Welcome to the NavList Message Boards.

NavList:

A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    or...
       
    Reply
    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:
    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 unsubscribe, email NavList-unsubscribe@fer3.com
    -~----------~----~----~----~------~----~------~--~---
    

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.
    Email:

    Email Settings

    Posting Code:

    Custom Index

    Subject:
    Author:
    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site