//创建面 支持球面和平面坐标

var polygon = viewer.entities.add({

                polygon: {

                    hierarchy: {

                        positions: Cesium.Cartesian3.fromRadiansArray([ ]),

                    },

                    outline: true,

                    outlineColor: Cesium.Color.RED,

                    outlineWidth: 3,

                    material: Cesium.Color.YELLOW,

                },

            });

var pyPositions = polygon.polygon.hierarchy.getValue(Cesium.JulianDate.now()).positions;

 //中心点

var pCenter = Cesium.BoundingSphere.fromPoints(polyPositions).center;