MySQL ST_Distance_Sphere Polyfill

One of the cool things about MySQL 5.7 is the fact that it sports a few spatial convenience functions (since 5.7.6), allowing one to do operations on geometric values.

One of those convenience functions is ST_Distance_Sphere, which allows one to calculate the (spherical) distance between two points.

Recently I was working an project where I needed said function, yet unfortunately they were running some version of MySQL 5.6 … on which ST_Distance_Sphere isn’t available.

Instead of requesting to upgrade the MySQL server, I decided to polyfill ST_Distance_Sphere instead. It’s really easy since it’s a function, and it basically is nothing more than the Haversine Formula which I, as a mapping aficionado, know how to juggle.

DELIMITER $$

DROP FUNCTION IF EXISTS `ST_Distance_Sphere`$$

CREATE FUNCTION `ST_Distance_Sphere` (point1 POINT, point2 POINT)

	RETURNS FLOAT
	no sql deterministic
	BEGIN
		declare R INTEGER DEFAULT 6371000;
		declare `φ1` float;
		declare `φ2` float;
		declare `Δφ` float;
		declare `Δλ` float;
		declare a float;
		declare c float;
		set `φ1` = radians(y(point1));
		set `φ2` = radians(y(point2));
		set `Δφ` = radians(y(point2) - y(point1));
		set `Δλ` = radians(x(point2) - x(point1));

		set a = sin(`Δφ` / 2) * sin(`Δφ` / 2) + cos(`φ1`) * cos(`φ2`) * sin(`Δλ` / 2) * sin(`Δλ` / 2);
		set c = 2 * atan2(sqrt(a), sqrt(1-a));

		return R * c;
	END$$

DELIMITER ;

Run the little snippet above on your server after having selected a database first. Once executed it’ll persistently be available (just like a Stored Procedure) for you to use. Usage is the same as if it were natively available:

SELECT ST_Distance_Sphere(
  POINT(-87.6770458, 41.9631174),
  POINT(-73.9898293, 40.7628267)
);

// ~> 1148978.6738241839 (in metres)

Happy Mapping! 🙂

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