[vtkusers] Possible Bug in vtkPolyDataToImageStencil

[Jesús Spí­nola]

Hello,

I'm using the vtkPolyDataToImageStencil class to cut parts of a dataset. It
works fine for several polygons but I have a case with a star-shaped polygon
with a strange result. I've attached several images with the resuts (
http://hades.udg.es/~chus/images.tar.bz2 )

For example, when I make the stencil with an hexahedron the result is ok (
see noStencilHexahedron.png and stencilHexahedron.png, that's before cutting
and after cutting with the stencil, respectively ).

But when constructing another kind of polygon I get a strange result. First
I thought the coordinates I was giving were wrong, so I created and actor
with the same polydata to see if it was wrong, but the actor is rendered as
I expected, so the polydata is ok. You can see the original image before
cutting is noStencilstarShape.png. After cutting with the stencil I get
stencilOnlyStarShape.png. Then you can see the polygon created for the
stencil in this image stencilWithPolyDataStarShape.png.

The original dicom images i used for this examples are:
http://www.creatis.insa-lyon.fr/~jpr/PUBLIC/gdcm/gdcmSampleData/imgdisplay_testcases/dish_p05.dcm
<http://www.creatis.insa-lyon.fr/%7Ejpr/PUBLIC/gdcm/gdcmSampleData/imgdisplay_testcases/dish_p05.dcm>for
the hexahedron and
http://www.creatis.insa-lyon.fr/~jpr/PUBLIC/gdcm/gdcmSampleData/imgdisplay_testcases/dish_p09.dcm
<http://www.creatis.insa-lyon.fr/%7Ejpr/PUBLIC/gdcm/gdcmSampleData/imgdisplay_testcases/dish_p09.dcm>for
the star shape.

The coordinates for the star shape ( refering to pixels coordinates, where
1,1 is the first pixel ) are
(133, 257)
(199, 233)
(169, 169)
(233, 199)
(257, 133)
(281, 199)
(345, 169)
(315, 233)
(381, 257)
(315, 281)
(345, 345)
(281, 315)
(257, 381)
(233, 315)
(169, 345)
(199, 281)

My code looks like this ( it's the same for the hexahedron and for the star
shape )

int vertices = getNumberOfVerticesOfThePolygon();
vtkPoints *points = vtkPoints::New();
vtkCellArray *vertexs = vtkCellArray::New();
vertexs->InsertNextCell( vertices + 1 );
int polyX, polyY;
 double x, y;
for( int i = 0; i < vertices; i++ )
{
      getPolygonVertex( i, polyX, polyY ) )

      // to transform the pixel coordinates to world points coordinates
      x = origin[0] + (polyX-1.0)*spacing[0];
      y = origin[1] + ( polyY-1.0)*spacing[1];

      points->InsertPoint( i , x, y, 0.0 );
      vertexs->InsertCellPoint( i );
}
// to close the polygon
vertexs->InsertCellPoint( 0 );
vtkPolyData *polyData = vtkPolyData::New();
polyData->SetPoints( points );
polyData->SetLines( vertexs );

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

m_polygonalPolyDataStencil = vtkPolyDataToImageStencil::New();
m_polygonalPolyDataStencil->SetInput( extruder->GetOutput() );
extruder->Delete();

stencil = vtkImageStencil::New();
stencil->SetInput( m_imageData ); // m_imageData is of type vtkImageData,
contains the original dicom dataset
stencil->ReverseStencilOn();
stencil->SetBackgroundValue( m_backgroundValue );
stencil->SetStencil( m_rectangularPolyDataStencil->GetOutput() );
....

m_imageViewer->SetInput( stencil->GetOutput() ); // m_imageViewer is of type
vtkImageViewer2

I want to know if this is because of an error of my code or if it's due to
some bug in the implicated classes.

As a side note, other workmates that are using this class had also problems
like this on the sharpen vertexs of the polygons. Maybe it's because the
algorithm is a kind of scanline method and when the same pixel in the
polygon is the begin and the end of the region that it encloses the
algorithm fails.

Thanks in advance!
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