TechWatch: Super Space Clothoids

[Rodney]

It's always interesting to see how tech folds back upon itself.

The latest buzz word in cg hair is something of a convergence between hair and cloth.

 

Super Space Clothoids Whitepaper SIGGRAPH 2013

 

There is tech/math going on here which I don't claim to follow but when I suggest folks consider using geometry for hair this is the general idea and when one considers the possibilities much of what is outlined can already be created with A:M.

[Shelton]

Makes me think of what Robert was doing with cloth?

 

Steve

[robcat2075]

Heavens to Clotheroids!

 

I have no idea, really

 

I just briefly glanced at it. What are they doing that's new? Is it that the cloth tries to maintain an initial shape? Our cloth can do that.

[Rodney]

From one of the authors (Florence Bertails-Descoubes):

 

The main challenge consists in finding appropriate and compact discrete models for capturing nonlinear (and sometimes nonsmooth) phenomena, in a both robust and efficient way.

 

I'm thinking this translates (naively) to:

 

Efficiently recreate curved and variable styles of hair... and um... vines.

 

Starting place:

Thin elastic filaments in real world such as vine tendrils, hair ringlets or curled ribbons often depict a very smooth, curved shape that low-order rod models ? e.g., segment-based rods ? fail to reproduce accurately and compactly.

 

In this paper, we push forward the investigation of high-order models for thin, inextensible elastic rods by building the dynamics of a G2-continuous piecewise 3D clothoid: a smooth space curve with piecewise affine curvature. With the aim of precisely integrating the rod kinematic problem, for which no closed-form solution exists, we introduce a dedicated integration scheme based on power series expansions. It turns out that our algorithm reaches machine precision orders of magnitude faster compared to classical numerical integrators. This property, nicely preserved under simple algebraic and differential operations, allows us to compute all spatial terms of the rod kinematics and dynamics in both an efficient and accurate way.

 

Combined with a semi-implicit time-stepping scheme, our method leads to the efficient and robust simulation of arbitrary curly filaments that exhibit rich, visually pleasing configurations and motion. Our approach was successfully applied to generate various scenarios such as the unwinding of a curled ribbon as well as the aesthetic animation of spiral-like hair or the fascinating growth of twining plants

.

 

Here's a paper from that author that details 'the problem' they are trying to resolve, namely that of issues with maintaining curvature (and specifically piecewise affine curvature) when using inverse kinematics:

 

http://hal.inria.fr/docs/00/65/89/96/PDF/s...lothoids-EG.pdf

 

She has some more of her research/papers posted here:

 

http://bipop.inrialpes.fr/~bertails/publis.html

 

While there is a whole lot to read there at that last link... it's very interesting stuff.

[robcat2075]

We have curved hair, don't we?

 

Maybe they mean faster rendering?

[Rodney]

Maybe they mean faster rendering?

 

That would only be one part of the solution. Faster rendering is mostly a hardware issue.

In my view, the goal at this point is primarily to make the process 'artist friendly' and I should add 'director friendly' too.

Hair to this point has largely been a technical dance that only a few highly trained and knowledgeable folks could wrangle.

Where the money for research is currently, is where they are pushing hair toward physical animation that behaves as real hair would.

At that point it just gets directed and tweaked by the artist and director.

If the style itself is wrong then alter the physical environment to suit.

 

In A:M's case this isn't as big a deal because the artist is usually the director too.

But the big companies with corporate looks cannot have hair behaving in one way for a two second shot and another way for the next two seconds, and another for a third, etc.

So this is largely an issue of control.

The director says, "The hair needs to be more curly and flop to the side like this(motions back and forth)."

The animator then sets up the scene and it works.

The physical part of the equation is to create space (reality) for diverse voices to communicate.

 

The part without the solution still seems to be that of controlling hair in a predictable way (in this case apparently with inverse kinematics).

 

As always my view is considerably naive. If I could read the math I might have a clue.