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PostPosted: Fri, 26-10-07, 21:29 GMT 
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Hi all,

being a theoretical physicist, I happen to know quite a bit about this exciting subject of scattering of light on atmospheric particles or droplets (Mie Theory). I also know about the realization of Mie atmospheres in Celestia. So I thought this mainstream subject might very well interest some of you...

In this thread I plan to collect interesting literature, discuss the precise effects of the Mie parameters for defining great atmospheric lighting in Celestia and show some concrete results of such considerations.

Of course your contributions are MOST welcome!


Let me start with some basic references.

This paper is kind of classical (despite it's bad scanning quality ;-) ) and Celestia's code has profited quite a bit from it.

http://www.celestialmatters.org/users/t ... 93_nis.pdf

From the same authors, there are papers about realizing very nice real-time cloud simulations that are very economical in CPU/GPU time. Here is an impressive video sequence of what can be done this way.

Fast Real-Time Cloud Simulation by Nishita et al.
(click for full screen!)

A more recent, very exciting paper is this one

http://www.vis.uni-stuttgart.de/%7Escha ... hitzel.pdf

So far so good,


enjoy,
Fridger

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PostPosted: Fri, 26-10-07, 21:59 GMT 
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Next, here is a few video sequences of how my Celestia sunsets and illuminated clouds near sunset look like (of course all this requires the latest CVS code or at least the 1.5.0pre3 release for Windows.

Later, we shall discuss how all these atmospheric effects arise and how they can be reproduced on your own computer.

The video AVI format is unfortunately not replayed with the of-the-shelf Windows Media player codecs. In Windows , you should anyhow install the neat (cross-platform) VLC player

Download the Versatile Cross-Platform VLC Media Player from here

or the MPlayer, for example.

I am sure you all know why the bare BMNG colors are so dark: they have been reduced to the idealized case of an Earth WITHOUT atmosphere! So the atmosphere setup MUST render the Earth in this typical bright blue, if observed from space. Have a look how mine looks like (with BMNG texture):

Image


Enjoy,
Fridger

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PostPosted: Fri, 26-10-07, 23:34 GMT 
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Hey there...

Thanks very much for the information good doctor. I know I already asked
you about this stuff, so the knowledge base here is appreciated. Of course,
that assumes that I can understand it... We'll see.

Thanks again, Bob

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PostPosted: Sat, 27-10-07, 17:50 GMT 
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Recently I've been looking for suitable references on Venus' mie forward scattering.. (photographs)

So far my impression is: the amount of forward scattering is quite low, color is essentially white (?!), and the atmospheric "ring of light" is visible, although not as dramatic as Titan's. I might try some tests soon.


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PostPosted: Sat, 27-10-07, 19:35 GMT 
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Well that was interesting...

I liked the atmospheric display near the bottom too. You're telling me that
Mie theory - as applied to Celestia - can approach these kinds of imagery?

Boy, that would be something.

Thanks, Bob

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PostPosted: Sat, 27-10-07, 20:17 GMT 
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t00fri wrote:
Image


Fridger, despite the great work, I find the results on Titan and on those shots a bit "cold", a little bit too "synthetic".
If you watch the real photos, there is a something more subtle, a something that gives us (for now) the facility to detect which one is the CG.
Do you see what I mean? What could we do to improve this point?


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PostPosted: Sat, 27-10-07, 20:24 GMT 
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Here is the basic paper on fast cloud simulations by Nishita et al.

Basic Paper on Fast Cloud Simulations (Nishitaet al.)

Bye Fridger

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PostPosted: Sat, 27-10-07, 20:29 GMT 
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ElChristou wrote:

Fridger, despite the great work, I find the results on Titan and on those shots a bit "cold", a little bit too "synthetic".
If you watch the real photos, there is a something more subtle, a something that gives us (for now) the facility to detect which one is the CG.
Do you see what I mean? What could we do to improve this point?


Sorry, no. The Earth images shown are at a fairly large distance. I think only HDR could do significantly better.

As to Titan, the code is still far from perfect. It's just not very good yet for dense atmospheres.

Right now the first priority question is to find out what is the BEST the present code can provide. Only then we shourt start talking about concrete code improvements.

