GLTF压缩的技术方法

倾斜摄影模型分层单体化

以蓝田新城osgb模型为例

一、将osgb模型转换为3Dtiles数据

(软件地址(osg2cesiumApp)：https://github.com/fanvanzh/3dtiles/blob/master/README.md )

二、获取模型位置高程，在cesium中加载此模型，查看贴地状态

var ellipsoid = viewer.scene.globe.ellipsoid;   //得到当前三维场景的椭球体
var terrainProvider = viewer.scene.terrainProvider;
var CesiumEventHandler = new Cesium.ScreenSpaceEventHandler(viewer.scene.canvas);
CesiumEventHandler.setInputAction(function (movement) {
    var cartesian = viewer.camera.pickEllipsoid(movement.position, ellipsoid);
    if (cartesian) {
        var cartographic = Cesium.Cartographic.fromCartesian(cartesian);  //将笛卡尔坐标转换为地理坐标
        var longitudeDegree = Cesium.Math.toDegrees(cartographic.longitude);
        var latitudeDegree = Cesium.Math.toDegrees(cartographic.latitude);
        //x为longtitude,y为latitude,terrain是地形privider
        var positions = [
            Cesium.Cartographic.fromDegrees(longitudeDegree, latitudeDegree),
        ];
        var promise = Cesium.sampleTerrainMostDetailed(terrainProvider, positions);
        Cesium.when(promise, function (updatedPositions) {
            var terrainHeight = updatedPositions[0].height;
            console.log(terrainHeight);
        });
    }
}, Cesium.ScreenSpaceEventType.LEFT_CLICK);

// 加载 3D tiles
function load3DTiles(viewer, url) {

    var tileset = viewer.scene.primitives.add(
        new Cesium.Cesium3DTileset({
            url: url,
            ellipsoid: viewer.scene.globe.ellipsoid,
            // clampToGround: true,
            heightReference: Cesium.HeightReference.CLAMP_TO_GROUND,
            height: 447.4957209101552
        })
    );
    viewer.zoomTo(tileset);

三、下载模型所在位置影像图，绘制模型平面轮廓，在同一位置复制多个叠加面，创建顶面和底面两个属性字段，计算高程起点及建筑高度，对数据进行修改叠加

四、导入cesiumLab,使用shp文件生成矢量楼块3Dtiiles文件，设置参数如下

五、将矢量3dtiles作为classification type分类瓦片数据加载，分类对象设置为仅3dTiles

{
文献参考：
动态3D贴片交互：https://www.cesium.com/blog/2018/11/05/dynamic-3d-tiles-annotations/
Cesium3DTileset ：https://cesium.com/docs/cesiumjs-ref-doc/Cesium3DTileset.html
classificationType ：https://cesium.com/docs/cesiumjs-ref-doc/ClassificationType.html?classFilter=classificationType
}

function loadClassificationTileset(viewer, url) {
    var classificationTileset = viewer.scene.primitives.add(
        new Cesium.Cesium3DTileset({
            id: "LTXCbuilding",
            url: url,
            classificationType: Cesium.ClassificationType.CESIUM_3D_TILE
        })
    );
    classificationTileset.style = new Cesium.Cesium3DTileStyle({
        color: 'rgba(255, 0, 0, 0.01)'
    });
}

6、添加交互

var selectedFeature = {
    "feature": undefined,
    "Color": new Cesium.Color()
};
var handler = new Cesium.ScreenSpaceEventHandler(viewer.scene.canvas);
handler.setInputAction(function (movement) {
    var pickedFeature = viewer.scene.pick(movement.endPosition);
    if (Cesium.defined(selectedFeature.feature)) {
        selectedFeature.feature.color = Cesium.Color.WHITE.withAlpha(0.01);
        selectedFeature.feature = undefined;
    }
    if (pickedFeature && pickedFeature !== selectedFeature.feature) {
        selectedFeature.feature = pickedFeature;
        Cesium.Color.clone(pickedFeature.color, selectedFeature.Color);
        pickedFeature.color = Cesium.Color.YELLOW.withAlpha(0.5);
    }

}, Cesium.ScreenSpaceEventType.MOUSE_MOVE); // MOUSE_MOVE

成果