学习cesium，关于图层界面的切换

最近学习cesium的3d引擎，有关图层切换的例子比较少，在官网上看见了一些例子加以自己的理解。投机了一种近似于图层切换的效果。

这种图层切换每次点击按钮时，会把其他的数据和实体给删除。然后再创建或加载一个新的

闲话不多说我们直接上代码

sandcastle.addtoolbarbutton('basic styling', function() {
                viewer.datasources.add(cesium.geojsondatasource.load(url, {
                    stroke: cesium.color.hotpink,
                    fill: cesium.color.pink.withalpha(0.5),
                    strokewidth: 3
                }));
            });
            sandcastle.addtoolbarbutton('按钮',function() {

                var position = cesium.cartesian3.fromdegrees(116.39053344726561,39.89604077881996, 0.0);
                var hpr = new cesium.headingpitchroll(cesium.math.toradians(135), 0.0, 0.0);
                var orientation = cesium.transforms.headingpitchrollquaternion(position, hpr);

                var model = viewer.entities.add({
                    id:'01',
                    position : position,
                    orientation : orientation,
                    model : {
                        uri : url,
                        minimumpixelsize : 128,
                        maximumscale : 20000
                    }
                });

   
            },"toolbar");

            sandcastle.reset = function() {
                viewer.datasources.removeall();
                viewer.entities.removebyid('01')//根据id删除entity

                //设置相机为home为起点
                viewer.camera.lookat(cesium.cartesian3.fromdegrees(116.39053344726561,39.89604077881996, 2631.082799425431), new cesium.cartesian3(0.0, -4790.0, 3930.0));
                viewer.camera.lookattransform(cesium.matrix4.identity);
            };

//sandcastle_end
            sandcastle.finishedloading();