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    Re: GPS Accuracy Now.
    From: Richard B. Emerson
    Date: 2000 May 02, 17:05 EDT

    Ed Kitchin writes:
     > With the reality that the government has now taken off "selective 
    availability", does this mean that the DGPS is now an obsolete piece of 
    equipment? What kind of accuracy can one expect to be the norm now? 1 - 5 
    meters? Does anyone know?
     > Ed
    DGPS accuracy won't increase with SA switched off, it will remain the
    same: 10 meters CEP for 95% probability (there's a 95% confidence you
    are within 10 meters of whatever the fix is).  Raw GPS without SA gives a
    15 meter CEP.
    A more interesting comparison is the areas of the two circles of
    probability (centered on the fix position).  With a 15 meter radius,
    the circle has about 700 square meters and only about 310 square
    meters with DGPS.  In short, DGPS doesn't become obsolete with SA off.
    There is, however, an interesting question about LORAN-C now that SA
    has been switched off.  Presently LORAN's supposed to be supported
    until 2008.  Some official statements about navigation suggest LORAN
    might not make it that long.  Given the current cost of GPS receivers
    and the cost of the sole commercial loran receiver (Furuno's LC-90 -
    selling for about $1100[!] and getting $500 on eBay), to say nothing
    of the cost of maintaining LORAN chains, it seems to me this is a "you
    do the math" story.
    S/V One With The Wind, Baba 35

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