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    Direct methods of sight reduction.
    From: Geoffrey Kolbe
    Date: 2002 Apr 12, 08:33 +0100

    Arthur Pearson wrote:
    >Also, Herbert states below that "When starting from a wildly wrong DR
    >position, St. Hilaire will get you the right fix, albeit only after 2 or
    >3 iterations. That's not surprising, because direct methods will not
    >even need a DR."  What are the "direct methods"?
    An analytic solution to the two star sight problem was given by:
    James A Van Allen, "An Analytical Solution of the Two Star Sight Problem of
    Celestial Navigation", Journal of The Institute of Navigation, Vol.28, No.
    1, Spring 1981, pp 40-43.
    This solution yields the two possible positions of the observer in a closed
    analytic form without any prior knowledge of position (DR or assumed), any
    trigonometric ambiguities, or any graphical work. It is also readily
    adaptable to a programmable calculator.
    Of course, running this calculation again using a third star and one of the
    first two stars resolves the basic ambiguity of which of the two possible
    positions is actually yours.
    Yours aye,
    Geoffrey Kolbe.

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