Ellipse entity not changing position continuously in animation

I have an entity with ellipse graphics like this:
var start = viewer.entities.add({

name: ‘Start’,

position: cartesianArray[0],

ellipse: {

semiMinorAxis: 30,

semiMajorAxis: 30,

material: Cesium.Color.BLACK.withAlpha(1.0)




Now i have an array of interpolated points on which i would like to move this entity in animation. To change the position of entity i call
start.position = newposition


But this doesn’t work, it only changes the position of the entity on last array element of points (on last animation frame) for all the calls in between it remains on same position (starting position). The same code worked for billboards. I don’t know why it doesn’t work with ellipse. Please help.


Here is an example for how to move an ellipse using a CallbackProperty:

var viewer = new Cesium.Viewer(‘cesiumContainer’);

var lon = -120;
var lat = 40;

function getPosition() {
lon += 0.05;
return Cesium.Cartesian3.fromDegrees(lon, lat);

position: new Cesium.CallbackProperty(getPosition, false),
ellipse : {
semiMinorAxis : 300000.0,
semiMajorAxis : 300000.0,
material : Cesium.Color.BLUE.withAlpha(0.8)