Gps Accuracy

[+Mike+Mary]

I had a couple of DNFs yesterday afternoon, partly because I couldn't get reasonable GPS fix. The first was probably tree cover, but the second was on open moorland where there was variation of up to 10m. Claimed accuracy was 6-12m. A few hours later it was behaving perfectly again, taking me within 2-3m of the cache site.

 

It could just be my yellow Etrex showing its age, but are there other factors which might cause this range of error in the open?

[+Jango & Boba Fett]

In open moorland the most likely explanation would be poor constellation geometry. Those of us who can remember using GPS before January 1994 when their were fewer than 24 operating satellites can remember sitting around waiting for decent positioning on a regular basis. In simple terms if all the visible satellites are in one part of the sky then your "ranging lines" will be converging at very small angles so any slight change in the pseudo range will result in a "jump" in position.

[+Moote]

Increased humidity can do this, as it absorbs the Microwaves, I gave a fuller explanation of this sometime back.