Hi. After seeing Star Wars this past weekend, I'm consumed by the idea of
sci-fi modeling and effects. Call me a sucker for special effects. But
anyway, I was thinking of a laser blast. I managed to get a nice green laser
by using two emissive medias, one with a green cylindrical density and one
with a white cylindrical density slightly smaller than the green, all
contained in a CSG merge of a cylinder and two spheres. It looks pretty good
I think. I know that emmisive media doesn't really emit light, but I was
naively expecting that it's color would affect nearby objects when radiosity
is used, in the same way that a white sphere would pick up some green from a
green wall. in the global settings, media was set to "on".

Is the above the expected behavior of emitting media? if this is the
expected behavior, how would you go about faking a green light emitting from
the media? just attach a small light_source to the laser blast object with a
suitable fade power and fade distance?

-r

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"Ross" <rli### [at] everestkcnet> wrote in message
news:42ada0e8$1@news.povray.org...
> Hi. After seeing Star Wars this past weekend

Hiya Ross. I still haven't seen the Episode 3 yet. Sounds like it had
something for you, at least.

> was thinking of a laser blast. I managed to get a nice green laser
> by using two emissive medias, one with a green cylindrical density and one
> with a white cylindrical density slightly smaller than the green, all
> contained in a CSG merge of a cylinder and two spheres. It looks pretty
> good
> I think. I know that emmisive media doesn't really emit light, but I was
> naively expecting that it's color would affect nearby objects when
> radiosity
> is used, in the same way that a white sphere would pick up some green from
> a
> green wall. in the global settings, media was set to "on".

Should be okay then. media on goes in radiosity block, just so you weren't 
mistakenly putting it into global_settings only.

> Is the above the expected behavior of emitting media? if this is the
> expected behavior, how would you go about faking a green light emitting
> from
> the media? just attach a small light_source to the laser blast object with
> a
> suitable fade power and fade distance?

area_light like that could enhance it a lot, sure, but then you need to
either let it interact with the media or tell it not to.

Checking here with a test media object and radiosity I see you might need to
increase 'count' to 500 or more, especially if the laser isn't in close
proximity to the other scene objects. Perhaps even increasing 'brightness'
to more than 1. In fact, there might be other settings which could prove
better but it looks to me like a light would be less likely to cause trouble
such as radiosity can if you attempt to maximize the interactions from it
(texture tweaking, etc.).

Bob Hughes

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Hi Ross and Bob,

I saw the film the last weekend. There was a topic from the last year
here related on lasers you could search it.

Regards,
Oleguer





news:42adcec3$1@news.povray.org...
> "Ross" <rli### [at] everestkcnet> wrote in message
> news:42ada0e8$1@news.povray.org...
>> Hi. After seeing Star Wars this past weekend
>
> Hiya Ross. I still haven't seen the Episode 3 yet. Sounds like it had
> something for you, at least.
>
>> was thinking of a laser blast. I managed to get a nice green laser
>> by using two emissive medias, one with a green cylindrical density and 
>> one
>> with a white cylindrical density slightly smaller than the green, all
>> contained in a CSG merge of a cylinder and two spheres. It looks pretty
>> good
>> I think. I know that emmisive media doesn't really emit light, but I was
>> naively expecting that it's color would affect nearby objects when
>> radiosity
>> is used, in the same way that a white sphere would pick up some green 
>> from
>> a
>> green wall. in the global settings, media was set to "on".
>
> Should be okay then. media on goes in radiosity block, just so you weren't 
> mistakenly putting it into global_settings only.
>
>> Is the above the expected behavior of emitting media? if this is the
>> expected behavior, how would you go about faking a green light emitting
>> from
>> the media? just attach a small light_source to the laser blast object 
>> with
>> a
>> suitable fade power and fade distance?
>
> area_light like that could enhance it a lot, sure, but then you need to
> either let it interact with the media or tell it not to.
>
> Checking here with a test media object and radiosity I see you might need 
> to
> increase 'count' to 500 or more, especially if the laser isn't in close
> proximity to the other scene objects. Perhaps even increasing 'brightness'
> to more than 1. In fact, there might be other settings which could prove
> better but it looks to me like a light would be less likely to cause 
> trouble
> such as radiosity can if you attempt to maximize the interactions from it
> (texture tweaking, etc.).
>
> Bob Hughes
>
>
>

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"Bob Hughes" <bob### [at] charternet> wrote in message
news:42adcec3$1@news.povray.org...

> Checking here with a test media object and radiosity I see you might need
to
> increase 'count' to 500 or more, especially if the laser isn't in close
> proximity to the other scene objects. Perhaps even increasing 'brightness'
> to more than 1. In fact, there might be other settings which could prove
> better but it looks to me like a light would be less likely to cause
trouble
> such as radiosity can if you attempt to maximize the interactions from it
> (texture tweaking, etc.).
>
> Bob Hughes
>
>
>

With radisotiy on, and media on in the radisotiy block, I tried a 28 frame
animation with the laser blast travelling quite close to a box. the overall
lighting of the scene does change as the object with emissive media travels,
but not in a real meaningful way. (then i spent two hours trying to get
mencoder to work properly...). It's a little hard to explain in detail, but
the increase in light doesn't obviously correspond to the movement of the
object. It's a little jumpy. There are two media statements, one uses
something like "emission <0, 1, 0>*4" and one uses something like "emission
<1, 1, 1>*8" and each have a simple cylindrical color map in their density
statements. For radiosity, I moved "count" up to 700 and generally changed
some of the values that the docs say lead to higher quality. I can't expect
much help without posting the scene, but I can't post it at the moment.

I think I'll just play with adding a lightsource that moves with the media
object. It feels like this will allow more flexibility and fine tuning.

Thanks!

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