openlayer 加载geojson数据不显示问题

json数据没问题

加载geojson后无法显示图形

解决:发现少加了个策略

equipmentDatasLayer = new OpenLayers.Layer.Vector('数据图层', {  projection: new OpenLayers.Projection('EPSG:4326'),  protocol: new OpenLayers.Protocol.HTTP({  url: 'map.json',  format: new OpenLayers.Format.GeoJSON({read: function(json,type,filter){    var geojson = new OpenLayers.Format.GeoJSON();      var features =geojson.read(json,"FeatureCollection");//FeatureConllection与json数据中type对应    refreshData(features);}})  }),  strategies: [new OpenLayers.Strategy.Fixed()],styleMap: equipmentDatas_style});