[vtkusers] vtkPolyData to be used with vtkImageStencil.

[Dean Inglis]

Hi Anja,

have a look at VTK/Examples/GUI/Tcl/ImageTracerWidget.tcl

you need a closed polydata, and you need to extrude normal
to the plane of your points, which is the x-y plane so the extrusion
vector is 0,0,1.  Also, I would back up the z-coord of the
x-y points by a small amount, say 0.5, then extrude by 1.
You could then use vtkImageAccumulate to calculate the ROI
histogram and basic image stats (min,max,mean,stdev).

Dean


So, my code is as follows:

/************************************ back up behind the x-y plane a wee bit
  float zoffset =-0.5;
/************************************

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

             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);

/********************************************** close the loop
            strips->InsertCellPoint(0);
/**********************************************

            polydata->SetStrips(strips);

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

/********************************************** k hat direction
             extrude->SetVector(0, 0, 1);
/**********************************************

             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 :(