NavList:

   

Reply

George,
Yes in [NavList 7769] you have the value of e, and is agree with yours.

Also as in [NavList 7769], the values for a are:
WGS84       a = 6378137 [m] = 6378137/1852 [nm] = 3443.918467
SPHERE  a = 360*60/2/PI = 3437.746771 [nm]

-----Mensaje original-----
De: NavList@fer3.com [mailto:NavList@fer3.com] En nombre de George Huxtable
Enviado el: jueves, 26 de marzo de 2009 15:47
Para: NavList@fer3.com
Asunto: [NavList 7788] Re: Interpolation of Meridional Part Table


The plot thickens-

Andres calculates, from the expression he gives in [7784]

WGS84

a = 6378137 [m] = = 6378137/1852 [nm]

f = 1.0/298.257223563

 The result is:

MP( 45.000000 ) = 3019.058271357112100000

The expression Andres quoted used eccentricity (epsilon) rather than the 
flattening f that he tells us is f = 1.0/298.257223563 for WGS84. However, 
we can deduce one from the other using the expression given in Meeus, in 
which
eccentricity = square root of ((2 * f)  - (f * f)) for which I have taken 
the result to be 0.08181919, exactly in keeping with Earle's figure.

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

On the other hand, I have tried to do exactly the same thing with my pocket 
calculator and with the following values, taken from Earle-
E= 0.08181919
A = 3437.7468, the Earth's equatorial radius in geodetic miles.
Latitude L= 45

and here's a transcription of the equation I've used, now corrected, which 
runs on a 20-year-old Casio programmable calculator-
M=A*LN(TAN(45+.5*ABSL)*((1-E*SINABSL)/(1+E*SINABSL))^(E/2))

and that gives me M(45�) = 3013.648, which conforms with Bowditch, and not 
(quite) with Andres..

Why do Andres and I differ (slightly), and why do I agree with Bowditch, 
when Andres and I are trying to calculate the same thing with the same 
quantities, using what appears to be the same expression?

You can see that I've rejoined the nit-picking purists, as my natural home.

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.





--~--~---------~--~----~------------~-------~--~----~
Navigation List archive: www.fer3.com/arc
To post, email NavList@fer3.com
To , email NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---

   

Reply