How to append overlapping polyDatas?

Support
1

I have multiple polygons defined by a set of point coordinates. These polygons could be on each three axes and might overlap each other. I want to create a binary mask from these polygons and extract all the voxels that are in at least one of the polygons using a vtkImageStencil. When I tried to use vtkAppendPolyData i get weird results.

Consider these two polygons coordinates:
[(0, 200, 0), (200, 200, 0), (200, 150, 0), (0, 150, 0), ]:

image

[(0, 200, 0), (100, 200, 0), (100, 0, 0), (0, 0, 0),]:

image

After this pipeline:
vtkAppendPolyData → vtkCleanPolyData → vtkTriangleFilter → vtkStripper,
The result is this:
image

But I want something like this (basically voxel-wise OR of the polygons):
image

2

Turns out I was really over-complicating it. There was no need for turning the points in to polygon and polydata, I just has to use vtkLassoStencilSource and merged all the stencil sources using vtkImageStencilSource
Check out this test file:
https://gitlab.kitware.com/vtk/vtk/-/blob/v9.2.0/Imaging/Core/Testing/Python/TestLassoStencil.py

And here’s my code snippet:

...
image_data = reader.GetOutput()

points_all = [
    [(50, 0, 100), (100, 0, 100), (100, 200, 100), (50, 200, 100)],
    [(0, 200, 100), (200, 200, 100), (200, 150, 100), (0, 150, 100), ],
]
final_stencil = vtk.vtkImageStencilData()
for point_set in points_all:
    points = vtk.vtkPoints()
    for p in point_set:
        points.InsertNextPoint(p)

    lasso_stencil = vtk.vtkLassoStencilSource()
    lasso_stencil.SetPoints(points)
    lasso_stencil.SetInformationInput(image_data)
    lasso_stencil.Update()

    final_stencil.Add(lasso_stencil.GetOutput())
stencil = vtk.vtkImageStencil()
stencil.SetInputData(image_data)
stencil.SetStencilData(final_stencil)
stencil.SetBackgroundValue(500)