Poles
Poles
Join Date: Aug 2006
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Geographic or Geodetic latitude : angle between equitorial plane and normal to the observers horizontal plane.
Geometric or Geocentric latitude : angle between line joing the observer to the geocentre of the earth. Geocentre is the point where earths axis crosses the equitorial plane.
The difference between them at poles and equator is 0 and maximum difference occurs at 45 deg lat where it is approx 11.4 deg., geographic higher than the geometric lat.
And from what I can recall, the precession rate varies as well, as the axis of earth's rotation is along geometric axis.
For a more detailed and very complicated explanation, visit http://www2.ncdc.noaa.gov/docs/klm/html/i/app-i4.htm
Regards,
Divdby0
Geometric or Geocentric latitude : angle between line joing the observer to the geocentre of the earth. Geocentre is the point where earths axis crosses the equitorial plane.
The difference between them at poles and equator is 0 and maximum difference occurs at 45 deg lat where it is approx 11.4 deg., geographic higher than the geometric lat.
And from what I can recall, the precession rate varies as well, as the axis of earth's rotation is along geometric axis.
For a more detailed and very complicated explanation, visit http://www2.ncdc.noaa.gov/docs/klm/html/i/app-i4.htm
Regards,
Divdby0
Join Date: Sep 2002
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maximum difference occurs at 45 deg lat where it is approx 11.4 deg.
edit: yes, it's way off.
At sea level, the relation ship between geocentric latitude C and geodetic D is:
C = arctan ( (1-F)^2 * tan D)
where F is the "flattening", which for earth is 1/298 approx
That means that the following are some examples:
D=0 -> C=0
D=30 -> C=29.83
D=45 -> C=44.81
D=60 -> C=59.83
D=90 -> C=90
So the difference 45 deg geodetic is 0.19 degrees - which is 11.4 MINUTES approx, not degrees.
Last edited by Mad (Flt) Scientist; 17th Jul 2007 at 16:53.
11.4' it is.Join Date: Sep 2002
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Since 90=90, they are technically in the same place. For a symmetrical earth.
BUT - if the earth isn't symmetrical, so that at the geodetic north pole - where the horizon is at right angles to the pole on the equator - you could drill "straight down" i.e. at right angles to the local horizon and NOT hit the centre of the earth, then they wouldn't be the same place.
I can't see how that's a practical possibility for the earth, but maybe some smart geographer has found the earth's a bit squint.
BUT - if the earth isn't symmetrical, so that at the geodetic north pole - where the horizon is at right angles to the pole on the equator - you could drill "straight down" i.e. at right angles to the local horizon and NOT hit the centre of the earth, then they wouldn't be the same place.
I can't see how that's a practical possibility for the earth, but maybe some smart geographer has found the earth's a bit squint.
