title: GeoFire retrieve all queries within a range when moving.
body: <p>I'm trying to retrieve all elements from my GeoFire database when moving. For example: when walking around I want to retrieve in realtime the locations of elements around me (moving or not moving).  </p>
  
  <p>If I use the following code:</p>
  
  <pre><code>var geoQuery = geoFire.query({
              center: [52.35500, 4.931000],
              radius: 0.1 //kilometers
  });
  
  var onKeyEnteredRegistration = geoQuery.on("key_entered", function(key, location, distance) {
              console.log(key + " entered query at " + location + " (" + distance + " km from center)");
          });
  </code></pre>
  
  <p>I only receive updates when the keys are changing position (and entering my query). Is there a possibility to retrieve all elements within a certain range as a sort of a snapshot? And from there monitor realtime?</p>
  
  <p>I could of course query the whole database and then use </p>
  
  <pre><code>GeoFire.distance(location1, location2)
  </code></pre>
  
  <p>But this looks like a very expensive option. </p>