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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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