Issues working SubD UVs, imported and native Rhino 7

Hi All,

I’m having some issues trying to get the exact unwrap for organic products.

If the model comes from Modo, where you can edit the UV in hard and soft mode with the same number of points, you can see that it looks perfect in the native program, but once you import it in Rhino, the UVs are preserved but don’t look right when you convert the mesh to SubD.
The other problem is that the UV Editor doesn’t let you edit the UVs in Soft mode, it only remembers the original UVs that probably create that strange look on the soft surfaces.
I don’t know if there is an option when you convert the obj to subD that gives better results.

The other way to deal with this was extracting the control poly from the obj in Rhino and do the unwrap again. The result is much better, but it comes with a new problem, the UV editor shows a subdivided version of the SubD that makes the adjustment of points far more complicated than with just the real control points.

What do you think?

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@Jussi_Aaltonen - do you have any comment/opinion on this? Thanks…

-Pascal

@laborda

Hi, I will need to investigate this. It looks as if Modo and Rhino interpolate texture coordinates along SubD faces in a different way.

Could you send me that garment model right after importing it into Rhino? If you don’t want to share that file in public you can upload directly to me using our upload page.

What file format you use to export from Modo?

Rhino doesn’t do nativa UV-editing of SubD vertex texture coordinates. Unwrap and UVEditor work by applying the texture coordinates to a lower subdivision level of the SubD object render mesh and setting that mesh as a custom mapping primitive to the SubD object. That is what you see when you run UVEditor.

Thanks @Jussi_Aaltonen

You can try importing the obj file created in Modo.

Mesh from Modo.obj (8.3 KB)

I found a strange behavior of the UVeditor depending on the order you use it.
If you check the Modo mesh first in UVeditor and then convert it to SubD, the editor shows a non-divided mesh, but if you convert the original mesh directly to SubD the result is subdivided.

The way UVEditor works is causing lots of confusion.
When you start the UVEditor you see two meshes:

  1. The mesh that substitutes the object itself and previews how the UV’s look in 3d
  2. Flat meshes in UV space that you can edit
    image

Those meshes are generated based on either

  1. custom mesh mapping primitive if selected channel has Custom object mapping,
  2. low level subdivision render mesh if object is a SubD or
  3. the object render mesh.

Custom object mapping is applied as soon as you click on Apply on the UVEditor or when you run Unwrap.

So if you run UVEditor on the imported mesh and click Apply then from that on the object has a custom object mapping with a copy of that mesh as the custom mapping primitive. And when you then make a SubD from that mesh object that new SubD will have the exact same custom object mapping with that same mesh primitive.

We will investigate the possibilities for native SubD vertex UV editing in Rhino 8 RH-65620

Thanks for the file @laborda
I logged a bug for this: RH-65621 SubD vertex texture coordinate interpolation not compatible with Modo

Thanks @Jussi_Aaltonen for the explanation and support, I wish you find a solution for these issues because it’s really difficult to handle UVs from SubD models right now, and even more complicated if it comes from Modo.

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