function position_layer (layer_id) {
         var divW = document.getElementById(layer_id).img.width;
		 var divH = document.getElementById(layer_id).img.height;
		 var dW = divW.replace(/px/g, ""); var dH = divH.replace(/px/g, "");
		 var posX = (window.innerWidth / 2)-(dW/2) ; var posY = (window.innerHeight / 2)-(dH/2) ; 
		 var resX = (posX+"px"); var resY = (posY+"px");
		 document.getElementById(layer_id).style.left = resX;
		 document.getElementById(layer_id).style.top = resY;
         
        }