computeBoundingBox() {

		if ( this.boundingBox === null ) {

			this.boundingBox = new Box3();

		}

		const boundingBox = this.boundingBox;
		const instanceInfo = this._instanceInfo;

		boundingBox.makeEmpty();
		for ( let i = 0, l = instanceInfo.length; i < l; i ++ ) {

			if ( instanceInfo[ i ].active === false ) continue;

			const geometryId = instanceInfo[ i ].geometryIndex;
			this.getMatrixAt( i, _matrix$1 );
			this.getBoundingBoxAt( geometryId, _box$1 ).applyMatrix4( _matrix$1 );
			boundingBox.union( _box$1 );

		}

	}
Computes the bounding box, updating {@link BatchedMesh#boundingBox}.
Bounding boxes aren't computed by default. They need to be explicitly computed,
otherwise they are `null`.