How to convert Alt/Az as seen from Earth surface in (x,y,z) position w.r.t Earth center?

General
1

I know how an antenna located on Earth surface is poiting to an object in space, by means of Altitude and Azimuth.

I would like to show the pointed object in the 3d view, so, as far as I can understand, I need its position in (x,y,z) format (Cartesian3 object?)

But I can’t undrestand exactly which is the exact process to follow.

I am using this example to make experiments; I added one point on surface by adding these lines inside function addMultiplePoints() :

viewer.entities.add({
position: Cesium.Cartesian3.fromDegrees(290.6, -35.78),
point: {
  color: Cesium.Color.RED,
  pixelSize: 18,
},
label: {
  text: "MLG",
  font: "14px Helvetica",
  pixelOffset: new Cesium.Cartesian2(0.0, 20),    
},
description : "MLG"
});

Now I have to add a point with specific location w.r.t this point, say Alt=30, Az=0.

I am trying with this… but nothing happens; indeed, in this code there is no origin point for the coordinates…

  H2pointing = {"alt" : 30, "az" : 0};
  clock = 90 - H2pointing.az;
  cone = 90 - H2pointing.alt;
  H2spherical = new Cesium.Spherical(clock, cone, 10);
  console.log(clock);
  console.log(cone);
  console.log(H2spherical);
  H2cartesian = Cesium.Cartesian3.fromSpherical(H2spherical, null);


viewer.entities.add({
position: H2cartesian,
point: {
  color: Cesium.Color.BLUE,
  pixelSize: 18,
},
label: {
  text: "Hayabusa2",
  font: "14px Helvetica",
  pixelOffset: new Cesium.Cartesian2(0.0, 20),    
},
description : "Hayabusa2"
});

So, assuming my calculations are right (are they?), how do I center this point on previous point?

note: “cone” and “clock” are defined in documentation https://cesium.com/docs/cesiumjs-ref-doc/Spherical.html

  • “clock” The angular coordinate lying in the xy-plane measured from the positive x-axis and toward the positive y-axis.

  • “cone” the angular coordinate measured from the positive z-axis and toward the negative z-axis.

  • “magnitude” The linear coordinate measured from the origin.