After recently posting the "Beginners guide to: Groom" I was asked a few questions about Yeti most of which about clumping specifically. I didn't really know yeti at the time but I spent some time learning how it works and thought I should share what I learned :)
Before we start though, if you're completely new to grooming please go an read my previous tutorial as this one will not discuss the fundamentals of hair and clumping
Part one: The basics - clumping around strands
The most basic way of clumping in yeti is to clump strands around already generated hairs and this would be my go to method for creating fully procedural furs.
First you want to create three identical node chains using scatter, grow and any comb or other styling based nodes. The reason you want to include any styling nodes in all three chains is because the direction of strands is inherited from whatever they are clumped to which means that if you only groomed the primary curves, any stray strands would just stand up straight. Also, styling all three chains inherently introduces some variation within the clumps which is vital for creating natural looking fur.
Once you have all of your curves created it is time to create some clump nodes. Input one of the clump node is for the strands that you want to get clumped whereas input two is for the strands you want to use to generate the clumps. In my opinion it is important to make sure that you have more than just one level of clumping as this creates much more natural looking grooms (those of you who have read my previous groom tutorial will recognize this as the "hierarchy of form" I spoke about.
That's about it, this type of clumping is pretty straight forward but if you find that I did not explain this well enough than the images below should help a little :)
Part two: Clumping around groom or nurbs curves
So one thing to notice about the first part is that it doesn't allow for much control. As I'm sure you know the easiest way to gain control over hair is by creating a groom node on mesh. Once you have the groom created and have set its' radius of influence simply import the groom into your main yeti node graph. If you now tried to connect the groom to the second input of a clump node you'll be met by this error message
"[Fri Dec 09 10:21:56 2016] Yeti 2.0.12: ( clumping_primary in yeti_clump_tutorialShape ) No fibres found in second input, clumping will be ignored."
This is because the clump node expects the second input to be another hair system, however, there is a really simple fix for this... The convert node.
To use the convert node just connect the groom to input one and your geometry import node into the second import. Now just plug the convert node into your clumping node and your done!
(Note: If you do not know how to import nurbs curves, simply select all of your curves and create a set in the maya create menu. You can then import this set into your yeti node as a "guide set")
Before you go
I hope this quick tips tutorial has been helpful for you, if you want me to go into any more detail check my previous groom tutorial or feel free to contact me and I may look into doing a much more in depth tutorial specifically on yeti.
Also, if you want to look further into learning yeti check out the resources listed below!
See ya :)
Bjørn Blaabjerg (TheCaptainFusion)
Description: Probably the largest and most complete tutorial series on yeti around the internet right now, Definitely watch all of his videos if you want to learn yeti!
Rouhollah Toghyani - How to create realistic 3D hair and fur
Description: A great little write up of the full grooming workflow with plenty of awesome illustrations and breakdowns of the process.
The official doccumentation
Description: It's simple enough really, if you don't understand a node just visit the documentation, sure it's pretty dry to read pages of the stuff but it's always worth learning a software from it's developers