Open Layers 3获得Google Maps baselayer？

我已经阅读了一些有关此事的帖子以及示例链接

但是我发现很难理解他们在示例中是如何做到的:

var gmap = new google.maps.Map(document.getElementById('gmap'), {
  disableDefaultUI: true,
  keyboardShortcuts: false,
  draggable: false,
  disableDoubleClickZoom: true,
  scrollwheel: false,
  streetViewControl: false
});

var view = new ol.View({
  // make sure the view doesn't go beyond the 22 zoom levels of Google Maps
  maxZoom: 21
});
view.on('change:center', function() {
  var center = ol.proj.transform(view.getCenter(), 'EPSG:3857', 'EPSG:4326');
  gmap.setCenter(new google.maps.LatLng(center[1], center[0]));
});
view.on('change:resolution', function() {
  gmap.setZoom(view.getZoom());
});

var vector = new ol.layer.Vector({
  source: new ol.source.GeoJSON({
    url: 'data/geojson/countries.geojson',
    projection: 'EPSG:3857'
  }),
  style: new ol.style.Style({
    fill: new ol.style.Fill({
      color: 'rgba(255, 255, 255, 0.6)'
    }),
    stroke: new ol.style.Stroke({
      color: '#319FD3',
      width: 1
    })
  })
});

var olMapDiv = document.getElementById('olmap');
var map = new ol.Map({
  layers: [vector],
  interactions: ol.interaction.defaults({
    altShiftDragRotate: false,
    dragPan: false,
    rotate: false
  }).extend([new ol.interaction.DragPan({kinetic: null})]),
  target: olMapDiv,
  view: view
});
view.setCenter([0, 0]);
view.setZoom(1);

olMapDiv.parentNode.removeChild(olMapDiv);
gmap.controls[google.maps.ControlPosition.TOP_LEFT].push(olMapDiv);

我必须创建多少个DOM元素？它是否正确？

我通过像这样的结构得到一个错误.这是我得到的错误:

Cannot read property 'parentNode' of null

有关如何在OL3中实施Google地图的任何线索？

该尝试已弃用,请查看以下内容:https://github.com/mapgears/ol3-google-maps