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Finally managed to get some time to implement 4th order Runge-Kutta for an
improved clothing animation program. I started all over again, from scratch.
No cloth-cloth or cloth-solid collission testing yet. That will come later.
This message includes one of the test animations. The higher quality
animation is available at
http://geitenkaas.dns2go.com/experiments/cloth07test3_640x480.divx412.avi
(787,532 bytes)or
http://geitenkaas.dns2go.com/experiments/cloth07test3_640x480.mpg (1,282,052
bytes).
Check http://geitenkaas.dns2go.com/experiments/ for more animations. The
cloth07 series is the latest series, created using the Runge-Kutta method I
mentioned above.
And please don't ask me why I positioned that piece of sheet nearby the top
edge of the screen ;-)
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Post a reply to this message
Attachments:
Download 'cloth07test3_320x240.mpg' (473 KB)
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Looks pretty fast to me (how much iterations per frame?), and of
course really stable. Kudos.
Next thing you'll want to do: Xavier Provot's hybrid cloth technique
:) And of course the famous "Large Steps in Cloth Simulation" paper
(Pixar! Pixar!)
Never mind me, I haven't had my morning coffee yet.
Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vip bg
TAG e-mail : pet### [at] tagpovrayorg
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It's obviously made of gum this time, not fibre... :o)
Does your collision detection work with any shape?
Hugo
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From: Tony[B]
Subject: Re: first tests with 4th order RK (clothing)
Date: 26 Feb 2002 08:40:41
Message: <3c7b9059@news.povray.org>
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Wow! It actually stabilizes! Amazing. Very nice. Keep it up! :)
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It looks great how if converges to a quiet state, even though it still looks
a little bit rubbery at first.
I'm glad you've got some excellents results in so few days!
Keep up the good work.
Fernando.
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Looks good. The rippling movement is nice. How many points define this cloth?
The corners of the cloth look like they are under alot of tension. Have you tried
fixing more points around the corners (3 or 4, or more points)? It might help to
get rid of the "about to break" look that most cloth sims with fixed points seem
to display.
MJL
--
prism{0,.1,30#local I=1;#while(I<30)#local B=asc(substr(// Mark James Lewin
"#K?U_u`V[RG>3<9DGPL.0EObkcPF'",I,1))-33;<div(B,10)-4mod(B,10)+5*div(I,21)-
6>#local I=I+1;#end,-4pigment{rgb 9}rotate-x*90translate 15*z}//POV-Ray 3.5
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This is just a first test. In more 'serious' scenes I won't fix cloth at
just a few single nodes. But still I want to get rid of that 'about to
break' problem. The first solution I can think of is decreasing the step
size and increasing the stiffness of the springs.
The animation I submitted before used timesteps of 0.04 and 20 steps per
frame. The animation with this message uses timesteps of 0.08 and 10 steps
per frame.
Both sheets are 50x50 nodes (or atoms).
As you can see the sheet of the new animation (cloth07test4, the one
attached to this message) needs more time to settle down and the sheet is
more flexible. That's caused by the larger time step. Maybe using 5th or 6th
order Runge-Kutta would even improve the thing more? So my next question
would be: I would like to know HOW them people (mister Runge and mister
Kutta?) got to that Runge-Kutta algorithm.
A part of the R-K algorithm: Vnew = Vold + (K1+ 2*K2 + 2*K3 + K4) / 6
Why oh why wouldn't it be Vnew = Vold +(K1 + 3*K2 + 2*K3 + K4) / 8 or
something else? Maybe someone told/taught it me some time ago when I wasn't
paying attention. If I know how them people got that formula, I would be
able to get higher order algorithms by myself.
Apache
http://geitenkaas.dns2go.com/experiments/
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Attachments:
Download 'cloth07test4_320x240.mpg' (547 KB)
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Aha! I know now why the latest rubber sheet needs more time to stop moving.
The program dampes only once per time step. So with 10 time steps per
animation frame there's less damping than with 20 time steps per animation
frame.
I should fix this bug...
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Apache wrote:
> The first solution I can think of is decreasing the step
> size and increasing the stiffness of the springs.
That came to my mind too. I'm sure you also know how much that will slow the
simulation down by too :-)
>
> As you can see the sheet of the new animation (cloth07test4, the one
> attached to this message) needs more time to settle down and the sheet is
> more flexible. That's caused by the larger time step.
Does this cloth have the same number (and strength) springs too? I would not have
expected this large a change in flexibility by changing the time step (and
consequently the number of steps) alone.
> Maybe using 5th or 6th
> order Runge-Kutta would even improve the thing more? So my next question
> would be: I would like to know HOW them people (mister Runge and mister
> Kutta?) got to that Runge-Kutta algorithm.
I confess to know little of these methods. These links explain 2nd and 4th order
RK. They may be of some use.
http://nacphy.physics.orst.edu/ComPhys/DIFFEQ/mydif2/node5.html
http://nacphy.physics.orst.edu/ComPhys/DIFFEQ/mydif2/node6.html
Math has never been a strong point for me.
--
prism{0,.1,30#local I=1;#while(I<30)#local B=asc(substr(// Mark James Lewin
"#K?U_u`V[RG>3<9DGPL.0EObkcPF'",I,1))-33;<div(B,10)-4mod(B,10)+5*div(I,21)-
6>#local I=I+1;#end,-4pigment{rgb 9}rotate-x*90translate 15*z}//POV-Ray 3.5
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