FollowupID: 728802 Submitted:
Monday, May 30, 2011 at 10:43
Andrew & Jen posted:
Setting aside the possible error due to an incorrect datum, GPSs experience "drift". Assuming you have a modern and sensitive unit, if you put the it in one place and observe it for about 20 or 30 mins, the coords will drift around by up to 40m.
One of the reasons for this is the fact that the GPS
is continually calculating it's position by triangulation from a number of satellites, some of which are low down on the horizon while others are higher. Your position on the earth (not altitude) is more accurate if the majority of the signals are coming from well spread out, low down satellites.
If you have a tracking option and put it on the most detailed scale, after a while a pattern will develop like a multi pointed star and the centre of the star is the most accurate indicator of position.
If you need to accurately record a position, this is about the only way to do (unless you have a differential unit)