Celestia Forums

Hello,

I am here to get some questions answered and whatever.
I have downloaded the 1.5.0 pre2 version.

First is that I have a pretty good understanding of how to work Celestia, From the SSC files to basic controls so forth. I looked at some of the topics here on the forum, and it led me to the Celestia Motherlode where I found a nice assortment of add-ons and docmentation and scripts.

But it seems that the SSC manual there haven't been updated (It is for Version 1.3.2) and it raised some questions:

There is a piece of code that isn't covered in the manual, It is the following:



If you don't mind, will someone explain the meanings of the code here, it looks nice on Earth. I just want to know how to work with it.

Also, I seen the Terraformed Mars texture by Don. Edwards. It is very good, kudos to you Don. I was wandering where I might get tips on creating and working with such, I would like to pratice with. I have a been, but the detail on Mars pretty good. Earth-likes seem alright but the hardest on my opinion is making gas planet textures, making the fancy swirls and bands of clouds. Tips on all types of planets appreicated.

I guess will close with my comments on the new Celestia prerelease. I read through the the Celestia 1.5.0 pre2 topic here on the User section. I see all the bugs and what nots there but I think Chris was on the right track with star rendering. It looks nice to look at the sun from Earth.



But at Mercury and Pluto its seems the look of the Sun is backwards. I see where Chris was going with this a bit, closer to the star, get rid of the big glare, and see the texture. At pluto it is a bit too bright, from what I learn in my textbooks.

Mercury:


Pluto:


Also I have made a system for the Epsilon Eridani system, with a Earth-like and two gas giants. When I look at the star, Celestia crashes on me. There is a problem I have found. I also chose 70 Oph A and B binary for a system. 70 Oph B has a gas giant with many moons (maybe, I think goes to far out for there size. Any way to test the stablity of a system?) I used Cham's nebula pack 2, and used a recolored gas giant texture (to get an idea what to give the look for it.) One moon has a entire ocean on its surface, I just wanted information about having such enviroment on a moon, like distance from parent planet and star and others.

Here is an image of it, I dubed it Nibiru Prime and Nibiru III or Oceanic:


Well that is all the questions I have so far, I believe. I was exploring and didn't travel to far from the Home planet. Thanks for your time to help and work on such a excellent program.

And also my system information for the Eps Eri bug:

Windows Vista 32-bit
AMD Athlon(tm) 64 X2 Dual Core Processor 3800+, 2.00 GHz each
1918 MB of RAM
nVidia's GeForce 6150 SE, Forceware 101.41
With full OpenGL 2.0 support.

(If you need more info, just ask.)
Thanks you.

Kunkle wrote:Hello,

Hi!

There is a piece of code that isn't covered in the manual, It is the following:

[

Code: Select all

                        Mie 0.001
      MieAsymmetry -0.25
      Rayleigh [ 0.001 0.0025 0.006 ]
      MieScaleHeight 12


If you don't mind, will someone explain the meanings of the code here, it looks nice on Earth. I just want to know how to work with it.

Those SSC parameters are supposed to have the same meanings as the traditional physics meanings given to those terms. See, for example, http://www.ess.uci.edu/~cmclinden/link/xx/node18.html

To the extent that Celestia does not reproduce the visual effects that those terms describe, it is a bug in Celestia. (My understanding is that Chris is planning to improve them some more before the final release of v1.5.0)

Also, I seen the Terraformed Mars texture by Don. Edwards. It is very good, kudos to you Don. I was wandering where I might get tips on creating and working with such, I would like to pratice with. I have a been, but the detail on Mars pretty good. Earth-likes seem alright but the hardest on my opinion is making gas planet textures, making the fancy swirls and bands of clouds. Tips on all types of planets appreicated.

I'll leave it to Don or someone else to comment in detail, but my understanding is that a lot of very patient artistic work is required.

[...]

Also I have made a system for the Epsilon Eridani system, with a Earth-like and two gas giants. When I look at the star, Celestia crashes on me.

Most of Celestia's crashes are caused by bugs in graphics drivers. You need to download and install the most recent Vista graphics drivers from Nvidia. They're up to v158.18 now.

If Celestia still crashes after you've installed the driver update, you'll have to provide the details of your SSC catalog.

