sculpting

Houdini topo transfer - aka wrap3 /  by Xuan Prada

For a little while I have been using Houdini topo transfer tools instead of Wrap 3. Not saying that I can fully replace Wrap3 but for some common and easy tasks, like wrapping generic humans to scans for both modelling and texturing, I can definitely use Houdini now instead of Wrap 3.

Wrapping generic humans to scans

  • This technique will allow you to easily wrap a generic human to any actor’s scan to create digital doubles. This workflow can be used during modeling the digital double and also while texturing it. Commonly, a texture artist gets a digital double production model in t-pose or a similar pose that doesn’t necessary match the scan pose. It is a great idea to match both poses to easily transfer color details and surface details between the scan and the production model.

  • For both situations, modeling or texturing, this is a workflow that usually involves Wrap3 or other proprietary tools for Maya. Now it can also easily be done in Houdini.

  • First of all, open the ztool provided by the scanning vendor in Zbrush. These photogrammetry scans are usually something around 13 – 18 million of polygons. Too dense for the wrapping process. You can just decimate the model and export it as .obj

  • In Maya align roughly your generic human and the scan. If the pose is very different, use your generic rig to match (roughly) the pose of the scan. Also make sure both models have the same scale. Scaling issues can be fixed in Wrap3 or Houdini in this case, but I think it is better to fix it beforehand, in a vfx pipeline you will be publishing assets from Maya anyway. Then export both models as .obj

  • It is important to remove teeth, the interior of the mouth and other problematic parts from your generic human model. This is something you can do in Houdini as well, even after the wrapping, but again, better to do it beforehand.

  • Import the scan in Houdni.

  • Create a topo transfer node.

  • Connect the scan to the target input of the topo transfer.

  • Bring the base mesh and connect it to the source input of the topo transfer.

  • I had issues in the past using Maya units (decimeters) so better to scale by 0.1 just in case.

  • Enable the topo transfer, press enter to activate it. Now you can place landmarks on the base mesh.

  • Add a couple of landmarks, then ctrl+g to switch to the scan mesh, and align the same landmarks.

  • Repeat the process all around the body and click on solve.

  • Your generic human will be wrapped pretty much perfectly to the actor’s scan. Now you can continue with your traditional modeling pipeline, or in case you are using this technique for texturing, move into Zbrush, Mari and or Houdini for transferring textures and displacement maps. There are tutorials about these topics on this site.

Transferring texture data

  • Import the scan and the wrapped model into Houdini.

  • Assign a classic shader with the photogrammetry texture connected to its emission color to the scan. Disable the diffuse component.

  • Create a bakeTexture rop with the following settings.

    • Resolution = 4096 x 4096.

    • UV object = wrapped model.

    • High res object = scan.

    • Output picture = path_to_file.%(UDIM)d.exr

    • Format = EXR.

    • Surface emission color = On.

    • Baking tab = Tick off Disable lighting/emission and Add baking exports to shader layers.

    • If you get artifacts in the transferred textures, in the unwrapping tab change the unwrap method to trace closest surface. This is common with lidar, photogrammetry and other dirty geometry.

    • You can run the baking locally or on the farm.

  • Take a look at the generated textures.

Meshlab polygon reduction /  by Xuan Prada

Meshlab is probably the only available solution (proprietary Lidar software doesn't count) when you have to deal with very heavy poly count. I'm working with some complex terrains, some of them up to 50 million polys and Maya or Zbrush just can't handle that. I'm reducing the poly count considerably fast in Meshlab with its polygon reduction tools.

  • This terrain has more than 16 million polys. Maya can't handle this very well, and Zbrush can't manage memory to even open it. Just import it in Meshlab.
  • You will be using the Quadric Edge Collopse Decimation tool a lot.
  • There are different strategies available, I like to use the percentage one. In this case by 0.5
  • I'll be getting an 8 million poly terrain.
  • I just run the tool one more time to get a 4 million terrain. I can work in Maya with this :)

Dealing with Ptex displacement /  by Xuan Prada

Render using Ptex displacement.

What if you are working with Ptex but need to do some kind of Zbrush displacement work?
How can you render that?

As you probably now, Zbrush doesn't support Ptex. I'm not a super fan of Ptex (but I will be soon) but sometimes I do not have time or simply I don't want to make proper UV mapping. Then, if Zbrush doesn't export Ptex and my assets don't have any sort of UV coordinates, can't I use Ptex at all for my displacement information?

Yes, you can use Ptex.

Base geometry render. No displacement.

  • In this image below, I have a detailed 3D scan which has been processed in Meshlab to reduce the crazy amount of polygons.
  • Now I have imported the model via obj in Zbrush. Only 500.000 polys but it looks great though.
  • We are going to be using Zbrush to create a very quick retopology for this demo. We could use Maya or Modo to create a production ready model.
  • Using the Zremesher tool which is great for some type of retopology tasks, we get this low res model. Good enough for our purpose here.
  • Next step would be exporting both model, high and low resolution as .obj
  • We are going to use these models in Mudbox to create our Ptex based displacement. Yes, Mudbox does support Ptex.
  • Once imported keep both of them visible.
  • Export displacement maps. Have a look in the image below at the options you need to tweak.
  • Basically you need to activate Ptex displacement, 32bits, the texel resolution, etc)
  • And that's it. You should be able to render your Zbrush details using Ptex now.

Clarisse UV interpolation /  by Xuan Prada

When subdividing models in Clarisse for rendering displacement maps, the software subdivides both geometry and UVs. Sometimes we might need to subdivide only the mesh but keeping the UVs as they are originally.

This depends on production requirements and obviously on how the displacement maps were extracted from Zbrush or any other sculpting package.

If you don't need to subdivide the UVs first of all you should extract the displacement map with the option SmoothUV turned off.
Then in Clarisse, select the option UV Interpolation Linear.

By default Clarisse sets the UVs to Smooth.

You can easily change it to Linear.

Render with smooth UVs.

Render with linear UVs.

Mudbox and UDIMs /  by Xuan Prada

When you’re going to texture an asset which already have a displacement map, probably you’ll want to apply that displacement to your mesh before start the painting process.

In my pipeline, I usually apply the displacement map in Mudbox and then I export the high resolution mesh to Mari.

The problem here is that Mudbox doesn’t allow you to work with displacement maps and multiple UV shells.

I tried below to find a solution for this problem.

  • Check your UV mapping in Maya.
  • I’m using these simple displacement maps here.
  • One map for each UV shell.
  • Export as .Obj
  • Open in Mudbox and subdivide.
  • Go to maps -> sculpt model using displacement map.
  • Select your mesh and your displacement map.

As you’ll realize, Mudbox doesn’t allow you to choose different maps for each UV shell which means that Mudbox will be able only to sculpt using the displacement map for U0-1 V1-0 coordinates. Big problem.

The way which I’ve found to solve this problem is:

  • Go back to Maya.
  • Select your mesh and open de UV Texture Editor.
  • Select one of the UV shells which is outside of the default U0-1 V1-0 range.
  • Open the script editor and type -> polyEditUV -u -1 -v 0 ;
  • You’ll notice that the second UV shell is placed in the default UV shell but was moved 1 exact position. Then your displacement texture  will match perfectly.
  • Export again as .obj
  • Now you’ll can use your displacement map in Mudbox without problem.
  • Repeat the process for each UV shell.
  • Commands to move UV shells 1 exact position.

Move left -> polyEditUV -u -1 -v 0 ;

Move right -> polyEditUV -u 1 -v 0 ;

Move up -> polyEditUV -u 0 -v 1 ;

Move down -> polyEditUV -u 0 -v -1 ;