CREATE FUNCTION CalculateDistance
(@StartLongitude float,
 @StartLatitude float,
 @EndLongitude float,
 @EndLatitude float)

RETURNS decimal(7,1)

AS

BEGIN
    DECLARE @lat1 float
    DECLARE @lat2 float
    DECLARE @long1 float
    DECLARE @long2 float
    DECLARE @LongDistance float
    DECLARE @LatDistance float
    DECLARE @EarthRadius smallint
    DECLARE @ChordLength float
    DECLARE @CentralAngle float

    SET @lat1 = RADIANS(@StartLatitude)
    SET @lat2 = RADIANS(@EndLatitude)
    SET @long1 = RADIANS(@StartLongitude)
    SET @long2 = RADIANS(@EndLongitude)
    SET @LongDistance = @long2 - @long1
    SET @LatDistance = @lat2 - @lat1
    SET @EarthRadius = 3959

    -- Calucate Chord Length
    SET @ChordLength = SQUARE(SIN(@LatDistance /2)) + COS(@lat1) * COS(@lat2) * SQUARE(SIN(@LongDistance /2))
    SET @CentralAngle = 2 * ATN2(SQUARE(@ChordLength),SQUARE(1-@ChordLength))

    RETURN ROUND(@CentralAngle * @EarthRadius, 1)
END