Hi,

I'm working on my annual Christmas card, and I'm trying to use media to
simulate a string of Christmas lights.  It looks pretty good so far, but
two questions have arisen:

1)  Are the media effects dependent on the scale of the container?  For
example, if my light bulb is contained by a 5 inch or a 50 inch sphere,
should I expect different results?

2)  Can I have more than one media container in a scene?  I have tried
to surround each bulb with its own container (a sphere),  but it seems
that only one of the containers works.  The rest don't do anything.

Any thoughts?

Thanks,

Eric

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Eric Gundersen wrote:
> 
> 1)  Are the media effects dependent on the scale of the container?  For
> example, if my light bulb is contained by a 5 inch or a 50 inch sphere,
> should I expect different results?
>

Media density (per unit of volume) remains constant no matter how you scale the
container. This means the same media in a smaller container will look more
transparent, because there is less media to "see through".
If you want the transparency of the media to appear the same after scaling, you
can do this: let's say Si is the initial scale of your media(container), Sf is
the final scale, and D is the initial density. The new density for the scaled
media is:
(pow((Si.x * Si.y * Si.z) / (Sf.x * Sf.y * Sf.z), 1/3) * D)

> 2)  Can I have more than one media container in a scene?  I have tried
> to surround each bulb with its own container (a sphere),  but it seems
> that only one of the containers works.  The rest don't do anything.
> 

Of course you can have multiple containers. Are you sure you did it right? All
containers need to be hollow, and they all must have a media attached. Here's a
simple example, with two media containers:

sphere{
  <-1,0,0>,1
  pigment{rgbf 1}
  interior{media{emission 1}}
  hollow
}
sphere{
  <1,0,0>,1
  pigment{rgbf 1}
  interior{media{emission 1}}
  hollow
}

-- 
Margus Ramst

Personal e-mail: mar### [at] peakeduee
TAG (Team Assistance Group) e-mail: mar### [at] tagpovrayorg

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Thanks.  I appreciate the input!

Margus Ramst wrote:

> Eric Gundersen wrote:
> >
> > 1)  Are the media effects dependent on the scale of the container?  For
> > example, if my light bulb is contained by a 5 inch or a 50 inch sphere,
> > should I expect different results?
> >
>
> Media density (per unit of volume) remains constant no matter how you scale the
> container. This means the same media in a smaller container will look more
> transparent, because there is less media to "see through".
> If you want the transparency of the media to appear the same after scaling, you
> can do this: let's say Si is the initial scale of your media(container), Sf is
> the final scale, and D is the initial density. The new density for the scaled
> media is:
> (pow((Si.x * Si.y * Si.z) / (Sf.x * Sf.y * Sf.z), 1/3) * D)
>
> > 2)  Can I have more than one media container in a scene?  I have tried
> > to surround each bulb with its own container (a sphere),  but it seems
> > that only one of the containers works.  The rest don't do anything.
> >
>
> Of course you can have multiple containers. Are you sure you did it right? All
> containers need to be hollow, and they all must have a media attached. Here's a
> simple example, with two media containers:
>
> sphere{
>   <-1,0,0>,1
>   pigment{rgbf 1}
>   interior{media{emission 1}}
>   hollow
> }
> sphere{
>   <1,0,0>,1
>   pigment{rgbf 1}
>   interior{media{emission 1}}
>   hollow
> }
>
> --
> Margus Ramst
>
> Personal e-mail: mar### [at] peakeduee
> TAG (Team Assistance Group) e-mail: mar### [at] tagpovrayorg

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In article <3A14A2F2.7A599C3E@flash.net>, gun### [at] flashnet wrote:

> I'm working on my annual Christmas card, and I'm trying to use media 
> to simulate a string of Christmas lights.

Hmm, are you using MegaPOV? If so, you might want to check out the glow 
patch. It might be a good alternative to media for this.


> 1)  Are the media effects dependent on the scale of the container?  For
> example, if my light bulb is contained by a 5 inch or a 50 inch sphere,
> should I expect different results?

Yes. The appearance of media is determined by the distance you see 
through it. If you scale something up by 2, everything will appear twice 
as bright, shadows cast by scattering or absorbing media will be twice 
as dark, etc. because there is twice as much media between any two 
points.


> 2)  Can I have more than one media container in a scene?  I have tried
> to surround each bulb with its own container (a sphere),  but it seems
> that only one of the containers works.  The rest don't do anything.

You can have as many containers as you want, they are just ordinary 
objects. Are you making sure that all the containers have "hollow" 
specified and are not in any non-hollow objects?

-- 
Christopher James Huff
Personal: chr### [at] maccom, http://homepage.mac.com/chrishuff/
TAG: chr### [at] tagpovrayorg, http://tag.povray.org/

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