There is a problem I have found. I also chose 70 Oph A and B binary for a system. 70 Oph B has a gas giant with many moons (maybe, I think goes to far out for there size. Any way to test the stablity of a system?)

http://www.orbitsimulator.com/ by Tony Dunn

I used Cham's nebula pack 2, and used a recolored gas giant texture (to get an idea what to give the look for it.) One moon has a entire ocean on its surface, I just wanted information about having such enviroment on a moon, like distance from parent planet and star and others.

I'll leave it to others to discuss the relevant physics.

And also my system information for the Eps Eri bug:

Windows Vista 32-bit
AMD Athlon(tm) 64 X2 Dual Core Processor 3800+, 2.00 GHz each
1918 MB of RAM
nVidia's GeForce 6150 SE, Forceware 101.41
With full OpenGL 2.0 support.

Thanks for the Gravity Simulator and the information, Selden.

Selden said:

Most of Celestia's crashes are caused by bugs in graphics drivers. You need to download and install the most recent Vista graphics drivers from Nvidia. They're up to v158.18 now.

Well, I am having troubles with that installation of the new drivers, it said that I don't have 32-bit Vista, and I do. I sent nVidia the news, but any of you have an idea about this, please tell me. I really want to play Dawn of War again. (The 100.65 left a DirectX bug, and Dawn of War can't found some spooge driver. 158 drivers was suppose to fix it. I then realise that 6150 was not on the supported GPU's list for the 100.65...).

Oh yea, also they was a problem with the Don. Edwards 8k DDS Cloud map here on the Motherlode, http://www.celestiamotherlode.net/catalog/earthcloud.php, that it causes lines in the texture, here and there, and regular clouds there and here. Any fixes for this?



Thank You.

Kunkle... set the cloud speed to 0 and all will be well.

selden wrote:

Kunkle wrote:Hello,

Hi!

There is a piece of code that isn't covered in the manual, It is the following:

[

Code: Select all

                        Mie 0.001
      MieAsymmetry -0.25
      Rayleigh [ 0.001 0.0025 0.006 ]
      MieScaleHeight 12


If you don't mind, will someone explain the meanings of the code here, it looks nice on Earth. I just want to know how to work with it.

Those SSC parameters are supposed to have the same meanings as the traditional physics meanings given to those terms. See, for example, http://www.ess.uci.edu/~cmclinden/link/xx/node18.html

To the extent that Celestia does not reproduce the visual effects that those terms describe, it is a bug in Celestia. (My understanding is that Chris is planning to improve them some more before the final release of v1.5.0)

Selden,

I doubt that anybody who has never worked with Mie theory can understand the meaning of Celestia's 6 new atmosphere parameters from this WEB page quotation of yours. But I admire your art of finding a WEB page for every question that might arise in life

Also I disagree with the rest of your statements, except that Chris is indeed working to improve the atmosphere rendering.

Just one example: Mie asymmetry: in your web reference the range is

g>1 for forward hemisphere scattering, g<1 for backward hemisphere scattering. In Celestia the Mie asymmetry parameter ranges instead between -1 and +1.

Here is a slightly more concise definition of the six new parameters for atmospheres:

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.


A good way to practice with these 6 parameters is to try and understand why I assigned these values to their present values, when I modelled Titan's atmosphere

See here:

http://www.celestiaproject.net/forum/viewtopic ... 16&start=0

Well, in my early days as a theoretical physicist I even wrote scientific papers about Mie theory

Bye Fridger

Fridger,

Thanks for the definitions!

Ah okay, cloud speed equals zero. Thank you, bh.

Thanks t00fri, I was able to understand the it a bit from the web site, but I couldn't figure how to use it in Celestia. I think about praticing with it, see what does what exactly when it is rendered.

What is the difference between Forward and Back Scattering? Is it like when the light defected but still moves forward direction for forward; light is reflected backwards for back scattering?

Thank you.

Kunkle wrote:
...
What is the difference between Forward and Back Scattering? Is it like when the light defected but still moves forward direction for forward; light is reflected backwards for back scattering?

Thank you.

In order to make you develop a feeling for the meaning of the Mie asymmetry parameter with strong enhancement of backward scrattering, I precisely referred you to my Titan thread!

OK, since you didn't study that, apparently, here is an image that shows directly what back scattering looks like. This requires a large NEGATIVE Mie asymmetry parameter:



The top image is from Cassini imaging, the bottom image is with my atmosphere parameters within Celestia.

Bye Fridger

Indeed Fridger, thank you for explaining, and for providing the example! Those definitions should go directly into the next SSC parameters definition manual.