Remove THREE.Group() and replace with THREE.Object3D().

[J-Rojas]

Groups change the render sort order globally, so using these in model loading may cause unintended side-effects.

[jihoonl]

It looks like original code still uses Group(). ColladaLoader.js OBJLoader.js

Would you PR on the main repo as well to check if it would cause side effect? This code is basically a copy from main repo with small changes for z-axis hack.

[J-Rojas]

Sure, I can try, however those are just meant as examples, not production level code. They are slow to merge changes at the moment because they are doing a huge refactor.

More context: Group is identical to Object3D, except it creates a new condition for the render order in the scene. The render list is a globally sorted list and it prioritizes Groups first over Object3Ds. If you load a model and try to include it into a Group with a non-zero renderOrder, these internally generated Groups model will be rendered in ways that are unexpected due to the global render sorting. The groups here really bear no significance since they have renderOrder == 0 and they aren't intended to manage the render order in anyway, so this change avoids this potential side effect.

[J-Rojas]

See this PR. This gentlemen would like to address the strangeness of the global rendering order. His PRs have been ignored.

mrdoob/three.js#19526

[jihoonl]

I see. Ok thanks for the explanation.