POV-Ray : Newsgroups : povray.general : problem with turbulence in 'fog' Server Time: 17 Jun 2019 06:35:15 GMT
  problem with turbulence in 'fog' (Message 1 to 10 of 10)  
From: Kenneth
Subject: problem with turbulence in 'fog'
Date: 3 Dec 2017 22:55:01
Message: <web.5a2480375c387c0f89df8d30@news.povray.org>
Unless I'm completely mistaken about what to expect, it seems that turbulence
does not work at all when used in plain fog, even though it's supposed to.

In POV-Ray's demo scenes (scenes/interior/) there are two fog files, 'foglayr'
and 'foglyr2'. Run either one of those, and wildly increase the turbulence
amounts. There is still no turbulence that I can see. Tested in the latest
3.8.0-alpha and in 3.7.1-beta9

BTW, warp{turbulence...} doesn't work in fog either; it throws a fatal error.


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From: Alain
Subject: Re: problem with turbulence in 'fog'
Date: 3 Dec 2017 23:13:35
Message: <5a24851f$1@news.povray.org>
Le 17-12-03 à 17:52, Kenneth a écrit :
> Unless I'm completely mistaken about what to expect, it seems that turbulence
> does not work at all when used in plain fog, even though it's supposed to.
> 
> In POV-Ray's demo scenes (scenes/interior/) there are two fog files, 'foglayr'
> and 'foglyr2'. Run either one of those, and wildly increase the turbulence
> amounts. There is still no turbulence that I can see. Tested in the latest
> 3.8.0-alpha and in 3.7.1-beta9
> 
> BTW, warp{turbulence...} doesn't work in fog either; it throws a fatal error.
> 
> 

I noted the same thing way back using version 3.5.


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From: clipka
Subject: Re: problem with turbulence in 'fog'
Date: 3 Dec 2017 23:38:48
Message: <5a248b08$1@news.povray.org>
Am 03.12.2017 um 23:52 schrieb Kenneth:
> Unless I'm completely mistaken about what to expect, it seems that turbulence
> does not work at all when used in plain fog, even though it's supposed to.
> 
> In POV-Ray's demo scenes (scenes/interior/) there are two fog files, 'foglayr'
> and 'foglyr2'. Run either one of those, and wildly increase the turbulence
> amounts. There is still no turbulence that I can see. Tested in the latest
> 3.8.0-alpha and in 3.7.1-beta9

Not sure, but maybe try toying around with `turb_depth`.

According to the source code, the turbulence parameter does /something/.


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From: omniverse
Subject: Re: problem with turbulence in 'fog'
Date: 4 Dec 2017 01:35:00
Message: <web.5a24a58480800e7eb6328ee20@news.povray.org>
clipka <ano### [at] anonymousorg> wrote:
> Am 03.12.2017 um 23:52 schrieb Kenneth:
> > Unless I'm completely mistaken about what to expect, it seems that turbulence
> > does not work at all when used in plain fog, even though it's supposed to.
> >
> > In POV-Ray's demo scenes (scenes/interior/) there are two fog files, 'foglayr'
> > and 'foglyr2'. Run either one of those, and wildly increase the turbulence
> > amounts. There is still no turbulence that I can see. Tested in the latest
> > 3.8.0-alpha and in 3.7.1-beta9
>
> Not sure, but maybe try toying around with `turb_depth`.
>
> According to the source code, the turbulence parameter does /something/.

Yep it does work. while back I couldnít get it to show any turbulence and
finally did, donít remember exactly what the reason was. Clipka might be onto
something.

 Oh yeah it was one of the example scenes of fog type 2, ground fog, I was
checking with 3.7.1 beta. Thought it was something about thickness or distance,
when I get home Iíll take a look.


