function addOverlay($bds_lat1, $bds_lon1, $bds_lat2, $bds_lon2, $img_src, $opacity = 100){
		 $_overlay = array(
			"bounds" => array(
				"ne"=>array(
					"lat"=>$bds_lat1,
					"long"=>$bds_lon1
				),
				"sw"=>array(
					"lat"=>$bds_lat2,
					"long"=>$bds_lon2
				)
			),
			"img" => $img_src,
			"opacity" => $opacity/10
		 );
		 $this->adjustCenterCoords($bds_lon1,$bds_lat1);
         $this->adjustCenterCoords($bds_lon2,$bds_lat2);
		 $this->_overlays[] = $_overlay;
		 return count($this->_overlays)-1;
	 }