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I have Bowditch-1966 and I performed meridional part calculations using its 
formulas sometimes ago.� Will try this one and let you know.

A-09



----- Original Message ----
From: George Huxtable 
To: NavList@fer3.com
Sent: Thursday, March 26, 2009 3:28:10 AM
Subject: [NavList 7780] Re: Interpolation of Meridional Part Table

Still on about meridional parts-

In [7774], I offered a copy of the paper that Andres referred to,

"A Comment on Navigation Instruction. Michael A. Earle
The Journal of Navigation, Volume 58, Issue 02, May 2005, pp 337-340",

partly because it contained an equation that had been bugging me, because I 
couldn't get it to provide the numerical answers I expected, nor anywhere 
near.

No takers for that paper yet, though there's plenty of time. But instead, 
I'll try pushing the problem into the collective faces of Navlist, by 
attaching just that puzzling equation, and asking for other opinions.

I should add that in another paragraph, Earle provides the following values 
for a WGS84 spheroidal Earth.-

a=3437.7468 geodetic miles
eccentricity (given by Greek letter epsilon in the equation) 0.08181919

and that if you're not familiar with the expression "ln", which stands for 
"natural log", or "log-to-the-base e", and if you don't have that function 
available on board, it happens to be 2.3026... times the more-familiar 
log-to-the-base 10.

and that the two vertical bars surrounding the latitude La imply "take it as 
a positive number, whether it's North or South".

So I ask anyone who might feel the urge to apply that equation to a trial 
latitude La of 45�, and report back his result of that exercise. As I see 
it, it should correspond to the value in Bowditch for meridional-parts 45�, 
given as 3013.6, within a few parts in a thousand. If others find that it 
does, then I'm getting something wrong, which is always possible. Otherwise, 
I'll go back to the author of the original paper.

================

Why did I start to investigate that equation in the first place? Mainly, it 
was to get some numbers out of it, because Earle makes quite a big thing 
about divergences with Bowditch, but gives no clue as to how big those 
divergences are going to be. But in addition, my hackles always rise when I 
read words such as "... it is a simple matter to ..."., because my 
experience has been that it usually isn't.

George.contact George Huxtable, at� george@hux.me.uk
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. 



      

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