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UV unwrap crashes ZBrush

ZBrush Usage Questions
#1

Hi:) I want to unwrap a high poly mesh of a castle (ca. 5 million polys) generated from photogrammetry. The mesh is cleaned and retopologized and I tried control painting, but ZBrush crashes every time.

Is there a limit for the polygon count?
How can I define the polygon count to 3 million before zremeshing or subdividing? I can’t type in more than 100.

Unwrapping a lower subdiv version with 140 000 polys doesn’t work either. I extracted a small part of the mesh with only 25 000 polys and the unwrap worked.

Does ZBrush crash because of my not so powerful pc with 8 GB RAM, intel core i7-2700 CPU 3.4 GHz, Windwos 7? All other operations like Sculpting oder ZRemesher worked.
I have another pc (with 16 GB RAM, intel core i7-4770K CPU 3.4 GHz, Windows 8.1 and a Nvidia Quadro K2000D), but the demo trial on this pc is outdated. I am a university student and I use ZBrush only for educational purposes.

If I decimate the mesh to under 3 million polys, too many details are lost and the castle looks undesiraby low res in the Unreal Engine even with a normal map.
My idea is to split the castle into parts, unwrap them separately and put them together, but this would lead to many overlapping parts which I would like to avoid. Is there another workflow for that or would you disadvise me to split the castle?

Or does the unwrap crash ZBrush due to something different?

Kind regards

#2

You do want to have a low polygon count for UV mapping. But that doesn’t mean you have to lose details.

Clone your model and remesh that to a low count like 5, 10 or even 20K polygons. UV map that and then subdivide it to have a number of polygons approximately equal to the original model. Now append the original to the new version and use Project All to copy the details from the source model. Once done you can delete the original.

You will now have a multi-resolution mesh with UV mapping and still have all the details from the original model.

1 Like
#3

Thanks a lot! I will try this immediately

#4

Thank you very much:) It worked perfectly.

Could you please help me with another issue?

I have 6 textures for the one mesh (see screenshot, 6 different jpg files, each has 8k and was generated by the photogrammetry software ReCap).

I remapped one single texture (one uv tile, also generated by ReCap) on to the new uv map (generated by ZBrush) in xNormals. But in that case the whole texture has a 6 times lower resolution, because I only use one 8k texture instead of six 8k textures for the mesh.
I could enlarge the uv shells (generated from ZBrush) and spread them over 6 tiles in Maya, but what do I have to do then?

How can I transfer the 6 existing textures to the new uv map generated by ZBrush?ReCap_8k_Textur3.JPG

#5

I don’t think you can do that in ZBrush as it has only one Texture channel. Unless I am mistaken you will have to make do with one 8k Texture Map.

#6

You would have to split the model into separate SubTools for each texture map.

One thing to keep in mind: An 8K map has 67,108,864 pixels. That means that a model (or in your case, each SubTool) would have to have about 60 million polygons in order to match the detail held by such a map.

#7

Ok I understand, thanks you helped me very much