# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Irregular Quadrilateral Center
From: Hewitt Schlereth
Date: 2015 Feb 4, 17:34 -0800
Thanks, Frank. Good example. I get the idea.

Past discussions of error ellipses, etc. left me with the impression the differences didn't matter all that much, at least for the celestial navigation I did from 35'-45' sailboats.

I'll be interested to see what David comes up with. You guys are way ahead of me when it comes to mathematical and graphical analyses

At sea, my practice was to 'take five and average' and 'eyeball the most likely-looking spot' in a cocked hat. Then if the LOP or dot made sense vis a vis the DR, I figured I was in the ball park. Well, at least on the plotting sheet. :-)

Hewitt

On Feb 4, 2015, at 1:46 PM, Frank Reed <NoReply_FrankReed@fer3.com> wrote:

Hewitt, you wrote:
"Imagine where the figure would balance on a pin or actually cut the shape out and do it."

That doesn't work. Consider the case of a long, narrow triangle from three LOPs. The best estimate of the position is actually very close to the short side of the triangle rather than out in the middle of the triangle, which is where the center of mass (balance point) would be located. The shape of the figure (triangle, quadrilateral, complicated polygon) is seriously misleading. It provides neither an estimate of the correct fix, nor a proper estimation of the size and shape of the error ellipse!

Frank Reed
Conanicut Island USA

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