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Subject: Re: Sextant Positions versus Map Datums?
From: Rodney Myrvaagnes (rodneym@XXX.XXX)
Date: Thu Jan 17 2002 - 23:47:48 EST
On Thu, 17 Jan 2002 13:22:32 -0800, Hal Mueller wrote:
>
>Sextant positions are referenced to the surface of this ellipsoid,
>not to a sphere.
Sextant positions measure from gravity vertical, to the extent they measure from anything. That is inherent in a water surface. To the
extent that gravity remains normal to the astronomers' ellipsoid, your statement makes sense.
However, even assuming that perfection, how would anyone using a sextant distinguish that vertical from the vertical of a sphere? An
observatory can establish its celestial coordinates with a lot of measurements over time. A sextant doesn't have that luxury.
And, gravity has lots of local variation.
How does the WGS84 ellipsoid compare with the astronomers one?
Rodney Myrvaagnes J36 Gjo/a
"Religious wisdom is to wisdom as military music is to music."
"What contemptible scoundrel stole the cork from my lunch?" -- W. C Fields
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