# Display VTK Wedge in Slicer as Segmentation

**URL:** <https://discourse.slicer.org/t/display-vtk-wedge-in-slicer-as-segmentation/24838>\
**Category:** Development\
**Tags:** segmentation, vtk\
**Created:** [August 19, 2022, 6:43pm UTC](https://discourse.slicer.org/t/display-vtk-wedge-in-slicer-as-segmentation/24838 "2022-08-19T18:43:58Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![connorh](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/connorh/32/79802_2.png) [@connorh](https://discourse.slicer.org/u/connorh)\
**Post date:** [August 19, 2022, 6:43pm UTC](https://discourse.slicer.org/t/display-vtk-wedge-in-slicer-as-segmentation/24838/1 "2022-08-19T18:43:58Z")

</div>

I’m trying to split a segment based on its rotational position (e.g. only getting a 15 deg wedge of the segmentation). I’m thinking the way to do this is to create a vtkWedge shape and take its intersection with the existing segmentation.

 ![image](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/a/0/a0cd42b5de958c3446a4e0c1ae6184ed7deb5dc7.jpeg)

I’m creating a vtkWedge right now but I’m looking for something like “GetOutput()” that exists for a vtkSphere ([example](https://slicer.readthedocs.io/en/latest/developer_guide/script_repository.html#specify-a-sphere-by-multiple-control-points)), so that I can assign my wedge shape to a segmentation node. Any suggestions? Here’s my existing code to create a wedge:

```auto
#Create Wedge Shape
wedge = vtk.vtkWedge()
wedge.GetPoints().SetPoint(0,0,0,0)
wedge.GetPoints().SetPoint(1,0,1,1)
wedge.GetPoints().SetPoint(2,0,1,1)
wedge.GetPoints().SetPoint(3,1,0,0)
wedge.GetPoints().SetPoint(4,1,0,1)
wedge.GetPoints().SetPoint(5,1,1,1)

#Create segmentation node from Wedge - can't figure this out

```

Thanks in advance!

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<div class="post-metadata">

**Author:** ![lassoan](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/lassoan/32/13_2.png) [@lassoan](https://discourse.slicer.org/u/lassoan)\
**Post date:** [August 20, 2022, 9:01pm UTC](https://discourse.slicer.org/t/display-vtk-wedge-in-slicer-as-segmentation/24838/2 "2022-08-20T21:01:39Z")

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`vtkWedge` is just a cell. You need to create a vtkPolyData, add points to it, then create a vtkWedge cell, add the point IDs to it, and then add the cell to the polydata. You can check out VTK examples for details, for example this [example that adds a triangle cell](https://kitware.github.io/vtk-examples/site/Cxx/Meshes/AddCell/).

You can create a segment from polydata using `AddSegmentFromClosedSurfaceRepresentation` as shown in [this example in the script repository](https://slicer.readthedocs.io/en/latest/developer_guide/script_repository.html#get-histogram-of-a-segmented-region).

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<div class="post-metadata">

**Author:** ![connorh](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/connorh/32/79802_2.png) [@connorh](https://discourse.slicer.org/u/connorh)\
**Post date:** [August 23, 2022, 4:41pm UTC](https://discourse.slicer.org/t/display-vtk-wedge-in-slicer-as-segmentation/24838/3 "2022-08-23T16:41:35Z")

</div>

Hi Andras, thanks - that was very helpful - I’m close but I can’t get my wedge to work out - it seems like the vtkPolyData isn’t getting the correct faces, so from my 6 points defining the wedge, I get faces/triangles (0,1,2), (0,2,3), (0,3,4), (0,4,5) rather than my wedge shape.  
 ![image](https://us1.discourse-cdn.com/flex002/uploads/slicer/original/3X/d/c/dcbce12b72ee62808f6bbbde2cd702d5443f2939.png)

Here’s my code:

```auto
modelNode = slicer.mrmlScene.AddNewNodeByClass("vtkMRMLModelNode")

# Create segmentation
segmentationNode = slicer.mrmlScene.AddNewNodeByClass("vtkMRMLSegmentationNode")
segmentationNode.CreateDefaultDisplayNodes() # only needed for display

wedge = vtk.vtkWedge()
points = vtk.vtkPoints()

pt0 = np.array([0,0,0])
dx = np.array([1,0,0])
dx = np.array([0,1,0])
dx = np.array([0,0,1])

#define 6 coordinates for wedge
pts = [pt0, pt0 + dx + dy, pt0 + dx, pt0 + dz, pt0 + dx + dy + dz, pt0 + dx + dz]

for i in range(6):
  points.InsertNextPoint(pts[i])
  #slicer.modules.markups.logic().AddControlPoint(pts[i][0],pts[i][1],pts[i][2])

for i in range(6):
  wedge.GetPointIds().SetId(i,i)

wedges = vtk.vtkCellArray()
wedges.InsertNextCell(wedge)

wedgePD = vtk.vtkPolyData()
wedgePD.SetPoints(points)
wedgePD.SetPolys(wedges)
modelNode.SetAndObservePolyData(wedgePD)

# Import the model into the segmentation node
slicer.modules.segmentations.logic().ImportModelToSegmentationNode(wedgeMN, segmentationNode)

```

I’ve also tried to manually define the faces without any impact:

```auto
faces = [5, # number of faces
             3, 0, 1, 2, # number of ids on face, ids
             3, 3, 5, 4,
             4, 1, 4, 5, 2,
             4, 0, 2, 5, 3,
             4, 1, 0, 3, 4]

wedge.SetFaces(faces)
wedge.Initialize()

```

Thanks for the help!

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<div class="post-metadata">

**Author:** ![lassoan](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/lassoan/32/13_2.png) [@lassoan](https://discourse.slicer.org/u/lassoan)\
**Post date:** [August 23, 2022, 5:10pm UTC](https://discourse.slicer.org/t/display-vtk-wedge-in-slicer-as-segmentation/24838/4 "2022-08-23T17:10:56Z")

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Wedge is a volumetric cell, so it may need to be placed in a vtkUnstructuredGrid. However, I’m not sure if unstructured grid can be imported into a segmentation.

Overall, it may be simpler to create a wedge out of triangle cells and add them to a vtkPolyData.

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<div class="post-metadata">

**Author:** ![connorh](https://sea2.discourse-cdn.com/flex002/user_avatar/discourse.slicer.org/connorh/32/79802_2.png) [@connorh](https://discourse.slicer.org/u/connorh)\
**Post date:** [August 23, 2022, 6:01pm UTC](https://discourse.slicer.org/t/display-vtk-wedge-in-slicer-as-segmentation/24838/5 "2022-08-23T18:01:43Z")

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Took your approach and just made wedge of triangles and it works great. Thank you!