manipulate_stl.py

# retrieve the original stl file
stl_reader = vtk.vtkSTLReader()
stl_reader.SetFileName('path_to_stl')
stl_reader.Update()
stl_poly_data = stl_reader.GetOutput()

# triangulate the stl
triangleFilter = vtk.vtkTriangleFilter()
triangleFilter.SetInputConnection(stl_reader.GetOutputPort())
triangleFilter.Update()

# extract the boundary edge
featureEdges = vtk.vtkFeatureEdges()
featureEdges.SetInputData(triangleFilter.GetOutput())
featureEdges.SetBoundaryEdges(1)
featureEdges.SetFeatureEdges(0)
featureEdges.SetNonManifoldEdges(0)
featureEdges.SetManifoldEdges(0)
featureEdges.Update()
boundaryMesh = featureEdges.GetOutput()
print('get boundary mesh: ', boundaryMesh.GetNumberOfLines())

# init all the container holders for the stiching data
trianglePolyData = vtk.vtkPolyData()
triangles = vtk.vtkCellArray()
points = vtk.vtkPoints()
triangle = vtk.vtkTriangle()
totalLines = boundaryMesh.GetNumberOfLines()
# Start loop thru each edge line from the boundary edge
for i in range(0, totalLines):
    cell = boundaryMesh.GetCell(i)
    pointIds = cell.GetPointIds()
    pointsPerEdge = pointIds.GetNumberOfIds() # expect each edge line has 2 points
    p = boundaryMesh.GetPoint(pointIds.GetId(0))
    nextPoint = boundaryMesh.GetPoint(pointIds.GetId(1))
    # first triangle:
    # (xa,ya,za),
    # (xb,yb,zb)
    # (xb,yb,0)
    points.InsertNextPoint(p[0], p[1], p[2])
    points.InsertNextPoint(nextPoint[0], nextPoint[1], nextPoint[2])
    points.InsertNextPoint(nextPoint[0], nextPoint[1], 1100)
    triangle.GetPointIds().SetId(0, i)
    triangle.GetPointIds().SetId(1, i + 1)
    triangle.GetPointIds().SetId(2, i + 2)
    triangles.InsertNextCell(triangle)
    # second triangle:
    #(xb,yb,0)
    #(xa,ya,0)
    #(xa,ya,za)
    points.InsertNextPoint(nextPoint[0], nextPoint[1], 1100)
    points.InsertNextPoint(p[0], p[1], 1100)
    points.InsertNextPoint(p[0], p[1], p[2])
    triangle.GetPointIds().SetId(0, i + 3)
    triangle.GetPointIds().SetId(1, i + 4)
    triangle.GetPointIds().SetId(2, i + 5)
    triangles.InsertNextCell(triangle)
        
# clean up the data and ready for writing data into file
trianglePolyData.SetPoints(points)
trianglePolyData.SetPolys(triangles)
trianglePolyData.BuildLinks()

appendPoly = vtk.vtkAppendPolyData()
appendPoly.AddInputData(trianglePolyData)
appendPoly.AddInputData(stl_poly_data)
appendPoly.Update()

cleanPoly = vtk.vtkCleanPolyData()
cleanPoly.SetInputData(appendPoly.GetOutput())
cleanPoly.Update()

writerFinal = vtk.vtkSTLWriter()
writerFinal.SetFileTypeToBinary()
writerFinal.SetInputData(cleanPoly.GetOutput())
writerFinal.SetFileName('data/3D_data/demoparts/test2.stl')
writerFinal.Update()
writerFinal.Write()