NavList:

   

Reply

A degree of latitude of course depends on how you define the surface you 
calculate it on. Suppose you want to know it for the WGS'84 ellipsoid 
the following applies:

semi major axis (a) = 6378137.000
inverse flattening (Finv) = 298.257223563

the formulas you need for the calculation:
e2=(1/Finv)*2-(1/Finv)^2
mu = a/SQRT(1-e2*SIN(phi)^2)
rho = a*(1-e2)/SQRT((1-e2*SIN(phi)^2)^3)

1" lat = rho*SIN(1/3600)
1" lon = COS(phi)*mu*SIN(1/3600)

If we fill those in for 53 degrees north, the semi major axis and 
inverse flattening we get:
e2 = 0.00669437999
mu = 6391797.44772
rho = 6376233.57268

1" lat = 30.913m
1" lon = 18.649m

If you need 1 minute you simply multiply with 60, for one degree 
multiply with 3600.

Nicol�s



Lu Abel wrote:
> This seems quite silly, but I realize that I don't know the "official" 
> definition of a degree of latitude.  
>
> I'm sure most on this list know that the earth is an oblate spheroid -- 
> it's fatter than it is tall.   This means if I cut the earth in half 
> through its poles, the resulting cross-section looks like an ellipse, 
> wider than it is tall, rather than a perfect circle.   And this 
> elliptical cross-section can lead to two possible definitions of a 
> degree of latitude.
>
> If take a cross-section of the earth and draw an angle one degree up 
> from the equator, is the place where this line intersects the surface of 
> the earth the first (degree) parallel?   Or is the first parallel one 
> ninetieth of the way from the equator to the pole?
>
> Years ago I took an offshore navigation course that taught the various 
> "sailings," including use of the Meridional Parts table from Bowditch to 
> determine a rhumb line course when traversing long distances (especially 
> those with dramatic north-south differences).   (Meridional Parts give 
> the "stretch" in the latitude scale required at various latitudes to 
> create a Mercator chart).   As I recollect, the meridional parts down 
> near the equator are actually slightly less than 1.00000, which would 
> indicate that the first of my two definitions is the correct one.
>
> I know there are some experts in cartography on the list, I'm sure this 
> is trivial for them.
>
> Lu Abel
>
> >
>
>
>
>
>   


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

   

Reply