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From: omniverse
Subject: Re: problem with turbulence in 'fog'
Date: 4 Dec 2017 04:00:01
Message: <web.5a24c7b380800e7e9c5d6c810@news.povray.org>
"omniverse" <omn### [at] charternet> wrote:
> clipka <ano### [at] anonymousorg> wrote:
> > Am 03.12.2017 um 23:52 schrieb Kenneth:
> > > Unless I'm completely mistaken about what to expect, it seems that turbulence
> > > does not work at all when used in plain fog, even though it's supposed to.
> > >
> > > In POV-Ray's demo scenes (scenes/interior/) there are two fog files, 'foglayr'
> > > and 'foglyr2'. Run either one of those, and wildly increase the turbulence
> > > amounts. There is still no turbulence that I can see. Tested in the latest
> > > 3.8.0-alpha and in 3.7.1-beta9
> >
> > Not sure, but maybe try toying around with `turb_depth`.
> >
> > According to the source code, the turbulence parameter does /something/.
>
> Yep it does work. while back I couldnít get it to show any turbulence and
> finally did, donít remember exactly what the reason was. Clipka might be onto
> something.
>
>  Oh yeah it was one of the example scenes of fog type 2, ground fog, I was
> checking with 3.7.1 beta. Thought it was something about thickness or distance,
> when I get home Iíll take a look.

Hmmm. Not what I was thinking. The scene file is ..scenes\advanced\mist.pov and
it was ground fog, but what it was the turbulence itself I had to increase
drastically to see it good. Also increasing 'distance' to make it more apparent
closest to camera, otherwise it tends to wash out in itself and scene
background.

Still can't see obvious turbulent fog above the water in that scene either, so
it looks almost like a surface texture.

Here's the fog statement I used, changed more before posting this, with a
curious thing about turb_depth 0.5 and other values used for that. Please take a
look at that mist.pov if you will:

fog{
    color rgb 0.7 //Gray70
    fog_type 2
    fog_alt 0.67
    fog_offset 0
    distance 4
    turbulence <0.8, 0.2, 0.8>*9
   // turb_depth 0.5 // 0.5 same as without any?
    omega 0.6
    lambda 1.2
    octaves 6
}


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From: omniverse
Subject: Re: problem with turbulence in 'fog'
Date: 4 Dec 2017 04:25:00
Message: <web.5a24cdaa80800e7e9c5d6c810@news.povray.org>
"Kenneth" <kdw### [at] gmailcom> wrote:
> Unless I'm completely mistaken about what to expect, it seems that turbulence
> does not work at all when used in plain fog, even though it's supposed to.
>
> In POV-Ray's demo scenes (scenes/interior/) there are two fog files, 'foglayr'
> and 'foglyr2'. Run either one of those, and wildly increase the turbulence
> amounts. There is still no turbulence that I can see. Tested in the latest
> 3.8.0-alpha and in 3.7.1-beta9
>
> BTW, warp{turbulence...} doesn't work in fog either; it throws a fatal error.

I should have looked at the aforementioned scene file(s) before posting last
time.

There seems to be better parameter values to use for making the turbulent fog
appear, and even so maybe it isn't doing what you would expect of it because of
the inherent design of fog. Or to put it another way, that it isn't like media.
Not sure if I'm right on that point, but anyway...

fog{
    color rgbt <.7,.7,.7,.25>
    fog_type 2
    fog_alt 5 // increased
    fog_offset 0
    distance 1.5*50 // 50X original
    turbulence <.15, .15, .15>
    //omega 0.35
    //lambda 1.25
    //octaves 5
}

That shows it non-uniformly without ramping up turbulence alone. However...
those omega, lambda and octaves parameters seem to cause trouble so leaving them
out (or as default?) looked best to me.

Now notice I had to increase distance (again) to desaturate the foreground, just
like I did for the mist.pov scene. While also thickening the fog vertically too.

Perhaps this is about the fog setup after all.

Bob


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From: Kenneth
Subject: Re: problem with turbulence in 'fog'
Date: 4 Dec 2017 07:45:01
Message: <web.5a24fa5080800e7e89df8d30@news.povray.org>
"omniverse" <omn### [at] charternet> wrote:

> Hmmm. Not what I was thinking. The scene file is ..scenes\advanced\mist.pov
> and it was ground fog, but what it was the turbulence itself I had to
> increase drastically to see it good. Also increasing 'distance' to make
> it more apparent closest to camera, otherwise it tends to wash out in itself
> and scene background.
>
> There seems to be better parameter values to use for making the turbulent fog
> appear, and even so maybe it isn't doing what you would expect of it
> because of the inherent design of fog. Or to put it another way, that it
> isn't like media.

