Entfernung zwischen 2 Koordinaten

<?php
/*
    This Software calculates distance in km between 2 coordinates.

    Copyright (C) 2020 Guido Richter / tintenkobold.de

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License [http://www.gnu.org/licenses/] for more details.
*/

/* calculate distance in km between 2 coordinates. when mode=SQL is set, a usable query string will be returned.
x2 and y2, x1 and y1 have to be column names of the sql table */

function distance_2coordinates($x1,$y1,$x2,$y2,$mode=0)
{
	$f = 0.017453292519943;
	$r = 6370;
	if($mode=='SQL')
	{
		$ret = 'ACOS(SIN('.$x1.'*PI()/180)*SIN('.$y2.'*PI()/180)+COS('.$x1.'*PI()/180)*COS('.$y2.'*PI()/180)*COS(('.$x2.'*PI()/180)-'.$y1.'*PI()/180))*'.$r;
		return $ret;
	}
	else
	{
		$a_lat 	= $y1 * $f;
		$a_lon 	= $x1 * $f;
		$b_lat 	= $y2 * $f;
		$b_lon 	= $x2 * $f;
		return acos(sin($b_lat)*sin($a_lat)+cos($b_lat)*cos($a_lat)*cos($b_lon-$a_lon))*$r;
	}
}

?>