     let list = []
        for (let i = 0; i < num; i++) {
          let lng = 120.38105869 + Math.random() * 0.5
          let lat = 31.10115627 + Math.random() * 0.5
          list.push(
            new DC.Position(
              lng,
              lat,
              1000 * Math.random(),
              3600 * Math.random()
            )
          )
        }
        return list
      }

      DC.config.baseUrl = '../libs/dc-sdk/resources/'
      let viewer = new DC.Viewer('viewer-container')
      let bas