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    Re: 3 Lop's
    From: Fred Hebard
    Date: 2004 Nov 14, 23:21 -0500

    On Nov 14, 2004, at 11:01 PM, Alexandre Eremenko wrote:
    
    > Can anyone explain, under what circumstances one could
    > possibly want to determine her position from 3 LOP's?
    > It is hard to imagine (for me) such circumstances.
    > (Hard but possible).
    >
    
    With two LOPs, there are no degrees of freedom left to estimate the
    accuracy of the fix.  With three, if the "cocked hat" is reasonably
    small, you have some confidence; if large, you know it's not so good.
    I expect a least squares solution also could not estimate errors from
    two LOPs.
    
    With regard to more LOPs, and fewer replications per LOP, versus fewer
    LOPs with more replications,  George Huxtable's anomalous dip comes
    into play.  An LOP could be off by 10 miles because of anomalous dip
    (abnormal refraction near the horizon) and all your replications would
    not pick it up.  A second LOP from a body 180 degrees away in azimuth
    would cancel out the error from the first.  I would guess that fewer
    cuts of more bodies would be better; one would want enough cuts to have
    confidence that the sight is reasonably accurate, maybe 1' for large
    ships, 5' for yachts?
    
    BTW, where is George?  It's unusual for him not to have posted lately.
    
    Fred
    
    
    

       
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