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    Re: What is a degree of latitude?
    From: Nicol�s de Hilster
    Date: 2008 Mar 23, 21:08 +0100

    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:
    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.
    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
    > >
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