cesium 创建 Primitive 水体

效果 

  let instances = []
      instances.push(
        new Cesium.GeometryInstance({
          geometry: new Cesium.PolygonGeometry.fromPositions({
            positions: Cesium.Cartesian3.fromDegreesArray(points), //positions, //
            height: 117,
            extrudedHeight: 120, //相对0开始挤出
            vertexFormat: Cesium.EllipsoidSurfaceAppearance.VERTEX_FORMAT
          })
        })
      )
      let aperWater = this.waterEffect2()
      let waterPrimitive = new Cesium.Primitive({
        geometryInstances: instances,
        appearance: aperWater, //modelMatrix: modelMatrix,
        asynchronous: false,
        show: true
      })
      let water = this.ffCesium.viewer.scene.primitives.add(waterPrimitive)
    },
    waterEffect2() {
      //水渲染效果2
      const aperWater = new Cesium.EllipsoidSurfaceAppearance({