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    Re: Resolution of systematic error
    From: Robert Eno
    Date: 2007 Mar 5, 19:44 -0500

    Peter Fogg wrote (clipped)
    "Let's start at the beginning. What is a position line? It is the position
    expressed as a line (for our purposes - really an arc that, extended,
    completes a circle around the SSP). It is the position that has been derived
    via a mathematical process. It is a rational artefact. It is the ONLY
    position that can be rationally derived from a specific body at a specific
    altitude at a specific moment.
    To say that this is not an expression of the position, that the position
    lies at an indeterminate point that could be located anywhere at all in the
    whole wide universe, except along the position line, is a bit of a furphy.
    I do understand and appreciate the statistical 25% / 75% argument. However,
    statistics are most useful navigationally, it seems, when employed to deal
    with superfluous data. An example of this is the derivation of a fix from
    within encompassing LOPs, where the sum of least squares can be used to
    derive the centre of the shape.
    Another way to put this is that statistics can be a good servant but a bad
    It seems to me more useful to eliminate random error as much as possible at
    source, rather than worrying later about the resulting indeterminate nature
    of a fix derived from random sights.
    For practical nav in a small boat or for any moving target great analysis is
    probably not worth the effort, but as many contributors to this list work
    from a known position on land and are mainly interested in what accuracy
    they can achieve, some appreciation of these methods could be useful. While
    we're on that theme, the traditional triangle formed from 3 LOPs is less
    than ideal. Four or more position lines is better.
    Robert comments:
    thankyou, thankyou, thankyou and thankyou del la puissance treize (to the
    power of 13)  It is ironic that with a last name like Fogg, you have done
    more to clear up the miasma of confusing arguments on this topic than has
    any previous poster (with no insult intended towards the other
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    To , send email to NavList-@fer3.com

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