Maya - Zbrush : FBX Import/Export consistently breaks random polygons into tris and splits vertices

Alex_J

I am working between Maya LT 2018 and Zbrush 2018, however this is an issue I've come across time and again when I was working in Zbrush 4r8 as well. 

Simply, I export an fbx with standard settings from Maya, and when I import it into Zbrush, you get what you see in the picture. Seemingly random quads will be split and vertices will be disconnected. I can't find an answer with google, so I'm hoping somebody here may have had the problem and solved it. My guess is a simple bug related to the newer versions communicating with eachother? I'll do some troubleshooting with different FBX versions, but it would be nice to know what is really going on.
*Update: link to Zbrush Central support thread : here
*Update: Tried different FBX versions and an OBJ export, same results. I tried initializing zbrush, same results. One curious thing is that I had applied a color fill in zbrush to part of the object, and even though I have changed material ID's inside Maya, that color fill returns even when I reimport the FBX again. So there is some kind of information traveling from Zbrush to Maya, separate from the material ID, and it's sticking around even when I edit the mesh, change materials, etc. This could be problem, but I have to figure out what this information is, and how to clear it / reset it.

*** I am not using GoZ.

benjaminredman

Try exporting the mesh as an .OBJ file. That may solve this issue.

Alex_J

Thanks for the reply. I forgot to add in the update that I did export as an OBJ, but the broken polygons still remained. Additionally, sometimes more than half of the model will be blackened, like the face normals were inverted, but it clears away with a touch of the smooth brush. In fact, the face normals are all correct, and this further leads me to believe there is some bit of information Zbrush is tagging the mesh with that travels with it to maya, and despite what alterations I make in Maya, that information stays there, and then causes conflicts when I bring the mesh back into Zbrush.

I've tried about everything I can think of and have wasted too much time with this issue, so I think it will be worthwhile to go to the Zbrush forums and try and get some official help there. Will update with a solution when I find one. I'm just surprised I cannot find any mention of this particular issue anywhere online.

Alex_J

Got a clean export/import with an OBJ and the following settings : 



I was just shooting in the dark, not sure what point groups refers to, but anyway at least now I can move a mesh around and not have to do clean up every time. Still, I'd like to understand what is really happening behind the scenes and causing my standard FBX workflow to be so screwy.

throttlekitty

I assume that you've checked your mesh before sending to ZB, but you're positive there's no double faces going on here? ie, Box selecting a single face doesn't show two or more in the poly count hud?

From those obj export settings, does this happen if you flip materials back on? I had an issue with maya to to some other software a long-ass time ago that would duplicate faces into a new subobject because of a wonky material assignment. That really shouldn't be an issue with ZB, but it might be worth a shot to remove and reapply your material at object level.

Alex_J

I ran a mesh cleanup in addition to carefully inspecting everything myself. I haven't tried with the OBJ and materials flipped on, but I'll run that test here in a bit. 

About the materials, I am always assigning a material per mesh island. In other words, I don't assign materials via components. In this case, one material covers the entire character except for the head, which is a second material. 

Alex_J

Further info, after I imported the OBJ into zbrush without issues, I did nothing to the mesh, exported as an FBX from Zbrush, and then reimported. Everything A-okay after that. Not sure what that experiment tells me, but it seems I neutralized whatever was causing the issue. 

I'm crunching to get this model done today, but after I get away from it for a minute I'll have to think back and try to figure what, if anything, I did for this model that was unusual from my typical workflow.