HEllo group, and pov ray gurus i am currently stugggling at making a realistic
smoke, but whenever i' scale it up, smoke appears completely black and white and
let's no light throught it, i played with scaling options of emissions but my
objective it to provide some real transluscent smoke like in realist chimney
that pump quite low emissions that when we've seen in the 19 century industrial
chimenys !

here is the code that is not working when scaling thanhs to lowmuller pages !
when i cale it to about 150 all i get is completly black and white smoke that
not let light through... it now that emission directive shoud de scalled down
(divided by the bontainer scale, but no way)

sphere{ <0,0,0>, 1.5  // increased from 1 to 1.5, because of the turbulent
pattern !!!
        pigment { rgbt 1 }
        hollow

 interior{ //---------------------
    media{ method 3
//           emission 0.6
           scattering{ 1, // Type 1 = isotropic scattering, 2 = Mie haze, 3 =
Mie murky
                          // Type 4 = Rayleigh scattering,  5 =
Henyey-Greenstein scattering
                       <1,1,1>*3.00   // color of scattering haze
                       extinction  1.50  //  // 0 ~ 1 extinction
                       // how fast the scattering media absorbs light
                       // useful i.e. when the media absorbs too much light
                    // eccentricity i.e. -0.6 ~ +0.6 (if type>1 )
           } // end scattering

           density{ spherical // or: boxed
                    turbulence 0.85
                    color_map {
                    [0.00 rgb 0] // density at the border of the media
                    [0.05 rgb 0]
                    [0.20 rgb 0.2]
                    [0.30 rgb 0.6]
                    [0.40 rgb 1]
                    [1.00 rgb 1] // densitiy at the center of the media
                               } // end color_map
           } // end of density

           samples 1,1     // 3,3 for adaptive sampling
           intervals 3     //
           confidence 0.9  //
     } // end of media
----------------------------------------------------------------------
  } // ------------------ end of interior
 scale 1
 rotate<0,0,0>
 translate < -0.5, 1.50 + 0.20,0>
} //------------------ end of "Rauch"

please somebody help me i am stuck

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emission 0.6
<1,1,1>*3.00


When you scale up the object, you want to divide those numbers by the 
same amount. So if you "scale 100", add "/ 100" to the end of those 
lines. That will reduce the density proportionately and should keep it 
looking about the same.

Post a reply to this message

Am 05.09.2010 20:14, schrieb rodv92:
> HEllo group, and pov ray gurus i am currently stugggling at making a realistic
> smoke, but whenever i' scale it up, smoke appears completely black and white and
> let's no light throught it, i played with scaling options of emissions but my
> objective it to provide some real transluscent smoke like in realist chimney
> that pump quite low emissions that when we've seen in the 19 century industrial
> chimenys !

Here are a few hints:

- Don't use emission; real-life smoke does not emit visible light. It 
scatters and it absorbs - nothing else.

- For scattering media, always set extinction to 1.0; any other value is 
bogus.

- You'll probably want a /bit/ of absorption. Do use "absorption" for 
that, not the scattering's "extinction" parameter.

- Expect some media types' effects to scale not-quite-linearly. Don't 
expect you can compensate for a "scale 150" simply by a corresponding 
division of emission & scattering parameters; you'll probably need to 
tweak a bit. If you start with a "scale 10" you may get a better feeling 
how scaling affects the media, and how to compensate.

(And finally - I hope I'm not stepping on your toes here - try not to 
type so fast; it may help the legibility of your postings ;-))

Post a reply to this message

> HEllo group, and pov ray gurus i am currently stugggling at making a realistic
> smoke, but whenever i' scale it up, smoke appears completely black and white and
> let's no light throught it, i played with scaling options of emissions but my
> objective it to provide some real transluscent smoke like in realist chimney
> that pump quite low emissions that when we've seen in the 19 century industrial
> chimenys !
>
> here is the code that is not working when scaling thanhs to lowmuller pages !
> when i cale it to about 150 all i get is completly black and white smoke that
> not let light through... it now that emission directive shoud de scalled down
> (divided by the bontainer scale, but no way)
>

The aspect of media depends heavily on the lenght of the ray as it 
travel through it. Scaling up means that the travel lenght increases by 
the scaling amount. To compensate, you must reduce the density by the 
same value.

