computeBoundingBox() {

		const geometry = this.geometry;
		const count = this.count;

		if ( this.boundingBox === null ) {

			this.boundingBox = new Box3();

		}

		if ( geometry.boundingBox === null ) {

			geometry.computeBoundingBox();

		}

		this.boundingBox.makeEmpty();

		for ( let i = 0; i < count; i ++ ) {

			this.getMatrixAt( i, _instanceLocalMatrix );

			_box3.copy( geometry.boundingBox ).applyMatrix4( _instanceLocalMatrix );

			this.boundingBox.union( _box3 );

		}

	}
Computes the bounding box of the instanced mesh, and updates {@link InstancedMesh#boundingBox}.
The bounding box is not automatically computed by the engine; this method must be called by your app.
You may need to recompute the bounding box if an instance is transformed via {@link InstancedMesh#setMatrixAt}.