Bye Fridger

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PostPosted: Sat, 27-10-07, 21:41 GMT 
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t00fri wrote:
Sorry, no. The Earth images shown are at a fairly large distance. I think only HDR could do significantly better.

As to Titan, the code is still far from perfect. It's just not very good yet for dense atmospheres.

Right now the first priority question is to find out what is the BEST the present code can provide. Only then we shourt start talking about concrete code improvements...


Ok, let's take Titan, you say the code is not good for dense atmosphere, right. Now do you consider the actual Titan Mie setting is not optimum for the present code? (I thought it was almost ok...)


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PostPosted: Sat, 27-10-07, 21:53 GMT 
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ElChristou wrote:
t00fri wrote:
Sorry, no. The Earth images shown are at a fairly large distance. I think only HDR could do significantly better.

As to Titan, the code is still far from perfect. It's just not very good yet for dense atmospheres.

Right now the first priority question is to find out what is the BEST the present code can provide. Only then we shourt start talking about concrete code improvements...


Ok, let's take Titan, you say the code is not good for dense atmosphere, right. Now do you consider the actual Titan Mie setting is not optimum for the present code? (I thought it was almost ok...)


Yes, apart from minor twists, the rendering of Titan's atmosphere is now surprisingly good globally, but there are many aspects /in detail/ where improvements are needed. Also we do of course only have partial info about the atmospheric phenomena on Titan.

I am presently optimizing the Mie parameters on Mars. Here the atmosphere is not dense and we have lots of detailed photos.

Like this one

Image

Caption: View from Mars Victoria Crater taken by the Opportunity Rover (2006). The sand is rich in reddish iron oxides, which are also suspended as dust in the CO2 atmosphere, leading to pink-red light scattering. Water ice clouds move at ~10 meters per second and should lead to snowing in some areas.

This is of course to be contrasted with this great blue sunset on Mars. The latest image was recorded recently (April 15, 2015) by NASA's Curiosity Mars rover!
Attachment:
blueSunsetMars.jpg
blueSunsetMars.jpg [ 19.23 KiB | Viewed 3230 times ]

http://www.jpl.nasa.gov/spaceimages/det ... d=PIA19401


Bye Fridger

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PostPosted: Sat, 27-10-07, 22:04 GMT 
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t00fri wrote:
...
This is of course to be contrasted with this great blue sunset that is very well known:


:shock:

Well known... but not to me... :oops:... what a shot!

The present settings will give you the possibility to reproduce this one?


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PostPosted: Sat, 27-10-07, 22:15 GMT 
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ElChristou wrote:
t00fri wrote:
...
This is of course to be contrasted with this great blue sunset that is very well known:


:shock:

Well known... but not to me... :oops:... what a shot!

The present settings will give you the possibility to reproduce this one?


Of course, that's the game ;-)

Bye Fridger

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PostPosted: Sat, 27-10-07, 23:47 GMT 
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Wow...

Don't let US distract you Doctor Schrempp. Leave the man alone for a while
Christophe. :lol:

Great stuff here.
Many thanks, Bob

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PostPosted: Sun, 28-10-07, 10:04 GMT 
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I found it impossible to get anywhere near that first image of Victoria crater. The sky always looked too dark. I can get the sky to look a little brighter but then Mars looked ridiculous from space. I was able to come up with a workaround for that though. With my models of mars, I use a second planet entry with no mesh and give it the same orbit and old atmosphere. Then I can tweak the sky setting. When the view is near the surface, the sky can be modified to whatever color which disappears during sunset or sunrise. During those times the new atmosphere code takes over and comes close to the second image from Pathfinder.
cartrite


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PostPosted: Sun, 28-10-07, 11:05 GMT 
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Note to Dr. Schrempp...

I read your reference papers, but I'm afraid that most of this is way
beyond my educational background. Still, I did appreciate the references, and
I did learn something from the excursion. Boy, you people are taking some
SERIOUS measures to get the correct views going in Celestia. VERY much
appreciated by the Brain-Dead.

A quick aside though... Would any of this implementation of MIE have
anything to do with my specularity problems? I managed to install 1.4.1 and
now I can run both versions of Celestia. I have NO problems in 1.4.1...

Just FYI.

As always, thanks from Bob

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