Algorithmically not very different, but used in another context.

I hope you like it, and I'll be glad to receive your comments and
suggestions.

Fernando González del Cueto
Mexico City.

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Attachments:
Download 'newcloth15.m1v.mpg' (314 KB)

Nice. But it falls too slow and has too much elasticity.

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"Tony[B]" <ben### [at] catholicorg> wrote in message
news:3c4e3b65@news.povray.org...
> Nice. But it falls too slow and has too much elasticity.

Yes, I forgot to increase the time steps, but I thought it still looked cool
and didn't want to try it again :)

Saludos,

Fernando

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> I hope you like it, and I'll be glad to receive your comments and
> suggestions.

very, very, VERY nice. Beside the time scale it's amazing.
Is it difficult to put more objects underneath the cloth?

Congratulations!
regards
SY

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Very nice, the last constrained end stretches a bit far before being
released but it's not of too much importence.

One thing very few seam to be attempting is tearing, maybe it's on your
agenda?

"Fernando González del Cueto" <fcu### [at] yahoocom> wrote in message
news:3c4e36a8@news.povray.org...
> Algorithmically not very different, but used in another context.
>
> I hope you like it, and I'll be glad to receive your comments and
> suggestions.
>
> Fernando González del Cueto
> Mexico City.
>

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How do you handle self-collission detection?

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"Juergen Scharfy" <sch### [at] surfeuat> wrote in message
news:3c4e7519@news.povray.org...
> > I hope you like it, and I'll be glad to receive your comments and
> > suggestions.
>
> very, very, VERY nice. Beside the time scale it's amazing.
> Is it difficult to put more objects underneath the cloth?
>
> Congratulations!
> regards
> SY


Thanks Jürgen! I'm glad you liked it.

I have only experimented with a sphere, and I suppose that there may be
other simple objects that can be easily included (maybe a standing cone?)
and other simple objects would require some additional work, like a box.

More complex (non convex, especially) objects would be much more difficult.

I hope I can try with more objects soon.

Thanks again,

Fernando.

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Fernando González del Cueto wrote:

> Algorithmically not very different, but used in another context.
> 
> I hope you like it, and I'll be glad to receive your comments and
> suggestions.
> 
> Fernando González del Cueto
> Mexico City.


Wow, very nice!
Imagine what all could be behind it! :-)
-- 
Sebastian H.

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Is this number 1 of 7?

Jim

"Fernando González del Cueto" <fcu### [at] yahoocom> wrote in message
news:3c4e36a8@news.povray.org...
> Algorithmically not very different, but used in another context.
>
> I hope you like it, and I'll be glad to receive your comments and
> suggestions.
>
> Fernando González del Cueto
> Mexico City.
>

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This looks really good! To avoid the fixed points being streched that much before
releasing, you could look at the strain they are under, and release them after a
certain limit is reached. There would be more consistency in the simulation then.

How fast are these simulations?

MJL


--
text{ttf"timrom.ttf"concat(#local O=1;#while(O<7)chr(val(substr(concat(#local Q=
1;#while(Q<7)str(asc(substr("???<?>",Q,1))-56,0,0),#local Q=Q+1;#end""),O,2))),#
local O=O+2;#end"").1,0pigment{rgb 9}translate-<1,.3,-2>} // MJL

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"Jim Kress" <dea### [at] kressworkscom> wrote in message
news:3c4f3a29$1@news.povray.org...
> Is this number 1 of 7?
>
> Jim

¿?

I'm sorry but I didn't understand your question.

Fernando.

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"Jens Berg Churchill" <jbc### [at] themaxorg> wrote in message
news:3c4e97fd$1@news.povray.org...
> Very nice, the last constrained end stretches a bit far before being
> released but it's not of too much importence.
>
> One thing very few seam to be attempting is tearing, maybe it's on your
> agenda?

Yes, I also think the elasticity is bit exaggerated, but that's why I made
it plastic-like, where this kind of behaviour is allowable.

