# How to append overlapping polyDatas?

**URL:** https://discourse.vtk.org/t/how-to-append-overlapping-polydatas/11799
**Category:** Support
**Tags:** python
**Created:** [June 23, 2023, 8:40am UTC](https://discourse.vtk.org/t/how-to-append-overlapping-polydatas/11799 "2023-06-23T08:40:25Z")
**Posts on this page:** 2
**Page:** 1

<div class="post-metadata">

### Author: ![somso2e](https://discourse.vtk.org/user_avatar/discourse.vtk.org/somso2e/32/7322_2.png) [@somso2e](https://discourse.vtk.org/u/somso2e)
#### Post date: [June 23, 2023, 8:40am UTC](https://discourse.vtk.org/t/how-to-append-overlapping-polydatas/11799/1 "2023-06-23T08:40:25Z")

</div>

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](https://discourse.vtk.org/uploads/default/original/2X/8/8ddc17280e31a745480ccf32c49a0ce3f34efa1b.png)

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

![image](https://discourse.vtk.org/uploads/default/original/2X/6/61ac74f79d7fbfbdcfb4094dc28ab3efff28be7c.png)

After this pipeline:  
vtkAppendPolyData → vtkCleanPolyData → vtkTriangleFilter → vtkStripper,  
The result is this:  
 ![image](https://discourse.vtk.org/uploads/default/original/2X/5/553aa26b05d3a753e7070b5dff07b9a70474cc8b.png)

But I want something like this (basically voxel-wise OR of the polygons):  
 ![image](https://discourse.vtk.org/uploads/default/original/2X/1/15b1b8634a5602ed50d13dba78f159dbdb79de69.png)

---

<div class="post-metadata">

### Author: ![somso2e](https://discourse.vtk.org/user_avatar/discourse.vtk.org/somso2e/32/7322_2.png) [@somso2e](https://discourse.vtk.org/u/somso2e)
#### Post date: [June 25, 2023, 8:53am UTC](https://discourse.vtk.org/t/how-to-append-overlapping-polydatas/11799/2 "2023-06-25T08:53:46Z")

</div>

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](https://gitlab.kitware.com/vtk/vtk/-/blob/v9.2.0/Imaging/Core/Testing/Python/TestLassoStencil.py)

And here’s my code snippet:

```python
...
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)

```