cesium中的视锥体如何移动

在Cesium中，可以通过修改相机的位置和方向来移动视锥体。以下是一个简单的示例代码，演示如何在Cesium中移动一个视锥体：

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

//创建视锥体
var frustum = new Cesium.PerspectiveFrustum({
    fov : Cesium.Math.PI_OVER_THREE,
    aspectRatio : viewer.canvas.clientWidth / viewer.canvas.clientHeight,
    near : 1.0,
    far : 1000.0
});
var cameraPosition = new Cesium.Cartesian3(-2275637.879546224, 5009377.085697311, 3211428.4418059286);
var cameraDirection = new Cesium.Cartesian3(-0.3347522433899313, 0.6567759537293052, -0.6758204380859216);
var cameraUp = new Cesium.Cartesian3(0.6567759537293052, 0.7534987645965692, 0.01608423270374519);
var cameraRight = new Cesium.Cartesian3(0.6758204380859216, -0.01608423270374519, -0.7376365223584079);
frustum.setTransform(Cesium.Matrix4.computeView(cameraPosition, cameraDirection, cameraUp, cameraRight));

//创建视锥体边框
var vertices = frustum.computeCullingVolume().getPlanes()[0].getRectangle().vertices;
var positions = new Cesium.Cartesian3.fromArray(vertices);
var indices = [0, 1, 1, 2, 2, 3, 3, 0, 4, 5, 5, 6, 6, 7, 7, 4, 0, 4, 1, 5, 2, 6, 3, 7];
var geometry = new Cesium.Geometry({
    attributes : {
        position : new Cesium.GeometryAttribute({
            componentDatatype : Cesium.ComponentDatatype.DOUBLE,
            componentsPerAttribute : 3,
            values : Cesium.Cartesian3.packArray(positions)
        })
    },
    indices : indices
});
var geometryInstance = new Cesium.GeometryInstance({
    geometry : geometry,
    attributes : {
        color : Cesium.ColorGeometryInstanceAttribute.fromColor(Cesium.Color.YELLOW)
    }
});
var primitive = new Cesium.Primitive({
    geometryInstances : [geometryInstance],
    appearance : new Cesium.PerInstanceColorAppearance({
        flat : true,
        translucent : false
    })
});
viewer.scene.primitives.add(primitive);

//移动相机
var camera = viewer.camera;
var scratchCartesian1 = new Cesium.Cartesian3();
var scratchCartesian2 = new Cesium.Cartesian3();
var scratchCartesian3 = new Cesium.Cartesian3();
var scratchMatrix = new Cesium.Matrix4();
var scratchFrustum = new Cesium.PerspectiveFrustum();
viewer.clock.onTick.addEventListener(function(clock) {
    var time = clock.currentTime.secondsOfDay;
    var distance = 100000.0;
    var angle = Cesium.Math.toRadians(time * 10);
    var direction = new Cesium.Cartesian3(Math.cos(angle), Math.sin(angle), 0.0);
    var position = Cesium.Cartesian3.add(camera.position, Cesium.Cartesian3.multiplyByScalar(direction, distance, scratchCartesian1), scratchCartesian2);
    var target = Cesium.Cartesian3.add(position, Cesium.Cartesian3.negate(camera.direction, scratchCartesian3), new Cesium.Cartesian3());
    var up = new Cesium.Cartesian3(0.0, 0.0, 1.0);
    var right = Cesium.Cartesian3.cross(camera.direction, up, new Cesium.Cartesian3());
    var transform = Cesium.Matrix4.computeView(position, target, up, right, scratchMatrix);
    camera.setView({ transform : transform });
    frustum.setTransform(transform);
    positions = new Cesium.Cartesian3.fromArray(frustum.computeCullingVolume().getPlanes()[0].getRectangle().vertices);
    var attributes = geometry.attributes;
    attributes.position.values = Cesium.Cartesian3.packArray(positions);
    geometry = new Cesium.Geometry({
        attributes : attributes,
        indices : indices
    });
    geometryInstance = new Cesium.GeometryInstance({
        geometry : geometry,
        attributes : {
            color : Cesium.ColorGeometryInstanceAttribute.fromColor(Cesium.Color.YELLOW)
        }
    });
    primitive = new Cesium.Primitive({
        geometryInstances : [geometryInstance],
        appearance : new Cesium.PerInstanceColorAppearance({
            flat : true,
            translucent : false
        })
    });
    viewer.scene.primitives.remove(primitive);
    viewer.scene.primitives.add(primitive);
});

在这个示例中，我们首先创建了一个PerspectiveFrustum对象，并将其应用于相机的位置、方向和上向量，从而得到相机的视野范围。然后，我们使用相机的setView方法，将相机的位置和方向设置为一个新的值，以实现相机的移动。接下来，我们使用新的相机位置和方向，重新计算视锥体的顶点位置，并更新视锥体的线框模型。最后，我们将该模型从场景中移除，并再次添加到场景中，以更新视锥体的显示。

注意：视锥体的顶点位置是根据相机的位置和方向计算得出的，因此当相机移动时，视锥体的顶点位置也会发生变化。