Celestia preview of Titan Flyby on Feb 15

[t00fri]

Hi Losty,

many thanks for testing. I was hoping that someone might take the time to do so. So we know now that my above Titan flyby scenario is about right (within the accuracy of Jestr's orbit), and also that the older cassini.xyz orbit is /qualitatively/ not too different, but numbers for the minimum altitude do differ. We also know that at least for the next Titan flyby, Jestr's orbit is doing better than the old one.

I can reproduce all your shots you have provided and the numerical data are precisely correct.

Clearly, the further we shall be working in the future with Jestr's orbit, the larger the expected errors, as he pointed out already.

Nevertheless, the accuracy is probably good enough for playing or qualitatively previewing the next few flyby's.

Bye Fridger

[t00fri]

I have
roughly recreated t00fris view with latest prerelease
(1.4.0pre6) and jestrs xyz, I suspect his graphics setup is
quite different from the lowly computer I use, but Titan does
look the same when paused at the same time.

http://img.photobucket.com/albums/v200/ ... eation.jpg

Ah, so he IS using Jestr's xyz file.

But how do we know that Jestr's is more realistic than the
one that already comes with Celestia? Why are they
different?

If you would at least read what has been written ...!

As clearly stated above:

I have carefully checked that there is NO qualitative
difference between the old cassini.xyz flyby scenario
(that you are using with the PRE versions) and Jestr's. So
your disagreement with my flyby image above is not
understandable! You probably just made a mistake
somewhere which cost me hours. ...

I have also stated that Jestr's orbit does significantly better
for the minimum altitude of the flyby's, as compared to the
official data from the familiar PDF document about the Cassini
Tour events. So there are quantitative differences that
clearly speak in favour of Jestr's orbit for the near future.

For the Dec '04 Titan flyby, for example, Jestr's orbit
is virtually perfect:

Jestr: min. altitude : 1181 Km at 11:45 UTC
old orbit.xyz: 1800 Km

official data: 1200 Km at 11:45 UTC!

For the Feb 15 flyby, I have detailed above that the min. altitude
is also significantly better with Jestr's orbit.

For the Huygens landing site, Jestr's orbit does very well.
Moreover, it has a complete and beautiful landing animation.
The old orbit does not include the landing of Huygens.

I have also explained above that the old orbit did not take
account of the December orbit corrections made close to
Saturn.

[symaski62]

cel://Follow/Sol:Cassini/2005-02-15T07:04:22.59973?x=YuBQzaxXUiSBDA&y=zUdWIjOuCDU&z=sgX79BQbl1F+/////////w&ow=0.435039&ox=0.666193&oy=-0.597432&oz=0.100019&track=Sol:Saturn:Titan&select=Sol:Saturn:Titan&fov=25.313326&ts=0.000000&ltd=0&rf=40851&lm=49152

^^

2005-02-15 07h04m22.59973s 801.63KM ^^

[jestr]

OK the new XYZ file I made for Cassini was downloaded using Horizons Telnet service with orbit sample points every 4 hours usually but every 5minutes for every flyby (except those of Saturn).When I replayed the whole xyz in Celestia however I noticed that many times Cassini would go straight through the moon ( Titan).So for these occasions I changed the xyz using Toti's XYZ builder script.The flybys I adjusted are as follows
2005 September 7th Titan flyby
2006 September 7th Titan flyby
2006 October 25th Titan flyby
2007 Jan 29th Titan flyby
2007 February 22nd Titan flyby
2007 March 10th Titan flyby
2007 March 25/26 Titan flyby
2007 April 10/11 Titan flyby
2007 April 26th Titan flyby
2007 May 12th Titan flyby
2007 Jun 13th Titan flyby
All the others are as downloaded from Horizons ,I havent got xyz orbits for the moons (though it is quite possible for a period of a few years I guess),so I havent checked how much the moon orbits are out,but I dont think its by too much.Hope this helps.Jestr

[t00fri]

Evil Dr. Ganymede:

Here is the proof that your above arguments are NOT correct!

1) The top image below is the WITH the clouds and
without any rotation applied. It obviously agrees with your
image above.

2) The second image is WITHOUT the clouds and you
can clearly see the much sharper terminator. I have told you
to switch off the clouds! I have also specified clearly that my
image was done with my recent Titan update texture that is
available for anyone. Also for YOU.

3) I have simply rotated the whole scenario 2) by 180
degrees. Obviously it now is identical to my first image
above that you disbelieved.

All these three images refer to exactly the same time and
distance between Cassini and Titan. The values are printed on top.

[Evil Dr Ganymede]

Gah! You know what the damn problem was?

