How to get correct distance between tracked entity and camera in Cesium Js?

Question

I want to get distance between an entity and camera in meters. To achieve that I'm passing cartesian3 positions of camera and entity in Cesium.Cartesian3.distanceSquared. It seems distance is calculating properly when the entity is not being tracked. But Tracked entity distance seems higher even though the camera is nearly moving along with the tracked entity.

I'm not getting how to get correct distance between any entity (tracked/without tracked) and camera.

Entity can be anywhere on earth or in air and distance should not be the travelling distance.

viewer.clock.onTick.addEventListener(function (clock) {
  let epos = entity.position.getValue(clock.currentTime);
  let campos = viewer.camera.position;
  let distancebetween = Cesium.Cartesian3.distanceSquared(epos, campos);
  if (viewer.trackedEntity){
    console.log("Tracked:" + distancebetween);
  }else{
    console.log("NotTracked:" + distancebetween);
  }
});

Here is the Sandcastle link of what I'm trying to do.

emackey · Accepted Answer · 2022-01-03 19:28:42Z

0

You might have better luck using the camera's "world position" rather than its position within its own current coordinate frame. For example:

let campos = viewer.camera.positionWC;

I don't recommend using fields starting with an underscore, such as _positionCartographic. Those are intended to be private variables, and can change between Cesium releases without any notice.

answered Jan 3, 2022 at 19:28

emackey

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Jacky · Accepted Answer · 2022-01-03 15:13:20Z

0

I don't know why distance between camera position Cartesian3 value and entity Cartesian3 value is not correct. However, I have sorted out that converting Camera's Cartographic position to Cartesian3 is calculating correct distance.

Replaced:

let campos = viewer.camera.position;

with

let camPosCart3 = Cesium.Cartographic.toCartesian(viewer.camera._positionCartographic);

and it is working fine.

It would be appreciable if someone would have any explanation on this.

Regards,

answered Jan 3, 2022 at 15:13

Jacky

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