In article <3976fd4b@news.povray.org>, "Luke Church" 
<Luk### [at] churchkaroocouk> wrote:

> I have a cylindrical shape that contains an emission media, however I 
> wanted to vary the density, so that it decayed exponentially 
> (preferably but linear would do) as it approached the edge of the 
> shape, after several hours trying to play around with it I though I 
> would ask for help.

Try the poly_wave waveform:

density {cylindrical poly_wave 2
    color_map {
        [0.0 rgb <1, 0, 0>]
        [0.5 rgb <0.5, 0, 0.5>]
        [1.0 rgb <0,0,1>]
    }
}

You could also adjust the color_map to get close to the same effect, but 
it would be more difficult.


> A second question I have is as to the interaction between media, 
> radiosity and animations. Will either media or radiosity produce a 
> 'gitter' effect that is caused by random sampling, e.g. jitter and/or 
> crand keywords?

In the official version, radiosity currently doesn't work well with 
media. Specifically, the radiosiy samples never enter the container 
object, and media isn't calculated for the radiosity samples. MegaPOV 
fixes this, and these changes will probably make it into the next 
official release.
As for the "gitter" effect...were you trying to type "glitter" or 
"jitter"? Oh, well...both media and radiosity can produce random 
effects, though these can be minimized with certain settings. This is 
easier to do with MegaPOV radiosity and media method 3...with the 
official version, you basically have to increase your samples and adjust 
variance and confidence until the "grainyness" isn't visible enough to 
be a problem. This can be very slow...though emitting media is probably 
the fastest.
I don't have any experience with radiosity, so I can't help you there.


> PS - Damned Outlook Express has converted my comments into ftp links -
> please ignore them!

You can get around this by using "// comment" instead of "//comment". 
The extra space after the slashes keeps it from happening.

-- 
Christopher James Huff - Personal e-mail: chr### [at] maccom
TAG(Technical Assistance Group) e-mail: chr### [at] tagpovrayorg
Personal Web page: http://homepage.mac.com/chrishuff/
TAG Web page: http://tag.povray.org/

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