Celestia Forums

Attached is a new Saturn-rings texture, which I created using the NASA image on this page:
http://photojournal.jpl.nasa.gov/catalog/PIA08389
As the page says "This natural color mosaic was acquired by the Cassini spacecraft as it soared 39 degrees above the unilluminated side of the rings."

I wondered about the "unilluminated" aspect, but even the quick PNG produced in Photoshop yielded pretty good results. Attached along with the texture is an image from my setup of Celestia with the new rings. I set Celestia's date and vantage point to those in the NASA image on this page ( http://photojournal.jpl.nasa.gov/catalog/PIA08388 ). The agreement doesn't look bad, but when I have more time, I may refine the rings to have a little more transparency in their darker areas. In the meantime, enjoy!


INSTALLING THE TEXTURE:
In the folder in which you installed Celestia, first open the textures folder, then the lores folder. Then find the file named saturn-rings.png. Rename this to something like saturn-ringsORIG.png in case you ever want to revert to using Celestia's standard Saturn ring texture. Now just download the attached new "saturn-rings.png" into said lores folder. Restart Celestia and you'll see the new rings around Saturn.

EDIT 1: Hmmm. I thought attaching the PNG would allow you to download it. But on seeing the post I don't see how to do that. Is there a way to attach the PNG file so it can be downloaded?

EDIT 2: Oh, I see. Just right click on the image and select Save Image As...

I did such ringes already in 2007 when the Cassini data were released. The hardest problem is the data in the ring's alpha channel. You didn't loose a word about what you put there.

Here is my respective post from Oct 2007:
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Of course the saturn rings in Celestia do have an alpha channel. You just have to know how to extract it! .

The alpha channel of the rings was actually the more tedious part of the work, largely done by Grant Hutchison (and some help & discussions by me).

The alpha channel contains the earthbound hires measurements of the ring transparency as a grayscale image. The transparency was obtained by measuring the amount of transmitted light during the passage of the rings in front of a star (28 Sgr of known brightness)! The RGB part of the saturn-ring texture then is to contain ONLY the ring albedo (reflective part)! A clean separation of these two intrinsically different components is not quite easy...

Hence you cannot simply combine the two textures without doing some proper "renormalization"...

Bye Fridger
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Here is the link to the 28 Sgr transit data that we used:

http://pds-rings.arc.nasa.gov/ringocc/ringocc.html

Here is the link to some 2007 shots of my Saturn rings:

viewtopic.php?f=2&t=11559&hilit=Saturn+ring&start=19
here is more images from 2009
viewtopic.php?f=6&t=14380&start=1

CC's recent work about the same subject also seems to have passed unnoticed...

Fridger

Fridger,

Yes, as the article states, the mosaic was based on the "unilluminated" side of the rings. Perhaps a way needs to be devised to assign different parameters to the illuminated and unilluminated sides.

Either way, after comparing your photos of your 2007 post with the NASA mosaic, one has to wonder why they lack of the F-ring, lack of any delineation in the Huygens gap and so oddly delineate the C-ring. Was it your source material or your methodology?

VikingTechJPL wrote:Fridger,

Yes, as the article states, the mosaic was based on the "unilluminated" side of the rings. Perhaps a way needs to be devised to assign different parameters to the illuminated and unilluminated sides.

Illumination and thus reflectivity (albedo) and ring transparency are two entirely different characteristic features of the rings. The transparency has to be encoded in the alpha channel of the ring texture while the albedo is related to its RGB properties.

Either way, after comparing your photos of your 2007 post with the NASA mosaic, one has to wonder why they lack of the F-ring, lack of any delineation in the Huygens gap and so oddly delineate the C-ring. Was it your source material or your methodology?

The F-ring is certainly present, but due to the alpha channel data derived from 28 SGR passage acrross the rings, it appears relatively weak (see further below). NASA images meant for the public are usually exaggerating such faint features for obvious reasons.

My sources were the official 2007 Ciclops images that you also used 6 years later. They were quoted in the thread I referred to above. If you had taken a little more reading time, you would not have missed them.

Fridger

Here is a zoomed-in screenshot of my above Saturn ring texture. Can you see the F-ring now??
I still use my old texture in celestia.Sci.

[Click on image by all means for a bigger image]


Via a number of faint star images from the other ring side, you can also see the transparency of rings implemented from the 28 Sgr passage data. You still didn't make clear what data you used for your ring's alpha channel? Once more, we are talking about transparency NOT about illumination or un-illumination...

Fridger,

Because I have been quite familiar with the Ciclops data and had taken the time to read it prior to my last post, why do you resort to snide remarks like ". . . If you had taken a little more reading time, . . ."?

As is so evident in your own 2007 post ( viewtopic.php?f=2&t=11559&hilit=Saturn+ring&start=19 ), the two NASA images clearly show the F-ring and a highly different appearance of the C-Ring and Huygens gap compared to the images of your texture. Your insistence of the accuracy of your implementation of the Ciclops data and that you used the same source image for your rings remains unconvincing.

GW

From the Ciclops site, here are images showing the considerable differences of the natural color mosaics of the illuminated and unilluminated sides of the rings. The top image was taken Nov. 26, 2008 "from 10 degrees below the illuminated (southern) side of the rings ". The bottom image was taken May 9, 2007 "by the Cassini spacecraft as it soared 39 degrees above the unilluminated (northern) side of the rings"
This suggests that a single texture will inadequately represent the appearance of the rings, and that their transparency is only one of a number of factors that will have to be considered.

Here are the pages where anyone interested can find the above images in very high resolution:
http://www.ciclops.org/view/5404/A_Full ... urns_Rings
http://www.ciclops.org/view.php?id=3858

Thanks, Lodgy. For anyone interested, the Ciclops site ( http://www.ciclops.org/?js=1 ) definitely has a lot of great material, including loads of photographs that suggest how different Saturn's rings look from many different directions and under many different lighting conditions.

As Chris Laurel (who understands what's involved far more than the rest of us) has clearly explained, faithfully depicting the rings is not such an easy task. But I'm sure we'll keep trying.

Have a great weekend.

GW

Here's another site that looks like it has data-sets and a lot of other info about Saturn's rings:
http://pds-rings.seti.org/saturn/

It's part of NASA's PDS Small Bodies Node:
http://pdssbn.astro.umd.edu/index.shtml

Loads of info here about the rings of Jupiter, Uranus and Neptune too.

lodgy wrote:Thank you Viking, the subject is very interesting.
Links are good.

VikingTechJPL wrote:Fridger,
..., why do you resort to snide remarks like ". . . If you had taken a little more reading time, . . ."?
GW

Beware of trolls, there were long as there had been more and t00fri is a fan...

If I may here...

You two seem to be under the mistaken impression that Fridger (the Good Doctor) is up to nothing more
then trouble for newbies. This is FAR FROM the TRUTH.

The Good Doctor has been a very MAJOR force in the overall development of Celestia almost from the
ground up. He has also insured that Celestia is based on fact and scientific accuracy.

Now, the Good Doctor does have a bit of an ego, and he can be difficult to understand at times -
especially for someone as Brain-Dead as myself. That notwithstanding, however, Celestia would not
be as accurate as it is without a number of major scientific improvements initiated, created, and investigated
via modern scientific theory and facts - ALL created by Fridger in his undying efforts to improve aspects
of ACCURACY within Celestia.

Just FYI...

Good luck with YOUR improvements too. A little discussion about what may be right is always
good for the overall improvement of our favorite program.

Many thanks, Brain-Dead Bob