I also thought a little about the tearing idea, but I realized it wouldn't
be easy at all to implement. My approximate current agenda is:

* rewrite my code in order to optimize it and add some new ideas
* add wind
* try using OpenGL to have a real-time simulation

Thanks for your comments,

Fernando.

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"Apache" <apa### [at] yahoocom> wrote in message
news:3c4ec1a3$1@news.povray.org...
> How do you handle self-collission detection?

I don't! :)

I'm fortunate that it looks like it doesn't cross through itself, but it
does. :/

Fernando.

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> Wow, very nice!
> Imagine what all could be behind it! :-)

Thank you very much, I'm glad you liked it!

Fernando.

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"Mark James Lewin" <m_j### [at] yahoocomau> wrote in message
news:3C4F38D1.7601C583@yahoo.com.au...
> This looks really good! To avoid the fixed points being streched that much
before
> releasing, you could look at the strain they are under, and release them
after a
> certain limit is reached. There would be more consistency in the
simulation then.
>
> How fast are these simulations?
>
> MJL

That's a very good idea! Thanks

Well, the speed depends on how fine you want the mesh, and how small you
make the time steps. Sometimes I take unnecesarily small steps and it takes
ages! And sometimes I'm too optimistic and get overflows at the middle of
the simulation for taking too large steps.

In this particular case, hmmm... I think it took about 2-3 seconds per
frame. Later I have to render each frame, of course!

Thanks for your comments and good suggestion!

Fernando.

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On Tue, 22 Jan 2002 22:04:20 -0600, Fernando González del Cueto
<fcu### [at] yahoocom> wrote:

>Algorithmically not very different, but used in another context.

>I hope you like it, and I'll be glad to receive your comments and
>suggestions.

It's *way* too elastic, like raw rubber or latex.

Cloth elasticity comes from the fact that it is made of interwoven
threads, be they elastic or not. Tensile forces 'tighten up' the
threads and make the cloth thinner, but the threads themselves don't
elongate, or at least not relevantly much.

The easiest way to model this is to cap strain at some value. The
looser the cloth, the higher the value. It is also much easier to
tweak as the only thing you have to do is measure the tensile strain
of your cloth (at the expense of the sample :) ).

Keep in mind that I haven't actually modelled cloth, only solids, so
though I think I know the theory, I have no experience at it. Trust me
or not at your own risk :)


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG      e-mail : pet### [at] tagpovrayorg

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I like it very much.

I  am trying, from time to time, to build an external tool wich could
generate clothes as mesh2 files from a pov scene, but I have to fight with
instability. do you? how do you handle it?

Chaps.

"Fernando González del Cueto" <fcu### [at] yahoocom> wrote in message
news:3c4e36a8@news.povray.org...
> Algorithmically not very different, but used in another context.
>
> I hope you like it, and I'll be glad to receive your comments and
> suggestions.
>
> Fernando González del Cueto
> Mexico City.
>

Post a reply to this message

"Chaps" <cha### [at] yahoocom> wrote in message
news:3c5009ef@news.povray.org...
> I like it very much.
>
> I  am trying, from time to time, to build an external tool wich could
> generate clothes as mesh2 files from a pov scene, but I have to fight with
> instability. do you? how do you handle it?
>
> Chaps.

Hi Chaps. I'm still trying to have a more robust algorithm, but meanwhile,
my only solution is to take smaller time steps.

Fernando.

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"Peter Popov" <pet### [at] vipbg> wrote in message
news:c9vv4us4j8706qsvtgem59flufjv5qudhc@4ax.com...
> On Tue, 22 Jan 2002 22:04:20 -0600, Fernando González del Cueto
> <fcu### [at] yahoocom> wrote:
>
> >Algorithmically not very different, but used in another context.
>
> >I hope you like it, and I'll be glad to receive your comments and
> >suggestions.
>
> It's *way* too elastic, like raw rubber or latex.

Yes, I also think it is too elastic, and that's why I gave it that plastic
texture, so it does not look like a cloth.

