Hiya Ken ---

No sweat! BTW, I found it rather simply, by searching for great-circle (note the hyphen) on yahoo.com. There were links to all sorts of related air nav stuff, like databases of long/lat cooridnates for all major cities/airports, et al. You might want to take a look for future reference.

I did a management app for an air cargo company years back where I had to wrestle with these issues and it was a bear. Good luck!!


>Hi John,
>
>Wow... thanks!! I actually spent two hours in our local library scanning math books. They all described the issue well but NONE offered the formula!
>
>Thanks again,
>
>Ken
>
>>
>>Try the following: (In Km)
>>
>>Convert longitude and latitude to radians: (long or lat * Pi/180)
>>theta = lon2 - lon1
>>dist = acos(sin(lat1) × sin(lat2) + cos(lat1) × cos(lat2) × cos(theta))
>>if (dist < 0)
>> dist = dist + pi
>>endif
>>dist=dist*6371.2