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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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