Question

I have the problems with my function which needs to calculate distance between given coordinates. As I can see problem is with negative values, and I am running out of ideas how to solve this, so if someone can help me I will really appreciate it!

DELIMITER $$

CREATE DEFINER=`sfff_user`@`%` FUNCTION `GetUserDistance`(lat VARCHAR (20), lon VARCHAR (20), userLat VARCHAR (20), userLon VARCHAR (20)) RETURNS int(11)
BEGIN
    DECLARE distance INT (11);

    IF ISNULL(lat) OR ISNULL(lon) OR lat = '' OR lon = '' THEN
        RETURN 0;
    ELSE
        SELECT
            3956 * 2 * ASIN(SQRT(POWER(SIN((lat - ABS(userLat)) * PI() / 180 / 2), 2) + COS(lat * PI() / 180) * COS(ABS(userLat) * PI() / 180) * POWER(SIN((lon - userLon) * PI() / 180 / 2), 2)))
        INTO
            distance;

        RETURN distance;
    END IF;

END

For example result for this call:

select GetUserDistance(44, 21, 44, 21) as distance; is 0 which is ok

But look at this:

select GetUserDistance('-15.4167', '28.2833', '-15.4167', '28.2833') as distance; 

is 2129 which is insane!

So if you can take a look it would be verry nice to have correct function, since I am dying to solve this 🙁

Thanks.

Answer 1

For safe side you should CAST VARCHAR to DECIMAL and as @Scharron said no need of ABS try:

CREATE FUNCTION `GetUserDistance`(arg_lat VARCHAR (20), arg_lon VARCHAR (20), arg_userLat VARCHAR (20), arg_userLon VARCHAR (20)) RETURNS int(11) NO SQL
BEGIN
    DECLARE distance INT (11);
    DECLARE lat, lon, userLat, userLon DECIMAL(14,4);

    SET lat = CAST(arg_lat AS DECIMAL(14,4));
    SET lon = CAST(arg_lon AS DECIMAL(14,4));
    SET userLat = CAST(arg_userLat AS DECIMAL(14,4));
    SET userLon = CAST(arg_userLon AS DECIMAL(14,4));

    IF ISNULL(lat) OR ISNULL(lon) OR lat = '' OR lon = '' THEN
        RETURN 0;
    ELSE
        SELECT
            3956 * 2 * ASIN(SQRT(POWER(SIN((lat - userLat) * PI() / 180 / 2), 2) + COS(lat * PI() / 180) * COS(ABS(userLat) * PI() / 180) * POWER(SIN((lon - userLon) * PI() / 180 / 2), 2)))
        INTO
            distance;

        RETURN distance;
    END IF;
END