Re: GPS

http://www.millenniumsend.com/?page=resources&section=resources

Has an essay on GPS. Might answer some questions and is written for
roleplayers so very little tech talk.

----- Original Message -----
From: "B Lin" <lin@rxkinetix.com>
To: <gzg-l@csua.berkeley.edu>
Sent: Tuesday, September 03, 2002 6:55 PM
Subject: RE: GPS

> For a really basic description of GPS:
>
> http://www.garmin.com/aboutGPS/
>
> Currently civilian GPS is about the same accuracy as military GPS
(about
3m) but when SA (Selective Availability) was active the accuracy for
civilians was 100's of m to 1.5 km.  The military turned off SA a few
years
ago.
>
> The military reserves the right to add SA whenever they wish as GPS is
a
military system which they happen to allow civilians to use.  As it is a
US
military system it makes our European Allies a bit nervous and they are
setting up their own GPS satellite network.
>
> Differential GPS depends on known land sites to send out GPS signals -
effectively becoming another GPS satellite, however they are limited by
radio range to be effective.  Such locations would be known or easily
discovered and could be knocked out in a war, since they have to
transmit to
be effective.
>
> Who says military research doesn't have civilian applications? :)
>
> --Binhan
>
>
>
> > -----Original Message-----
> > From: John Sowerby [mailto:sowerbyj@fiu.edu]
> > Sent: Tuesday, September 03, 2002 11:41 AM
> > To: gzg-l@csua.berkeley.edu
> > Subject: Re: GPS
> >
> >
> >
> > >I'm not sure what you mean by "open system". The GPS
> > system's always been
> > >pretty open, at least the civilian side.
> >
> > When first out, the errors in position using civilian GPS
> > could be quite
> > large, particularly in terms of elevation, all due to the
> > futzing of the
> > signal by the military. Now, even the standard receivers are
> > much better,
> > as the military have relaxed the rules somewhat.
> >
> > >>2) Can differential GPS (multi-receiver) defeat or significantly
> > >>attenuate the futzing up signal? (That is, can't
> > differential GPS be used
> > >>in such a way as to amerliorate the effects of signal uncertainty
> > >>introduction)?
> > >
> > >Yes. However, both the mobile and stationary receivers have
> > to have one or
> > >more satellites in common. The correction is on a
> > satellite-by-satellite
> > >basis, so the more you have in common the better.
> >
> > Which is almost a given, as the fixed reference point changes
> > with locality
> > anyway.
> >
> > As for usage of GPS, when my father in law to be can plot a
> > course for the
> > yacht using his computer, and the thing can steer itself through the
> > channels in the Port of Miami and down to the Keys, or across to the
> > Bahamas relying on the laptop and the boat's differential GPS
> > system (two
> > receivers and a reference station in South Florida), then the
> > system can no
> > longer be futzed up too badly.
> >
> > John.
> >
> >
> >