Createa a polygonal disk with a hole in the center. The disk has zero
    height. The user can specify the inner and outer radius of the disk, and
    the radial and circumferential resolution of the polygonal representation.

    Parameters
    ----------
    center : np.ndarray or list
        Center in [x, y, z]. middle of the axis of the disc.

    inner : flaot
        The inner radius

    outer : float
        The outer radius

    normal : np.ndarray or list
        direction vector in [x, y, z]. orientation vector of the cone.

    r_res: int
        number of points in radius direction.

    r_res: int
        number of points in circumferential direction.

def Disc(center=(0.,0.,0.), inner=0.25, outer=0.5, normal=(0,0,1), r_res=1,
         c_res=6):
    """
    Createa a polygonal disk with a hole in the center. The disk has zero
    height. The user can specify the inner and outer radius of the disk, and
    the radial and circumferential resolution of the polygonal representation.

    Parameters
    ----------
    center : np.ndarray or list
        Center in [x, y, z]. middle of the axis of the disc.

    inner : flaot
        The inner radius

    outer : float
        The outer radius

    normal : np.ndarray or list
        direction vector in [x, y, z]. orientation vector of the cone.

    r_res: int
        number of points in radius direction.

    r_res: int
        number of points in circumferential direction.
    """
    src = vtk.vtkDiskSource()
    src.SetInnerRadius(inner)
    src.SetOuterRadius(outer)
    src.SetRadialResolution(r_res)
    src.SetCircumferentialResolution(c_res)
    src.Update()
    return vtki.wrap(src.GetOutput())