> Cloth elasticity comes from the fact that it is made of interwoven
> threads, be they elastic or not. Tensile forces 'tighten up' the
> threads and make the cloth thinner, but the threads themselves don't
> elongate, or at least not relevantly much.

That's right. The threads are very inelastic. But the equations describing
that must be very complicated. You can simplify your model if you ignore the
"tightening" of the threads and compensate with a bit of more elasticity to
the cloth.

I'm now trying to reach an alternative way to solve this, but I still have
to work many hours :)

Thanks for your comments,

Sbogom!

Fernando

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On Thu, 24 Jan 2002 11:28:44 -0600, Fernando González del Cueto
<fcu### [at] yahoocom> wrote:

>That's right. The threads are very inelastic. But the equations describing
>that must be very complicated. You can simplify your model if you ignore the
>"tightening" of the threads and compensate with a bit of more elasticity to
>the cloth.

You can impose a penalty on elasticity if strain goes above a certain
value. Not cap it altogether but penalize it strongly so that the
cloth tends to preserve its original shape without being too elastic.

I would use a strongly non-linear stress-strain relationship if I were
you. Try logarithmic for a start, or exp(-x*t). This way for higher
stresses there'll be almost no increase in strain.

And then you may consider material failure :)


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG      e-mail : pet### [at] tagpovrayorg

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These cloth animations of yours are truly amazing!
This one, as many others have said, is a tad too stretchy, but the way it
folds when it falls and how it behaves when the corners are released is very
realistic (too slow, but nonetheless realistic- like a slo-mo of it).

"Fernando González del Cueto" <fcu### [at] yahoocom> wrote in message
news:3c4e36a8@news.povray.org...
> Algorithmically not very different, but used in another context.
>
> I hope you like it, and I'll be glad to receive your comments and
> suggestions.
>
> Fernando González del Cueto
> Mexico City.
>

Post a reply to this message

Thank you! I'm glad you liked it!

I'm right now working on an entirely different algorithm, to avoid all these
problems, but it is somewhat complicated, so I don't know if I will able to
implement it correctly.

Thanks again,

Fernando.


"Mahalis" <don### [at] fakeycom> wrote in message
news:3c50a0b3$1@news.povray.org...
> These cloth animations of yours are truly amazing!
> This one, as many others have said, is a tad too stretchy, but the way it
> folds when it falls and how it behaves when the corners are released is
very
> realistic (too slow, but nonetheless realistic- like a slo-mo of it).
>
> "Fernando González del Cueto" <fcu### [at] yahoocom> wrote in message
> news:3c4e36a8@news.povray.org...
> > Algorithmically not very different, but used in another context.
> >
> > I hope you like it, and I'll be glad to receive your comments and
> > suggestions.
> >
> > Fernando González del Cueto
> > Mexico City.
> >
>
>

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I do the same, but i need to change time step each time I change the
"accuracy" of the mesh, and I don't like tries and error algorithm :o(.

I've been driven to a site where there are some studies about cloth
stability with large step calculus, but I did not succeed to get something
out of this stuff yet.( http://www-2.cs.cmu.edu/~baraff/papers/).

Chaps.

"Fernando González del Cueto" <fcu### [at] yahoocom> wrote in message
news:3c503d0f@news.povray.org...
>
> "Chaps" <cha### [at] yahoocom> wrote in message
> news:3c5009ef@news.povray.org...
> > I like it very much.
> >
> > I  am trying, from time to time, to build an external tool wich could
> > generate clothes as mesh2 files from a pov scene, but I have to fight
with
> > instability. do you? how do you handle it?
> >
> > Chaps.
>
> Hi Chaps. I'm still trying to have a more robust algorithm, but meanwhile,
> my only solution is to take smaller time steps.
>
> Fernando.
>

Post a reply to this message

"Chaps" <cha### [at] yahoocom> wrote in message
news:3c514dd3@news.povray.org...
> I do the same, but i need to change time step each time I change the
> "accuracy" of the mesh, and I don't like tries and error algorithm :o(.
>
> I've been driven to a site where there are some studies about cloth
> stability with large step calculus, but I did not succeed to get something
> out of this stuff yet.( http://www-2.cs.cmu.edu/~baraff/papers/).

