A point on a sphere having spherical polar angles theta and phi has
xyz coordinates
R ( sin theta cos phi, sin theta sin phi, cos theta).
Theta would be (90 degrees -latitude) and phi would be longitude.
Another point having angles theta', phi' would have coordinates:
R ( sin theta' cos phi', sin theta' sin phi', cos theta').
The dot product of these two is R*R cos G, where G is the 'global'
angle between the two points. This should work out to
cos G = sin theta sin theta' (cos (phi-phi')) + cos theta cos theta'
The 'great circle' distance you are after between the points is
R * G. (G in radians, of course)
Put that all in a spreadsheet, and you'll be ready to go.
--
Mike
===============================================================
Mike Moloney
moloney@nextwork.rose-hulman.edu
Dept of Physics & Applied Optics (812) 877 8302
Rose-Hulman Institute of Technology Terre Haute, IN 47803 http://www.rose-hulman.edu/~moloney/index.html