How to get separate boundary for a tube?

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1

For a tube without cap, I want to obtain the two cap.

The boundary is calculated as:

fe = vtk.vtkFeatureEdges()
fe.SetInputData(tubePoly)
fe.BoundaryEdgesOn()
fe.FeatureEdgesOff()
fe.NonManifoldEdgesOff()
fe.ManifoldEdgesOff()
fe.Update()

stripper = vtk.vtkStripper()
stripper.SetInputData(fe.GetOutput())
stripper.Update()

boundaryPoly = vtk.vtkPolyData()
boundaryPoly.SetPoints(stripper.GetOutput().GetPoints())
boundaryPoly.SetPolys(stripper.GetOutput().GetLines())

The boundary has been successfully obtained:

image
image802×763 28.5 KB

Then, I want to separate the two caps. And one cap is set as red color, the other one is given green color. But, the render result is:

image

We can see that there is only one yellow actor. I think the yellow color is the blending of red and green, which means the coordinate of two caps is the same. The two caps is built as:


points = boundaryPoly.GetPoints()
poly1 = boundaryPoly.GetCell(0)
id1 = [poly1.GetPointIds().GetId(i) for i in range(poly1.GetNumberOfPoints())]
poly2 = boundaryPoly.GetCell(1)
id2 = [poly2.GetPointIds().GetId(i) for i in range(poly2.GetNumberOfPoints())]
print('pointer of cap polydata: ', id(poly1), id(poly2))
print('point id of cap polydata: ', id1, id2)

cap1 = vtk.vtkPolyData()
cap1.SetPoints(points)
cap1Polygon = vtk.vtkCellArray()
cap1Polygon.InsertNextCell(poly1)
cap1.SetPolys(cap1Polygon)
cap1.Modified()
#
cap2 = vtk.vtkPolyData()
cap2.SetPoints(points)
cap2Polygon = vtk.vtkCellArray()
cap2Polygon.InsertNextCell(poly2)
cap2.SetPolys(cap2Polygon)
cap2.Modified()

cap1Mapper = vtk.vtkPolyDataMapper()
cap1Mapper.SetInputData(cap1)
cap1Actor = vtk.vtkActor()
cap1Actor.SetMapper(cap1Mapper)
cap1Actor.GetProperty().SetOpacity(0.5)
cap1Actor.GetProperty().SetColor(1, 0, 0)

cap2Mapper = vtk.vtkPolyDataMapper()
cap2Mapper.SetInputData(cap2)
cap2Actor = vtk.vtkActor()
cap2Actor.SetMapper(cap2Mapper)
cap2Actor.GetProperty().SetOpacity(0.5)
cap2Actor.GetProperty().SetColor(0, 1, 0)

The printed information is:

pointer of cap polydata:  1443206601792 1443206601792
point id of cap polydata:  [0, 1, 18, 16, 14, 12, 10, 8, 6, 4, 0] [2, 3, 5, 7, 9, 11, 13, 15, 17, 19, 2]

We can see that the pointer of vtkPolyData is the same, but the point ids are note the same. It make me confuzed.

My purpose: generate two seperate caps.
Any suggestion is appreciated~~~~

The complete code to reproduce my result is:


import vtkmodules.all as vtk

vpoints = vtk.vtkPoints()
vpoints.InsertNextPoint(0, 0, 0)
vpoints.InsertNextPoint(1, 1, 1)

line = vtk.vtkPolyLine()
line.GetPointIds().SetNumberOfIds(2)
line.GetPointIds().SetId(0, 0)
line.GetPointIds().SetId(1, 1)

lines = vtk.vtkCellArray()
lines.InsertNextCell(line)

polyln = vtk.vtkPolyData()
polyln.SetPoints(vpoints)
polyln.SetLines(lines)

tuf = vtk.vtkTubeFilter()
tuf.SetCapping(False)
tuf.SetNumberOfSides(10)
tuf.SetInputData(polyln)
tuf.SetRadius(2)
tuf.Update()

