PHP calculates the distance between two coordinates

<?phpdefine (' Earth_radius ', 6378.137);//Earth radius define (' PI ', 3.1415926);/** * Calculates the distance between two sets of latitude coordinates * PARAMS:LAT1 latitude 1; lng1 Longitude 1 ; lat2 latitude 2; lng2 longitude 2; Len_type (1:m or 2:km); * return m or km */function getdistance ($lat 1, $lng 1, $lat 2, $lng 2, $len _type = 1, $decimal = 2) {   $radLat 1 = $lat 1 * P i/180.0;   $radLat 2 = $lat 2 * pi/180.0;   $a         = $radLat 1-$radLat 2;   $b         = ($lng 1 * pi/180.0)-($lng 2 * pi/180.0);   $s = 2 * ASIN (sqrt (Pow (sin ($a/2), 2) + cos ($radLat 1) * cos ($radLat 2) * POW (sin ($b/2), 2)));   $s = $s * earth_radius;   $s = round ($s *);   if ($len _type > 1)   {       $s/=;   }      Return round ($s, $decimal);} Echo getdistance (39.908156,116.4767, 39.908452, 116.450479, 1);//output distance/m

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