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    Re: Linear regression and other tools
    From: Brad Morris
    Date: 2018 Oct 12, 11:35 -0400
    Hello Tony

    You wrote:  I'm going to interleave the sights

    In a 20 minute round of observations the travel of the vessel will likely be within the noise of CN.   Let us assume a velocity of 6 knots.  In 20 minutes, that means you traveled just 2 nautical miles.  The uncertainty of the horizon will yield errors on that order of magnitude.

    Tony, you may find this older discussion useful. 
    In it, we discuss CN, accuracy and the clocked hat, but it is very germaine to the current discussion.  Which is, where exactly is your fix.  (As a very careful note: Frank took issue with my estimate of 10NM, and stated that CN, with care, can provide 3NM.)  CN is meant for ocean navigation.  When you get close to shore, switch to coastal piloting.  

    Squeezing a random error (not systemic, as you have noted!) isn't going to do much to improve your ocean navigation.  You are still within that same bounded box of uncertainty.  

    Let me flip it.  You managed to improve your accuracy, mid ocean, by 0.5NM.  Does it matter?

    Brad




     




    On Fri, Oct 12, 2018, 9:02 AM Tony Oz <NoReply_TonyOz@fer3.com> wrote:

    Dear Antoine,

    I am not going to extend anything beyond the measured interval, I'm going to interleave the sights (HCij) of each body: take HC11, then HC21, then HC31, then HC12, and so on, if there are three (i=3) bodies to sight. The j-index is the sight number within each body's sequence.

    The value of the variable t should always be chosen within the interval between the first sight of the last body and the last sight of the first body, so that there will be NO extrapolations ever.

    Please comment.

    Warm regards,

    Tony

    60°N 30°E

    PS

    I see no point in taking several sights of the same body and only then to turn for the next one. My feeling is that unless I have to move the index arm significantly - there will be no chance the next sight will have an error of different sign, the error trend will stay along the series. Not enough randomness of error(s) is introduced between the measurements.

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