Your texture file has a bloody great blank section in it! The boundary between that and the mapped part looks exactly like a terminator. And given that I don't have your texture (all I have is the surface that came with the default distribution which looks nothing like your updated texture), and haven't seen it in full, there was no way for me to know this. That part immediately behind and to the right of Cassini in your top image is illuminated, correct? But it's not actually remotely obvious that all the portion near the terminator is illuminated in your texture, it just looks dark. Which is why I was claiming that the illumination angle was wrong.

Now that you've actually demonstrated to me that WITH an atmosphere you get the same view that I did, it drew my attention to the illuminated section in the bottom right corner of your top image.

To me, without close examination of the image, it looks like the terminator is to the LEFT of Cassini in your top , and curving round to the right below it. Which looks completely different to the image with the atmosphere turned on.

So that's what confused me. I wasn't "arguing" anything. I merely could not see how the two images could be the same, because your texture - accurate though it may be given what we know - gave the appearance that the terminator was in the wrong place. All I wanted to know was why they were different, I wasn't accusing you of anything. Thpugh to be honest, I'm not interested in a 'qualitative' comparison, I wanted what I saw to be the same as what you made quantitatively too - but it appears that it wouldn't be unless I had jestr's file.

Either way, perhaps you might consider making the unknown parts of your texture lighter in colour so it is easier to see that they are being illuminated.

I found your titan texture, so hopefully if I get hold of jestr's xyz file I will be able to duplicate your image.

[Evil Dr Ganymede]

OK the new XYZ file I made for Cassini was downloaded using Horizons Telnet service with orbit sample points every 4 hours usually but every 5minutes for every flyby (except those of Saturn).When I replayed the whole xyz in Celestia however I noticed that many times Cassini would go straight through the moon ( Titan).So for these occasions I changed the xyz using Toti's XYZ builder script.The flybys I adjusted are as follows

Thanks. OK, I can feel confident that your xyz file is accurate .
I'll see if I can download that from the motherlode and get the same view that Fridger does.

[Evil Dr Ganymede]

I downloaded Jestr's addon, unzipped it all into the Celestia extras folder, and renamed the old cassini.xyz, and now I can't see Cassini at all and it doesn't show up when I enter it into the text window. It made a folder called "Cassini_Huygens_Landed_CMOD" and put everything in there in the extras folder. I tried moving the files to one directory level higher, and still nothing appeared.

Any idea what I'm doing wrong?

[t00fri]

I downloaded Jestr's addon, unzipped it all into the Celestia extras folder, and renamed the old cassini.xyz, and now I can't see Cassini at all and it doesn't show up when I enter it into the text window. It made a folder called "Cassini_Huygens_Landed_CMOD" and put everything in there in the extras folder. I tried moving the files to one directory level higher, and still nothing appeared.

Any idea what I'm doing wrong?

don't rename cassini.xyz in data! Just leave it there.
The folder 'Cassini_Huygens_Landed_CMOD' should be in extras. Eliminate any further possible add-ons related to cassini.

[Evil Dr Ganymede]

I downloaded Jestr's addon, unzipped it all into the Celestia extras folder, and renamed the old cassini.xyz, and now I can't see Cassini at all and it doesn't show up when I enter it into the text window. It made a folder called "Cassini_Huygens_Landed_CMOD" and put everything in there in the extras folder. I tried moving the files to one directory level higher, and still nothing appeared.

Any idea what I'm doing wrong?

don't rename cassini.xyz in data! Just leave it there.
The folder 'Cassini_Huygens_Landed_CMOD' should be in extras. Eliminate any further possible add-ons related to cassini.

If I don't remove the original cassini.xyz file, then how does Celestia know what the updated trajectory is?

Anyway, I did what you said, and now I get this:


I'm using your texture from:
http://www.celestiaproject.net/~t00fri/images/titan-new2k.png

So why am I still not seeing exactly what you see at that time? I'm seeing a lot more illuminated terrain to the right of cassini there than in your second image that you posted further up this page. (and before you ask, I have no ambient light turned on)

[t00fri]

I'm using your texture from:
http://www.celestiaproject.net/~t00fri/images/titan-new2k.png

So why am I still not seeing exactly what you see at that time? I'm seeing a lot more illuminated terrain to the right of cassini there than in your second image that you posted further up this page. (and before you ask, I have no ambient light turned on)
_________________

Well, the first thing that is obvious is this horrible purple haze: I bet you still have a corresponding entry in solarsys.ssc. Comment it out. It's really horrible

After this is done you will see the surface details much more clearly, including the Huygens landing site at 1 o'clock (after a rotation by 180 degrees).

As to the sharpness of the terminator, this may well depend on the /rendering path/ that is used. I have a 'high-end' FX5900 Ultra card and correspondingly use 'OpenGl 2.0' rendering. This does not render any haze, for example. My suspicion is that the switched-on haze layer in your image provides this softer illumination (make physical sense at least). My guess is that you will agree much better with my image, once the haze is gone.

