def plane_errors(axes, covariance_matrix, sheet='upper',**kwargs):
    """
    kwargs:
    traditional_layout  boolean [True]
        Lay the stereonet out traditionally, with north at the pole of
        the diagram. The default is a more natural and intuitive visualization
        with vertical at the pole and the compass points of strike around the equator.
        Thus, longitude at the equator represents strike and latitude represents
        apparent dip at that azimuth.
    """

    level = kwargs.pop('level',1)
    traditional_layout = kwargs.pop('traditional_layout',True)

    d = N.sqrt(covariance_matrix)

    ell = ellipse(**kwargs)
    bundle = dot(ell, d[:2])
    res = d[2]*level

    # Switch hemispheres if PCA is upside-down
    # Normal vector is always correctly fit
    #if traditional_layout:
    #if axes[2,2] > 0:

    if axes[2,2] > 0:
        res *= -1

    if sheet == 'upper':
        bundle += res
    elif sheet == 'lower':
        bundle -= res

    _ = dot(bundle,axes).T

    if traditional_layout:
        lon,lat = stereonet_math.cart2sph(_[2],_[0],_[1])
    else:
        lon,lat = stereonet_math.cart2sph(-_[1],_[0],_[2])

    return list(zip(lon,lat))