preload_image_object = new Image();
      // set image url
      image_url = new Array();
      image_url[0] = "/wp-content/themes/tdgintegrated/images/mapicon-on.png";
      image_url[1] = "/wp-content/themes/tdgintegrated/images/bggrad.png";
	  image_url[2] = "/wp-content/themes/tdgintegrated/images/hiddengrad.png";

       var i = 0;
       for(i=0; i<=2; i++) {
         preload_image_object.src = image_url[i];
	   }