如何在OpenLayers中获取绘制框的坐标？

var map = new ol.Map({
  // 地图容器的ID
  target: 'map',
  // 地图图层
  layers: [
    new ol.layer.Tile({
      source: new ol.source.OSM()
    })
  ],
  // 初始视图
  view: new ol.View({
    center: ol.proj.fromLonLat([0, 0]),
    zoom: 2
  })
});

var drawInteraction = new ol.interaction.Draw({
  type: 'Circle',
  // 绘制结束时的回调函数
  finishCondition: function(event) {
    return ol.events.condition.singleClick(event) && event.originalEvent.button === 0;
  }
});
map.addInteraction(drawInteraction);

drawInteraction.on('drawend', function(event) {
  var geometry = event.feature.getGeometry();
  var coordinates = geometry.getCoordinates();
  console.log(coordinates);
});