OpenLayers5在EPSG:4326下以m为单位画圆
var circleIn3857 = new Circle(transform([121.4659, 31.2], 'EPSG:4326', 'EPSG:3857'), 1000,'XY');
var circleIn4326 = circleIn3857.transform('EPSG:3857','EPSG:4326');
转载自：https://blog.csdn.net/guimaxingtian/article/details/85262937
