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    Re: Eprf Vs, Trf
    From: Geoffrey Kolbe
    Date: 2009 Dec 20, 09:33 +0000

    John  [NavList 11289] posted a re-capitulation of his EP running fix
    method as preferable to the Traditional Running Fix, where a new EP
    is taken to be where the LOPs intersect.
    
    Of the two diagrams John attached to his post, he says:
    
       As you can see, uncertainly in the EPRFs are continually
    >corrected, and limited, by succeeding LOPs.  For comparison, the 2nd
    >figure shows the TRF results using the same LOPs and DR estimates.
    >The track and fix locations vary radically, with some fix locations
    >beyond possibilities.  (Also the TRF is even a bit more messy and more
    >plotting work.)
    
    I not sure that this is right. In the EPRF diagram, the area of
    uncertainty on the final DR position is just the same as on the
    first. If the area of uncertainty is due to errors in course held and
    distance run, we would expect the area of uncertainty to grow
    correspondingly with each successive fix. Pretty soon, the areas of
    uncertainty would grow so that it would not matter which method you
    were using, EPRF or TRF. The only circumstance in which John's
    proposed constant area errors would be a correct would be if that was
    the error in the original position (not shown) and all subsequent
    errors in course held and distance run are small compared to this
    original area of uncertainty.
    
    I also note that the new LOP always manages to go through the area of
    uncertainty on the current DR. What if it did not? What would John do then?
    
    Geoffrey Kolbe
    
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