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    Re: The Nonsensical Running Fix
    From: John Karl
    Date: 2010 Oct 25, 09:55 -0700

    Yes Garry, in the article I'm considering the long-run fix, where the accuracy of the LOP far exceeds the accuracy of the EP, such as after a long DR run (many hours, or even days) followed by an LOP of 1-2 mile uncertainty (could be a celestial LOP, or others). An example of the opposite case, the short-run fix, is in the classic round of stars in a slow moving vessel where the relative position among the LOPs would have superior accuracy compared to the location of the individual LOPs. This is where the traditional running fix, TRF, is valid, as discussed in the AF manuals.

    I argue that it's completely wrong to use the TRF in a long-run situation, where we're really making an estimate because of the large uncertainty in the EP. And in logically making estimates, we want to use all the information available, make no unnecessary assumptions, and make no contradictions.

    The TRF completely ignores information about the location of the ship along LOP1. But in actual reality, we always have some idea of where our ship is. So the TRF fails to use all available information.

    Furthermore, as can be seen from Figure 3 in the article, the traditional running fix assumes the component of estimated track perpendicular to LOP1 is exact, while in contrast, it assumes that the component of the estimated track along LOP1 is capable of unlimited error. Thus it nonsensically allows the orientation of LOP1 to decree the directions of exact information and of arbitrarily large error, when it's obvious that whatever the direction and magnitude of dead-reckoning errors, they're independent of LOP1's orientation. So that's a contradiction piled upon unjustified assumptions, all while disregarding available information. Is there a worse approach to estimation logic?

    (The concept of relative uncertainty and most probable position is a completely different topic: It's treated rather naively by AFPAM 11-216 with an equation that's dimensionally incorrect; it's too complex to be of interest to Ocean Voyager; and to most NavList members, including me. Nonetheless, a trivial example of a known directionally-dependent uncertainty is attached, showing how the DR uncertainty is reduced by the recent LOP.)


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