build_2axes
EXPRESS specification:
FUNCTION
build_2axes
(* Modified for LPM/6 *)(ref_direction : direction) : LIST [2:2] OF direction;
LOCAL
d : direction := NVL(normalise(ref_direction),
dummy_gri || direction([1.0,0.0]));
END_LOCAL;
RETURN([d, orthogonal_complement(d)]);
END_FUNCTION
;