Calculate distance between 2 coordinates/latlong

Create Function [dbo].fn_calc_distance2latlong
(
      @Lat1 Float(18), 
      @Long1 Float(18),
      @Lat2 Float(18),
      @Long2 Float(18),
      @ReturnType VarChar(10)
)

Returns Float(18)

AS

Begin

  Declare @R Float(8);
  Declare @dLat Float(18);
  Declare @dLon Float(18);
  Declare @a Float(18);
  Declare @c Float(18);
  Declare @d Float(18);

  Set @R = 
        Case @ReturnType 
        When 'Miles' Then 3956.55 
        When 'Kilometers' Then 6367.45
        When 'Feet' Then 20890584
        When 'Meters' Then 6367450
        Else 20890584  
        End

  Set @dLat = Radians(@lat2 - @lat1);

  Set @dLon = Radians(@long2 - @long1);

  Set @a = Sin(@dLat / 2) 
             * Sin(@dLat / 2) 
             + Cos(Radians(@lat1))
             * Cos(Radians(@lat2)) 
             * Sin(@dLon / 2) 
             * Sin(@dLon / 2);
  --Set @c = 2 * Asin(Min(Sqrt(@a)));
  Set @c = 2 * Atn2(sqrt(@a),sqrt(1-@a));

  Set @d = @R * @c;
  Return @d;

End 
Go



select dbo.fn_calc_distance2latlong('37.7749300 ','-122.4194200','34.0522222','-118.2427778','Miles')
select dbo.fn_calc_distance2latlong('37.7749300 ','-122.4194200','34.0522222','-118.2427778','Kilometers')
select dbo.fn_calc_distance2latlong('37.7749300 ','-122.4194200','34.0522222','-118.2427778','Meters')
select dbo.fn_calc_distance2latlong('37.7749300 ','-122.4194200','34.0522222','-118.2427778','Feet')