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Subject: Direct methods of sight reduction.
From: Dr. Geoffrey Kolbe (geof@XXX.XXX)
Date: Fri Apr 12 2002 - 03:33:09 EDT
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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