title: google maps: update image overlay
body: <p>I'm trying to update an image overlay on a google map on the fly. I can create a new overlay object, but I can't figure out how to modify it. Can I update the overlayImage object </p>
  
  <pre><code>var overlayImage = new google.maps.GroundOverlay("myimage.png", imageBounds);
  </code></pre>
  
  <p>I want to modify overlayImage on zoom change, but I can't pass it through the function. I also can't find it in the 'map' object.</p>
  
  <pre><code>google.maps.event.addListener(map, 'zoom_changed', function(overlayImage) {
  
  }
  </code></pre>
  
  <p>How do I update myimage.png when the zoom level is changed?</p>