# NavList:

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

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Re: Resolution of systematic error
From: Gary LaPook
Date: 2007 Mar 02, 03:40 -0800
Well, maybe it wouldn't be, in fact it might be many  thousands of miles away but that is very unlikely (though with a probability greater than zero.)

But, the basic assumption in plotting the fix, after you have eliminated the systematic or constant error leaving only random errors, is that you are most likely located at the point where you are equal distant from the position lines and this is generally taken to be in the center of the triangle. "If a fix is obtained from three or more lines of position, and the error of each line is normal and equal to that of the others, the most probable position is the center of the figure. By  'center' is meant that point within the figure which is equidistant from the sides."  Bowditch, volume 2, chapter III article 308, 1977 ed.; and see volume 1, chapter XVII, article 1708 , 1977 ed. Although it is "possible" to be way outside of the triangle you must make some practical assumptions otherwise everything becomes Jell-O.

What is your argument that after eliminating the systematic error that the fix is more likely to be outside the triangle than inside?

Gary LaPook

Geoffrey Kolbe wrote:

Gary LaPook wrote:

So, you adjust each of your LOPs in the direction of the ZNs by 10 NM each and end up with your second diagram with the dashed lines now illustrating the corrected LOPs.  You still have a cocked hat but it is smaller and its size it now determined only by random errors. Your actual position will then be within the triangle, not outside so I don't see how you get to the fix positioned in the third diagram, What am I missing?

Why will the actual position then be within the triangle?

Geoffrey Kolbe

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