Openlayers中Feature与WKT之间的转换，Feature坐标系的转换

一、Feature 转WKT 且带坐标系的转换

     var strwkt = new ol.format.WKT().writeFeature(feature, {
                dataProjection: targetcrs,//目标坐标系
                featureProjection:crs  //当前坐标系
            });

 二、WKT转Feature 

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

三、Feature 坐标系转换（支持全部图形）

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

四、利用WKT转换Feature坐标系（这种不支持GEOMETRY不为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获得的Feature 会没有原始Feature对应的Properties