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PostPosted: Wed, 03-09-08, 15:24 GMT 
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Friends,

a "controlled" setting of the Mie parameters requires considerable understanding of Mie optical scattering theory beyond the level that we can possibly expose here.

For reference purposes, I recall again the formal definitions of the 6 Mie parameters as given by ChrisL quite some time ago:

Mie
A float value giving the fraction of light scattered per kilometer at the planet's surface ('sea level')

MieAsymmetry
Henyey-Greenstein phase function parameter for wavelength independent scattering. A floating point value between -1 and 1, with -1 indicating complete backscattering, 1 complete forward scattering, and 0 isotropy.

MieScaleHeight
Scale height for wavelength independent scattering particles. Height in kilometers at which wavelength independent scattering is 1/e of the value at the surface

Rayleigh
Wavelength dependent scattering coefficients. Three values giving fraction of red, green, and blue light scattered per kilometer at the planet's surface. To simulate Rayleigh scattering, they should be in ratios that fit the 1/wavelength^4 behavior, though this is not required.

RayleighScaleHeight
Scale height for wavelength dependent scattering. Currently ignored; MieScaleHeight is used for both Rayleigh and Mie scattering.

Absorption
Three values giving the fraction of red, green, and blue light absorbed per kilometer at the planet's surface.

-----------------------------------------------------

Let me add some further qualitative remarks about the essential effects these parameters have:

  • A larger (negative) MieAsymmetry than on Earth (e.g. -0.55)
    is responsible for the conspicuous "ring of light"
    when the atmosphere is backlit (cf TITAN!)
  • the Rayleigh RGB values indicate the color components that are to be prominent in the highest part of the illuminated atmosphere
  • the Absorption RGB values specify the amount of absorption as visible in the backlit color composition of the "ring of light". R=0.0 means red remains (i.e undergoes ZERO absorption)! Etc.


Fridger


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PostPosted: Wed, 03-09-08, 16:13 GMT 
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t00fri wrote:
a "controlled" setting of the Mie parameters requires considerable understanding of Mie optical scattering theory beyond the level that we can possibly expose here.


Well, obviously I have NO understanding of the theory (or use of) Mie scattering effects. However, the
values I used did not originate with me. They came from your own posts I believe. At any rate, makes not
any difference as far as I am concerned now. Have corrected the problem, and the textures now look good
from space. :wink:


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PostPosted: Wed, 03-09-08, 16:39 GMT 
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BobHegwood wrote:
t00fri wrote:
a "controlled" setting of the Mie parameters requires considerable understanding of Mie optical scattering theory beyond the level that we can possibly expose here.


Well, obviously I have NO understanding of the theory (or use of) Mie scattering effects. However, the
values I used did not originate with me. They came from your own posts I believe. At any rate, makes not
any difference as far as I am concerned now. Have corrected the problem, and the textures now look good
from space. :wink:

What did you do to correct it?
cartrite


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PostPosted: Wed, 03-09-08, 16:52 GMT 
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Fridger, I noticed some problems with the sunset (at ground level) using your last settings for night lights. The atmosphere is so "dense" (seems the ultra polluted air above Mexico city!) that the sun become almost invisible before complete sunset... What can we do to keep the good setting for space view and keep the sun visible?


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PostPosted: Wed, 03-09-08, 17:04 GMT 
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cartrite wrote:
What did you do to correct it?


I simply removed the MieScaleHeight definition from the SSC file.
Works for me... :wink:

I could have revised the definition so that it worked too (using something over 20) but since I
really have no idea what the hell I'm doing here, I simply removed the definition. All I know is that
Mars' atmosphere looks very nice now, and using the settings as they have been defined in the add-on.

Thanks, Brain-Dead


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PostPosted: Wed, 03-09-08, 17:10 GMT 
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ElChristou wrote:
Fridger, I noticed some problems with the sunset (at ground level) using your last settings for night lights. The atmosphere is so "dense" (seems the ultra polluted air above Mexico city!) that the sun become almost invisible before complete sunset... What can we do to keep the good setting for space view and keep the sun visible?


Hmm, ...that's not so easy since that "pollution effect" is a reflection of the large negative MieAsymmetry needed for other purposes. Try reducing MieAsymmetry -0.35 -> -0.25. That improves the sunset. But I am not sure if there is not a "price to pay" elsewhere. You may also reduce the 3 Absorption values by a common factor. But the effect will barely be strong enough.

Fridger


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PostPosted: Wed, 03-09-08, 17:35 GMT 
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BobHegwood wrote:
cartrite wrote:
What did you do to correct it?


