VTK9 create different stencil than vtk8

Support
1

Hello,
I am having some weird results while trying to update my VTK.

I am converting a VTK polydata to Image data with the following code:
vtkSmartPointer VtkPolyDataToImage(vtkPolyData* poly, vtkImageData* templateImage)
{
vtkSmartPointer image = vtkSmartPointer::New();
image->DeepCopy(templateImage);

// fill the image with foreground voxels:
short inval = 1;
short outval = 0;
vtkIdType count = templateImage->GetNumberOfPoints();
for (vtkIdType i = 0; i < count; ++i)
{
image->GetPointData()->GetScalars()->SetTuple1(i, inval);
}

// polygonal data → image stencil:
vtkSmartPointer pol2stenc =
vtkSmartPointer::New();
pol2stenc->SetInputData(poly);
pol2stenc->SetOutputOrigin(image->GetOrigin());
pol2stenc->SetOutputSpacing(image->GetSpacing());
pol2stenc->SetOutputWholeExtent(image->GetExtent());
pol2stenc->Update();

// cut the corresponding white image and set the background:
vtkSmartPointer imgstenc = vtkSmartPointer::New();
imgstenc->SetInputData(image);
imgstenc->SetStencilConnection(pol2stenc->GetOutputPort());
imgstenc->ReverseStencilOff();
imgstenc->SetBackgroundValue(outval);
imgstenc->Update();

vtkSmartPointer outputImage = imgstenc->GetOutput();
return outputImage;
}

However, After upgrading the created image is different (like 0.2 max difference).

Do you have any idea about what could the issue here ? Is it a known issue ?

Thanks in advance

2

Can you explain what you mean by “0.2 max difference”? I don’t understad what the “0.2” refers to.

The vtkPolyDataToImageStencil class has only been stylistically modified between VTK 8.2.0 and VTK 9.2.5. The algorithm hasn’t changed.

3

Sure ! I remeshed the image back to an STL and computed the difference between the 2 meshes (vtk 8 one and vtk9 one) (point by point euclidean distance). That is what gave me the 0.2 difference.

4

You weren’t directly comparing the images to each other? What did you use to do the remeshing? And what was the voxel spacing?

5

No I did not because I first saw the error on remeshed STL’s and I did not think about the meshing part… Which will also be impacted by that vtk9 → vtk9 upgrade

here is the code used to remesh the image : Meshing code text code | WTOOLS (using marching cube)

Voxel spacing is 0.15

6

The vtkQuadricDecimation filter has definitely been changed since VTK 8.2.

To check vtkPolyDataToImageStencil, please do a voxel-by-voxel comparison of the image outputs. Or if that isn’t possible, then compare the vtkMarchingCubes meshes without decimating them first.

7

Perfect thanks a lot for your help ! Hopefully that will provide some new information and perhaps a solution.