rawdata,
I assume you are looking for the co-ordinates of the runway midpoint. I have never done such a thing and I am sure there are guys here that will be able to give you more intelligent ideas than what I give, but the following comes to mind :
do it by construction ie take a piece of graph paper and set up a grid scale eg 1 block = 1 second or 1 minute of lat/long, depending on what is suitable. Then plot the co-ords of the thresholds. Measure the halfway point and then look up the co-ords on the grid scale.
I dunno if it will work, just an idea that came to mind.
Some nav computers have the ability to work out co-ordinates based on a starting point and a given great circle bearing and distance, but I think is more for en-route navigation and won't be appropriate for what you want.
Another idea just sprang to mind. Why not subtract the N/S lat from each other and the E/W long - divide by 2 and then subtract from or add to original co-ords <img src="rolleyes.gif" border="0"> Could work, dunno - try it and let us know.
Regards
4g
<img src="smile.gif" border="0">
[ 24 December 2001: Message edited by: 4g_handicap ]</p>