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Subject: [Nml] Mathematical Advancement of a celestial COP
From: Buck Godwin (bgodwin@XXX.XXX)
Date: Sat Oct 24 1998 - 00:23:47 EDT
On Fri, 23 Oct 1998 14:39:07 -0700, you wrote:
>
>The COP from the earlier of the two observations must be advanced
>along the DR course. In terms of the center of the circle, I propose ...
strange you should mention this just hours after i was reading an
article in Navigation, The Journal of the Institute of Navigation.
according to the article, the problem of obtaining a direct fix from 2
observatinos with an advanced (or retired) COP has not been solved
analytically. in a nutshell, assuming the observer moves along a
rhumb line, you have to advance each point on the COP along a
loxidromic spiral to its new locus. the new loci no longer lie on a
circle, so the algorithm is not strictly valid. the 1997 article by
Stanley W. Gery references 4 other articles between 1977 and 1981 in
the same publication on the same subject.
as a practical suggestion, take a run of sights on body 1 and a run on
body 2. pick a time between the two runs. extrapolate the first set
forward and second set backward to the chosen time.
Buck Godwin
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