如何将OpenLayers多边形转换为圆？

// 创建多边形对象
var polygon = new ol.geom.Polygon([
  [[-10, -10], [10, -10], [10, 10], [-10, 10], [-10, -10]]
]);

// 创建圆对象
var circle = new ol.geom.Circle(
  ol.proj.transform([-10, -10], 'EPSG:4326', 'EPSG:3857'),
  10000
);

// 将多边形转换为圆
circle = polygon.getExtent().getCenter().concat(polygon.getExtent().getWidth() / 2);

// 创建图层和地图对象
var vectorLayer = new ol.layer.Vector({
  source: new ol.source.Vector({
    features: [new ol.Feature(circle)]
  })
});

var map = new ol.Map({
  layers: [vectorLayer],
  target: 'map',
  view: new ol.View({
    center: [0, 0],
    zoom: 2
  })
});