Newsgroups: comp.robotics
Path: brunix!sgiblab!swrinde!gatech!news-feed-2.peachnet.edu!umn.edu!gold!roger034
From: roger034@gold.tc.umn.edu (Brynn Rogers)
Subject: Re: Electronic Compass wanted
Message-ID: <CosK0J.4p3@news.cis.umn.edu>
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Organization: University of Minnesota
References: <1994Apr24.094514.1@ashley.cofc.edu>
Date: Mon, 25 Apr 1994 01:30:17 GMT
Lines: 42

In article <1994Apr24.094514.1@ashley.cofc.edu>,
 <parkerp@ashley.cofc.edu> wrote:
>We have just acquired an Eagle GPS unit with an NMEA data output port.  We 
>. . .
>
>The U.S. Defense Department (creator of the GPS system), in its infinite 
>wisdom, has crippled the system for civilian use to prevent full 
>utilization by competing military.  Although the system is capable of 
>accuracy down to 10 or 15 meters the military degrades the system with 
>"Selective Availability" by intentionally introducing random errors which 
>result in reduced accuracy of about 100 meters.  Other factors such as 
>signal-to-noise ratio and satellite positions will also influence accuracy.

  Actually what you get is better than that.  All you have to do is average
10 readings or so together and you have eliminated the random signal that the
DOD inserts.   Also I hear that they are probably going to do away with
the random stuff because it isn't real effective at giving people a less
accurate position.

  A buddy of mine who works with this a lot says that with 2 recievers,
one at a known location (say an airport) you can tell the relative
location of the second reciever down to better than a foot.  With a system
like this you can land planes more accurately than the microwave landing
system, at a very small fraction of the cost (of MLS).

  He ways griping because they could not get funding on a method of getting
sub-millimeter (no misprint) positioning accuracy with the current GPS
sattelites.  How is that possible?  If you count exactly how many waves you
get on the carrier wave you know exactly where you are.  I think that this
also might only work in the relative mode (2 recievers, one at a fixed, known
location).


  For any type of outdoor autonomous robot (except the most inexpensive)
GPS recievers seem like an excellent navigation system.
A tougher puzzle is to always know where you are indoors.

Brynn
roger034@gold.tc.umn.edu    They let Alumni have accounts now!

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