// selected as the merged box axes.
final Quaternion kQ0 = Quaternion.fetchTempInstance(), kQ1 = Quaternion.fetchTempInstance();
kQ0.fromAxes(rkBox0._xAxis, rkBox0._yAxis, rkBox0._zAxis);
kQ1.fromAxes(rkBox1._xAxis, rkBox1._yAxis, rkBox1._zAxis);
if (kQ0.dot(kQ1) < 0.0) {
kQ1.multiplyLocal(-1.0);
}
final Quaternion kQ = kQ0.addLocal(kQ1);
kQ.normalizeLocal();