Originally Posted by
Euclideanplane
Indeed. I may have misread Vilters, who didn't actually say "only a compass". For dead reckoning you compute the wind triangle using a compass, additionally you need information about wind speed and true airspeed. Which the compass obviously does not provide.
Anyway, GPS provides heading information anyway, in addition to whatever else information you need, so I am not sure I see the point. You use whatever instruments available to tell you where your are and where you are headed.
Pedantic mode: Pure GPS does not provide direction, only position. However if you move in a randomly oriented straight line, GPS will tell you which direction you have moved in, and then you can then re-orient yourself to go in the direction you really wanted. Of course most devices (such as modern phones) have a compass and accelerometer.