Celestia Forums

The latest images from Cassini indicate we need some changes to Suturn's atmosphere definition.


http://ciclops.lpl.arizona.edu/PR/2004B25/PR2004B25A.html

Can anyone suggest better settings?

Here's a Cel URL to take one to my guesitimate of Saturn being in the same position in Celestia...
cel://Follow/Sol:Saturn/2004-02-27T04:12:01.99901?x=AKbMArUxeE2gDA&y=iiWhrc8joLz+/////////w&z=la4jcFr0cUl0/////////w&ow=0.839040&ox=0.085886&oy=0.527160&oz=-0.103624&select=Sol:Saturn&fov=41.514980&ts=-1.000000<d=0&rf=38819&lm=130

Increasing the "height" to around 3000 seems to provide the lighter band seen at the top of the planet, but it also puts a band around the base of the planet for me, which is not seen in the real image.

Also this image seems to indicate that Celestia's ring shadows are not dark enough. They look much darker to me in the real image than they appear in Celestia.

Grr... I think screwed up the Cel URL somehow since it ends up looking at the sun for me rather than at Saturn.

Your URL works fine for me.

Also, you may have missed the comment on the CSICLOPS' "approach page" that

The image contrast and colors have been slightly enhanced to aid visibility.

That makes it a little hard to judge how much change would be appropriate. It's clear the opacity of the rings in Celestia isn't high enough, though.

Hi all,

below I compare the Saturn texture that I made a few months ago (from Bjorn Johnsson's recent 2k data)
in comparison with the very latest Cassini true color photo (see above).

Not so bad altogether, but we see a most important deficiency: The opacity of the rings is far too low in Celestia (you see the planet shining through on the top right!). This implies that the planet is too bright in the top half, since the shadows of the rings are not dark enough...We got some work to do here...

In case you have'nt spotted it right away, the top one is from Celestia
You may also observe that the rings need quite a bit of tuning: The outer rings (rel. to Cassini) are not dark enough and the separations of the inner ones are also not correctly modelled...

Bye Fridger

And it looks like the ring shadows (ring onto planet) need to be made much darker too...

JackHiggins wrote:And it looks like the ring shadows (ring onto planet) need to be made much darker too...

Jack, if the rings are made less transparent, then the ring shadows will get darker automatically. We don't want to make the shadows darker without fixing the rings, because that'll just look weird.

Grant

JackHiggins wrote:And it looks like the ring shadows (ring onto planet) need to be made much darker too...

Jack,

that's of course, one of the main issues which was discussed recently in the developer forum...

There was other independent (but less direct) information already that in Celestia, the opacity of the rings is too low and thus the darkness of the ring shadows insufficient. This (final) photo underlines the issue further, although the amount of processing always remains an unknown...

Bye Fridger

grant wrote:Jack, if the rings are made less transparent, then the ring shadows will get darker automatically. We don't want to make the shadows darker without fixing the rings, because that'll just look weird.

Whoops... That was pretty obvious...

Not so bad,but a strip is missing.i don?t think the problems are only the rings.The Saturn texture could be improved as well.When Cassini gets near the planet,maybe we will soon have a 4k texture.Am I right?

below I compare the Saturn texture that I made a few months ago (from Bjorn Johnsson's recent 2k data)
in comparison with the very latest Cassini true color photo (see above).

Not so bad altogether, but we see a most important deficiency: The opacity of the rings is far too low in Celestia (you see the planet shining through on the top right!). This implies that the planet is too bright in the top half, since the shadows of the rings are not dark enough...We got some work to do here...

In case you have'nt spotted it right away, the top one is from Celestia
You may also observe that the rings need quite a bit of tuning: The outer rings (rel. to Cassini) are not dark enough and the separations of the inner ones are also not correctly modelled...

Bye Fridger

[/quote]

danielj wrote:Not so bad,but a strip is missing.i don?t think the problems are only the rings.The Saturn texture could be improved as well.When Cassini gets near the planet,maybe we will soon have a 4k texture.Am I right?

But you sure realize that the Saturn "surface" we are seing is not solid but gaseous and thus the "bands" may also change with time...like in case of Jupiter.

Of course, a 4k resolution would be a great step forward...

Bye Fridger

The subtle purple "atmosphere light-scattering" effect is also interesting.
Instrumenting this in Celestia will be a great advance in simulation quality.

If you don't mind me saying so...

