let position = new SampledPositionProperty();
// 計算時間去，起始時間為當前，結束時間為10秒后
let time1 = JulianDate.now();
let time2 = Cesium.JulianDate.addSeconds(time1 , 10, new Cesium.JulianDate());
// 添加位置
let c31 = Cesium.Cartesian3.fromDegrees(120.3321766, 36.2241208, 35);
let c32 = Cesium.Cartesian3.fromDegrees(120.3339342, 36.2165777, 25);
position.addSample(time1 , c31);
position.addSample(time2 , c32);

export default class ExtendSampledPositionProperty extends SampledPositionProperty {
    lastPosition: undefined | Cartesian3;
    constructor(
        referenceFrame = ReferenceFrame.FIXED,
        numberOfDerivatives = 0
    ) {
        super(referenceFrame, numberOfDerivatives);
        this.lastPosition = undefined;
    }

    /**
     * @description: 解決getValue返回undefined導致entity獲取不到坐標消失問題
     * @param {JulianDate} time
     * @param {*} result
     * @return {*}
     */
    getValue(time: JulianDate, result = new Cartesian3()) {
        let p = this.getValueInReferenceFrame(
            time,
            ReferenceFrame.FIXED,
            result
        );
        if (p) {
            this.lastPosition = p.clone();
            return p;
        } else {
            return this.lastPosition;
        }
    }
}