# NavList:

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

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The Darn Old Cocked Hat + Trimble
From: Hanno Ix
Date: 2013 Mar 17, 20:33 -0700

“ I can either talk correctly or understandably – not both. “  -  Heisenberg

David:

There is an alternative to Heisenberg's one-liner: I can talk incorrectly and still not be understood.

I will concede: claim a) is wrong in fact and wording. It should be:
The distribution of the distance Fix-TL is not a normal distribution. It is a Rayleigh distribution.
Also, I did not consider jerky movements of the target (TL) , nor an incorrect placement of the TL on the map.
Terrible!

Withthout going into your math of my claim b):
A little exasperated I looked for help in explaining what I had in mind. I found a very good description of
navigation errors written by the folks at Trimble. I have attached it. Apparently, they use the same concepts
I was talking about. They arrive at pretty much the same results and show the same plots
(e.g. Rayleigh histogram and appendix). It is true I did assume knowledge of the TL, they do not.
This difference does matter if you use GPS in air-to-air missiles or if you locate points recorded by history.
However consider this:

GPS:  6 feet radial error around the TL; 1/1000 of the CelNav error yet cumbersome.
CelNav:  6000 feet radial error (~ 1 sm) ; 1000 times GPS error  but excellent fix

To me Bayesian Inversion Theory etc. is misplaced when it comes to CelNav .

BTW:
In my memos , I proceeded to describe my search for a minimum of the error which involved moving
around the estimated location in relation to the DOCH on a median. I did that with a simulation.
I think I found quite a simple and practical approximation by saying the best place to assume the
TL is at least close to the CG of the DOCH.

Regards

h

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