If you scale the container up by x150, then you must divide the density 
of the media by the same amount:
media{emission 0.6/150...
scattering{1, 1*3/150...
Altrernatively, you can divide the values in the color_map by that value 
instead of dividing the main density of the media:
     [0.00 rgb 0]
     [0.05 rgb 0]
     [0.20 rgb 0.2/150]
     [0.30 rgb 0.6/150]
     [0.40 rgb 1/150]
     [1.00 rgb 1/150]


Normaly, extinction should remain at 1, it's default value.
Also, normaly, smoke don't emit any light unless it's overheated to some 
ridiculous temperature. I'd replace the emission by some actual fading 
light_source near the top of the chemeny if you realy need some glow up 
there.

Some complementary notes about media sampling:

The default method is method 3

samples only take a single integer value. You can add a second value, 
but it will be ignored. method 1 and 2 DO use 2 values.

confidence is not needed and not used. Only usefull when using method 1 
ou 2.

You use samples 1. It will take only one sample ether as the ray enter 
the container or at the middle point. Both will give you the wrong 
result. The minimum value for samples should be 3 and defaults to 10.

NEVER EVER use intervals! It defaults to 1 and should be left at that 
value. It must only be used with method 1 or method 2.
"samples 30" is faster than "samples 5 intervals 3" for twice the total 
samples count. I know, I've done some testing and found that using ONLY 
samples you may have about 10 times as many samples as you get using 
samples and intervals for about the same render time.
A media with samples 300 rendered in about the same time as the same 
media with samples 5 intervals 5
intervals can also cause artefacts to appear.



Alain

Post a reply to this message

Alain <aze### [at] qwertyorg> wrote:

> > HEllo group, and pov ray gurus i am currently stugggling at making a realistic
> > smoke, but whenever i' scale it up, smoke appears completely black and white and
> > let's no light throught it, i played with scaling options of emissions but my
> > objective it to provide some real transluscent smoke like in realist chimney
> > that pump quite low emissions that when we've seen in the 19 century industrial
> > chimenys !
> >
> > here is the code that is not working when scaling thanhs to lowmuller pages !
> > when i cale it to about 150 all i get is completly black and white smoke that
> > not let light through... it now that emission directive shoud de scalled down
> > (divided by the bontainer scale, but no way)
> >
>
> The aspect of media depends heavily on the lenght of the ray as it
> travel through it. Scaling up means that the travel lenght increases by
> the scaling amount. To compensate, you must reduce the density by the
> same value.
>
> If you scale the container up by x150, then you must divide the density
> of the media by the same amount:
> media{emission 0.6/150...
> scattering{1, 1*3/150...
> Altrernatively, you can divide the values in the color_map by that value
> instead of dividing the main density of the media:
>      [0.00 rgb 0]
>      [0.05 rgb 0]
>      [0.20 rgb 0.2/150]
>      [0.30 rgb 0.6/150]
>      [0.40 rgb 1/150]
>      [1.00 rgb 1/150]
>
>
> Normaly, extinction should remain at 1, it's default value.
> Also, normaly, smoke don't emit any light unless it's overheated to some
> ridiculous temperature. I'd replace the emission by some actual fading
> light_source near the top of the chemeny if you realy need some glow up
> there.
>
> Some complementary notes about media sampling:
>
> The default method is method 3
>
> samples only take a single integer value. You can add a second value,
> but it will be ignored. method 1 and 2 DO use 2 values.
>
> confidence is not needed and not used. Only usefull when using method 1
> ou 2.
>
> You use samples 1. It will take only one sample ether as the ray enter
> the container or at the middle point. Both will give you the wrong
> result. The minimum value for samples should be 3 and defaults to 10.
>
> NEVER EVER use intervals! It defaults to 1 and should be left at that
> value. It must only be used with method 1 or method 2.
> "samples 30" is faster than "samples 5 intervals 3" for twice the total
> samples count. I know, I've done some testing and found that using ONLY
> samples you may have about 10 times as many samples as you get using
> samples and intervals for about the same render time.
> A media with samples 300 rendered in about the same time as the same
> media with samples 5 intervals 5
> intervals can also cause artefacts to appear.
>
>
>
> Alain

