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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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