I simply removed the MieScaleHeight definition from the SSC file.
Works for me... :wink:

I could have revised the definition so that it worked too (using something over 20) but since I
really have no idea what the hell I'm doing here, I simply removed the definition. All I know is that
Mars' atmosphere looks very nice now, and using the settings as they have been defined in the add-on.

Thanks, Brain-Dead
What is your CloudHeight on Mars?
cartrite


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PostPosted: Wed, 03-09-08, 19:37 GMT 
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cartrite wrote:
What is your CloudHeight on Mars?


Here's what I have in my solarsys.ssc file:

CloudHeight 80
# Height data from http://www.space.com/scienceastronomy/0 ... louds.html
CloudSpeed 32
# Average speed determined from slowest and fastest observed speeds.

Thanks, Bob


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PostPosted: Wed, 03-09-08, 19:49 GMT 
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BobHegwood wrote:
cartrite wrote:
What is your CloudHeight on Mars?


Here's what I have in my solarsys.ssc file:

CloudHeight 80
# Height data from http://www.space.com/scienceastronomy/0 ... louds.html
CloudSpeed 32
# Average speed determined from slowest and fastest observed speeds.

Thanks, Bob
CloudHeight 80? I learned something new today. I didn't think they were so high. Anyhow, that is why you are having a problem. The atmosphere is clipping the cloud mesh. If you lowered the cloud height the problem would disappear. If this is really a problem, maybe you should fill out a bug report at Shatters or SourceForge.
cartrite


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PostPosted: Wed, 03-09-08, 20:01 GMT 
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t00fri wrote:
ElChristou wrote:
Fridger, I noticed some problems with the sunset (at ground level) using your last settings for night lights. The atmosphere is so "dense" (seems the ultra polluted air above Mexico city!) that the sun become almost invisible before complete sunset... What can we do to keep the good setting for space view and keep the sun visible?


Hmm, ...that's not so easy since that "pollution effect" is a reflection of the large negative MieAsymmetry needed for other purposes. Try reducing MieAsymmetry -0.35 -> -0.25. That improves the sunset. But I am not sure if there is not a "price to pay" elsewhere. You may also reduce the 3 Absorption values by a common factor. But the effect will barely be strong enough.

Fridger


Tx, will do some test.


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PostPosted: Wed, 03-09-08, 20:16 GMT 
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Bob,
I read that web page a little closer and found this sentence interesting.
Quote:
There were detected with a camera that senses ultraviolet and infrared light, so there is no conventional picture of them.
The page makes no mention of the average cloud height that can be seen. I got my CloudHeight about 10 and my MieScaleHeight 30.
cartrite


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PostPosted: Wed, 03-09-08, 20:23 GMT 
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cartrite wrote:
CloudHeight 80? I learned something new today. I didn't think they were so high. Anyhow, that is why you are having a problem. The atmosphere is clipping the cloud mesh. If you lowered the cloud height the problem would disappear. If this is really a problem, maybe you should fill out a bug report at Shatters or SourceForge.


Actually, I took the more conservative approach to the cloud height data from the web site referenced in my
post. The actual cloud height is listed on that site as being as high as 100 km from the surface of Mars.

No problems here. As long as the depiction I get of Mars' atmosphere agrees with what my intuition tells
me, I am happy. The planet is rendered fine now on my machine. :wink:

Then too, I can always adjust it when better data becomes available, or if I suddenly grow some new
brain cells.

Thanks, Bob


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PostPosted: Mon, 29-09-08, 17:48 GMT 
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Okay,

I found this "scattersim" on SourceForge, but now I would have to start to learn how to compile on Windows for just this small, yet hopefully incredibly helpful tool for making good atmosphere Mie chooses.

So my question to you is: Could please someone create binaries for us noobs for the different platforms (Linux, Mac, Windows) and put them online?
I think this would be a help to all planetbuilders. (Okay, at the moment I am not one of them, but always looking for helpful tools for the repository.)

Regards,

Guckytos


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 Post subject:
PostPosted: Tue, 30-09-08, 17:56 GMT 
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Here's a zip file containing a Windows executable for scattersim:

http://www.shatters.net/~claurel/celest ... tersim.zip

To start, try running it with one of the cfg files in src/tools/atmosphere. The simplest usage is:

scattersim titan.cfg

There are other command line options; type scattersim -h to see them.

--Chris


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 Post subject:
PostPosted: Wed, 01-10-08, 18:29 GMT 
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chris wrote:
Here's a zip file containing a Windows executable for scattersim:

http://www.shatters.net/~claurel/celest ... tersim.zip

To start, try running it with one of the cfg files in src/tools/atmosphere. The simplest usage is:

scattersim titan.cfg

There are other command line options; type scattersim -h to see them.

--Chris


Thanks, chris.

Will try it out, but first I have to finish some documentation tasks.

Guckytos


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