Hello Alain, thanks for the reply, it solved most of my issues. there is only
little problem left, when i scaale up, the bounding sphere appears in a light
shadowy grey even if a specify correct transmit value, i do not know if it is
linked to the fog, sky sphere above plan cloud etc...
if you could shed some light on the issue a would appreciate

Post a reply to this message

> Alain<aze### [at] qwertyorg>  wrote:

>>> HEllo group, and pov ray gurus i am currently stugggling at making a realistic
>>> smoke, but whenever i' scale it up, smoke appears completely black and white and
>>> let's no light throught it, i played with scaling options of emissions but my
>>> objective it to provide some real transluscent smoke like in realist chimney
>>> that pump quite low emissions that when we've seen in the 19 century industrial
>>> chimenys !
>>>
>>> here is the code that is not working when scaling thanhs to lowmuller pages !
>>> when i cale it to about 150 all i get is completly black and white smoke that
>>> not let light through... it now that emission directive shoud de scalled down
>>> (divided by the bontainer scale, but no way)
>>>
>>
>> The aspect of media depends heavily on the lenght of the ray as it
>> travel through it. Scaling up means that the travel lenght increases by
>> the scaling amount. To compensate, you must reduce the density by the
>> same value.
>>
>> If you scale the container up by x150, then you must divide the density
>> of the media by the same amount:
>> media{emission 0.6/150...
>> scattering{1, 1*3/150...
>> Altrernatively, you can divide the values in the color_map by that value
>> instead of dividing the main density of the media:
>>       [0.00 rgb 0]
>>       [0.05 rgb 0]
>>       [0.20 rgb 0.2/150]
>>       [0.30 rgb 0.6/150]
>>       [0.40 rgb 1/150]
>>       [1.00 rgb 1/150]
>>
>>
>> Normaly, extinction should remain at 1, it's default value.
>> Also, normaly, smoke don't emit any light unless it's overheated to some
>> ridiculous temperature. I'd replace the emission by some actual fading
>> light_source near the top of the chemeny if you realy need some glow up
>> there.
>>
>> Some complementary notes about media sampling:
>>
>> The default method is method 3
>>
>> samples only take a single integer value. You can add a second value,
>> but it will be ignored. method 1 and 2 DO use 2 values.
>>
>> confidence is not needed and not used. Only usefull when using method 1
>> ou 2.
>>
>> You use samples 1. It will take only one sample ether as the ray enter
>> the container or at the middle point. Both will give you the wrong
>> result. The minimum value for samples should be 3 and defaults to 10.
>>
>> NEVER EVER use intervals! It defaults to 1 and should be left at that
>> value. It must only be used with method 1 or method 2.
>> "samples 30" is faster than "samples 5 intervals 3" for twice the total
>> samples count. I know, I've done some testing and found that using ONLY
>> samples you may have about 10 times as many samples as you get using
>> samples and intervals for about the same render time.
>> A media with samples 300 rendered in about the same time as the same
>> media with samples 5 intervals 5
>> intervals can also cause artefacts to appear.
>>
>>
>>
>> Alain
>
> Hello Alain, thanks for the reply, it solved most of my issues. there is only
> little problem left, when i scaale up, the bounding sphere appears in a light
> shadowy grey even if a specify correct transmit value, i do not know if it is
> linked to the fog, sky sphere above plan cloud etc...
> if you could shed some light on the issue a would appreciate
>
>

The use of fog is the most porbable cause of what you describe.

