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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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