kibana 添加的scripted field如何使用 vega绘制图片，请大神指教

kibana 添加的scripted field（startmap）如何使用 vega绘制图片。
 
使用URL查询，只有timestamp， 找不到startmap，
 
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url: {
      // Context == true means filters of the dashboard will be taken into account
      %context%: true
      // Specify on which field the time picker should operate
       %timefield%: "@timestamp"
     // %sessionid%:"21bfd8f4-13bf-49fd-90ff-30d36a3def79"
      // Specify the index pattern to load data from
      index: _all
      // This body will be send to Elasticsearch's _search endpoint
      // You can use everything the ES Query DSL supports here
      body: {
        // Set the size to load 10000 documents
        size: 10000
        // Just ask for the fields we actually need for visualization
        _source: ["@timestamp","startmap"]
      }
    }