how to get the boundingSphere for a whole scene in three.js?

Question

How to get the bounding sphere for a whole scene in three.js? I may try to get the bounding sphere for each object and compute the resulting union of them, but I think there may be a more straight forward method.

Answer 1

There are different methods to get a boundingSphere of multiple objects dynamically. You can get first the bounding box of all of them, and then create a sphere of that bounding box... here is a sample fiddle I have shaped on boundingSphere of a boundingBox.

Basically you put all the geometries into a Group, you get the Box3 of the group, and then you do getBoundingSphere from the Box3 and position at the center. Code in the fiddle would be this.

let g = new THREE.Group();
scene.add(g);
for (let i = 0; i < 5; i++) {

    // geometry
    var geometry = new THREE.BoxGeometry(20, 20, 20);

    // material
    var material = new THREE.MeshToonMaterial({
        color: 0xff0000,
        opacity: 0.7,
    });

    // mesh
    mesh = new THREE.Mesh(geometry, material);
    mesh.position.set(100 * Math.random(), 100 * Math.random(), 100 * Math.random());
    g.add(mesh);
}

//g.updateWorldMatrix(true);
var gridHelper = new THREE.GridHelper(400, 40, 0x0000ff, 0x808080);
gridHelper.position.y = 0;
gridHelper.position.x = 0;
scene.add(gridHelper);

let bbox = new THREE.Box3().setFromObject(g);
let helper = new THREE.Box3Helper(bbox, new THREE.Color(0, 255, 0));
scene.add(helper);

const center = new THREE.Vector3();
bbox.getCenter(center);

let bsphere = bbox.getBoundingSphere(new THREE.Sphere(center));
let m = new THREE.MeshStandardMaterial({
    color: 0xffffff,
    opacity: 0.3,
    transparent: true
});
var geometry = new THREE.SphereGeometry(bsphere.radius, 32, 32);
let sMesh = new THREE.Mesh(geometry, m);
scene.add(sMesh);
sMesh.position.copy(center);

EDITED: If you want to include in the boundingSphere for the scene including the lights (which could get you a huge sphere), just start from let bbox = new THREE.Box3().setFromObject(scene)