LOCAL
       d1, d2 : direction;
     END_LOCAL;
    d1 := NVL(normalise(axis), dummy_gri || direction([0.0,0.0,1.0]));
    d2 := first_proj_axis(d1, ref_direction);
    RETURN([d2, normalise(cross_product(d1,d2))\vector.orientation, d1]);