lowpoly Uvs warping on highpoly mesh-import uv on higher subdivision?

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  08 August 2013
lowpoly Uvs warping on highpoly mesh-import uv on higher subdivision?

Hi, im creating uvs for an organic shape, however the uvs are warping when moving up the subdivisions.
As i understand the best workflow is to sculpt, retopo, then export base level 0 for uv mapping, then re-import the unwrapped uv map back on to base level 0.
The issue occurs when scrolling back up the subdivisons, because there arn't enough polygons in the base mesh to define all the extrusions that appear on the high poly mesh. So as you move back up the subdivisions, the extrusions are more pronounced, which makes the textures warp. The base mesh is about 600 polys, which is subdivided 4 times.
I managed to get a sort of workaround, I retopologizing so the base mesh was 5000 polys, therefore more detail on the base mesh for uvs = not so much change when moving back up subdivisions = less stretching.
However this obviously leads to many more polygons when moving back up the subdivisions, like 300000 more, which isnt great for keeping polycount low.
It seems strange to only be able to import uvs on base level 0, as the object is obviously going to change as you move back up the sibdivisions, causing textures to warp.
Am i missing something? How do you uv higher subdivion levels to stop texture warping?
I have a couple of images if this isnt clear.
Thanks
 
  08 August 2013
you only have to do a retopo and create uvs for that mesh... bake between the old and the new mesh...
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  08 August 2013
Hi Oglu, thanks for the reply.
Im not sure i understand what you mean? I am only retopoing and uv-ing one mesh. What am i baking between meshes? there is only one mesh?
Is there any chance you could elaborate?
Thanks in advance
 
  08 August 2013
bake the normal or displacement map...
why do need a highres mesh if you dont bake anything...
or the other way around why do you need a lowres if you use the highres for rendering...
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  08 August 2013
Quote: bake the normal or displacement map...
why do need a highres mesh if you dont bake anything...

If i was baking high res detail on to low res(im not - im rendering high res), say a displacement map, would this still cause the textures to stretch, as the uvs are made for the undisplaced surface?
Quote: or the other way around why do you need a lowres if you use the highres for rendering...

I am doing it this way, rendering highres. I thought it was common practice to uv a low res mesh even when rendering a high res mesh? It is much easier to uv map 3000 polys than 3,000,000.
Do i have the workflow wrong?
 
  08 August 2013
if you like to render a still rendering the highres is fine... until you hit the limitations of your computer cause you need hundreds of those objets in one scene...

for animation you need to render the low version and use displacement maps to get it working... you cant animate a million poly creature...

if you like to go the highres route just do a "transfer detail" to get all the detail on your new retopo mesh...
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  08 August 2013
The object is terrain, so it wont be animated, however it will be rendered as part of an animation. Does this mean it should be ok to just render the high res mesh directly in Maya (mental ray) as displacement just adds polys at render time anyway?
wont using transfer detail still cause the uvs to stretch out as that detail is added?
Im still confused as to how to uv map something that is high res like this? or get uvs on something this high res if i can only import on base mesh 0?
 
  08 August 2013
if your level0 mesh is dens enough
and the quads are evenly distributed there should be minimal uv distortion...
could you post a screengrab..?
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  08 August 2013
Sure, i think ive sorted it, fingers crossed. Will link you to my picasa where i have a few pictures. https://picasaweb.google.com/104810...feat=directlink Heres whats going on in them:
workflow1(the not so good way):
-exporting level 0
-Uv mapping
-importing uv on to level0

Photo1-using workflow1:
the mesh on the left im exporting the base: 617 polys.
the mesh on the right im exporting a retopolgised base to increase the base poly count: 4875 - so there is more detail for uvs.
Photo 2:
Same meshes both moved up 2 subdivisions. you can see they both stretch but the more dense one (right) dosnt as much. The main difference here is poly count: left: 9872. Right: 78000.
Moving back up the subidivion levels i will have way more polygons on the right one, for no extra detail. This is just to get back to the same detail level (but has more polys)

Workflow2(the better way):
-exporting level 2/3:
-uv mapping
-importing the the uv'ed mesh itself (not just importing uvs to existing mesh, you cant because its not base mesh)
-using 'transfer detail' to get the mesh back up to the same poly count as it used to be.

Photo3: While it says base mesh 0 its actually level 3 that i exported from the original mesh.
Photo4: Up 2 subdivisions to level 2 - matching level 5 on the original. Keeps all the detail from the original, with the same poly count. Very little texture warping.

Is workflow 2 the correct way? Its finding a balance between exporting a mesh with enough polys to define enough detail, so the textures wont stretch, while not too many polys that it becomes impossible to uv.
Now i just need to see if this will work on a billion poly mesh
 
  08 August 2013
have you turned on uv smoothing for the subD in mudbox..?
this is turned off by default...

and if you are using highres texture you wont notice the stretching in the final render...
do some tests...
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Last edited by oglu : 08 August 2013 at 07:36 AM.
 
  09 September 2013
Hi oglu, sorry its taken me a while to reply, i did as you suggested and managed to sort my uv stretching by importing the unwrapped mesh and transfering detail on to that, instead of importing uvs onto original mesh, and like you said uv smoothing.
Now im having a normal map issue, im baking a normal map from level 5 (53mil polys) on to level 3 (3mil polys) the bake works fine, when exporting a 16bit int tiff, but there is a huge detail loss i think between int and floating point, correct?
When i export a floating point tiff the detail is there but the normal is very washed out like its not been gamma corrected or something, does this matter?
it isnt behaving when in maya either:
16bit int tiff - works but not detailed enough:
https://picasaweb.google.com/lh/pho...at=d irectlink
16bit fp tiff - dosnt work but seems more detailed:
https://picasaweb.google.com/lh/pho...at=d irectlink
You will also notice that the normals seem reversed or something, objects look flipped. Ive tried reversing normals, but that didnt work.
Do you have any idea why its doing this? i read mudbox uses lzw tiff compression, is this true and could this be causing me issues? Thanks
 
  10 October 2013
Hi flares,

I am going to say something off the wall but could your stretching be from not relaxing the uvs in 3ds max or maya?

In max I use pelt mapping and then I throw a chequer board pattern on my model. Something if you see squares which are not square then you would get a stretching of the texture, and then I would relax the uvs until I get a square chequer.

Just thought I would mention in case this was overlooked.

The model I recenlty finished had no stretching of textures, and I applied my uvs to the lowest level as you did.
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http://www.asimoventerprises.co.uk
 
  10 October 2013
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