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From: ssingh@frc2.frc.ri.cmu.edu (Sanjiv Singh)
Subject: Re: GPS Accuracy?
In-Reply-To: mike@l44db.jsc.nasa.gov's message of Mon, 23 Aug 1993 01:01:18 GMT
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References: <1993Aug23.010118.29544@aio.jsc.nasa.gov>
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Date: Mon, 23 Aug 1993 15:31:30 GMT
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Trimble Navigation puts out a (surprisingly) easy to read booklet
on GPS.  Its called 

	GPS: A Guide to the Next Utility.

Its free if you call Trimble at (408) 481-2900.

In answer to Mike's question, here are a couple of paras from the
booklet.

About commercial code vs. military code:

> ...there are two forms of pseudo-random code, one called the 
> "C/A code" and the other called "P code".  The C/A code is the
> one all the civilian recivers use.  It is of lower frequency than 
> the P code and is thought by some to be less precise.  ... New
> reciever designs, for a variety of complicated reasons, are proving
> that there is practically no difference in the accuracy of
> measurements made with either P or C/A code.


About getting cm repeatibility, I think this may be a matter of how
long you are willing to wait to get an estimate. To wit:

> Surveyors have been using GPS for several years now to calculate
> positions right down to the last centimeter! These ultra-precise 
> measurements are based on at leat fifteen minutes of GPS data
> collection at a stationary location ... and the use of a complex
> computer program.


My copy of the booklet was is dated 1989 so the specs must have improved
significantly by now.  Perhaps Trimble has updated their numbers.




--
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Sanjiv Singh                                    ssingh@ri.cmu.edu
Field Robotics Center                           (412) 268-5895
Carnegie Mellon University
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