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Smoothing Groups Error - Zbrush to UE4

I have been struggling with the issue of smoothing groups since last weekend when my FBX files created with Zbrush 4r7 returned the following error once imported to Unreal Engine 4:

Warning: No smoothing group information was found in this FBX....

I having been searching everywhere for the past few days now and I have not found any advice for Zbrush users. Only export advise for users of other applications. I am really hoping that someone here knows more or can point me in the right direction!

These are the key questions that I am struggling with:

  • What is a smoothing group?

  • Should I be using/worrying about them?

  • How does Zbrush handle them? (or do I need to use Blender?)

  • At what point in the workflow should they be assigned?

  • Do all of my game models for UE4 need smoothing groups?

Product Version: UE 4.11
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asked May 09 '16 at 02:03 PM in Using UE4

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Crixus
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2 answers: sort voted first

Hi Crixus,

In Zbrush smoothing groups are called poly groups. This link will show you how to create them.

https://www.youtube.com/watch?v=6AfV2hmSmqo

Smoothing groups are something that are very necessary on some models and not so important on others. If your model is of an organic nature you will definitely need them. If your model is mainly hard angles, then they wont mean as much. That being said, I almost always use them. Without them sometimes you can see the individual triangles in the geometry once its imported into the engine. Although you can create smoothing groups in Zbrush, I personally think its easier to make them in an external program like Maya, Max, or Blender. They are something that can change as you model, but using them from the beginning can be useful. In Max they are assigned automatically be default. You can of course change it if you like, but normally the defaults work fine. There are some instances where customizing your smoothing groups will be necessary in order to have accurate smoothing.

I don't know if Blender automatically exports them, but I'm pretty sure that Zbrush does if they exist. In 3ds Max you actually have to check it in the export dialog, so it might be like that in Blender as well. This is an image taken from the Autodesk website demonstrating smoothing groups.

alt text

Hope this helps :)

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answered May 10 '16 at 04:18 AM

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worldlearner0411
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avatar image Crixus May 10 '16 at 01:20 PM

Firstly, thank you for your answer, it has helped clarify some things. Unfortunately where I started out just creating concept art I did not learn about all of the important aspects of 3d asset creation for games.

I had heard something about being able to assign smoothing groups by polygroup, however polygroups themselves are not smoothing groups. All of my models have polygroups, Hard surface or not. But I have no idea how to assign smoothing groups based on those polygroups.

I am starting to see why smoothing groups are necessary for some models. For example I have a handgun which looks great in the insanely high poly concept art I made, but the actually game asset does not look right around the grip area and im sure having one smoothing group for the polys of the grip will fix this.. I guess the question left now is how!

PS I might be getting Maya LT for animation purposes (still need to see what has been trimmed down from Maya) So if you know of any videos demonstrating how to assign smoothing groups in maya and then export them for UE4 it could be really useful.

avatar image worldlearner0411 May 10 '16 at 02:03 PM

I apologize...I must have been mistaken. I was under the impression that poly groups were smoothing groups, however under careful thought I realized that I have always used poly groups under the context of smoothing groups. Poly groups can be created using smoothing groups so I assumed it was the same thing :) honest mistake.

This link will show you how to create smoothing groups inside of Maya:

https://www.youtube.com/watch?v=a1hOFIGatgc

This link will show you how to export in Maya:

https://knowledge.autodesk.com/support/maya-lt/learn-explore/caas/CloudHelp/cloudhelp/2016/ENU/MayaLT/files/GUID-51B5F746-12B0-4AB5-9701-A0A740D0ADA5-htm.html

Exporting the smoothing groups I would imagine would be in the export dialog box somewhere. That being said, since Maya does not have any formal smoothing groups (according to the video) it might just export them automatically as the normals of the object.

The documentation showing how to export from Maya LT says that you you have a limited poly count on exports not going to UE4, but that if you go directly to UE4 the restriction is lifted. (and it shows how to do this)

Good luck :)

avatar image Crixus Jun 17 '16 at 08:10 PM

Thank you worldlearner0411, your replies have been very helpful. I really do appreciate it.

On further research it turns out that ZBrush does not have an equivalent tool to the smoothing groups in 3DS Max, however, I have been using Maya LT for some animation work and the way it handles smoothing groups by defining hard and soft edges is really easy and intuitive. Thanks again!

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Ok, so first off, while I have very little experience in Zbrush, I do have plenty in other apps such as Maya/MODO/Blender. Smoothing groups on export is usually something we would set. The fact that you do not know what smoothing groups are when working with game art is quite crucial. Smoothing groups allow polygons on a mesh to basically appear smooth on the surface, rather than let's say jagged or well not smooth. TBH, I wouldn't worry too much about smoothing groups, what I would be worrying about is if you are optimizing your mesh form hi-poly to low-poly. If your mesh looks fine without them, good to go, if the deform in strange way while animating, then you should figure out how to export them with smoothing groups if possible. but yes another way would be to import them to Blender and then export with Smoothing Group option.

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answered May 09 '16 at 05:00 PM

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VictorBurgos
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