Distance between points

CREATE FUNCTION [dbo].[DistanceBetween] (@Lat1 AS real, 
@Long1 AS real, @Lat2 AS real, @Long2 AS real)
RETURNS real
AS
BEGIN
DECLARE @dLat1InRad AS float(53);
SET @dLat1InRad = @Lat1 * (PI()/180.0);
DECLARE @dLong1InRad AS float(53);
SET @dLong1InRad = @Long1 * (PI()/180.0);
DECLARE @dLat2InRad AS float(53);
SET @dLat2InRad = @Lat2 * (PI()/180.0);
DECLARE @dLong2InRad AS float(53);
SET @dLong2InRad = @Long2 * (PI()/180.0);
DECLARE @dLongitude AS float(53);
SET @dLongitude = @dLong2InRad - @dLong1InRad;
DECLARE @dLatitude AS float(53);
SET @dLatitude = @dLat2InRad - @dLat1InRad;
/* Intermediate result a. */
DECLARE @a AS float(53);
SET @a = SQUARE (SIN (@dLatitude / 2.0)) + COS (@dLat1InRad) 
* COS (@dLat2InRad) 
* SQUARE(SIN (@dLongitude / 2.0));
/* Intermediate result c (great circle distance in Radians). */
DECLARE @c AS real;
SET @c = 2.0 * ATN2 (SQRT (@a), SQRT (1.0 - @a));
DECLARE @kEarthRadius AS real;
/* SET kEarthRadius = 3956.0 miles */
SET @kEarthRadius = 6376.5;        /* kms */
DECLARE @dDistance AS real;
SET @dDistance = @kEarthRadius * @c;
RETURN (@dDistance);
END