如何获取cesium上多边行的可视区域的经纬度

要获取Cesium上多边形的可视区域的经纬度，可以使用Cesium的Camera对象和BoundingSphere对象。以下是一个示例代码：

//获取多边形的BoundingSphere对象
var boundingSphere = Cesium.BoundingSphere.fromPoints(polygonPositions);

//获取当前Camera的视图范围
var camera = viewer.camera;
var frustum = new Cesium.PerspectiveFrustum();
frustum.aspectRatio = camera.frustum.aspectRatio;
frustum.fov = camera.frustum.fov;
frustum.near = camera.frustum.near;
frustum.far = camera.frustum.far;
var cullingVolume = new Cesium.CullingVolume(frustum, camera.positionWC);

//获取多边形的可视区域
var visible = cullingVolume.computeVisibility(boundingSphere);

//如果多边形在可视范围内，则获取其经纬度范围
if (visible !== Cesium.Intersect.OUTSIDE) {
  var cartographic = Cesium.Rectangle.fromBoundingSphere(boundingSphere);
  var west = Cesium.Math.toDegrees(cartographic.west);
  var south = Cesium.Math.toDegrees(cartographic.south);
  var east = Cesium.Math.toDegrees(cartographic.east);
  var north = Cesium.Math.toDegrees(cartographic.north);
  console.log(west, south, east, north);
}

在代码中，首先通过多边形的顶点位置创建一个BoundingSphere对象，然后获取当前Camera的视图范围，将其与BoundingSphere对象进行比较，从而确定多边形是否在可视范围内。如果多边形在可视范围内，则使用Rectangle.fromBoundingSphere()方法获取其经纬度范围，并将其转换为度数并打印输出。