我需要为跟踪实体获得前视图,该视图将根据实体移动而变化.

当我为viewer.trackedEntity属性赋值时,相机会占据一定的位置.是否可以更改此位置以使摄像机直接位于跟踪实体的前方？

我怎么能为这个例子做这个？

var viewer = new Cesium.Viewer('cesiumContainer', {
    infoBox: false, 
    selectionIndicator: false,
    shouldAnimate: true, 
    terrainProvider: Cesium.createWorldTerrain()
});

var start = Cesium.JulianDate.fromDate(new Date(2015, 2, 25, 16));
var stop = Cesium.JulianDate.addSeconds(start, 360, new Cesium.JulianDate());

viewer.clock.startTime = start.clone();
viewer.clock.stopTime = stop.clone();
viewer.clock.currentTime = start.clone();
viewer.clock.clockRange = Cesium.ClockRange.LOOP_STOP;
viewer.clock.multiplier = 10;

viewer.timeline.zoomTo(start, stop);

var position = new Cesium.SampledPositionProperty();
position.addSample(start, Cesium.Cartesian3.fromDegrees(-118.243683, 34.052235, 500000));
position.addSample(Cesium.JulianDate.addSeconds(start, 250, new Cesium.JulianDate()), Cesium.Cartesian3.fromDegrees(-110, 35.5, 500000));
position.addSample(Cesium.JulianDate.addSeconds(start, 500, new Cesium.JulianDate()), Cesium.Cartesian3.fromDegrees(-86.134903, 40.267193, 500000));

var entity = viewer.entities.add({
    availability : new Cesium.TimeIntervalCollection([new Cesium.TimeInterval({
        start : start,
        stop : stop
    })]),
    position : position,
    orientation : new Cesium.VelocityOrientationProperty(position),
    model : {
        uri : 'https://cesiumjs.org/Cesium/Apps/SampleData/models/CesiumAir/Cesium_Air.gltf',
        minimumPixelSize : 64
    },
    path : {
        resolution : 1,
        material : new Cesium.PolylineGlowMaterialProperty({
            glowPower : 0.1,
            color : Cesium.Color.YELLOW
        }),
        width : 10
    }
});

viewer.trackedEntity = entity;

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var entity = viewer.entities.add({
    availability : new Cesium.TimeIntervalCollection([new Cesium.TimeInterval({
        start : start,
        stop : stop
    })]),
    position : position,
    orientation : new Cesium.VelocityOrientationProperty(position),
    model : {
        uri : 
'https://cesiumjs.org/Cesium/Apps/SampleData/models/CesiumAir/Cesium_Air.gltf',
        minimumPixelSize : 64
    },
    path : {
        resolution : 1,
        material : new Cesium.PolylineGlowMaterialProperty({
            glowPower : 0.1,
            color : Cesium.Color.YELLOW
        }),
        width : 10
    },
    viewFrom: new Cesium.Cartesian3(30, 0, 0),
});