Quadric

import vtk

def main():
    colors = vtk.vtkNamedColors()

    # create an ellipsoid using a implicit quadric
    quadric = vtk.vtkQuadric()
    quadric.SetCoefficients(0.5, 1, 0.2, 0, 0.1, 0, 0, 0.2, 0, 0)

    # The sample function generates a distance function from the implicit
    # function. This is then contoured to get a polygonal surface.
    sample = vtk.vtkSampleFunction()
    sample.SetImplicitFunction(quadric)
    sample.SetModelBounds(-0.5, 0.5, -0.5, 0.5, -0.5, 0.5)
    sample.SetSampleDimensions(40, 40, 40)
    sample.ComputeNormalsOff()

    # contour
    surface = vtk.vtkContourFilter()
    surface.SetInputConnection(sample.GetOutputPort())
    surface.SetValue(0, 0.0)

    # mapper
    mapper = vtk.vtkPolyDataMapper()
    mapper.SetInputConnection(surface.GetOutputPort())
    mapper.ScalarVisibilityOff()
    actor = vtk.vtkActor()
    actor.SetMapper(mapper)
    actor.GetProperty().EdgeVisibilityOn()
    actor.GetProperty().SetColor(colors.GetColor3d('AliceBlue'))
    actor.GetProperty().SetEdgeColor(colors.GetColor3d('SteelBlue'))

    # A renderer and render window
    renderer = vtk.vtkRenderer()
    renderer.SetBackground(colors.GetColor3d('Silver'))

    # add the actor
    renderer.AddActor(actor)

    # render window
    renwin = vtk.vtkRenderWindow()
    renwin.AddRenderer(renderer)

    # An interactor
    interactor = vtk.vtkRenderWindowInteractor()
    interactor.SetRenderWindow(renwin)

    # Start
    interactor.Initialize()
    renwin.Render()
    interactor.Start()

if __name__ == '__main__':
    main()