載入和設定實體樣式

• 支援兩種資料格式KML和CZML、GeoJson,但不論什麼格式最後都會轉化為Entity這就是Cesium的一個數據物件可以被根據時間和空間展示在Cesium上。 如下面這個實體資料物件的例子

var viewer = new Cesium.Viewer('cesiumContainer');

var blueBox = viewer.entities.add({
    name : 'Blue box',
    position: Cesium.Cartesian3.fromDegrees(-114.0, 40.0, 300000.0),
    box : {
        dimensions : new
 
 Cesium.Cartesian3(400000.0, 300000.0, 500000.0),
        material : Cesium.Color.BLUE
    }
});

var redBox = viewer.entities.add({
    name : 'Red box with black outline',
    position: Cesium.Cartesian3.fromDegrees(-107.0, 40.0, 300000.0),
    box : {
        dimensions : new Cesium.Cartesian3(400000.0, 300000.0, 500000.0),
        material : Cesium.Color.RED.withAlpha(0.5
 
),
        outline : true,
        outlineColor : Cesium.Color.BLACK
    }
});

var outlineOnly = viewer.entities.add({
    name : 'Yellow box outline',
    position: Cesium.Cartesian3.fromDegrees(-100.0, 40.0, 300000.0),
    box : {
        dimensions : new Cesium.Cartesian3(400000.0, 300000.0, 500000.0),
        fill : false,
        outline : true
 
,
        outlineColor : Cesium.Color.YELLOW
    }
});

• 上面的例子是已有的物件來展示的。下面講通過資料載入過來的實體資料，不同的資料型別有提供不同的載入方法如KmlDataSource。注意的是載入方法有一個可選引數就是載入時的一個引數如下code

var kmlOptions = {
    camera : viewer.scene.camera,
    canvas : viewer.scene.canvas,
    clampToGround : true
};
// Load geocache points of interest from a KML file
// Data from : http://catalog.opendata.city/dataset/pediacities-nyc-neighborhoods/resource/91778048-3c58-449c-a3f9-365ed203e914
var geocachePromise = Cesium.KmlDataSource.load('./Source/SampleData/sampleGeocacheLocations.kml', kmlOptions);

• 注意的是資料載入 是非同步的，所以我們所有的操作必須是在資料載入完成後才能進行，所以我們要利用載入資料返回的promise。它提供有的有一個Then函式。可以在裡面做對資料的處理以及樣式的新增和處理 ，同時載入模式時可以選擇進行插值。

    var kmlOptions = {
        camera : viewer.scene.camera,
        canvas : viewer.scene.canvas,
        clampToGround : true
    };
    // Load geocache points of interest from a KML file
    // Data from : http://catalog.opendata.city/dataset/pediacities-nyc-neighborhoods/resource/91778048-3c58-449c-a3f9-365ed203e914
    var geocachePromise = Cesium.KmlDataSource.load('./Source/SampleData/sampleGeocacheLocations.kml', kmlOptions);

    // Add geocache billboard entities to scene and style them
    geocachePromise.then(function(dataSource) {
        // Add the new data as entities to the viewer
        viewer.dataSources.add(dataSource);

        // Get the array of entities
        var geocacheEntities = dataSource.entities.values;

        for (var i = 0; i < geocacheEntities.length; i++) {
            var entity = geocacheEntities[i];
            if (Cesium.defined(entity.billboard)) {
                // Adjust the vertical origin so pins sit on terrain
                entity.billboard.verticalOrigin = Cesium.VerticalOrigin.BOTTOM;
                // Disable the labels to reduce clutter
                entity.label = undefined;
                // Add distance display condition
                entity.billboard.distanceDisplayCondition = new Cesium.DistanceDisplayCondition(10.0, 20000.0);
                // Compute latitude and longitude in degrees
                var cartographicPosition = Cesium.Cartographic.fromCartesian(entity.position.getValue(Cesium.JulianDate.now()));
                var latitude = Cesium.Math.toDegrees(cartographicPosition.latitude);
                var longitude = Cesium.Math.toDegrees(cartographicPosition.longitude);
                // Modify description
                var description = '<table class="cesium-infoBox-defaultTable cesium-infoBox-defaultTable-lighter"><tbody>';
                description += '<tr><th>' + "Latitude" + '</th><td>' + latitude + '</td></tr>';
                description += '<tr><th>' + "Longitude" + '</th><td>' + longitude + '</td></tr>';
                description += '</tbody></table>';
                entity.description = description;
            }
        }
    });

