Well, luckily I haven't got anyone around me who smoke, so I haven't
really studied any cigarette smoke in details, but if it is anything
like the smoke that comes when you blow out a match or a candle, then
maybe the smoke in this animation could go for cigarette smoke.

Well, obviously from the above, I need a lot of feedback to know if I'm
on the right track... ;)

It's supposed to be a demo scene for my particle system, which by the
way is in the beta testing stage if anyone missed my message in
povray.general.

The animation should be viewed with a gamma of at least about 1.8 to
look good.

Maybe you could compare this animation to the one at the address below,
and tell me which is more realistic and why.
http://www.studenter.hb.se/~arch/smokegen/anims/ashtray.avi
It's from the SmokeGen page:
http://www.studenter.hb.se/~arch/smokegen/smokegen.htm

Rune
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Attachments:
Download 'cigsmoke1.mpg' (305 KB)

From my onw (big) experience with cigarette smoke, it is very realistic. 

  But wait... let me burn one... hmmmm... 

  Seems that the real one is a bit more chaotic, but stays "straight" 
during a while, before the turbulence starts. Anyhow, it's definitely a 
very good simulation. 

-- 
Jaime Vives Piqueres

La Persistencia de la Ignorancia
http://www.ignorancia.org

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"Rune" <run### [at] mobilixnetdk> wrote in message
news:3cdfc63f@news.povray.org...
> Well, luckily I haven't got anyone around me who smoke, so I haven't
> really studied any cigarette smoke in details, but if it is anything
> like the smoke that comes when you blow out a match or a candle, then
> maybe the smoke in this animation could go for cigarette smoke.

    Well, as a non-smoker, I can't see why you would bother making cigarette
smoke out of something so cool.

    As a hundred more interesting uses I think it is very good. It misses
some of the granularity that smoke sometimes has, but maybe that's the
scale. And it seems to go chaotic very quickly. In a still room I would
expect it to stream a little longer.

    What I would like to see is the kind of double spiral that incense in a
still room sometimes makes... I've seen that go up 3-4 feet before almost
exploding into turbulence.

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Neither I have studied smoke, but here are some guesses:

Your animation:
- Thickness of smoke increases it's brightness. Is this realistic?
- Smoke seems to go upwards a bit too fast.

Smokegen animation:
- Far too thin line of smoke.

Nice to see your system moves to beta stage!  :o)

Regards,
Hugo

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Bill DeWitt wrote:
>     Well, as a non-smoker, I can't see why you would
> bother making cigarette smoke out of something so cool.

Err, thanks! ;)

Any ideas what else I could make it into?
[reading down further]
Ah, incense. Any other ideas, just so I have something more to choose
from? :)

> It misses some of the granularity that smoke
> sometimes has, but maybe that's the scale.

I can try to make it more grainy...

> And it seems to go chaotic very quickly. In a still
> room I would expect it to stream a little longer.

Hmm.

> What I would like to see is the kind of double spiral
> that incense in a still room sometimes makes... I've
> seen that go up 3-4 feet before almost exploding into
> turbulence.

As always, it difficult to precisely visualize for my inner eye what
something looks like from a written description, but I can give it a
try.

Anyway, I wonder what it is that causes the turbulence to happen in such
a sudden way...

Rune
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Jaime Vives Piqueres wrote:
> From my onw (big) experience with cigarette smoke,
> it is very realistic.

Weee... :)

>   But wait... let me burn one... hmmmm...

I take no responsibility for that. ;)

>   Seems that the real one is a bit more chaotic,
> but stays "straight" during a while, before the
> turbulence starts.

That's what Bill said too. I'll have to try to make it do that.

> Anyhow, it's definitely a very good simulation.

Thanks!

The good thing is that it parses and renders very fast because only very
few particles are used, and no media... :D

Rune
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"Rune" <run### [at] mobilixnetdk> wrote in message
news:3cdfc63f@news.povray.org...

Very convincing start.
As for criticism, the smoke shouldn't disappear (at least it seems that way
in the anim) but rather dissipate and spread out (until it loses visibility)

-tgq

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Rune wrote:
> 
> Well, luckily I haven't got anyone around me who smoke, so I haven't
> really studied any cigarette smoke in details, but if it is anything
> like the smoke that comes when you blow out a match or a candle, then
> maybe the smoke in this animation could go for cigarette smoke.
> 
> Well, obviously from the above, I need a lot of feedback to know if I'm
> on the right track... ;)
> 
> [...]

As Bill and Jaime pointed out the smoke moving straight upwards and
getting turbulent after some way is a classical effect. When you model it
mathematically this has to do with the characteristic length getting
longer and at some point the flow is reaching a critical rayleigh number
and changing from laminar to turbulent (from memory, not sure if totally
correct).

