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    Re: Marq St. Hilaire - Altitude intercept method
    From: Gary LaPook
    Date: 2007 Oct 26, 15:34 -0700

    Gary LaPook:
    
    John Cole asked:
    
    
    " I am curious as to kind of jobs they have that
    > provide the time to research and write this excellent stuff."
    
    My answer to that question is I only sleep 3 hour a night.
    
    gl
    >
    > John Cole
    
    On Oct 26, 3:28 pm, John Cole  wrote:
    > Andres is exactly right when he says "write(ing) without rigor can confuse
    > to the beginners in CN."  Another list member (I think it was Frank)
    > recently pointed out that correct use of terminology is important in
    > communicating with technically trained people. Yes indeed. George frequently
    > takes to task misquotes and sloppy use of terminology, and rightly so.
    > Having said that, most everyone knows the difference between CN on land in
    > an armchair and on a pitching boat in a gale and of course it is true that
    > in the practical world approximations and short cuts are made that are
    > entirely appropriate for those skilled in the art. (I wonder about the $12
    > watch though). But in presenting the subject to an audience I think the
    > presenter should first state the rigorous case using correct terminology and
    > then show how and why it may be simplified in practice or under special
    > circumstances.
    >
    > I find the back and forth banter between members highly educational as it
    > nearly always teases out the subject in a way that would never happen in
    > most classrooms, and I appreciate the huge amount of time and effort that
    > they devote to the task. I am curious as to kind of jobs they have that
    > provide the time to research and write this excellent stuff.
    >
    > John Cole
    >
    > > From: Andres Ruiz 
    > > Reply-To: 
    > > Date: Fri, 26 Oct 2007 10:46:55 +0200
    > > To: 
    > > Conversation: Marq St. Hilaire - Altitude intercept method
    > > Subject: [NavList 3621] Re: Marq St. Hilaire - Altitude intercept method
    >
    > > Gary, my question for you is: are you saying I and writing silly things????
    > > No mere controversy please. You can retract your question!
    >
    > > Language is for providing communication to people. Not is the same:
    > > "St. Hilaire's method created the exact same LOP as Sumner's method" or
    > > "Sumner and St. Hilaire methods produce the same LOP" or -In the practice of
    > > old celestial navigation the result of using Sumner or St-Hilaire LoPs is the
    > > near the same assumed usual circumstances.-
    >
    > > 2+2= 4
    > > 1.99+2.001 approx 4
    >
    > > Anybody with good background knowledge in navigation can filter the
    > > information and read between the lines, but write without rigor can confuse to
    > > the beginners in CN.
    >
    > > Of course navigation is an art, but also a science and the advances in
    > > sciences arise by understanding previous knowledge and acquiring new one.
    > > Are you agree?
    >
    > > To test the discrepancy between the to lines, imagine you are in the middle of
    > > the North Atlantic Ocean and a two days storm apart from your course several
    > > miles away. Now your DR position is far away from the true one. The
    > > differences of the results using the two methods depends on the assumed
    > > position, and increase, as the distance between the true and assumed position
    > > do.
    >
    > > ________________________________________
    > > De: NavList@fer3.com [mailto:NavList@fer3.com] En nombre de
    > > Gary J. LaPook
    > > Enviado el: viernes, 26 de octubre de 2007 9:48
    > > Para: NavList@fer3.com
    > > Asunto: [NavList 3620] Re: Marq St. Hilaire - Altitude intercept method
    >
    > > Gary LaPook writes:
    >
    > > My question for you is "how many angels  to you want to get dancing on the
    > > head of your pin?"
    >
    > > You are right, one line is a chord and one is a tangent but to the available
    > > level of accuracy of measuring the altitude and of plotting it on a chart they
    > > are the same for all practical purposes. For example, if you plotted two
    > > positions determined by the Sumner method 30 NM apart and drew the line
    > > between them making one LOP. Then you calculate the same LOP using St. Hilaire
    > > for a spot in the center of the two Sumner positions you are right, you would
    > > end up with two different LOPs that parallel each other. However, for any
    > > altitude up to 77� they would be less than .1 NM apart, that's right, one
    > > tenth of one nautical mile! How thick is the line your pencil makes on the
    > > chart? How accurate are all of your sextant sights? Do you always achieve one
    > > tenth of a minute accuracy? People on this list talk about getting .5 minute
    > > of accuracy as a very good result on a boat and with that level of accuracy
    > > the difference between a Sumner line and a St. Hilaire line only becomes an
    > > issue for sights above 86�. How many times have you taken sights above 86�?
    > > Navigation is the art and science of directing a vessel or aircraft safely
    > > from one place to another, it is not a mathematical exercise that you do at
    > > home on a computer to an accuracy of 42 significant figures. And I don't use
    > > "the analytic equation of each LoP on a Mercator chart" I draw a pencil line
    > > that has thickness and some level of inaccuracy in azimuth. Everything plotted
    > > on a chart is an approximation to some extent and for navigation purposes (not
    > > theoretical discussion purposes) the Sumner and St. Hilaire methods produce
    > > the same LOP.
    >
    > > gl
    >
    > > Andres Ruiz wrote:
    > > In messages: [NavList 3572], [NavList 3588], [NavList 3596] There is an error
    > > of concept.
    >
    > > Gary is not absolutely correct.
    >
    > > St. Hilaire's method created the exact same LOP as Sumner's method but
    > > only required doing the computation one time, saving work and reducing
    > > the chance for an error.
    >
    > > The Sumner and the St-Hilaire LoPs are not the same. One is secant to the
    > > circle of equal altitude and other is tangent. This means that the points in
    > > common between the CoP and the each LoP are different. If You get the analytic
    > > equation of each LoP on a Mercator chart You can see that the two lines are
    > > not the same.
    >
    > > For more details see the attached PDF.
    >
    > > Please, I want to hear more opinions.
    >
    > > Andr�s Ruiz
    > > Navigational Algorithms
    > >http://www.geocities.com/andresruizgonzalez
    
    
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