Yes, compared to lat and long. A good 2D GPS fix is easiest when you have a few satellites in different compass directions, say one at each of N,S,E,W. But for 3D, it is impossible to see a satellite underneath you. You have a bunch of them above you, and you need to difference the times of their signals&#x27; arrival.<p>For more, see here: <a href="http:&#x2F;&#x2F;gpsinformation.net&#x2F;main&#x2F;altitude.htm" rel="nofollow">http:&#x2F;&#x2F;gpsinformation.net&#x2F;main&#x2F;altitude.htm</a>