[Fwd: GPS Selective availability turned off]

[Doug Dotson]

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Message-ID: <391182B9.8011E745@clark.net>
Date: Thu, 04 May 2000 10:01:29 -0400
From: Doug Dotson <ddotson@clark.net>
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To: Robert Smallshire <r.smallshire@rdr.leeds.ac.uk>
Subject: Re: GPS Selective availability turned off
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I did some testing on my boat last night using my Garmin 128
with a Garmin DGPS beacon receiver. The Garmin web page
states that DGPS should improve the error of the new non-SA
position to 1-5 meters. Here are my tst results:

With SA:
    Normal: EPE = 50-70 ft
    DGPS: EPE = 20-24 ft

Without SA:
    Normal: EPE = 17-23
    DGPS: EPE = 38-40   !?!?!?

Go figure! I'm trying to find out why things are now worse
with DGPS.

Doug




Robert Smallshire wrote:

> > We have a couple of friends here that are working on those lines.
> > They say they expect DGPS to be somewhat better than non-SA GPS,
> > because it
> > would correct things like the atmospheric effect or I don't konw
> > which others...
>
> I only have experience of low-end (i.e. Garmin 12XL) and high-end (i.e.
> Trimble 4700) GPS equipment - presumably you're talking about mid-range DGPS
> equipment - the sort that uses corrections broadcast on FM? Non-SA has made
> no differece at all to our Trimble DGPS units - accuracy is still ± 20 mm -
> so I would say that DGPS is still several hundred times better that non-SA
> GPS.
>
> Rob Smallshire.
>
> --
> Cave-Surveying http://lists.tartarus.org/mailman/listinfo/cave-surveying


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