With fog, you start evaluating the fog between the camera and the 
container sphere, this gives you a value for the fog effect. You then 
evaluate the fog inside the hollow sphere giving you another value. And 
finaly, you evaluate the fog for the rest of the ray after the sphere up 
untill you hit something else or the background, giving you a third 
value. All those values are added toggether and don't summ up to the 
same as the fog alone when you never encounter the container. This 
especialy true when you reatch the background or a background feature as 
a sky_sphere.

The cure is usualy to use actual media instead of fog... With the 
obvious effect on the render time.


Alain

Post a reply to this message

Alain <aze### [at] qwertyorg> wrote:

> > Alain<aze### [at] qwertyorg>  wrote:

> >>> HEllo group, and pov ray gurus i am currently stugggling at making a realistic
> >>> smoke, but whenever i' scale it up, smoke appears completely black and white and
> >>> let's no light throught it, i played with scaling options of emissions but my
> >>> objective it to provide some real transluscent smoke like in realist chimney
> >>> that pump quite low emissions that when we've seen in the 19 century industrial
> >>> chimenys !
> >>>
> >>> here is the code that is not working when scaling thanhs to lowmuller pages !
> >>> when i cale it to about 150 all i get is completly black and white smoke that
> >>> not let light through... it now that emission directive shoud de scalled down
> >>> (divided by the bontainer scale, but no way)
> >>>
> >>
> >> The aspect of media depends heavily on the lenght of the ray as it
> >> travel through it. Scaling up means that the travel lenght increases by
> >> the scaling amount. To compensate, you must reduce the density by the
> >> same value.
> >>
> >> If you scale the container up by x150, then you must divide the density
> >> of the media by the same amount:
> >> media{emission 0.6/150...
> >> scattering{1, 1*3/150...
> >> Altrernatively, you can divide the values in the color_map by that value
> >> instead of dividing the main density of the media:
> >>       [0.00 rgb 0]
> >>       [0.05 rgb 0]
> >>       [0.20 rgb 0.2/150]
> >>       [0.30 rgb 0.6/150]
> >>       [0.40 rgb 1/150]
> >>       [1.00 rgb 1/150]
> >>
> >>
> >> Normaly, extinction should remain at 1, it's default value.
> >> Also, normaly, smoke don't emit any light unless it's overheated to some
> >> ridiculous temperature. I'd replace the emission by some actual fading
> >> light_source near the top of the chemeny if you realy need some glow up
> >> there.
> >>
> >> Some complementary notes about media sampling:
> >>
> >> The default method is method 3
> >>
> >> samples only take a single integer value. You can add a second value,
> >> but it will be ignored. method 1 and 2 DO use 2 values.
> >>
> >> confidence is not needed and not used. Only usefull when using method 1
> >> ou 2.
> >>
> >> You use samples 1. It will take only one sample ether as the ray enter
> >> the container or at the middle point. Both will give you the wrong
> >> result. The minimum value for samples should be 3 and defaults to 10.
> >>
> >> NEVER EVER use intervals! It defaults to 1 and should be left at that
> >> value. It must only be used with method 1 or method 2.
> >> "samples 30" is faster than "samples 5 intervals 3" for twice the total
> >> samples count. I know, I've done some testing and found that using ONLY
> >> samples you may have about 10 times as many samples as you get using
> >> samples and intervals for about the same render time.
> >> A media with samples 300 rendered in about the same time as the same
> >> media with samples 5 intervals 5
> >> intervals can also cause artefacts to appear.
> >>
> >>
> >>
> >> Alain
> >
> > Hello Alain, thanks for the reply, it solved most of my issues. there is only
> > little problem left, when i scaale up, the bounding sphere appears in a light
> > shadowy grey even if a specify correct transmit value, i do not know if it is
> > linked to the fog, sky sphere above plan cloud etc...
> > if you could shed some light on the issue a would appreciate
> >
> >
>
> The use of fog is the most porbable cause of what you describe.
>
> With fog, you start evaluating the fog between the camera and the
> container sphere, this gives you a value for the fog effect. You then
> evaluate the fog inside the hollow sphere giving you another value. And
> finaly, you evaluate the fog for the rest of the ray after the sphere up
> untill you hit something else or the background, giving you a third
> value. All those values are added toggether and don't summ up to the
> same as the fog alone when you never encounter the container. This
> especialy true when you reatch the background or a background feature as
> a sky_sphere.
>
> The cure is usualy to use actual media instead of fog... With the
> obvious effect on the render time.
>
>
> Alain

