Any way to get a bounding box from a three.js Object3D?

Question

I\'m loading an OBJ file using Three.js and OBJLoader.js. This returns a Three.Object3D object, which has what you\'d expect from a 3D model (position vector, up vector...)

Answer 1

Yes you would need something like this:

if (object instanceof THREE.Object3D)
{
    object.traverse (function (mesh)
    {
        if (mesh instanceof THREE.Mesh)
        {
            mesh.geometry.computeBoundingBox ();
            var bBox = mesh.geometry.boundingBox;

            // compute overall bbox
            minX = Math.min (minX, bBox.min.x);
            minY = Math.min (minY, bBox.min.y);
            minZ = Math.min (minZ, bBox.min.z);
            maxX = Math.max (maxX, bBox.max.x);
            maxY = Math.max (maxY, bBox.max.y);
            maxZ = Math.max (maxZ, bBox.max.z);
        }
    });

    var bBox_min = new THREE.Vector3 (minX, minY, minZ);
    var bBox_max = new THREE.Vector3 (maxX, maxY, maxZ);
    var bBox_new = new THREE.Box3 (bBox_min, bBox_max);

    scene.add (object);
}

EDIT:

This method is before the BoundingBoxHelper() or BoxHelper() were available

Answer 2

You don't need to iterate over all children of the object; there's a method in the library to do this: THREE.Box3#setFromObject: see the docs. For example, you can do:

var bbox = new THREE.Box3().setFromObject(obj);

to get the bounding box of obj, including all of its children, and accounting for any translations, rotations, etc.

Note that the BoundingBox helper is intended to draw a bounding box in the scene, not for just calculating the bounding box of some object.

Answer 3

For any shape, on its geometry object, there is a boundingBox property. This property holds a THREE.Box3 object. This Box3 object consists of two THREE.Vector3 objects, min and max.

var geometry = new THREE.CylinderGeometry(...);
var material = new THREE.LineBasicMaterial(...);
var mesh = new THREE.Mesh(geometry, material);

var boundingBox = mesh.geometry.boundingBox.clone();
alert('bounding box coordinates: ' + 
    '(' + boundingBox.min.x + ', ' + boundingBox.min.y + ', ' + boundingBox.min.z + '), ' + 
    '(' + boundingBox.max.x + ', ' + boundingBox.max.y + ', ' + boundingBox.max.z + ')' );

For more complex shapes, like those loaded from JSON Object files, the bounding box property is undefined by default. It must be computed explicitly.

var loader = new THREE.ObjectLoader();
loader.load(imagePath, function(object){

    geometry = object.children[0].children[0].geometry;  // substitute the path to your geometry

    geometry.computeBoundingBox();  // otherwise geometry.boundingBox will be undefined

    var boundingBox = geometry.boundingBox.clone();
    alert('bounding box coordinates: ' + 
        '(' + boundingBox.min.x + ', ' + boundingBox.min.y + ', ' + boundingBox.min.z + '), ' + 
        '(' + boundingBox.max.x + ', ' + boundingBox.max.y + ', ' + boundingBox.max.z + ')' );
}

Answer 4

If you want the bounding box position and size as the object appears in the scene, try the BoundingBoxHelper:

var helper = new THREE.BoundingBoxHelper(someObject3D, 0xff0000);
helper.update();
// If you want a visible bounding box
scene.add(helper);
// If you just want the numbers
console.log(helper.box.min);
console.log(helper.box.max);

The .boundingBox on the geometry doesn't account for translations, rotations, or scaling that may be applied to the parent mesh and etc. and I found it very difficult to adjust for that manually, but the helper does it for you.