POV-Ray : Newsgroups : povray.documentation.inbuilt : radiosity and media Server Time: 26 Jun 2019 20:05:35 GMT
  radiosity and media (Message 1 to 5 of 5)  
From: Christian Froeschlin
Subject: radiosity and media
Date: 1 Feb 2013 23:02:03
Message: <510c496b@news.povray.org>
I tend to forget how they work together, and then I rediscover that
the explanation given in the radiosity reference (3.3.4) regarding media
is rather terse ("Radiosity estimation can be affected by media" for
the media parameter).

There are different effects possible and it is not quite clear what
happens here. Can media get illuminated by radiosity? Does media reduce
the amount of light received by objects in the vicinity of an emitting
object? Does emissive media contribute light to radiosity calculations?
(the latter question is answered in the media documentation for
emission). Which effect is not possible, which is always
present, which is controlled by the parameter?

Media with photons and radiosity with normals are explained in
more detail in the tutorial section (2.3.7.7 / 2.3.8.4) that would
probably be a good place for some detail on radiosity + media
(with links from the radiosity and media reference?)


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From: James Holsenback
Subject: Re: radiosity and media
Date: 2 Feb 2013 04:25:09
Message: <510c9525$1@news.povray.org>
On 02/01/2013 06:02 PM, Christian Froeschlin wrote:
> I tend to forget how they work together, and then I rediscover that
> the explanation given in the radiosity reference (3.3.4) regarding media
> is rather terse ("Radiosity estimation can be affected by media" for
> the media parameter).
>
> There are different effects possible and it is not quite clear what
> happens here. Can media get illuminated by radiosity? Does media reduce
> the amount of light received by objects in the vicinity of an emitting
> object? Does emissive media contribute light to radiosity calculations?
> (the latter question is answered in the media documentation for
> emission). Which effect is not possible, which is always
> present, which is controlled by the parameter?
>
> Media with photons and radiosity with normals are explained in
> more detail in the tutorial section (2.3.7.7 / 2.3.8.4) that would
> probably be a good place for some detail on radiosity + media
> (with links from the radiosity and media reference?)

I'd agree, the reference passages you pointed out are indeed lacking, 
and some of the topics are expanded adequately in the tutorial. 
Expanding the missing topic (radiosity & media) seems to be the 
challenge ... I'm open to suggestions ;-)


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From: Kenneth
Subject: Re: radiosity and media
Date: 5 Feb 2013 16:55:01
Message: <web.51113755cb86620bc2d977c20@news.povray.org>
Christian Froeschlin <chr### [at] chrfrde> wrote:
> I tend to forget how they work together...
>
> There are different effects possible and it is not quite clear what
> happens here. Can media get illuminated by radiosity? Does media reduce
> the amount of light received by objects in the vicinity of an emitting
> object? Does emissive media contribute light to radiosity calculations?

There *was*/is a problem in POV-Ray with rad and media (in the current stable
v3.62 release and earlier) which sort of contributes to the 'lack of clarity' in
the docs. For object media (a sphere with a transparent pigment, for example),
any other objects or parts thereof that are inside the media sphere do not
receive radiosity lighting *from the media*--neither scattering nor emission
types--but objects OUTSIDE it do. ('Atmospheric' media doesn't have this
problem.) But it takes a rather particular/specialized test scene to show the
effect; it's usually not grossly obvious, due to other scene objects also
contributing rad light.


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From: Simon Copar
Subject: Re: radiosity and media
Date: 18 Apr 2013 23:25:01
Message: <web.51708070cb86620bf42173100@news.povray.org>
"Kenneth" <kdw### [at] gmailcom> wrote:
> Christian Froeschlin <chr### [at] chrfrde> wrote:
> > I tend to forget how they work together...
> >
> > There are different effects possible and it is not quite clear what
> > happens here. Can media get illuminated by radiosity? Does media reduce
> > the amount of light received by objects in the vicinity of an emitting
> > object? Does emissive media contribute light to radiosity calculations?
>
> There *was*/is a problem in POV-Ray with rad and media (in the current stable
> v3.62 release and earlier) which sort of contributes to the 'lack of clarity' in
> the docs. For object media (a sphere with a transparent pigment, for example),
> any other objects or parts thereof that are inside the media sphere do not
> receive radiosity lighting *from the media*--neither scattering nor emission
> types--but objects OUTSIDE it do. ('Atmospheric' media doesn't have this
> problem.) But it takes a rather particular/specialized test scene to show the
> effect; it's usually not grossly obvious, due to other scene objects also
> contributing rad light.

