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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Attachments:
Download 'aurora.jpg' (9 KB)

Preview of image 'aurora.jpg'

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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Hi Gail.

You have chosen a quite difficult "thing" to model,
but I like your idea.

Below is my suggestion for such an iso-surface.
Try to play around with the different constants.

-- 
Best regards,

Tor Olav

mailto:tor### [at] hotmailcom
http://hjem.sol.no/t-o-k/tokpicts.html
http://www.crosswinds.net/~tok


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


// ===== 1 ======= 3 ======= 3 ======= 4 ======= 5 ======= 6 ======= 7 =

#version unofficial MegaPov 0.6;
#include "colors.inc"

// ===== 1 ======= 3 ======= 3 ======= 4 ======= 5 ======= 6 ======= 7 =

$ SinX = function { 0.5*sin(x) }

$ Noise =
function {
   1.0*noise3d(x, 0, 2 + z/7)
  +0.2*noise3d(x*1.7, 0, z/4)
}

$ NoisySin = function { SinX(5*Noise(x, y, z), 0, 0) }

$ SheetY = function { y^2 - 0.04 } 

$ WavySheetY = function { SheetY(0, y + NoisySin(x, y, z), 0) }

$ Iso =
isosurface {
  function { WavySheetY(x, y, z) }
  max_gradient 5
  method 2
  contained_by { box { -5*<1, 1, 1>, 5*<1, 1, 1>} }
}

object {
  Iso
  pigment { color White }
  no_shadow
}

// ===== 1 ======= 3 ======= 3 ======= 4 ======= 5 ======= 6 ======= 7 =

background { color Blue/3 }

light_source { <-3, 3, -2>*100 color White }

camera {
  location <1, 1, -2>*5
  look_at <-1, -1, 0>
}

// ===== 1 ======= 3 ======= 3 ======= 4 ======= 5 ======= 6 ======= 7 =

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Gail Shaw <gsh### [at] monotixcoza> wrote:

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

> The color is also varied slightly.

Reminds me of the opening credits to Superman: The Movie. ;)

It looks too straight to me.  The pictures I've seen are more like swirls of
lit up mist with tendrils all throughout.  This looks more like a paint line
streaked upwards.  Not sure what method would either fix this or to offer
that might work better, I'm afraid, but keep trying.  It'll be really cool
if you get it to work.

Geoff

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The most common in our area are streaks of paint upwards on a pale green
background, but I certainly haven't seen all possible variations...

One thing struck me about the overall attempt to render an aurora:  I bet
you could submit a photograph of the real thing and a lot of people would
say it didn't look very realistic... because it doesn't :-)

BTW, I spent a few minutes going over the site below to see *all* the
pictures.  The animations (time-lapse photography, not rendered) are
awesome.  Well worth the visit.

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



"Geoff Wedig" <wed### [at] darwinepbicwruedu> wrote in message
news:3ac0d7b3@news.povray.org...
> Gail Shaw <gsh### [at] monotixcoza> wrote:
>
> > Now using multiple sine waves with different frequencies,
> > amplitudes and phase. (Thanks Christoph)
>
> > The color is also varied slightly.
>
> Reminds me of the opening credits to Superman: The Movie. ;)
>
> It looks too straight to me.  The pictures I've seen are more like swirls
of
> lit up mist with tendrils all throughout.  This looks more like a paint
line
> streaked upwards.  Not sure what method would either fix this or to offer
> that might work better, I'm afraid, but keep trying.  It'll be really cool
> if you get it to work.
>
> Geoff

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