如何检查铯实体是否可见/被遮挡

Question

Given an Entity, I'm trying to figure out if at a particular moment/frame, if one of the entities is viewable on the screen.

The closest I could find was Entity.isVisible, but it seems to just tally the explicit show properties. It returns true even if...

• Transparency is 0%
• The Entity is out of frame (eg. above the viewable area)
• The Entity is occluded (eg. on the other side of the Earth)

I also can't find any functions to convert the entity position to viewport coordinates to test if it is at least within the camera view cone.

I had one idea to measure the distance between the entity and the camera kinda like this Cesium.Cartesian3.distance(this.viewer.selectedEntity.position.getValue(Cesium.JulianDate.now()), this.viewer.camera.position); But obviously the acceptable distance needs to be based on the camera height, FOV and if the camera is even looking in that direction. I haven't yet been able to get the math to work for this solution.

How can I tell if an Entity is currently visible to the user?

Answer 1

One of the ways is to use BoundingSphere in the frustum culling. Then check if the bounding sphere of the entity is visible in the culling volume.

const viewer = new Cesium.Viewer('cesiumContainer');
const camera = viewer.camera;

const position = Cesium.Cartesian3.fromDegrees(23.9036, 54.8985);

const frustum = camera.frustum;
const cullingVolume = frustum.computeCullingVolume(
  camera.position,
  camera.direction,
  camera.up
);

const someEntity = viewer.entities.add({
    name: 'Some Point',
    position: position,
    point: {
        pixelSize: 14,
        color: Cesium.Color.GREEN
    }
});

// Bounding sphere of the entity.
let boundingSphere = new Cesium.BoundingSphere();
viewer.dataSourceDisplay.getBoundingSphere(someEntity, false, boundingSphere);

// Check if the entity is visible in the screen.
const intersection = cullingVolume.computeVisibility(boundingSphere);

console.log(intersection)
//  1: Cesium.Intersect.INSIDE
//  0: Cesium.Intersect.INTERSECTING
// -1: Cesium.Intersect.OUTSIDE

I have also made a Cesium Sandcastle example .