Hi Chaps!

What a coincidence! I spent nearly all day yesterday to try to understand
that document. Actually I did understand most of it, but I got badly stuck
with the C(x) condition vector... I believe there must be some errors, or at
least it is not very well explained, because in the Stretch Forces section
(4.2), C(x) is defined as a 2-dimensional vector:

C(x) = a (|wu(x)| - bu , |wv(x)| - bv )

However, in the shear and bend forces section (4.3), C(x) is defined as

C(x) = a * wu(x)^T * wv(x)

Which, I believe it is 1-dimensional, that is, a scalar.

And then, in the Forces and Force Derivatives section (4.1) it says that the
force can be computed like this:

f_i = -k dC(x)/dx_i * C(x)

But f_i is a 3-dimensional vector, so I believe there must be an error
because there is no dimensional agreement. I may be wrong, but I'm stuck.

Did you have the same problem?

Fernando.

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On Fri, 25 Jan 2002 13:21:46 +0100, "Chaps" <cha### [at] yahoocom> wrote:

>I've been driven to a site where there are some studies about cloth
>stability with large step calculus, but I did not succeed to get something
>out of this stuff yet.( http://www-2.cs.cmu.edu/~baraff/papers/).

Regarding cloths, you can find more of David Baraff & Andrew Wittkin's
papers and course notes online. They are the guys that are behind
Pixar's cloth simulation engine. Xavier Provot is also a
well-recognized name in the field. I believe Demetri Terzopolous has
recently been focusing on cloths rather than solids and he has some
interesting ideas like using dynamic NURBS (D-NURBS), or neural
networks, or state-space theory to simulate elastic dynamics.


Peter Popov ICQ : 15002700
Personal e-mail : pet### [at] vipbg
TAG      e-mail : pet### [at] tagpovrayorg

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Well! What can I say?
Its absolutely fantastic! =)
Congratulations.

Best Regards.


"Fernando González del Cueto" <fcu### [at] yahoocom> wrote in message
news:3c4e36a8@news.povray.org...
> Algorithmically not very different, but used in another context.
>
> I hope you like it, and I'll be glad to receive your comments and
> suggestions.
>
> Fernando González del Cueto
> Mexico City.
>

Post a reply to this message

Thank you JPGargoyle!

It's nice to know that you liked it!

Fernando.


"JPGargoyle" <jpg### [at] clixpt> wrote in message
news:3c533601$1@news.povray.org...
> Well! What can I say?
> Its absolutely fantastic! =)
> Congratulations.
>
> Best Regards.

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I should have some time before end of week, and I'll take a look at that.

May be I'll get illuminated.

Chaps

"Fernando González del Cueto" <fcu### [at] yahoocom> wrote in message
news:3c518884@news.povray.org...
> Hi Chaps!
>
> What a coincidence! I spent nearly all day yesterday to try to understand
> that document. Actually I did understand most of it, but I got badly stuck
> with the C(x) condition vector... I believe there must be some errors, or
at
> least it is not very well explained, because in the Stretch Forces section
> (4.2), C(x) is defined as a 2-dimensional vector:
>
> C(x) = a (|wu(x)| - bu , |wv(x)| - bv )
>
> However, in the shear and bend forces section (4.3), C(x) is defined as
>
> C(x) = a * wu(x)^T * wv(x)
>
> Which, I believe it is 1-dimensional, that is, a scalar.
>
> And then, in the Forces and Force Derivatives section (4.1) it says that
the
> force can be computed like this:
>
> f_i = -k dC(x)/dx_i * C(x)
>
> But f_i is a 3-dimensional vector, so I believe there must be an error
> because there is no dimensional agreement. I may be wrong, but I'm stuck.
>
> Did you have the same problem?
>
> Fernando.
>

Post a reply to this message