Help before I climb the bell tower and start shooting!

please :-)

I have a simple radiosity scene, a cylinder with ambient 1 encased in a much
bigger cylinder filled with cylindrical media.  For some reason I cant
fathom, I cant see the media.  If there some setting that needs to be turned
on for radiosity and media to interact

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Josh wrote:

> Help before I climb the bell tower and start shooting!
> 
> please :-)
> 
> I have a simple radiosity scene, a cylinder with ambient 1 encased in a much
> bigger cylinder filled with cylindrical media.  For some reason I cant
> fathom, I cant see the media.  If there some setting that needs to be turned
> on for radiosity and media to interact
> 
> 

Make sure the container cylinder is hollow.
Media on should be in the radiosity block.
Try a constant density to rule out the cylindrical pattern as being  the 
cause.

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And lo on Thu, 01 Jul 2004 09:31:08 -0500, Mike Raiford  
<mra### [at] hotmailcom> did spake, saying:

> Josh wrote:
>
>> Help before I climb the bell tower and start shooting!
>>  please :-)
>>  I have a simple radiosity scene, a cylinder with ambient 1 encased in  
>> a much
>> bigger cylinder filled with cylindrical media.  For some reason I cant
>> fathom, I cant see the media.  If there some setting that needs to be  
>> turned
>> on for radiosity and media to interact
>>
>
> Make sure the container cylinder is hollow.
> Media on should be in the radiosity block.
> Try a constant density to rule out the cylindrical pattern as being  the  
> cause.

I thought media would only function with a light_source producing a ray to  
sample along as stated in 6.8, AFAIK ambient, like emission, doesn't  
produce light in this way even using radiosity.

--
Phil Cook

-- 
All thoughts and comments are my own unless otherwise stated and I am  
happy to be proven wrong.

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"Josh" <som### [at] microsoftcom> wrote:
> Help before I climb the bell tower and start shooting!
>
> please :-)
>
> I have a simple radiosity scene, a cylinder with ambient 1 encased in a much
> bigger cylinder filled with cylindrical media.  For some reason I cant
> fathom, I cant see the media.  If there some setting that needs to be turned
> on for radiosity and media to interact

For the radiosity to affect media, you need "media on" in the radiosity
block in the global_settings.
The cylindrical pattern have a radius of one (1), you have to scale it to
the radius of your big cylinder. Set your media as scattering and adjust
it's density if it's to light or dense. Also, the big cylinder need to have
the hollow attribute or no media will ever show inside of it.

Alain

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Phil Cook wrote:

> I thought media would only function with a light_source producing a ray 
> to  sample along as stated in 6.8, AFAIK ambient, like emission, 
> doesn't  produce light in this way even using radiosity.

D'oh. To think, I just got done meddling with the same stuff and came to 
the conclusion that media *does* need a real light.

Hmm, for some reason the mention of an ambient 1 object escaped that 
tiny little pea up there in my skull ;)

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Mike Raiford wrote:

> Phil Cook wrote:
>>  AFAIK ambient, like emission,
>> doesn't  produce light in this way even using radiosity.

Erm.. Ambient does produce light, but the light does no react with the 
media. Media affects radiosity, radiosity does not affect media.

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> Make sure the container cylinder is hollow.
> Media on should be in the radiosity block.
> Try a constant density to rule out the cylindrical pattern as being  the
> cause.

"media on"  is showing my media ,thank you very much, I'll put the rifle
away for now...

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And lo on Thu, 01 Jul 2004 09:56:17 -0500, Mike Raiford  
<mra### [at] hotmailcom> did spake, saying:

> Mike Raiford wrote:
>
>> Phil Cook wrote:
>>>  AFAIK ambient, like emission,
>>> doesn't  produce light in this way even using radiosity.
>
> Erm.. Ambient does produce light, but the light does no react with the  
> media. Media affects radiosity, radiosity does not affect media.
>

*in this way* :)

3.7.5: "POV-Ray uses the ambient keyword to determine how much light  
coming from the ambient light source is reflected by a surface" and

6.7.3.1 "Computing real ambient light would take far too much time, so we  
simulate ambient light by adding a small amount of white light to each  
texture whether or not a light is actually shining on that texture."

So if you think about it what is the location of the ambient light source  
and how do you trace a ray along it it through the media to sample along?

Gods I've been fiddling with media to long :P

--
Phil Cook

-- 
All thoughts and comments are my own unless otherwise stated and I am  
happy to be proven wrong.

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Phil Cook wrote:

> And lo on Thu, 01 Jul 2004 09:56:17 -0500, Mike Raiford  
> <mra### [at] hotmailcom> did spake, saying:

> 
> *in this way* :)
> 
> 3.7.5: "POV-Ray uses the ambient keyword to determine how much light  
> coming from the ambient light source is reflected by a surface" and
> 
> 6.7.3.1 "Computing real ambient light would take far too much time, so 
> we  simulate ambient light by adding a small amount of white light to 
> each  texture whether or not a light is actually shining on that texture."

Doesn't radiosity attempt to approximate this?

Ambient has a totally different meaning in a radiosity scene. It emits 
light, It will illuminate nearby objects...

> So if you think about it what is the location of the ambient light 
> source  and how do you trace a ray along it it through the media to 
> sample along?

Hmm.. Not sure how radiosity works, but ... that would be the means to 
do it. I've lit entire scenes with an ambient sphere before. It's slow 
as molasses, but it does work.

> Gods I've been fiddling with media to long :P

Heh. I just started messing around with media. I've picked it up a few 
time before and prodded at it, but never really attempted to get the 
hang of it. It's certainly more tricky than radiosity.

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And lo on Thu, 01 Jul 2004 16:12:44 +0100, Phil Cook  
<phi### [at] nospamdeckingdealscouk> did spake, saying:

> And lo on Thu, 01 Jul 2004 09:56:17 -0500, Mike Raiford  
> <mra### [at] hotmailcom> did spake, saying:
>
>> Mike Raiford wrote:
>>
>>> Phil Cook wrote:
>>>>  AFAIK ambient, like emission,
>>>> doesn't  produce light in this way even using radiosity.
>>
>> Erm.. Ambient does produce light, but the light does no react with the  
>> media. Media affects radiosity, radiosity does not affect media.
>>
>
> *in this way* :)
>
> 3.7.5: "POV-Ray uses the ambient keyword to determine how much light  
> coming from the ambient light source is reflected by a surface" and
>
> 6.7.3.1 "Computing real ambient light would take far too much time, so  
> we simulate ambient light by adding a small amount of white light to  
> each texture whether or not a light is actually shining on that texture."
>
> So if you think about it what is the location of the ambient light  
> source and how do you trace a ray along it it through the media to  
> sample along?
>
> Gods I've been fiddling with media to long :P

And it's driving me nuts :)

In theory I suppose you could back-track for ambient light from the camera  
to the surface and use that as a ray to sample along I don't know if  
that's how ambient light interacts with media in povray

//simple code
global_settings{
radiosity{media on}}

//switch these round for comparision
//light_source{z*12 rgb 1}
cylinder{0,z*5 1 pigment{rgb 1} finish{ambient 1} translate z*10}

cylinder{0,z*7 8 pigment{rgbt 1} translate z*8 hollow  
interior{media{scattering{3, rgb 0.1}}}}
//end code

note that if you lower the scattering rgb the ambient cylinder appears  
brighter and vice versa, which indicates something is being altered by the  
media, but you don't get the spread light effect as with the light-source.

Anyone know?

--
Phil Cook

-- 
All thoughts and comments are my own unless otherwise stated and I am  
happy to be proven wrong.

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