Cesium Z軸0の円サンプル

const viewer = new Cesium.Viewer("cesiumContainer");
const entities = viewer.entities;
const scene = viewer.scene;
const globe = scene.globe;
/*
  globe.showGroundAtmosphere = false;
  globe.baseColor = Cesium.Color.TRANSPARENT;
  globe.translucency.enabled = true;
  globe.undergroundColor = undefined;
const baseLayer = viewer.scene.imageryLayers.get(0);
  baseLayer.colorToAlpha = new Cesium.Color(0.0, 0.016, 0.059);
  baseLayer.colorToAlphaThreshold = 0.2;
*/

// X,Yの円 (x−a)2+(y−b)2=r2
// 中心緯度経度 36,135,
// 半径300,000 m
let Hankei = 300000;
let Ido = 90.0;
let Keido = 135.0;

let centerXYZ = new Cesium.Cartesian3.fromDegrees(Keido, Ido);

// 中心ポイント
const centerPoint = viewer.entities.add({
  position: Cesium.Cartesian3.fromDegrees(Keido, Ido),
  ellipsoid: {
    radii: new Cesium.Cartesian3(10000.0, 10000.0, 10000.0),
    material: Cesium.Color.RED,
  },
});

console.log("center:"+centerXYZ);

let line_XY = [];

for( let theta = 0; theta <= 360; theta+= 40 ){
  
  let radi = theta * (Math.PI / 180)
  let X = centerXYZ.x + Hankei * Math.cos(radi);
  let Y = centerXYZ.y + Hankei * Math.sin(radi);

  line_XY.push(new Cesium.Cartesian3.fromElements(X, Y, centerXYZ.z));

  
  let point =  viewer.entities.add({
    position: Cesium.Cartesian3.fromElements(X, Y, centerXYZ.z),
    ellipsoid: {
      radii: new Cesium.Cartesian3(10000.0, 10000.0, 10000.0),
      material: Cesium.Color.YELLOW,
    },
  });
}

let line_Z_0 =  viewer.entities.add({
    polyline: {
      positions: line_XY,
     }
  });

viewer.zoomTo(viewer.entities);