tubePoly = tuf.GetOutput()
# mapper = vtk.vtkPolyDataMapper()
# mapper.SetInputData(tuf.GetOutput())
# actor = vtk.vtkActor()
# actor.SetMapper(mapper)
# renderer = vtk.vtkRenderer()
# renderer.AddActor(actor)
# renWin = vtk.vtkRenderWindow()
# renWin.AddRenderer(renderer)
# iren = vtk.vtkRenderWindowInteractor()
# iren.SetRenderWindow(renWin)
# iren.SetInteractorStyle(vtk.vtkInteractorStyleTrackballCamera())
# iren.Initialize()
# iren.Start()


fe = vtk.vtkFeatureEdges()
fe.SetInputData(tubePoly)
fe.BoundaryEdgesOn()
fe.FeatureEdgesOff()
fe.NonManifoldEdgesOff()
fe.ManifoldEdgesOff()
fe.Update()

stripper = vtk.vtkStripper()
stripper.SetInputData(fe.GetOutput())
stripper.Update()

boundaryPoly = vtk.vtkPolyData()
boundaryPoly.SetPoints(stripper.GetOutput().GetPoints())
boundaryPoly.SetPolys(stripper.GetOutput().GetLines())

points = boundaryPoly.GetPoints()
poly1 = boundaryPoly.GetCell(0)
id1 = [poly1.GetPointIds().GetId(i) for i in range(poly1.GetNumberOfPoints())]
poly2 = boundaryPoly.GetCell(1)
id2 = [poly2.GetPointIds().GetId(i) for i in range(poly2.GetNumberOfPoints())]
print('pointer of cap polydata: ', id(poly1), id(poly2))
print('point id of cap polydata: ', id1, id2)

cap1 = vtk.vtkPolyData()
cap1.SetPoints(points)
cap1Polygon = vtk.vtkCellArray()
cap1Polygon.InsertNextCell(poly1)
cap1Polygon.InsertNextCell(poly2)
cap1.SetPolys(cap1Polygon)
cap1.Modified()

cap2 = vtk.vtkPolyData()
cap2.SetPoints(points)
cap2Polygon = vtk.vtkCellArray()
cap2Polygon.InsertNextCell(poly2)
cap2.SetPolys(cap2Polygon)
cap2.Modified()

cap1Mapper = vtk.vtkPolyDataMapper()
cap1Mapper.SetInputData(cap1)
cap1Actor = vtk.vtkActor()
cap1Actor.SetMapper(cap1Mapper)
cap1Actor.GetProperty().SetOpacity(0.5)
cap1Actor.GetProperty().SetColor(1, 0, 0)

cap2Mapper = vtk.vtkPolyDataMapper()
cap2Mapper.SetInputData(cap2)
cap2Actor = vtk.vtkActor()
cap2Actor.SetMapper(cap2Mapper)
cap2Actor.GetProperty().SetOpacity(0.5)
cap2Actor.GetProperty().SetColor(0, 1, 0)

renderer = vtk.vtkRenderer()
renderer.AddActor(cap1Actor)
renderer.AddActor(cap2Actor)

renWin = vtk.vtkRenderWindow()
renWin.AddRenderer(renderer)
iren = vtk.vtkRenderWindowInteractor()
iren.SetRenderWindow(renWin)
iren.SetInteractorStyle(vtk.vtkInteractorStyleTrackballCamera())
iren.Initialize()
iren.Start()
2

Try vtkPolyDataConnectivityFilter to separate the caps.

1 Like
3

@dgobbi Thanks for kindly reply.

But, I also want to know why the pointer of poly1&poly2 is the same?

poly1 = boundaryPoly.GetCell(0)
poly2 = boundaryPoly.GetCell(1)

In my thought, it should be different.

4

A vtkDataSet does not store the cells as vtkCell objects, it stores them implicitly in one or more vtkCellArrays. So the first time you call GetCell(i), it builds a vtkCell object and returns it. And the next time you call GetCell(j), it re-uses the same object, but changes the point ids. See the code if you are curious:
Common/DataModel/vtkPolyData.cxx

1 Like