Centering a glTF geometry

No, you just have to pass a vector to Box3.getCenter() since the method expects the result object as a parameter.

Um, this method should work since it is actually used in the following viewer: https://gltf-viewer.donmccurdy.com/

Is your object centered when you drag it into the viewer? Besides, check out the code in this post: Model not casting/receiving shadows - #9 by Mugen87