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Re: That darned old cocked hat
From: Jeremy C
Date: 2010 Dec 13, 23:53 EST
From: Jeremy C
Date: 2010 Dec 13, 23:53 EST
George wrote:
In a message dated 12/11/2010 1:05:20 A.M. Central Asia Standard Tim,
george@hux.me.uk writes:
John Karl writes-
"Next we acquire three LOPs. They do not intersect at a common point. We
don’t know where the true fix is."
Let's say we do. Take an anchored vessel at a precisely known location, say
by GPS.
Measuring the altitude of a star does not alter that location. The
probability of the observation being towards or away depends only on the
random scatter of the observation itself, being precisely 50:50.
I guess it matters how precise we want to be. I've had numerous
observations with less than a 0.05' intercept and I assumed they were neither
towards nor away and would draw them directly through my AP. I've even had
a time or two where I've had 2 stars in the same twilight have no effective
intercept.
Of course I rarely shoot only 3 bodies (5 times in my long voyage of 2009,
mostly due to clouds) so I always end up with a multitude of cocked-hats to try
and figure out, but that is another story.
Jeremy