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