I think the Celestia Project is doing an incredible job of
getting us as close to the real thing as it does. When you stop
and think about what we're looking at here, it's simply mind-boggling
to me that it's as realistic as it is.

If this is going to turn into a wish-list for Saturn though, I'd like to see
the "spokes" and "patterns" of the rings in a better model.

Take care, Bob

Bob Hegwood wrote:If you don't mind me saying so...

I think the Celestia Project is doing an incredible job of
getting us as close to the real thing as it does. When you stop
and think about what we're looking at here, it's simply mind-boggling
to me that it's as realistic as it is.

If this is going to turn into a wish-list for Saturn though, I'd like to see
the "spokes" and "patterns" of the rings in a better model.

Take care, Bob

Grant is already working on it, I guess...

Bye Fridger

t00fri wrote:Grant is already working on it, I guess...

Well, a while back Chris did suggest that we could someday have circumferential as well as radial detail in ring textures (a broad ring texture would be wrapped around the planet, so that things like eccentric rings and spokes might be better modelled). But until then you're going to have to be content with radial detail.
I've just pieced together an opacity map of the rings at 10km resolution (taken directly from star-occultation data), which should help get the shadows right - the B ring is pretty much opaque over much of its width, which accounts for the density of the ring shadow visible in the photograph. Just need to get an albedo map together that is correctly proportioned, and we should be cooking.

Grant

Cool...

Thanks for your efforts here, Grant.

Take care, Bob

granthutchison wrote:

t00fri wrote:Grant is already working on it, I guess...

Well, a while back Chris did suggest that we could someday have circumferential as well as radial detail in ring textures (a broad ring texture would be wrapped around the planet, so that things like eccentric rings and spokes might be better modelled). But until then you're going to have to be content with radial detail.
I've just pieced together an opacity map of the rings at 10km resolution (taken directly from star-occultation data), which should help get the shadows right - the B ring is pretty much opaque over much of its width, which accounts for the density of the ring shadow visible in the photograph. Just need to get an albedo map together that is correctly proportioned, and we should be cooking.

Grant

Grant,

very interesting, indeed!
At the level of radial info only, what's wrong with the Cassini albedo:

Great work grant! Hope to see this in a pre version sometime soon!

I still think that the colors are not accurate.We can improve Saturn's atmosphere definition.The yellow band near the equatorial zone is weekly seen.The trnsitions for the band are more subtle,not so abrupt,the polar zones are bigger and there isn't so purple near the poles.Anyway,if you remember,Hubble's photo was a little different.Anyway,there is still one big trouble : You can see stars in the dark side of the planets,it's such as the nightside of the planet was part of the sky.This is very weird.And the shadow of the rings in the planet are also lacking

t00fri wrote:Hi all,

below I compare the Saturn texture that I made a few months ago (from Bjorn Johnsson's recent 2k data)
in comparison with the very latest Cassini true color photo (see above).

Not so bad altogether, but we see a most important deficiency: The opacity of the rings is far too low in Celestia (you see the planet shining through on the top right!). This implies that the planet is too bright in the top half, since the shadows of the rings are not dark enough...We got some work to do here...

In case you have'nt spotted it right away, the top one is from Celestia
You may also observe that the rings need quite a bit of tuning: The outer rings (rel. to Cassini) are not dark enough and the separations of the inner ones are also not correctly modelled...

Bye Fridger

danielj wrote:I still think that the colors are not accurate.We can improve Saturn's atmosphere definition.The yellow band near the equatorial zone is weekly seen.The trnsitions for the band are more subtle,not so abrupt,the polar zones are bigger and there isn't so purple near the poles.Anyway,if you remember,Hubble's photo was a little different.Anyway,there is still one big trouble : You can see stars in the dark side of the planets,it's such as the nightside of the planet was part of the sky.This is very weird.And the shadow of the rings in the planet are also lacking

...

I certainly agree that it makes sense to update Saturn's appearance to the latest photographic evidences. I will certainly do it. My image above was pre Cassini photograph.

But there is also no reason to hurry, since there is an attached warning that the public Cassini photos should not be used for scientific purposes (i.e. for Celestia ), since the image is not yet properly "balanced"/normalized.

Bye Fridger

danielj wrote:You can see stars in the dark side of the planets,it's such as the nightside of the planet was part of the sky.

That's a moon of Saturn, crossing the planet's disc.

Grant