What's the best AI traffic 'distance' calculation?

[thx]

Hi, all!

I'm programming a radar to keep track of AI traffic.

Anyone know the BEST code for determining the MOST ACCURATE distance of AI based on both our LAT and LON's?? I want to be quite specific cuz I'm using distance trend data to perform trajectory projection and closure rate calculations...

Is there another way to get accurate AI traffic distances?

I'm coding in VB using FSUIPC.

Thanks!

Danny

[jd]

this is what i use

Public Function fix_to_fix_distance(lat1 As Single, lon1 As Single, lat2 As Single, lon2 As Single) As Single

Dim pi As Double

Dim degtorad As Double

Dim latx1 As Double

Dim latx2 As Double

Dim lonx1 As Double

Dim lonx2 As Double

pi = 3.1415926535

degtorad = (pi / 180)

latx1 = lat1 * degtorad

latx2 = lat2 * degtorad

lonx1 = -lon1 * degtorad

lonx2 = -lon2 * degtorad

fix_to_fix_distance = ArcCos((Sin(latx1) * Sin(latx2)) + (Cos(latx1) * Cos(latx2) * Cos(lonx1 - lonx2)))

fix_to_fix_distance = fix_to_fix_distance * 180 * 60 / pi

End Function