'Tuple defining the default ``bounding_box`` limits.
``((y_low, y_high), (x_low, x_high))``'

@property
def bounding_box(self):

    a = self.a
    b = self.b
    theta = self.theta.value
    (dx, dy) = ellipse_extent(a, b, theta)
    return (((self.y_0 - dy), (self.y_0 + dy)), ((self.x_0 - dx), (self.x_0 + dx)))
