFilter =
>        vtkSmartPointer<vtkContourFilter>::New();
>
> contourFilter->SetInput(grid);
>
> vtkPolyData* surface = contourFilter->GetOutput();
>
> but the result has 0 points and 0 cells. Have I done something wrong
> with constructing the ImageData? Or using the ContourFilter?
>
> Thanks,
>
> David
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