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    Advancing position circles: Huxtable vs. Zevering
    From: Philip Bailey
    Date: 2006 Sep 20, 19:57 -0500

    I was interested to see that the Journal of Navigation have published
    (The Journal of Navigation (2006) 59(3), 521) George Huxtable's
    comments on K. Herman Zevering's previous article in that journal, as
    discussed in June on the old (Nav-L) list.  The journal allowed
    Zevering a rebuttal.

    George has previously explained why Zevering's proposal of simply
    translating a position circle given by the observation of one celestial
    body, in the direction of travel, to obtain a running fix from a second
    observation (possibly of another body), will not give accurate results.
    This is because the initial circle would in the general case change
    shape in a way apparently not accounted for by Zevering.

    George's arguments in the article are clear and appear to be correct;
    Zevering's reply conversely is long and opaque.  To give a flavour, the
    latter's conclusion is given below (meanings of his abbreviations in
    brackets):

    "The inherent construction principle of RFT/LSQ [running fix
    technique/Yallop-Hohenkerk Least-Squares solution program] derives from
    terrestrial RFT, which guarantees that the position backward-projected
    from the fix will lie on the original position circle.  In the
    celestial case this construction principle only conforms to GD-UT
    [GHA-Dec updating technique] when Zd is small.  RFT therefore merely
    represents a gimmick performed on the chart whereby the transferred
    position line does not actually represent a mathematically correctly
    transferred position circle.  The properties of a transferred position
    circle passing through the RFT/LSQ fixes depend on a given 2nd sight's
    properties and in the due-N case it cannot account consistently for the
    given run displacement at cardinal position points.   The implied GP
    transfer matching a particular set of RFT/LSQ fixes is in the general
    celestial case contrary to the run data.  There is no theoretical
    explanation for this."

    So what does _that_ mean?!


    Philip Bailey


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