Calculate the surface volume of an animal from its length and girth

    Args
    ----
    length: float or ndarray
        Length of animal (m)
    girth: float or ndarray
        Girth of animal (m)

    Returns
    -------
    surf:
        Surface area of animal (m^2)
    vol: float or ndarray
        Volume of animal (m^3)

def surf_vol(length, girth):
    '''Calculate the surface volume of an animal from its length and girth

    Args
    ----
    length: float or ndarray
        Length of animal (m)
    girth: float or ndarray
        Girth of animal (m)

    Returns
    -------
    surf:
        Surface area of animal (m^2)
    vol: float or ndarray
        Volume of animal (m^3)
    '''
    import numpy

    a_r   = 0.01 * girth / (2 * numpy.pi)
    stl_l = 0.01 * length
    c_r   = stl_l / 2
    e    = numpy.sqrt(1-(a_r**2/c_r**2))

    surf = ((2*numpy.pi * a_r**2) + \
           (2*numpy.pi * ((a_r * c_r)/e)) * 1/(numpy.sin(e)))

    vol  = (((4/3) * numpy.pi)*(a_r**2) * c_r)

    return surf, vol