Christoph

-- 
POV-Ray tutorials, IsoWood include,                 
TransSkin and more: http://www.tu-bs.de/~y0013390/  
Last updated 05 May. 2002 _____./\/^>_*_<^\/\.______

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Hugo wrote:
> - Thickness of smoke increases it's brightness.

Actually it doesn't, but it probably doesn't decrease in brightness as
much as it should.

> - Smoke seems to go upwards a bit too fast.

I agree.

> Nice to see your system moves to beta stage!  :o)

You're welcome to help testing it if you want. "Testing" also means to
make your own scenes and animations... :)

Rune
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Rune wrote:
> 
> 
> Anyway, I wonder what it is that causes the turbulence to happen in such
> a sudden way...
> 
> Rune
> --

Probably inversion, a layer of warm air on top of a colder
layer.

Nice animation BTW, Rune but my first reaction is similar to
Bill's; it would be great if you could see the nice little
'curlies' you see in incense (haven't looked at cigarette smoke
very closely). I have no idea how you would get this effect, but
I'm impressed already.

Remco

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TinCanMan wrote:
> Very convincing start.

Thanks!

> As for criticism, the smoke shouldn't disappear
> (at least it seems that way in the anim) but rather
> dissipate and spread out (until it loses visibility)

On my monitor that's basically what happens. But when I turn up the
brightness of my screen, the gamma value decreases, and then the smoke
looks much worse and disappears much more suddenly. I'll try to make the
smoke more suitable for a wider range of brightness and gamma values.

Rune
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Christoph Hormann wrote:
> As Bill and Jaime pointed out the smoke moving straight
> upwards and getting turbulent after some way is a
> classical effect.

I'm currently rendering my attempt at that effect. :)

> When you model it mathematically this has to do with
> the characteristic length getting longer and at some
> point the flow is reaching a critical rayleigh number
> and changing from laminar to turbulent (from memory,
> not sure if totally correct).

Sure. I think I understood 50% of the above text, but that was mostly
the fill words.

I think I can still simulate the effect in my particle system, but it's
not based on any physical models... As you probably know, my system is
very simplistic.

Rune
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Rune wrote:
> 
> [...]
> 
> Sure. I think I understood 50% of the above text, but that was mostly
> the fill words.

;-)

> I think I can still simulate the effect in my particle system, but it's
> not based on any physical models... As you probably know, my system is
> very simplistic.

I think in this case an exact physical simulation would be unnecessary. 
The optical effect is much more important.

Christoph

-- 
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TransSkin and more: http://www.tu-bs.de/~y0013390/  
Last updated 05 May. 2002 _____./\/^>_*_<^\/\.______

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Many others have already mentioned the
turbulences etc.

I wanted to address the 2D-Effect. Sometimes a
turbulence wraps about itself, and it looks like we
see a 2D-Slice of smoke when it does so.

Are you using some triangles for the representation of
the smoke?

Ah well. I'd be testing your system as well as
working on my own, if I wouldn't have too much
work floating around... Definitely need to get my
Computer's harddrive cleaned up from those
"Gerbera" excursions... Instead of cleaning newly
created "garbage", I left it for later, to have more time
for the image...

*sigh*

--
Tim Nikias
Homepage: http://www.digitaltwilight.de/no_lights/index.html
Email: Tim### [at] gmxde

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Looks nice, especially effective for a demo.
How did you specify the turbulence of the air?

MJL

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Christoph Hormann wrote:
> I think in this case an exact physical simulation would be
> unnecessary. The optical effect is much more important.

I hope I can get the optical effect right... :)

Rune
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Tim Nikias wrote:
> I wanted to address the 2D-Effect. Sometimes a
> turbulence wraps about itself, and it looks like
> we see a 2D-Slice of smoke when it does so.

Heh, yeah.

> Are you using some triangles for the
> representation of the smoke?

Yes. Bezier patches actually. I have already made attempts to address
the flat and twisted look, but so far only with limited success. It'll
look a little better in the next animation I'll post though.

> Ah well. I'd be testing your system as well as
> working on my own, if I wouldn't have too much
> work floating around...

And I should study some more for my exams. Nah, I can do that a little
later... ;)

Rune
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Remco de Korte wrote:
> Probably inversion, a layer of warm air on
> top of a colder layer.

You mean like more or less static layers of cold and warm air in the
room? Ah, I thought it might be something more complex, perhaps related
with warm air following the smoke or something like that.

> Nice animation BTW, Rune

Thanks! :)

> it would be great if you could see the nice little
> 'curlies' you see in incense (haven't looked at
> cigarette smoke very closely).

