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    Re: Lat/Lon by "Noon Sun" & The Noon Fix PROVE IT
    From: Brad Morris
    Date: 2009 Apr 29, 08:57 -0400

    Hi Jim


    I am a bit disappointed that you would use regression analysis.  Typically this is a least squares fit, but I am uncertain as to your exact methodology.


    Perhaps I misunderstood.  I thought your method was a mark-1 eyeball method.  


    Dave Walden has shown that a least squares curve fit provides a reasonable determination of latitude and longitude.  


    If regression analysis is required for each line on either side of LAN, then there is no inherent advantage over a curve fit. 


    Please Jim, just try another case.  This test we have devised is tough, agreed.  That was the intent.  Imagine the poor navigator who has lost his electronics

    and now wants to obtain a noon fix.  Will he sit down to manually perform a least squares fit (linear or curve)?  I think not!


    Best Regards




    From: NavList@fer3.com [mailto:NavList@fer3.com] On Behalf Of James N Wilson
    Sent: Tuesday, April 28, 2009 8:33 PM
    To: NavList@fer3.com
    Subject: [NavList 8092] Re: Lat/Lon by "Noon Sun" & The Noon Fix PROVE IT




    I'll attach my results from your first data set. To do more, I would have to automate it, since I'm lazy. Rather than prolong this event, I fudged and used regression analysis to fit lines through your data. The scatter was beyond what my eyeballs could handle.


    The results are:  Lat, 56°12.2'N, Lo, 9°53.6'W.


    As I examine the plot, I realize that I have committed the sin of extrapolation,

    i. e., the intersection of the lines is outside of the data range. In this case, I should have used data over a longer period. That should have moved the time of LAN a bit earlier. If I use the plot from my Navigation paper, the time difference between maximum altitude and LAN is 4m50s. That moves LAN earlier by 15s, consistent with the above.


    I enjoyed the learning, and I got quite a bit of that.


    Jim Wilson

    Shop now at www.ftd.com/16714

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