代码思路

Cesium的淹没效果主要使用到的是Cesium库中polygon的extrudedHeight属性。通过定时器对绘制的polygon进行高度增加同时将polygon的颜色设置成淡蓝色，从而实现淹没效果的展示。

实现的效果

淹没实现效果

代码展示

// 淹没效果
    function drawPolygon(){
        var waterHeight = 100;//初始设定的水位高度
        var targetHeight = Number((viewer.camera.positionCartographic.height/1000).toFixed(2)) * 100;
        console.log(targetHeight);
        var PolygonPrimitive = (function () {
            function _(positions) {
                this.options = {
                    name: '多边形',
                    polygon: {
                        hierarchy: [],
                        perPositionHeight: true,
                        extrudedHeight: 0,
                        material: new Cesium.Color.fromBytes(64, 157, 253, 150),
                    }
                };
                this.hierarchy = positions;
                this._init();
            }

            _.prototype._init = function () {
                var _self = this;
                var _updateHierarchy = function () {
                    return _self.hierarchy;
                };
                //实时更新polygon.hierarchy
                this.options.polygon.hierarchy = new Cesium.CallbackProperty(_updateHierarchy, false);
                this.timer = setInterval(() => {
                    if (waterHeight < targetHeight) {
                        waterHeight += 100;
                        if (waterHeight > targetHeight) {
                            waterHeight = targetHeight
                        }
                        viewer.entities.add({
                            name: '多边形',
                            polygon: {
                                hierarchy: positions,
                                perPositionHeight: true,
                                extrudedHeight: waterHeight,
                                material: new Cesium.Color.fromBytes(64, 157, 253, 150),
                            }
                        })
                    }
                }, 1000);
                //viewer.entities.add(this.options);
            };
            return _;
        })();

        var handler = new Cesium.ScreenSpaceEventHandler(viewer.scene.canvas);
        var positions = [];
        var poly = undefined;

        //鼠标单击画点
        handler.setInputAction(function (movement) {
            var cartesian = viewer.scene.camera.pickEllipsoid(movement.position, viewer.scene.globe.ellipsoid);
            if (positions.length == 0) {
                positions.push(cartesian.clone());
            }
            positions.push(cartesian);
        }, Cesium.ScreenSpaceEventType.LEFT_CLICK);
        //鼠标移动
        handler.setInputAction(function (movement) {
            var cartesian = viewer.scene.camera.pickEllipsoid(movement.endPosition, viewer.scene.globe.ellipsoid);
            if (positions.length >= 2) {
                if (!Cesium.defined(poly)) {
                    poly = new PolygonPrimitive(positions);
                } else {
                    if(cartesian != undefined){
                        positions.pop();
                        cartesian.y += (1 + Math.random());
                        positions.push(cartesian);
                    }
                }
            }
        }, Cesium.ScreenSpaceEventType.MOUSE_MOVE);
        //鼠标右键单击结束绘制
        handler.setInputAction(function (movement) {
            handler.destroy();
        }, Cesium.ScreenSpaceEventType.RIGHT_CLICK);
    }

PS：代码有点小Bug，暂时不想改了。如果您改好可以给我留言。