I'm not very sure of what the effect you refer to looks like, but the
animation I'm rendering now is probably a bit closer to it - I hope. ;)

BTW Remco, though it's not very much we hear from you, I've noticed a
few messages from you now and then. It's good to see that you're still
around here in the newsgroups. :)

Are there any projects you're working on at the moment?

Rune
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Mark James Lewin wrote:
> Looks nice, especially effective for a demo.

Thanks! Before it can be made a demo I have to clean up the code
though... ;)

> How did you specify the turbulence of the air?

Using the vturbulence function in POV-Ray 3.5 for the wind setting in my
particle system. It's a simple concept, but the tweaking of the effect
has been very time-consuming...

Rune
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Rune wrote:
> 
> Remco de Korte wrote:
> 
> BTW Remco, though it's not very much we hear from you, I've noticed a
> few messages from you now and then. It's good to see that you're still
> around here in the newsgroups. :)
> 

I have used POV a lot (a bit too much) for a project (a series)
I've worked on for about 18 months. I was already working on two
new titles when the publisher pulled the plug. When I started
with it it was the publisher who insisted I use 3D graphics (and
POV was the most obvious choice for me - free). 
Now I'm working on another series, for another publisher, and
the man in charge their wants no 3D graphics at all. It's a
fairly low price product where there shouldn't be too much
'fluff'.
I was a bit disappointed at first but actually I'm glad now
because I've been working on it about a year and with 7 titles
on the market and a handfull of other already or almost finished
it is enough work as it is.

I check out these groups once in a while (a bit more frequent
the last few days) as a sort of diversion. I only use POV for
small stuff and I keep a safe distance from the advanced stuff
people like you are working on. It is tempting but way beyond my
scope.

It is still interesting to see what is going here in the
animations department. 
Unfortunately I made the mistake of downloading the full version
of "Tripping the Rift" (is that the correct title). Now I know
what I'd _like_ to be doing (but never will).

How are things on your end (besides the continuing stream of
POVxperiments you keep producing)?
> 
> Rune
> --

Cheers!

Remco

BTW - about the smoke, I don't really know about the inversion,
it was just the first thing that occurred to me. The part about
the small curls in the smoke is true though. If you don't want
to take up smoking (you could make a living out of it) you could
buy some incense (it's cheap) to check it out. I'm not sure if
that behaves in the same way as cigarette smoke.

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"Rune" <run### [at] mobilixnetdk> wrote :
>
> As always, it difficult to precisely visualize for my inner eye what
> something looks like from a written description, but I can give it a
> try.

    I used to open my blinds just a crack in the early morning and set some
incense under the slit of sunlight that would come through. It allowed me to
study the internal shape of a stream of smoke fairly intently. I will try to
take a photo in the morning but here is a quick mouse sketch of the shape I
mean. This would be a horizontal cross section of the stream.

    I always thought that the shape allowed the smoke to store energy in a
smooth, protected inner spiral which works well as long as there is no
turbulence, but which comes apart completely as soon as one of the shells is
breached.

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Attachments:
Download 'new-2.jpg' (20 KB)

Preview of image 'new-2.jpg'

Bill DeWitt wrote:
> I will try to take a photo in the morning but here is a
> quick mouse sketch of the shape I mean. This would be a
> horizontal cross section of the stream.

Aha. I hope to see the photo, but judging from your sketch I don't think
it's something that's possible to simulate with my system...

Rune
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Remco de Korte wrote:
> I have used POV a lot (a bit too much) for a project
> (a series) I've worked on for about 18 months. I was
> already working on two new titles when the publisher
> pulled the plug.

So the titles weren't released? That's a shame...

I think you're lucky to be able to use POV-Ray for projects in the first
place though, but of course there are times when there are better
choices...

> Unfortunately I made the mistake of downloading the
> full version of "Tripping the Rift" (is that the
> correct title). Now I know what I'd _like_ to be
> doing (but never will).

Perhaps it is something that I ought to know, but what is "Tripping the
Rift"?

> How are things on your end (besides the continuing
> stream of POVxperiments you keep producing)?

I've just finished the third and final year of college and I'm having my
exams these months. After summer I'll start at university studying
computer science and multimedia. I really look forward to that.

A frightening amount of my free time I spend on POV-Ray and related
projects. I have also worked as a pre-beta tester of POV-Ray 3.5 since I
was invited to it over a year ago. The pre-beta testers and the TAG Team
have not only tested POV-Ray 3.5 but also done major parts of the work
on updating the documentation, scene and include files, which has not
been a small job. For nine months I have worked as scene and include
files coordinator, and it has taken some of my time, but it is nice to
be able to help.

Followup-to povray.off-topic ...

Rune
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