    var geojsonOptions = {
        clampToGround : true
    };
    // Load neighborhood boundaries from a GeoJson file
    // Data from : https://data.cityofnewyork.us/City-Government/Neighborhood-Tabulation-Areas/cpf4-rkhq
    var neighborhoodsPromise = Cesium.GeoJsonDataSource.load('./Source/SampleData/sampleNeighborhoods.geojson', geojsonOptions);

    // Save an new entity collection of neighborhood data
    var neighborhoods;
    neighborhoodsPromise.then(function(dataSource) {
        // Add the new data as entities to the viewer
        viewer.dataSources.add(dataSource);
        neighborhoods = dataSource.entities;

        // Get the array of entities
        var neighborhoodEntities = dataSource.entities.values;
        for (var i = 0; i < neighborhoodEntities.length; i++) {
            var entity = neighborhoodEntities[i];

            if (Cesium.defined(entity.polygon)) {
                // Use kml neighborhood value as entity name
                entity.name = entity.properties.neighborhood;
                // Set the polygon material to a random, translucent color
                entity.polygon.material = Cesium.Color.fromRandom({
                    red : 0.1,
                    maximumGreen : 0.5,
                    minimumBlue : 0.5,
                    alpha : 0.6
                });
                // Tells the polygon to color the terrain. ClassificationType.CESIUM_3D_TILE will color the 3D tileset, and ClassificationType.BOTH will color both the 3d tiles and terrain (BOTH is the default)
                entity.polygon.classificationType = Cesium.ClassificationType.TERRAIN;
                // Generate Polygon center
                var polyPositions = entity.polygon.hierarchy.getValue(Cesium.JulianDate.now()).positions;
                var polyCenter = Cesium.BoundingSphere.fromPoints(polyPositions).center;
                polyCenter = Cesium.Ellipsoid.WGS84.scaleToGeodeticSurface(polyCenter);
                entity.position = polyCenter;
                // Generate labels
                entity.label = {
                    text : entity.name,
                    showBackground : true,
                    scale : 0.6,
                    horizontalOrigin : Cesium.HorizontalOrigin.CENTER,
                    verticalOrigin : Cesium.VerticalOrigin.BOTTOM,
                    distanceDisplayCondition : new Cesium.DistanceDisplayCondition(10.0, 8000.0),
                    disableDepthTestDistance : 100.0
                };
            }
        }
    });

    // Load a drone flight path from a CZML file
    var dronePromise = Cesium.CzmlDataSource.load('./Source/SampleData/SampleFlight.czml');

    // Save a new drone model entity
    var drone;
    dronePromise.then(function(dataSource) {
        viewer.dataSources.add(dataSource);
        // Get the entity using the id defined in the CZML data
        drone = dataSource.entities.getById('Aircraft/Aircraft1');
        // Attach a 3D model
        drone.model = {
            uri : './Source/SampleData/Models/CesiumDrone.gltf',
            minimumPixelSize : 128,
            maximumScale : 2000
        };
        // Add computed orientation based on sampled positions
        drone.orientation = new Cesium.VelocityOrientationProperty(drone.position);

        // Smooth path interpolation
        drone.position.setInterpolationOptions({
            interpolationAlgorithm : Cesium.HermitePolynomialApproximation,
            interpolationDegree : 2
        });
        drone.viewFrom = new Cesium.Cartesian3(-30, 0, 0);
    });

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