From:
kgramp@csc.com
Sent: 7/15/2001 5:23:27 PM
To:
gpsstash@yahoogroups.com
Cc:
Bcc:
Subject:

RE: [gpsstash] multiple GPS readings for average



I believe averaging over a short period (say less than an hour, maybe even
less than 24 hours) is of little use. This is because the thing that
provides the biggest variation in measured position is the satellites being
used and their actual position. And this varies the most over hours and
days.
So doing an average over say 10 minutes will provide the illusion of a very
accurate position. But it is really a number of measurements close together
in a larger square with less accuracy. If you came back the next day you
would find another very accurate position, but in another part of the
square.

+----------------+
| ... |
| .. |
| .. |
| . . |
| .. |
| .. |
+----------------+
Only over many days would you see measurements all over the square.

The best determination of accuracy is the number being given by the GPS
device (even though the basis of this number is propriety). And this is
usually small if the visible satellites are spread. If this value is small
then you most probably have the best value you will get.

Remember also that when someone else comes looking for your cache, and say
your GPS device is giving an accuracy of 6 metres, then the visitor could
be anywhere 6 metres from the cache. So place the cache so they would have
a good chance of finding it when within 6 metres of it.

Karl.