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Subject: Re: Sextant Positions versus Map Datums?
Smith_Peter@XXX.XXX
Date: Wed Jan 16 2002 - 09:50:32 EST
On Tue 15 Jan 2002 7:51 PM in Navigation-L,
Jared Sherman [mailto:jared.sherman@XXX.XXX] said:
> Peter-
> <the horizontal difference is not significant ...the vertical. True?>
>
> Nope. Go from NAD27 to WGS84 and the world can move a mile
> instantly. How much it moves, and which way it moves, depends
> on the datum change and also on your position on the chart,
> i.e. some places "move" less than others.
Between datums, yes. The "horizontal difference" I was referring to
was between the ellipsoids that underlie the various datums. When you
project celestial LOP's onto either a sphere or one of these
ellipsoids, you get pretty much the same result. It's the landmarks
that appear to move when you compare charts built on different
datums, such as the Texas Capitol Dome in the example John Kabel
pointed out.
-- Peter
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