Latitude and Longitude in the Real World
Longitude
The longitude does not suffer from scientific complications. It is the same as it is for a spherical earth. This is because the ellipsoid is generated by rotation the ellipse about the polar axis. The parallels will therefore be circles just as in a sphere. The radius of these circles will be the moment arm, p. It will be found from the same formulae as for a sphere - except the radius Rn is used.
Longitude's only complication at this level is the problem of the origin. Today the zero of longitude is universally taken through the Royal Observatory in Greenwich England. In the past most major nations had their own zero of longitude, through their local observatory. This was natural as these institutions were responsible for setting standards for ship navigation, and from the 1500's until the middle of the 1900's survey standards.
As with latitude, there is a astrodetic longitude. This is what you get using the local gravity field to define up (bubble level for example). It is different from geodetic longitude at the few arc second (") level at most.
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