更新 cesium polylinegeometry position

要更新Cesium PolylineGeometry的位置，您可以使用以下步骤：

1. 获取现有的PolylineGeometry对象：

var polylineGeometry = polyline.geometry;

2. 获取现有的位置数组：

var positions = polylineGeometry.positions;

3. 更新位置数组中的值：

positions[0] = Cesium.Cartesian3.fromDegrees(lon1, lat1, height1);
positions[1] = Cesium.Cartesian3.fromDegrees(lon2, lat2, height2);
// 更改其他位置...

4. 将更新后的位置数组设置回PolylineGeometry对象：

polylineGeometry.positions = positions;

5. 更新PolylineGeometry对象的外观：

polyline.appearance = new Cesium.PolylineMaterialAppearance({
    material: Cesium.Material.fromType('Color', {
        color: Cesium.Color.YELLOW
    })
});

完整示例代码如下：

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

// 添加Polyline
var polyline = viewer.entities.add({
    name: 'Polyline',
    polyline: {
        positions: Cesium.Cartesian3.fromDegreesArrayHeights([
            -75, 35, 0,
            -125, 35, 0
        ]),
        width: 10,
        material: Cesium.Color.YELLOW
    }
});

// 获取现有的PolylineGeometry对象
var polylineGeometry = polyline.geometry;

// 获取现有位置数组
var positions = polylineGeometry.positions;

// 更新位置数组中的值
positions[0] = Cesium.Cartesian3.fromDegrees(-75, 40, 0);
positions[1] = Cesium.Cartesian3.fromDegrees(-125, 40, 0);

// 将更新后的位置数组设置回PolylineGeometry对象
polylineGeometry.positions = positions;

// 更新PolylineGeometry对象的外观
polyline.appearance = new Cesium.PolylineMaterialAppearance({
    material: Cesium.Material.fromType('Color', {
        color: Cesium.Color.RED
    })
});