Calculate distance between two sets lat/lon coordinates and Calculate destination lat/lon given a starting point lat/lon cordinates, bearing, and distance, and Calculate the bounding box

boundbox

// Calculating the bounding box 
function boundbox ($lat, $lon, $distance, $units="km") {

	return array ( "N" => getDestinationCoordinates ($lat,$lon,   0,$distance,$units),
					"E" => getDestinationCoordinates ($lat,$lon,  90,$distance,$units),
					"S" => getDestinationCoordinates ($lat,$lon, 180,$distance,$units),
					"W" => getDestinationCoordinates ($lat,$lon, 270,$distance,$units));


}

getDestinationCoordinates

// calculate destination lat/lon given a starting point, bearing, and distance
function getDestinationCoordinates ( $startlat, $startlon, $bearing, $distance , $units="km" ) 
{

  $radius = strcasecmp($units, "km") ? 3963.19 : 6378.137;
  $rLat = deg2rad($startlat);
	$rLon = deg2rad($startlon);
  $rBearing = deg2rad($bearing);
	$rAngDist = $distance / $radius;
  
  $rLatB = asin(sin($rLat) * cos($rAngDist) + cos($rLat) * sin($rAngDist) * cos($rBearing));
  $rLonB = $rLon + atan2(sin($rBearing) * sin($rAngDist) * cos($rLat), cos($rAngDist) - sin($rLat) * sin($rLatB));

	return array("lat" => rad2deg($rLatB), "lon" => rad2deg($rLonB));
}

getDistanceBetweenCoordinates

// calculate distance between two lat/lon coordinates
function getDistanceBetweenCoordinates ( $latA, $lonA , $latB, $lonB, $units="km" )
{		
  $radius = strcasecmp($units, "km") ? 3963.19 : 6378.137;
  $rLatA = deg2rad($latA);
  $rLatB = deg2rad($latB);

  $rHalfDeltaLat = deg2rad(($latB - $latA) / 2);
  $rHalfDeltaLon = deg2rad(($lonB - $lonA) / 2);

  return 2 * $radius * asin(sqrt(pow(sin($rHalfDeltaLat), 2) + cos($rLatA) * cos($rLatB) * pow(sin($rHalfDeltaLon), 2)));	

}