Calculate Distance in Miles from Latitude and Longitude

Create Function LatLonDistance(
        @Lat1 Float, 
        @Lon1 Float, 
        @Lat2 Float, 
        @Lon2 Float
) Returns Float
/*
        Faster way to calculate distance in miles using Latitude & Longitude.  
This is accurate in miles to about 4.5 decimal places, except for very small distances.

NOTE: 57.295779513082323 = 180.0 / PI
 (converts Lat/Lon degrees to spherical radians)

Ref: The formula is derived from the Spherical Law of Cosines,

  --RBarryYoung, 31-Jan-2009
*/ As
Begin
/* tests:
 select dbo.calculateDistance(31.0, -93.0, 31.1, -93.0)        --should be 6.9169 miles
 select dbo.calculateDistance(31.0, -93.0, 31.0, -93.1)        --should be 5.9290 miles
 select dbo.calculateDistance(20.0, -93.0, 20.0, -93.1)        --should be 6.4998 miles
 select dbo.calculateDistance(40.0, -93.0, 40.0, -93.1)        --should be 5.2987 miles
*/ Return 3963.0*acos(
    sin(@Lat1/57.295779513082323) 
        * sin(@Lat2/57.295779513082323) 
    + cos(@Lat1/57.295779513082323) 
        * cos(@Lat2/57.295779513082323) 
        * cos((@Lon2-@Lon1)/57.295779513082323)
)
End