Hi again! i appreciate very much your help.
the culprit in fact is a sky sphere to render a dawn sky.
i tried to replace it with a media, but the smoke container is still visible,
if you like i can send you my scene (or your friends) (it is quite nice) and
maybe you could see what could be done, sorry to bother you but pov ray has
quite a difficult learning curve :)
my mail is rodv92 at the gmail.com provider.

Rodrigo,

ps: are you french ?

Post a reply to this message

> Hi again! i appreciate very much your help.
> the culprit in fact is a sky sphere to render a dawn sky.
> i tried to replace it with a media, but the smoke container is still visible,
> if you like i can send you my scene (or your friends) (it is quite nice) and
> maybe you could see what could be done, sorry to bother you but pov ray has
> quite a difficult learning curve :)
> my mail is rodv92 at the gmail.com provider.
>
> Rodrigo,
>
> ps: are you french ?
>
>
>
>

A sky_sphere is a background feature. Any ray that encounter it have an 
undefined length.
This leads to some problem when you have any media or fog in some 
container. Whenever you reatch the background directly, you have 
undefined ray length. Whenever a ray encounter a transparent object, you 
effectively get 3 ray segments, 2 of whitch do have a precise, finite, 
length and one of undefinite length.
That's what causes the container to become visible.

A workaround:
Use a very large "world sphere". That's a unit sphere that have the 
pigment you would use for the sky_sphere, that is scaled up by a large 
value like 100000. Make that sphere hollow or use the "inverse" keyword 
so that media and fog can exist within.

Now, you no longer have undefined ray length.
You can post your scene on povray.scene-files if it's relatively small 
and self contained, or povray.binaries.scene-files for a large one 
needing some include or other resources. On that last group, you can 
post a zip containing your scene and all of it's parts.



native language, and, like most francophone in my area, I'm functionaly 
bilingual.


Alain

Post a reply to this message

> You can post your scene on povray.scene-files if it's relatively small
> and self contained, or povray.binaries.scene-files for a large one
> needing some include or other resources. On that last group, you can
> post a zip containing your scene and all of it's parts.
>
>
Small corection: it's povray.TEXT.scene-files for the smaller scenes.

Post a reply to this message

Alain <aze### [at] qwertyorg> wrote:

>
> > You can post your scene on povray.scene-files if it's relatively small
> > and self contained, or povray.binaries.scene-files for a large one
> > needing some include or other resources. On that last group, you can
> > post a zip containing your scene and all of it's parts.
> >
> >
> Small corection: it's povray.TEXT.scene-files for the smaller scenes.

Thanks for the suggestions,

and indeed i tried all the combinations :

sky_sphere
"world sphere"
sky by using media

all, unfortunately, make the container visible (however when using media the
container is partially visible (truncated with a white aura, maybe with some
adaptations it is the way to go...)

if somebody could get a look at my scene, the code is a bit messy, the sky
elements are at the beginning of the code, the smoke is quite at the end,
(you may also comment the code creating the trees)

Thanks in advance, it will help me to move on with my first POV ray scene.

http://news.povray.org/povray.binaries.scene-files/thread/%3Cweb.4c9cea4f846f1355e03d6d450%40news.povray.org%3E/

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