I decided I needed some atmospheric effects for my
irtc entry (which I will post once it's more than a few cylinders
and cones)

This is supposed to be the aurora borealis.  It's an isosurface
containing media with a function used in the density.

For those who live far enough north to see the real thing, does
it look right?

For the iso experts, is there any way I can randomly vary the
distance between the peaks of a sine wave?

Comments? suggestions?

Gail
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Gail Shaw wrote:
> 
> I decided I needed some atmospheric effects for my
> irtc entry (which I will post once it's more than a few cylinders
> and cones)
> 
> This is supposed to be the aurora borealis.  It's an isosurface
> containing media with a function used in the density.
> 
> For those who live far enough north to see the real thing, does
> it look right?

I don't know first hand, but i think you should vary the coloring.  

> 
> For the iso experts, is there any way I can randomly vary the
> distance between the peaks of a sine wave?
> 

Well then it is no more a sine wave :-)

You could for example use a pigment function with a gradient pigment to
have full control over the shape.  

You could also try a superposition of several sine waves scaled and
translated, but that would be mainly trial and error.

Christoph

-- 
Christoph Hormann <chr### [at] gmxde>
IsoWood include, radiosity tutorial, TransSkin and other 
things on: http://www.schunter.etc.tu-bs.de/~chris/

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>For the iso experts, is there any way I can randomly vary the
>distance between the peaks of a sine wave?


yes, the function you are looking for (I think) would look something like
this (assuming a sine wave along the x axis):

sin(  ( x + noise3d(x,y,z) )  * frequency_of_sine_wave*2*pi)

hope this helps,

Quadhall
(not an iso-expert, more of an iso-amateur)

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Christoph Hormann <chr### [at] gmxde> wrote in message
news:3AC0797B.B773C5E6@gmx.de...
>
>
> I don't know first hand, but i think you should vary the coloring.

Done.

> Well then it is no more a sine wave :-)

<g> I'd like a sine wave with a varying frequency

> You could also try a superposition of several sine waves scaled and
> translated, but that would be mainly trial and error.
>

That sounds like it has promice.

Thanks

Gail
--
*************************************************************************
* gsh### [at] monotixcoza                *   Step into the abyss,           *
* http://www.rucus.ru.ac.za/~gail/   *   and let go.        Babylon 5   *
*************************************************************************
* The difficult we do immediately, the impossible takes a little longer *
*************************************************************************

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This is an excellent start.  We see them here in the late fall and early
winter (when the air is clear) and your intent was unmistakable.

I composed a long response trying to describe the difference between what I
see in the sky and what I see in your image, but I don't have sufficient
command of the language.  So I decided to search for pictures on the web
instead.  These pictures look accurate to me:

http://www.ptialaska.net/~hutch/aurora.html

I have no idea how you might start modelling this in POV, but I wish you
luck and look forward to future results.

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Now using multiple sine waves with different frequencies,
amplitudes and phase. (Thanks Christoph)

The color is also varied slightly.

Gail
*************************************************************************
* gsh### [at] monotixcoza                *   Step into the abyss,           *
* http://www.rucus.ru.ac.za/~gail/   *   and let go.        Babylon 5   *
*************************************************************************
* The difficult we do immediately, the impossible takes a little longer *
*************************************************************************

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Spock <spo### [at] nospamcom> wrote in message news:3ac09b35$1@news.povray.org...
> This is an excellent start.  We see them here in the late fall and early
> winter (when the air is clear) and your intent was unmistakable.

Thank you

> I composed a long response trying to describe the difference between what
I
> see in the sky and what I see in your image, but I don't have sufficient
> command of the language.  So I decided to search for pictures on the web
> instead.  These pictures look accurate to me:
>
> http://www.ptialaska.net/~hutch/aurora.html

I found that site this morning and have been using those pics as references

> I have no idea how you might start modelling this in POV,

Lots and lots of media <grin>

Gail
*************************************************************************
* gsh### [at] monotixcoza                *   Step into the abyss,           *
* http://www.rucus.ru.ac.za/~gail/   *   and let go.        Babylon 5   *
*************************************************************************
* The difficult we do immediately, the impossible takes a little longer *
*************************************************************************

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Gail Shaw wrote:
> 
> Now using multiple sine waves with different frequencies,
> amplitudes and phase. (Thanks Christoph)
> 
> The color is also varied slightly.
> 
> Gail
> *************************************************************************
> * gsh### [at] monotixcoza                *   Step into the abyss,           *
> * http://www.rucus.ru.ac.za/~gail/   *   and let go.        Babylon 5   *
> *************************************************************************
> * The difficult we do immediately, the impossible takes a little longer *
> *************************************************************************
> 
>  [Image]

Very good!  However...

1 - The left and right edges should be less sharp and blend more into
the night.
2 - Add one more sine wave whose period is roughly the length of the
whole aurora and whose amplitude is roughly 1/4th of the length.

Or better yet, ignore me and do whatever you feel like.

-- 
Francois Labreque | The surest sign of the existence of extra-
    flabreque     | terrestrial intelligence is that they never
        @         | bothered to come down here and visit us!
  videotron.ca    |                             - Calvin

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Francois Labreque <fla### [at] videotronca> wrote in message
news:3AC0A349.2850430D@videotron.ca...
>
> 1 - The left and right edges should be less sharp and blend more into
> the night.
> 2 - Add one more sine wave whose period is roughly the length of the
> whole aurora and whose amplitude is roughly 1/4th of the length.

I'll look into that tonight

> Or better yet, ignore me and do whatever you feel like.

<grin> Now why would I do that???

Gail
*************************************************************************
* gsh### [at] monotixcoza                *   Step into the abyss,           *
* http://www.rucus.ru.ac.za/~gail/   *   and let go.        Babylon 5   *
*************************************************************************
* The difficult we do immediately, the impossible takes a little longer *
*************************************************************************

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Better by far from the first one, but you may want to make it more... how to
say this... thick? It isn't deep enough. That did not sound right, did it.
    Also, the Northern Lights look like they "Creep" in on the sky, you know
where it is and isn't, but the border between the two is almost invisible.
Hope I helped.

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