Been asked a few times so I though I would document what we are doing with the skin for the Ziva Anatomy characters.
To put it short we are skipping an isolated fascia pass and instead putting the fascia in the skin pass. So the skin contains fascia (zCloth), fat (zTissue) and skin (zCloth).
Here is a short example of that working:
Here is what each part is doing.
The inputs are the muscles/bones from the previous bakes. They are zBones in this rig.
fascia: This is a zCloth object. bend stiffness set to .1e-5 and collisions OFF. Pressure set at 1500.
fat: This is a zTissue with youngs modulus set to 3e3 and mass density set to 900. Much better settings for fat. collisions or ON
surface: this is the hero skin without a mouth sock or eye socks. bend stiffnes set to .1e-5. collisions are OFF
The fat is attached to the fascia. The fascia has pressure on it so is sucking in. Then the fat is colliding with the muscle and bone zBones. The benefit of this approach is speed and reliability. We can solve most human stuff with 2, sometimes 4 substeps. This gets around the cloth folding in on itself as well. The reason for the high pressure is that it has more work to do being coupled with a tissue.
The surface is attached to the fat.
Additionally, I have attachments from the bones to the fat to represent adhesion lines, areas where the fascia is sticking to muscles.
Painting the pressure: The thing that I am not a huge fan of is painting the pressure. Typically I have been lowering the pressure around the neck area to about 1000. In order to do that you need to make another material and make sure all other properties are the same, then set pressure to what you want and paint the weight map.
The future: What does this mean for the future? We are testing pressure and restScale on tissues and that looks promising. That means we can do away with fascia geo and just solve the fat/skin with same fidelity. Even faster solve times. The ultimate goal is to simulate all passes in one rig. We are getting closer and closer to that.
Any questions let me know, there is probably a lot to take in and more then happy to answer questions.