Newsgroups: comp.robotics
Path: brunix!sgiblab!spool.mu.edu!agate!doc.ic.ac.uk!cs.city.ac.uk!city!Paddington!ag538
From: ag538@city.ac.uk (SHORT T M)
Subject: Re: GPS Accuracy?
Message-ID: <ag538.746381366@Paddington>
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Organization: The City University
References: <1993Aug23.010118.29544@aio.jsc.nasa.gov>
Distribution: usa
Date: 26 Aug 93 16:09:26 GMT
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mike@l44db.jsc.nasa.gov (Mike Ross) writes:

>I've seen ads for single board GPS units.  Sounds like a great
>navigation aid might get a whole lot cheaper and perhaps within 
>reach of my financial, ahem, capabilities.  
>Does anyone know if I could get around 1 cm repeatibility if I
>averaged the signal?  I theorize the intentionally added error 
>is randomly dispersed about zero if taken over a long enough period.
>Note that I want repeatibility, not accuracy, in the centimeters.

To get that sort of result, you need differential positioning
whereby you have a second receiver on a previously known point. This
allows you to remove effects such as ionospheric delay. Also, to 
achieve this your receiver would need to receive both GPS frequencies.
many of these single board jobs leave out the L2, in order to keep
down the cost. Catch 22.

>Anyone got any ideas about how long that period would be?  Pardon me
>if this has already been thoroughly discussed in this group.  

If you managed to get 2 dual-frequency receivers, 15 minutes would
probably do.

>Pointers to further info would be appreciated.  Thanks.
The main receiver manufacturers are Ashtech and Trimble.

Tim

-- 
  Tim Short                              E-Mail: t.m.short@uk.ac.city
  Engineering Surveying Research Centre  Tel   : +44 71 477 8000 x3673
  City University, London                Fax   : +44 71 477 8570       
