It's an academic topic called "Spherical Geometry"
There is a plane which cuts the two coordinate pairs and the Earth
center. A 'triangle' is drawn from the center and the two given
points. The included angle is found from which the great circle
distance is derived.

Brian Whatcott

On Thu, 04 Dec 2003 14:57:11 -0800, "Lloyd Sumpter"
wrote:


That will do it - thanks! Curious about how those formulae were developed,
though...

Lloyd


On Thu, 04 Dec 2003 14:46:15 +0000, SpamJam wrote:

You want http://williams.best.vwh.net/avform.htm

"Lloyd Sumpter" wrote in message
news
Hi,

I'm writing a program for Linux that displays position (from GPS) on a
scanned-in chart, and would like it to calculate distance from current
position to the cursor.

How do you calculate distance between two points using lat/long? If
they're due North/South, I can do it ( 1 minute of lat = 1 NM) but how do
you calculate distance from longitude? Perhaps some formula based on the
circumfrence of the Earth at the equator and the latitude?

Lloyd Sumpter