def single_triangle():
    """ A single PolyData triangle """
    points = np.zeros((3, 3))
    points[1] = [1, 0, 0]
    points[2] = [0.5, 0.707, 0]
    cells = np.array([[3, 0, 1, 2]], ctypes.c_long)
    return vtki.PolyData(points, cells)