cesium polygon 悬浮在半空中

效果如下：

代码：

let arr = [
   [120.87140893447473, 31.877030830389447, 128.64],
   [120.87140872335587, 31.876963534304792, 128.64],
   [120.87202301763111, 31.87696299560446, 128.63],
   [120.87202432001283, 31.877030271988385, 128.63]
 ]
 arr = [].concat.apply([], arr)
 var orangePolygon = viewer.entities.add({
   name: 'Orange',
   polygon: {
     hierarchy: Cesium.Cartesian3.fromDegreesArrayHeights(arr),
     extrudedHeight: 0,
     perPositionHeight: false,
     material: Cesium.Color.ORANGE.withAlpha(0.5),
     outline: false,
     extrudedHeight: 128.5,
     height: 132.0
   }
 })
 viewer.zoomTo(viewer.entities)

其实就是polygon,给齐增加距离地面的属性extrudedHeight，以及高度height