Hi,

I'm trying to use scattering media inside a translucent sphere in order to
see various points of light inside the sphere as glowing orbs. (In case
you're wondering, I'm trying to model the "Christmas light" effect of the
bussard collector domes in the original starship Enterprise.)

Although this works, I'm having a problem with the scattering media looking
very grainy or sandy. Can someone please post a quick pointer on how to
adjust the apparent density of the media? I've tried to understand the
obtuse documentation on this subject and I'm pulling out what little is left
of my hair. ;)

Thanks!
Scott Gammans

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If you're using Povray Beta, you could try
and add method 3 intervals 1 to the
media description. This turns the adaptive
sampling method on.
If you want some more control,
use method 2 with at least 20 intervals. If
its not detailed enough, use more intervals.
Method 1 (the POV-Ray 3.1 media-type)
is almost always grainy, so you'd have to go
for some dozens of intervals (60? 70? 200?)


--
Tim Nikias
Homepage: http://www.digitaltwilight.de/no_lights/index.html

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Hmm.. already tried increasing the intervals *and* method 1... all it seemed
to do was slow down the rendering time even further.

I am indeed using POV-Ray 3.5 beta 12. I guess I should post a code example
to show what I'm doing right now...

#declare Bussard_Collector_Dome_Interior = interior {
     ior 1
     fade_distance 1
     fade_power 1001
     fade_color rgb <0.9,0.9,0.9>
     media {
          intervals 10
          samples 3,10
          confidence 0.99
          variance 0.1/128
          ratio 1
          scattering {2,   rgb<0.45,0.3,0.25>}
          method 2
          jitter 0
          density {spherical  scale 7.5}    // radius of dome is 7.5
     }
}

thanks...
Scott Gammans

"Tim Nikias" <tim### [at] gmxde> wrote in message
news:3C879572.D3E84AF2@gmx.de...
> If you're using Povray Beta, you could try
> and add method 3 intervals 1 to the
> media description. This turns the adaptive
> sampling method on.
> If you want some more control,
> use method 2 with at least 20 intervals. If
> its not detailed enough, use more intervals.
> Method 1 (the POV-Ray 3.1 media-type)
> is almost always grainy, so you'd have to go
> for some dozens of intervals (60? 70? 200?)
>
>
> --
> Tim Nikias
> Homepage: http://www.digitaltwilight.de/no_lights/index.html
>
>

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In article <3c878cca$1@news.povray.org>,
 "Scott Gammans" <nos### [at] yahoocom> wrote:

> Although this works, I'm having a problem with the scattering media looking
> very grainy or sandy. Can someone please post a quick pointer on how to
> adjust the apparent density of the media? I've tried to understand the
> obtuse documentation on this subject and I'm pulling out what little is left
> of my hair. ;)

For such a simple effect, you don't really need scattering media, you 
should do fine with emitting media and a spherical density, which will 
be faster. The grainy look is caused by the sampling method, you can 
reduce it by using more samples, or use method 2 or 3 in MegaPOV or 
POV-Ray 3.5.

-- 
Christopher James Huff <chr### [at] maccom>
POV-Ray TAG e-mail: chr### [at] tagpovrayorg
TAG web site: http://tag.povray.org/

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Tim Nikias <tim### [at] gmxde> wrote:
> If you're using Povray Beta, you could try
> and add method 3 intervals 1 to the
> media description. This turns the adaptive
> sampling method on.

  But method 3 is the default in POV-Ray 3.5. You don't need to explicitly
add it.

-- 
#macro N(D)#if(D>99)cylinder{M()#local D=div(D,104);M().5,2pigment{rgb M()}}
N(D)#end#end#macro M()<mod(D,13)-6mod(div(D,13)8)-3,10>#end blob{
N(11117333955)N(4254934330)N(3900569407)N(7382340)N(3358)N(970)}//  - Warp -

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In article <3c879737$1@news.povray.org>,
 "Scott Gammans" <nos### [at] yahoocom> wrote:

> Hmm.. already tried increasing the intervals *and* method 1... all it seemed
> to do was slow down the rendering time even further.

You only need 1 or 2 intervals, POV will make more as needed. Instead, 
increase the number of samples taken per interval, try "intervals 1 
samples 15" with "method 3".

-- 
Christopher James Huff <chr### [at] maccom>
POV-Ray TAG e-mail: chr### [at] tagpovrayorg
TAG web site: http://tag.povray.org/

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D'oh! I didn't realize that you could have multiple media statements inside
an interior declaration. Your technique works so much better... and renders
orders of magnitude faster.

http://www.scottgammans.com/cgi_enterprise/scattering_media.jpg
http://www.scottgammans.com/cgi_enterprise/emitting_media.jpg

That first render using scattering media took nearly two hours to complete,
didn't look right, and didn't use anti-aliasing. The second render using
emitting media took less than 2 minutes to complete, looks SO much closer to
what I am trying to achieve, and even threw in AA 0.3 for good measure.

Those damn Bussard collector domes have been giving me fits... your advice
was right on target. Thanks Christopher!! :)

--Scott Gammans

"Christopher James Huff" <chr### [at] maccom> wrote in message
news:chr### [at] netplexaussieorg...
> In article <3c878cca$1@news.povray.org>,
>  "Scott Gammans" <nos### [at] yahoocom> wrote:
> For such a simple effect, you don't really need scattering media, you
> should do fine with emitting media and a spherical density, which will
> be faster. The grainy look is caused by the sampling method, you can
> reduce it by using more samples, or use method 2 or 3 in MegaPOV or
> POV-Ray 3.5.

Post a reply to this message