[vtkusers] vtkPolyData to be used with vtkImageStencil.

[Anja Ende]

Hey Hendrik,

Ya, I just managed to figure that out but I do not know how to set the cell
data.

So, my code is as follows:

float pts[4][3] = {{-55.7812, 9.375, 0.0},
                {-18.2812, 49.6875, 0.0},
                {21.0938, 14.0625, 0.0},
                {5.15625, -29.0625, 0.0}};

             vtkFloatArray* pcoords = vtkFloatArray::New();
             pcoords->SetNumberOfComponents(3);
             pcoords->SetNumberOfTuples(4);
             for (int i=0; i<4; i++)
             {
                 pcoords->SetTuple(i, pts[i]);
             }
             // Create vtkPoints and assign pcoords as the internal data
array.
             vtkPoints* points = vtkPoints::New();
             points->SetData(pcoords);
             vtkPolyData* polydata = vtkPolyData::New();
               polydata->SetPoints(points);

            // Cell data.
            vtkCellArray* strips = vtkCellArray::New();
            strips->InsertNextCell(4);
            strips->InsertCellPoint(0);
            strips->InsertCellPoint(1);
            strips->InsertCellPoint(2);
            strips->InsertCellPoint(3);

            polydata->SetStrips(strips);

             vtkLinearExtrusionFilter* extrude =
vtkLinearExtrusionFilter::New();
             extrude->SetInput(polydata);
             extrude->SetScaleFactor(1);
             extrude->SetExtrusionTypeToNormalExtrusion();
             extrude->SetVector(1, 0, 0);

             vtkPolyDataToImageStencil* dataToStencil =
vtkPolyDataToImageStencil::New();
             dataToStencil->SetInput(extrude->GetOutput());

             vtkImageStencil* stencil = vtkImageStencil::New();
             stencil->SetInput(m_viewer->GetOutput());
             stencil->SetStencil(dataToStencil->GetOutput());
             stencil->ReverseStencilOff();
             stencil->SetBackgroundValue(128);

             stencil->Update();

Now, the output from the stencil is basically the original image. So,
nothing seems to be getting done :(

>> image voxels corresponding to your point cloud directly in the image data
array.

This could be an option. I have to figure out how I can access the
underlying image data, make a copy and manipulate it myself.

Cheers,
Anja

On 25/10/06, Hendrik Belitz <hendrik at darkon.info> wrote:
>
> Hi Anja,
>
> sorry for contacting you directly, but I only have read-only access to the
> vtk list from my office computer. I assume your stencil operation fails
> because your PolyData is lacking cell data which is AFAIK needed to build
> the stencil. I'm not absolutely sure what to do here, maybe the best way is
> not to use PolyDataToImageStencil at all, but to set the image voxels
> corresponding to your point cloud directly in the image data array.
>
> Regards
>  Hendrik
>
>  Hi everyone,
>
> I had asked this question a while back but did not get much response. I
> hope I have better luck this time.
>
> I am trying to create a vtkPolyData object that can be used with
> vtkPolyDataToImageStencil and vtkImageStencil. Basically, I want to extract
> a 2D region from my image.
>
> I tried the following after looking at some of the test files:
>
>
> //----------------------------------------------------------------------------------
>
>              float pts[4][3] = {{-55.7812, 9.375, 0.0 },
>                 {-18.2812, 49.6875, 0.0},
>                 {21.0938, 14.0625, 0.0},
>                 {5.15625, -29.0625, 0.0}};
>
>              vtkFloatArray* pcoords = vtkFloatArray::New();
>              pcoords->SetNumberOfComponents(3);
>              pcoords->SetNumberOfTuples(4);
>              for (int i=0; i<4; i++)
>              {
>                  pcoords->SetTuple(i, pts[i]);
>              }
>              // Create vtkPoints and assign pcoords as the internal data
> array.
>              vtkPoints* points = vtkPoints::New();
>              points->SetData(pcoords);
>              vtkPolyData* polydata = vtkPolyData::New();
>              polydata->SetPoints(points);
>
>              vtkPolyDataToImageStencil* dataToStencil =
> vtkPolyDataToImageStencil::New();
>              dataToStencil->SetInput(polydata);
>
>              vtkImageStencil* stencil = vtkImageStencil::New();
>              stencil->SetInput(myviewer->GetOutput());
>              stencil->SetStencil(dataToStencil->GetOutput());
>              stencil->ReverseStencilOff();
>              stencil->SetBackgroundValue(128);
>
>              stencil->Update();
>
>              stencil->Delete();
>              dataToStencil->Delete();
>              points->Delete();
>              pcoords->Delete();
>
>
> //----------------------------------------------------------------------------
>
> When I run this, it fails with the error: Can't build OBB tree- no data
> available.
>
> I guess this is because of the way I have set up the vtkPolyData. Can
> someone tell me how to set it up so this primitive example is working.
>
> Another question, for the vtkImageStencil to work, is it necessary that
> the input polydata is 'closed' or does it close the path by itself.
>
> I hope someone can help me with this.
>
> Best,
>
> Anja
>
>
>
> --
> program (pro'-gram) [n] A magic spell cast over a computer allowing
> it to turn one's input into error messages.
> tr.v. To engage in a pastime similar to banging one's head against a
> wall, but with fewer opportunities for reward.
>



-- 
Cheers,

Anja
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