title: OpenLayer3 - how to get coordinates of viewport
body: <p>I have a MapQuest displayed with OpenLayer3. I want to get coordinates of viewport (map area curretnly displayed). For the whole map this should be like this:(180,90) x (-180,-90). </p>
  
  <p>but I got: 
  Top-right longitude: 37570328.14272983
  Top-right latitude: 18941707.105292957
  Down-left longitude:-37570328.14272983
  Down-left latitude:-18941707.105292957 </p>
  
  <p>I have jsFiddle for it: <a href="http://jsfiddle.net/0d6d6kxf/2/">http://jsfiddle.net/0d6d6kxf/2/</a></p>
  
  <p>(click "Get viewport coords" div to get coords of current map)</p>
  
  <p>The command which I use for get coordinates is:
      var extent = map.getView().calculateExtent(map.getSize());</p>
  
  <p><strong>Why these result is not in degrees? How to get degree cordinates?</strong></p>
  
  <p>JS code:</p>
  
  <pre><code>$(document).ready(function(){
      object = new QuestMapWrapper();    
      object.openMap();
      object.getViewportCords();      
  });
  
  function QuestMapWrapper()
  {
    //private var
    var map;
    var view;
  
    //public var
    this.wrapperName="QuestMapWrapper";
  
    //methods
    this.openMap = function() {
  
      //$('#ol-viewport').show();
      //$('#gmap').hide();
  
  
      //set layers of one
      var layers = [
      new ol.layer.Tile({
        style: 'Road',
        source: new ol.source.MapQuest({layer: 'osm'})
      })]
  
      view = new ol.View({
      //center: ol.proj.transform([20, 52.702222], 'EPSG:4326', 'EPSG:3857'),
      center: ol.proj.transform([0., 0.0], 'EPSG:4326', 'EPSG:3857'),
      //center: [-73.979378, 40.702222],
      zoom: 1
      });
  
      map = new ol.Map({
        layers: layers,
        //renderer: exampleNS.getRendererFromQueryString(),
        target: 'map',
        view: view
      });
  
    }; 
  
    /** Set viewport details  */
    this.getViewportCords = function() {
  
      //var extent = view.calculateExtent( map.getSize() );   
      var extent = map.getView().calculateExtent(map.getSize());
  
      //var extent = map.getExtent().transform(map.projection, map.displayProjection)
  
      var factor = 1; // coordinates must be devided by 100000 to get real coord
  
      $('#tr-lon').text(extent[2] / factor);
      $('#tr-lat').text(extent[3] / factor);    
      $('#dl-lon').text(extent[0] / factor);
      $('#dl-lat').text(extent[1] / factor);    
    } 
  }
  </code></pre>