On Sat, 30 Aug 2003 19:13:47 +0100, Mike Lindsay
wrote:

In article , Gene Nygaard
writes
On 27 Aug 2003 20:30:05 GMT, (JJ Sinclair) wrote:

John Lee wrote.
Nowhere! However on the equator 1 second of longitude
equals 1 nautical mileWe also have 90 degrees between the equator and either pole. The
equator is always 0 degrees and the poles 90 degrees. But in between,
there are at least three different ways of measuring latitude:
geocentric latitude (the angle formed at the center of the Earth),
geodetic latitude (the one normally used, the angle formed between the
line normal to the tangent of the ellipsoid and the axis of rotation),
and the angles used in the parametric formulas representing an
ellipse. These don't agree with each other at any place not on the
equator or the poles.

Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/

Hmm, interesting...

What would the error be over, say 500km, if you used geocentric instead
of geodetic measurement?

In other words, does it matter?

If you are measuring the difference between two points, it will make
no difference whatsoever--assuming that you do the calculations
properly for the angles you are using. It's just that those two end
points will be at different latitudes, depending how you measure that
latitude.

That assumption has no guarantee of likelihood, if you are unaware
that there are different ways to measure latitude. It's sort of like
the Mars Climate Orbiter-turned-Crash-Lander. Those NASA engineers
could have converted pound force seconds to newton seconds--only
problem was, they didn't realize that they should be doing so.

Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/