Openlayers中Feature與WKT之間的轉換，Feature坐標系的轉換

1、Feature 轉WKT 且帶坐標系的轉換

     var strwkt = new ol.format.WKT().writeFeature(feature, {
                dataProjection: targetcrs,//目標坐標系
                featureProjection:crs  //當前坐標系
            });

 2、WKT轉Feature 

  var newfeature = new ol.format.WKT().readFeature(strwkt);

3、Feature 坐標系轉換（支持所有圖形）

  var geom = feature.getGeometry().transform(crs, targetcrs);
  feature.setGeometry(geom);

4、利用WKT轉換Feature坐標系（這種不支持GEOMETRY不為Circle）

  var strwkt = new ol.format.WKT().writeFeature(feature, {
                dataProjection: targetcrs,
                featureProjection:crs
            });
            var newfeature = new ol.format.WKT().readFeature(strwkt);

注意：方法4得到的Feature 會沒有原始Feature對應的Properties