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PostPosted: Sun, 01-03-15, 21:10 GMT 
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Greetings Fridger and all,

I'll try and study up more on how atmospheres are handled in Celestia. Meanwhile, I've been simulating Earth and Mars atmosphere's including cloud data from any vantage point.

http://www.unmannedspaceflight.com/inde ... ntry218019

http://laps.noaa.gov/allsky/allsky.cgi

That's it for now,

Steve


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PostPosted: Mon, 02-03-15, 8:18 GMT 
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scalbers wrote:
Greetings Fridger and all,

I'll try and study up more on how atmospheres are handled in Celestia. Meanwhile, I've been simulating Earth and Mars atmosphere's including cloud data from any vantage point.

http://www.unmannedspaceflight.com/inde ... ntry218019

http://laps.noaa.gov/allsky/allsky.cgi

That's it for now

Steve


Welcome back, Steve!

This sounds like a very interesting project of yours. I have a longterm interest in it, notably of course in the context of celestia.Sci development. While many features have been improved a lot or added compared to good old Celestia, atmospheres are still the same simplified Mie-theory level... But since I have a very longstanding experience with Mie theory as a scientist, I managed at least to find some pretty good combinations of Mie parameter settings so far.

It would be great if you could describe a bit more in detail what you did in your simulations.

Fridger

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PostPosted: Sun, 05-04-15, 15:06 GMT 
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Yes, this really brings science and art together. For the clear atmosphere I'm considering Rayleigh scattering for the gas component, and Mie scattering for aerosols. There are some details in this powerpoint presentation:

http://laps.noaa.gov/albers/ppt/allsky_ ... ation.pptx

And some more recent visualizations here (near bottom of page):

http://laps.noaa.gov/cgi/albers.homepage.cgi

On another note, there are various other rendering packages available that show atmospheric scattering. One is "Proland": http://proland.inrialpes.fr/

That's it for now,

Steve


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PostPosted: Fri, 26-06-15, 12:50 GMT 
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I found the writeup on Cornette Shanks vs HG very enlightening, especially the maple program.
It helped fully understand how to treat the g parameter.

What I was wondering is how to calculate the CFD for it, so it can be importance sampled

Your suppose to take the integral of the PDF, but I didn't have access to Maple and it looks nasty

For example for HG:
The CDF is Mu = (1/2g)(1+g^2 - (1-g^2 / 1 + 2gP-g)^2 )

Which is derived from P(mu) = 1/2 int -1 to mu ( (1-g^2) dmu / (1+g^2-2g mu)^3/2 )

So I assume to solve this for CS one would have to

P(mu) = 1/2 int -1 to mu ( 1.5 * (1.0 - g2) * (1.0 + mu* mu) /((2.0 + g2) * pow(1.0 + g2 - 2.0 * g * mu, 1.5)) )

right?


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PostPosted: Fri, 26-06-15, 17:34 GMT 
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Hi hepcatjk,

first of all: Welcome at CelestialMatters (CM)!

next: for the less initiated readers, let me do a little translation listing of the many acronyms in your post ;-) :
  • CS = Cornette & Shanks Physically reasonable analytic expression for the
    single-scattering phase function
    , APPLIED OPTICS / Vol. 31, No. 16 / 1 June 1992. While my lab pays for access to this journal, it is unfortunately not OpenAccess...Hence I am not allowed to quote the link.
  • HG = Henyey &Greenstein
  • CDF = Cumulative Distribution Function
  • PDF = Probability Density Function
    see e.g. also here: viewtopic.php?f=11&t=537

hepcatjk wrote:
I found the writeup on Cornette Shanks vs HG very enlightening, especially the maple program.
It helped fully understand how to treat the g parameter.

I guess you meant this: http://www.celestialmatters.org/users/t ... s2/out.pdf
Quote:
What I was wondering is how to calculate the CFD for it, so it can be importance sampled

Your suppose to take the integral of the PDF, but I didn't have access to Maple and it looks nasty

For example for HG:
The CDF is Mu = (1/2g)(1+g^2 - (1-g^2 / 1 + 2gP-g)^2 )

Which is derived from P(mu) = 1/2 int -1 to mu ( (1-g^2) dmu / (1+g^2-2g mu)^3/2 )

So I assume to solve this for CS one would have to

P(mu) = 1/2 int -1 to mu ( 1.5 * (1.0 - g2) * (1.0 + mu* mu) /((2.0 + g2) * pow(1.0 + g2 - 2.0 * g * mu, 1.5)) )

right?


Give me a little more time. I'll check it with Maple.

There are also many resources in the net about how to calculate CDF from PDF in general. E.g.

http://math.ucsd.edu/~tlaetsch/pdf/10C_CDFtoPDF.pdf
or Google for "relation between pdf and cdf"

Roughly: d/dx CDF(x) = PDF(x)

Fridger

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PostPosted: Fri, 26-06-15, 22:44 GMT 
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Thanks for clarifying my post

Also Steve.. love the work!
would love to chat...
we're up to something similar but have some different results


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