Adam Davis wrote:
>
> Correct me if I'm wrong, but I was under the impression that the gps receivers
> were set up to take their position at 1 second intervals.  Since their time is
> set by one of the gps receivers in the sky, then they should have taken the
> readings at the beginning of each second, which will be within msec of each
> other.
>

not necessarily, or even all that likely. Have you tested this?

> Aside from that, the gps receivers select 4 satellites, one to get the time, a
nd
> three the triangulate the position.  Both receivers would have to select the
> same satelite for time, and the same three for triangulation, in the same area
> for very good correlation.  There is a great chance that they would select the
> same four satellites, but not necessarily assign the same roles to the same
> sats.
>

GPS receivers try to get as many sats as possible. 3 is minimum for a shakey 2D
fix,
4 is minimum for a shakey 3D fix, more is better, although a sat low on the hori
zon
can add very little - they also have to have a favorable geometry.

> So, yes, I know I'm not going to get great positioning.  However, it will be
> significantly better than the 100M the SA affords.
>

> Secondly, 1M resolution is unrealistic(ie, low probability of being within 1
> meter of the real position given by the mean of the plots) even if you are
> willing to stay in one place for an hour or longer.  You can average and get t
o
> 5M accuracy if you take one reading every ten minutes for 24 hours, and after
36
> hours you can assume 1M.  After 36 hours the results don't improve much UNLESS
> you have a receiver which is significantly better than mine.

I was tracking buses - of extreme precision I know not.

--
Anniepoo
Need loco motors?
http://www.idiom.com/~anniepoo/depot/motors.html