Detect distance between geo points.

distance_between_geopoints.js

function deg2rad (angle) {
  return angle * .017453292519943295;
}

function distance($lat1,$lng1,$lat2,$lng2) 
{ 
  $lat1=deg2rad($lat1); 
  $lng1=deg2rad($lng1); 
  $lat2=deg2rad($lat2); 
  $lng2=deg2rad($lng2); 
  
  $delta_lat=($lat2 - $lat1); 
  $delta_lng=($lng2 - $lng1); 
  
  return round(6378137 * acos(cos($lat1) * cos($lat2) * cos($lng1 - $lng2) + sin($lat1) * sin($lat2))); 
 }