"Glenfiddich" wrote in message
...
On Sat, 21 Feb 2004 20:09:30 -0600, mah wrote:

Was toying with my gps recently and plotted a course from my home in the
midwest to London Heathrow. I know it uses great circle routing to
calculate the distance and course. Going from west to east it shows a
course of about 45 degrees. On the return trip it shows an intial
course of 310 degrees.

Now, to my old mind, I would have thought a reciprical course of 225 .
It is something in the spherical formula used for the great circle but

It's not the formula, it's the fact that the world is a sphere.
The formula only reflects this fact.

The Earth is an oblate spheroid.

The equation he seeks is on the web.