How to create an ellipse around Earth (satellite trajectory) ?

CesiumJS
1

I would like to create an ellipse that goes all around Earth, to represent a satellite' trajectory. I would like to give it a center, a semi major axis, a semi minor axis, an inclinaison. I have done this code, but it gives something not perfectly around Earth, or not properly located. I haven't found any answers on the internet since a week of research.

Perhaps, I should locate the center with Cartesian Coordinates but I don't know how, it seems that all objects are located with longitude, latitude and not x, y,z on cesium.

var greenCircle = viewer.entities.add({
    position: Cesium.Cartesian3.fromDegrees(90, 0),
    name : 'Green circle at height with outline',
    ellipse : {
        semiMinorAxis : 7000000.0,
        semiMajorAxis : 11000000.0,
        fill: false,
        outline: true,
        outlineColor: Cesium.Color.YELLOW,
        outlineWidth: 2.0

    }
});

2

Hi there,

When we render satellite trajectories in Cesium, we use Polylines with the pre-calculated positions. Here’s a quick example:

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

var semiMinorAxis = 7000000.0;

var semiMajorAxis = 11000000.0;

var positions = ;

for (var i = -180; i <= 180; i+=10) {

var axis = semiMinorAxis + Math.cos(i * Math.PI / 180.0) * (semiMajorAxis - semiMinorAxis);

positions.push(Cesium.Cartesian3.fromDegrees(i, 0, axis));

}

var entity = viewer.entities.add({

polyline : {

    positions : positions,

    followSurface : true,

    width : 4,

    material : Cesium.Color.RED

}

});

viewer.zoomTo(viewer.entities);

``

Thanks,

Gabby

1 Like
3

First, I wanted to thank @Gabby_Getz for this incredibly helpful response – I have been trying to figure this out and I don’t know how I haven’t seen this until now! I just wanted to fix the formatting. I should warn, however, that my use case only needed 2GB of RAM when I used SampledPositionProperty, but attempted to eat an entire 15GB when I tried to do the same thing with polylines. For context, I was visualizing the path of ~13,000 satellites. Even if you don’t have a ton of entities, I would recommend using SampledPositionProperty anyways since it gives you the option for animation.

With the disclaimer out of the way:

var viewer = new Cesium.Viewer(‘cesiumContainer’);
var semiMinorAxis = 7000000.0;
var semiMajorAxis = 11000000.0;
var positions = [];
for (var i = -180; i <= 180; i += 10) {
  var axis =
    semiMinorAxis +
    Math.cos(i * Math.PI / 180.0) * (semiMajorAxis - semiMinorAxis);
  positions.push(Cesium.Cartesian3.fromDegrees(i, 0, axis));
}
var entity = viewer.entities.add({
  polyline: {
    positions: positions,
    followSurface: true,
    width: 4,
    material: Cesium.Color.RED
  }
});

viewer.zoomTo(viewer.entities);