# Copying UVs from a high to low poly model?

I am working on several projects where each mesh has 3 LOD levels.

Originally I completed the Highest poly model, applied materials, uv mapped each mesh, duplicated the object and then optimized the duplicate. This worked fine and the material and UVs were set the same on all LODs.
Now I have been told that each object should only have one material and UV map. If I was simply to remove the materials the end result would be overlapping UVs, which is not acceptable obviously.

So I now face trying to match up the UVs from all the object LODs.Is there a way to copy the UVs from one object to another that has a different number of poly?

• I don't think you are understanding. I applied materials the the original object, and unwrapped the the uvs for each material effectively creating multiple uv maps per object. The object was then duplicated and edge lops were removed lowering the detail and poly. this will not damage your uv mapping so long as you do not move or add verts, you can however remove edge loops so long as they are not the seam edges. – Rabecca LaMont-likens Mar 29 '16 at 22:43
• Now the issue is that I must remove all but one material, thus causing the uvs to over lap, as each material was mapped individually and took up the full 1024 space. this would be simple if I only had one object to consolidate the maps for. How ever now I have 3 objects, essentially the same but with each having fewer total poly. Each objects UV Islands must share the same space on the map, allowing the textures made for the high poly model to also work for the lower poly ones with out the use of additional textures. Such as would be created when baking from a high poly model to a lower one. – Rabecca LaMont-likens Mar 29 '16 at 22:59
• It's absolutely not clear then what's the problem. If you only deleted edge loops from the unwrapped duplicated mesh, the UV mapping indeed won't be changed much; only that loop will dissappear, hence no changes can occur to texture mapping. UV mapping does not depend on materials, probably you're talking about textures. – Mr Zak Mar 29 '16 at 23:06
• This I think would be easier to explain If I could show you. unfortunately I have know way of doing so. But I thank you for attempting to understand my dilemma. – Rabecca LaMont-likens Mar 29 '16 at 23:19
• Maybe you want to work on your object until it satisfies the lowpoly lod level, then unwrap and duplicate, and add a subdivide modifier with the option 'subdivide uv' off. This way all you object will have the same uv layer – Yvain Mar 30 '16 at 11:22

You can try the "transfer data" tool (the modifier also works, sometimes...).

Here is a "HD" mesh with UV and texture

And here is a LD mesh without UV

Select your LD mesh first and then add your HD mesh to the selection with Shift+Right click. The last selected object is considered as active.
Open the tools bar with T. In the Tool tab, scroll to Edit and click on "Data Transfer: DATA" button

Choose the options that looks the best.

The UV has been transferred from the HD mesh to LD mesh.

Now you can create the seams from UV islands from the UV menu in image editor.

The LD mesh has Seams, UV and the texture is OK

• Selections are made with shift + left click, right click as indicated in this description. – Victor S Apr 5 at 19:45

Maybe you want to work on your object until it satisfies the lowpoly lod level, then unwrap and duplicate, This way all the objects copied from this one will have the same uv layer. After you can add a subdivide modifier with the option 'subdivide uv' off or cut loops yourself.

btw about: "each object should only have one material and UV map. If I was simply to remove the materials the end result would be overlapping UVs". You may have to use a same texture in multiple fashion on your mesh so having multiple uv layers can be necessary, in any case if you remove the material from the mesh you will have a default grey solid color but it has no influence whatsoever on your uvs. cheers

• the texture department are using PBR texturing the uvs can not over lap in any way. As for my issue I'm having a great deal of difficulty explaining this. The best way I can think of is this. Consider each material a separate mesh, making up a full building. Originally the building was split into parts to aloe for better resolution when the textures were made. This how ever this is proves to use to much resources for real time rendering.So I mush join all the parts and consolidate to one UV map. – Rabecca LaMont-likens Mar 31 '16 at 18:18
• This would be simple if I only had to do this for one LOD (Level Of Detail) Model but each model had a min of 3 LODs. the same texture must be able to be applied to all 3 LODs. If this was done with cycles rendering for film, or a 2d print this would not be an issue, but this is for a multi player video game. – Rabecca LaMont-likens Mar 31 '16 at 18:23
• So you want to bake a texture that contains the info for all your objects's materials ? if you add an uv layer for each object and make it small (comparing to the size of the image you will need) and bake while having set the new uv layer to active for rendering, the texture will create according to it so each of your meshes should be unwrapped and placed at its proper place (which means it wont overlap with another object) on the uv layout. You will have to do a lot of baking to one single image – Yvain Mar 31 '16 at 19:13
• Of course you must unwrap the new uv layer, once for each object and no you can't copy uv layers. – Yvain Mar 31 '16 at 19:45
• No you miss understand, I'm sorry I can't find a way to explain with out showing you I guess. I can't seem to find a way to explain it properly. I'm not baking anything I don't do any of the texture work. Thank you every one for your time in trying to help me it is greatly appreciated. – Rabecca LaMont-likens Mar 31 '16 at 22:58