It does not work for me. What am I missing? My scene (stripped down to the bare
minimum) is below. The function {} might seem strange - it is generated
externally, designed to cover a certain object with fire (object not included).

I expected the floor to be at least faintly illuminated by the fire, but it
isn't.

My version is RC6 compiled as arch linux package (RC7 is not yet available in
the package form).

#version 3.7;
#declare CAM=<0,-10,1.5>;
camera {
  location CAM
  look_at <0,0,1.7>
  right x
  up (image_height/image_width)*z
  sky z
}


global_settings {
  max_trace_level 10
  assumed_gamma 2.2

  radiosity {
    brightness 1
    count 180
    pretrace_start 0.08
    pretrace_end 0.01
    recursion_limit 2
    media on
  }

}

plane {
  z,0
  texture {
    pigment {
      wrinkles
      color_map {
 [0 color rgb <0.35,0.2,0.1>]
 [0.5 color rgb <0.25,0.2,0.2>]
 [0.8 color rgb <0.09,0.075,0.075>]
      }
      turbulence 0.3
      scale <10,0.3,1>
    }
    normal {
      bumps 0.1
      scale <0.2,0.5,1>
    }
    finish {
      ambient 1
      diffuse 1.5
      specular 0.3
      roughness 0.02
    }
    rotate 37
  }
}



cylinder {
  <0,0,0.85>,<0,0,3.2>,1.9
  interior {
    media {
      intervals 2
      emission 1
      density {
 function {
   max(0,exp(-3*(z-(1.122814)))-0.5*exp(-6*(z-(1.122814)))
-8*(x-(-0.483531))*(x-(-0.483531))-8*(y-(-1.046504))*(y-(-1.046504)) )
   +max(0,exp(-3*(z-(1.126421)))-0.5*exp(-6*(z-(1.126421)))
-8*(x-(-0.367037))*(x-(-0.367037))-8*(y-(-0.759095))*(y-(-0.759095)) )
   +max(0,exp(-3*(z-(1.139738)))-0.5*exp(-6*(z-(1.139738)))
-8*(x-(-0.581356))*(x-(-0.581356))-8*(y-(-0.585519))*(y-(-0.585519)) )
   +max(0,exp(-3*(z-(1.179992)))-0.5*exp(-6*(z-(1.179992)))
-8*(x-(-0.596242))*(x-(-0.596242))-8*(y-(-0.749582))*(y-(-0.749582)) )
   +max(0,exp(-3*(z-(1.213622)))-0.5*exp(-6*(z-(1.213622)))
-8*(x-(-0.358601))*(x-(-0.358601))-8*(y-(-0.733758))*(y-(-0.733758)) )
   +max(0,exp(-3*(z-(1.229194)))-0.5*exp(-6*(z-(1.229194)))
-8*(x-(-0.873088))*(x-(-0.873088))-8*(y-(-1.011451))*(y-(-1.011451)) )
   +max(0,exp(-3*(z-(1.243289)))-0.5*exp(-6*(z-(1.243289)))
-8*(x-(-0.496820))*(x-(-0.496820))-8*(y-(-0.302525))*(y-(-0.302525)) )
   +max(0,exp(-3*(z-(1.244577)))-0.5*exp(-6*(z-(1.244577)))
-8*(x-(-0.989911))*(x-(-0.989911))-8*(y-(-0.673642))*(y-(-0.673642)) )
   +max(0,exp(-3*(z-(1.250126)))-0.5*exp(-6*(z-(1.250126)))
-8*(x-(-0.588272))*(x-(-0.588272))-8*(y-(0.369979))*(y-(0.369979)) )
 }
 color_map {
   [0.2 color rgb 0]
   [0.5 color rgb <0.3,0,0>]
   [0.8 color rgb <1,1,0>]
   [0.9 color rgb 2*<1,1,1>]
 }
 warp {
   turbulence 0.44
   lambda 2
   omega 0.7
   octaves 3
 }
      }

    }
  }
  texture {
    pigment { color rgbft 1 }
  }
  hollow
}


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From: Simon Copar
Subject: Re: radiosity and media
Date: 22 Apr 2013 15:35:02
Message: <web.51755776cb86620b65a03f8f0@news.povray.org>
Never mind. Wrong topic and stupid question. The brightness is too low to have
any effect on radiosity.


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