Calculate Distance Between 2 GPS Coordinates

caclulateDistance.sql

CREATE FUNCTION [dbo].[CalculateDistanceBetweenGPSCoordinates](
	@Latitude1 float,
	@Longitude1 float,
	@Latitude2 float,
	@Longitude2 float,
	@ReturnUnits char(2) = 'MI'
)
RETURNS float
AS
BEGIN
	-- CONSTANTS
	DECLARE @EarthRadiusInMiles float = 3956.6;
	DECLARE @EarthRadiusInKm float = 6367.5;
	DECLARE @EarthRadius float = @EarthRadiusInMiles;
	
	IF (@ReturnUnits = 'KM')
	BEGIN
		SELECT @EarthRadius = @EarthRadiusInKm
	END
	
	DECLARE @PI  float;
	SET @PI = PI();
	-- RADIANS conversion
	DECLARE @lat1Radians float;
	DECLARE @long1Radians float;
	DECLARE @lat2Radians float;
	DECLARE @long2Radians float;
	SET @lat1Radians = @Latitude1 * @PI / 180;
	SET @long1Radians = @Longitude1 * @PI / 180;
	SET @lat2Radians = @Latitude2 * @PI / 180;
	SET @long2Radians = @Longitude2 * @PI / 180;

	RETURN Acos(
		Cos(@lat1Radians) * Cos(@long1Radians) * Cos(@lat2Radians) * Cos(@long2Radians) +
		Cos(@lat1Radians) * Sin(@long1Radians) * Cos(@lat2Radians) * Sin(@long2Radians) +
		Sin(@lat1Radians) * Sin(@lat2Radians)
	) * @EarthRadius;
END