Yes, I'm finally seeing 'an effect' in the mist.pov file (by changing
some things)-- although I'm not exactly sure what it is that I'm seeing(!) I
agree with your assesment, that the fog itself may be 'hiding' the turbulence
effect-- unless the various parameters all work together in a particular way.
Try this instead:

fog{
    color Gray70
    fog_type 2
    fog_alt 0.001
    fog_offset 1.3
    distance 15
   // turbulence (1 + 50*clock)*<.15, .15, .15>
    turbulence 40*<.15, .15, .15>
    turb_depth 1.5 // try changing to 0.0 then to 4.0
    omega 0.001 // to get rid of any 'graniness'
   // lambda .001 // 1.25
   // octaves 10  // 5
   // scale 3  // has NO effect on turbulence (or on anything else, as far
   // as I can see)
}

The 'white blotches' (the turbulence) appear to be visible on object *surfaces*,
although I can't see anything within the misty fog itself. And turb_depth seems
to be a necessary addition-- and within a small range of values (I think!) BTW,
those splotches can't be scaled; if your scene uses larger objects, the
splotches appear smaller. That seems like a limitation in itself.

> Still can't see obvious turbulent fog above the water in that scene either,
> so it looks almost like a surface texture.

I agree. My own main expectation of turbulence was that it should cause the fog
to appear 'lumpy' at it's own higher 'horizontal surface' (or pseudo-surface,
that is-- somewhere between fog_alt and fog_offset, depending on the density),
climbing 'above and below' that imaginary surface like real rolling fog. But
maybe that's a wrong supposition(?) But it raises the question of what
turbulence *is* supposed to be doing.

> However... those omega, lambda and octaves parameters seem to cause trouble
> so leaving them out (or as default?) looked best to me.
>
I think some of the parameters in the mist.pov file (and the other files) are
actually fighting against the turbulence appearance...like the turbulence value
is set way too low, and the omega value is too high (even at .35 or whatever.)
It makes me think that something in the underlying fog or turbulence code may
have changed in the (distant) past-- because the example scenes (and the
documentation) apparently expect the turbulence to be readily visible, which it
isn't now.

Meanwhile, I'm running some animation experiments on mist.pov and one of the
other files, to see what happens when various parameters change.


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From: Kenneth
Subject: Re: problem with turbulence in 'fog'
Date: 4 Dec 2017 07:55:00
Message: <web.5a24fe9c80800e7e89df8d30@news.povray.org>
Alain <kua### [at] videotronca> wrote:

>
> I noted the same thing way back using version 3.5.

Yeah, I noticed this 'apparent' non-turbulence effect way back in the v3.6.x
days as well... but I didn't feel bold enough to mention it then, because I
thought I was seeing something that no one else was seeing ;-)

I'm glad to know that I wasn't alone!


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From: Kenneth
Subject: Re: problem with turbulence in 'fog'
Date: 4 Dec 2017 08:00:00
Message: <web.5a25005980800e7e89df8d30@news.povray.org>
clipka <ano### [at] anonymousorg> wrote:

>
> Not sure, but maybe try toying around with `turb_depth`.
>
> According to the source code, the turbulence parameter does /something/.

You're right, there is *some* kind of effect (although I'm still experimenting
to determine what that 'something' is!) A non-zero turb_depth does seem to be
important; but some of the example fog files don't even have that parameter. I'm
not sure which one(s) though-- I think I 'saved' some changes to those files
during my experimentation. A bad thing to do, I know :-[  But I still have the
pristine files in my original 3.7.0 install...


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From: Kenneth
Subject: Re: problem with turbulence in 'fog'
Date: 4 Dec 2017 08:15:01
Message: <web.5a2502e480800e7e89df8d30@news.povray.org>
BTW, the doc's description of turb_depth is not very clear (at least to me):

"Additionally the fog turbulence may be scaled along the direction of the
viewing ray using the turb_depth amount. Typical values are from 0.0 to 1.0 or
more. The default value is 0.5 but any float value may be used."

What does 'may be scaled' mean? Is it the *size* of the turbulence
effect--scaling with distance-- or is it the *amount* of turbulence that
changes? The meaning is hard to discern, visually.


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