PHP - calculating distance from 2 locations
I have the following PHP function that gets the distance in miles from 2 longitude and latitude coordinates.  I found this snippet online but not sure about the math behind this and how it works.

    function getDistance($latitude1, $longitude1, $latitude2, $longitude2)
     {  
             $theta = $longitude1 - $longitude2;
             $distance = (sin(deg2rad($latitude1)) * sin(deg2rad($latitude2))) + (cos(deg2rad($latitude1)) * cos(deg2rad($latitude2)) * cos(deg2rad($theta)));
             $distance = acos($distance);
             $distance = rad2deg($distance);
             $distance = $distance * 60 * 1.1515;
              return (round($distance,2));
    } 


PHP - calculating distance from 2 locations
===

I have the following PHP function that gets the distance in miles from 2 longitude and latitude coordinates.  I found this snippet online but not sure about the math behind this and how it works.

    function getDistance($latitude1, $longitude1, $latitude2, $longitude2)
     {  
             $theta = $longitude1 - $longitude2;
             $distance = (sin(deg2rad($latitude1)) * sin(deg2rad($latitude2))) + (cos(deg2rad($latitude1)) * cos(deg2rad($latitude2)) * cos(deg2rad($theta)));
             $distance = acos($distance);
             $distance = rad2deg($distance);
             $distance = $distance * 60 * 1.1515;
              return (round($distance,2));
    } 