[jestr]

Evil Doctor,if you just put my addon in your extras (as you have now?),the new Cassini.ssc instructs Celestia to 'Modify' the existing definition for Cassini to use the new CassiniGrandTour.xyz file and a new model.Hope this makes it a little clearer..Jestr

[TERRIER]

Was/(is) Titan thought to have a purple haze, when viewed in visible light ?

[t00fri]

Was/(is) Titan thought to have a purple haze, when viewed in visible light ?

Certainly NOT. This is probably a leftover from earlier times. Comment the haze out in solarsys.ssc if you got some. It looks horrible...

Bye Fridger

[Evil Dr Ganymede]

Was/(is) Titan thought to have a purple haze, when viewed in visible light ?

Certainly NOT. This is probably a leftover from earlier times. Comment the haze out in solarsys.ssc if you got some. It looks horrible...

Bye Fridger

I'm not so sure you're completely right.

http://saturn.jpl.nasa.gov/multimedia/i ... ageID=1130

The image linked to above is a natural colour view (red/green/blue) and apparently there IS a blueish haze layer around the limb of Titan in true colour.

http://saturn.jpl.nasa.gov/multimedia/i ... ageID=1131
That said, this image shows the falsecolour "purple haze" image.

So it seems that there is a blueish haze, but in visible light it's not as extensive or vivid as the falsecolour image indicates.

[t00fri]

But we have discussed this false color outer atmosphere blue
layer in the UV spectral range extensively before.

From the caption:

The image has been falsely colored: The globe of Titan
retains the pale orange hue our eyes usually see, and both
the main atmospheric haze and the thin detached layer have
been brightened and given a purple color to enhance their
visibility.

I think this is the most recent 'natural color adaptation' of the
outer haze region:

The haze has been given colors that are close to what the
natural colors are believed to be. The view was also
sharpened to enhance the structure in the discrete feature.

The image was acquired at a distance of about 1 million
kilometers (621,371 miles) in a near ultraviolet filter that is
sensitive to scattering by small particles.

All this is unrelated to the surface bound purple haze that
Celestia incorrectly displays if the 'haze' statement is not
commented out in solarsys.ssc.

[Evil Dr Ganymede]

Yes, and if you look at the caption for the other image I linked to:

Following its first flyby of Titan, Cassini gazed back at the smog-enshrouded moon's receding crescent. This natural color view was seen by the spacecraft about one day after closest approach. The slight bluish glow of Titan's haze is visible along the limb.

That implies to me that there should be some blueish haze simulated in Celestia, visible from quite far away.

I agree that the really exaggerated purple haze is unrealistic, but there should still be SOMETHING there in visible light.

[t00fri]

Yes, and if you look at the caption for the other image I linked to:

Following its first flyby of Titan, Cassini gazed back at the smog-enshrouded moon's receding crescent. This natural color view was seen by the spacecraft about one day after closest approach. The slight bluish glow of Titan's haze is visible along the limb.

That implies to me that there should be some blueish haze simulated in Celestia, visible from quite far away.

I agree that the really exaggerated purple haze is unrealistic, but there should still be SOMETHING there in visible light.

What I am trying to argue is that these are phenomena at
vastly different distances from Titan's surface due to the
unusual thickness of its atmosphere: The outer bluish layer
has been spotted in UV light and is >1000 km above the
surface. Celestia's artificial purple haze layer is very close to
its surface. So NO connection whatsoever...

Bye Fridger

[Evil Dr Ganymede]

What I am trying to argue is that these are phenomena at
vastly different distances from Titan's surface due to the unusual thickness of its atmosphere: The outer bluish layer has been spotted in UV light and is >1000 km above the surface. Celestia's artificial purple haze layer is very close to its surface. So NO connection whatsoever...

Ah, I see what you mean now. Yes, the lower purple layer should be removed.

But the caption and image I linked to suggest that the outer blueish layer IS there in visible light, not just in UV. It just doesn't look quite as bad as the "purple haze" cassini image (which is seen through a UV filter), and as far as I know that upper haze has not been simulated in Celestia yet.

[t00fri]

But the caption and image I linked to suggest that the outer blueish layer IS there in visible light, not just in UV. It just doesn't look quite as bad as the "purple haze" cassini image (which is seen through a UV filter), and as far as I know that upper haze has not been simulated in Celestia yet.

You may easily do it yourself by modifying Titan's atmosphere parameters

Code: Select all

        Atmosphere {
                Height      200
                Lower       [ 0.477 0.356 0.214 ]
                Upper       [ 0.96 0.805 0.461 ]    <========
                CloudHeight   3
                CloudSpeed   65
                CloudMap "titan-clouds.*"
        }


E.g by using

Code: Select all

Upper       [ 0.36 0.205 0.761 ]


instead, it looks like this