Celestia Forums

After checking once more the official Cyclops (mosaic) maps for updates of Saturnian satellites,

http://ciclops.org/maps.php

the remarkably good Iapetus map ( Oct 17, 2008, 6199x3407 with coordinate frame) struck my eye. It is an update of the January 2008 release. Some days ago, while returning by train from a 3.5 weeks stay in another part of Germany, I set out to do a nice 4k Iapetus texture for Celestia, based on this official Ciclops map.

Despite the good quality of the input data, the task required quite a bit of image manipulation work before I was satisfied:

• cutting the texture data carefully out of the frame and reducing the size somewhat to 4096x2048;
• improving significantly many mosaic transitions along with contrast/brightness smoothing;
• coloring with GIMP based on the same true-color template as in my previous 4k Iapetus of the Celestia distribution, carefully eliminating noise and sharpening a bit;

Altogether, the result is based entirely on official and most recent Ciclops input, but looks considerably more pleasing. There is a vast amount of new hires mosaics compared to my previous 4k texture. Hires imaging meanwhile covers most of the moon. Therefore the new 4k iapetus should be a significant improvement compared to my present official texture in Celestia's hires directory...

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The fullsized (4k) PNG version you get here:
http://www.celestiaproject.net/~t00fri/images/ ... 08.png.zip
EDIT: I have made a minor update of the archive at 22:50 UT
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Have a click to see it bigger:

Simple cylindrical map strongly reduced to 1k:


Renderings in Celestia:



Comments?

Chris, do you want it for Celestia 1.6x??

Fridger

Here is another view of the icy side (only 3 attachements allowed)

Fridger

Fridger,

Yes, please commit this texture to SVN for 1.6.0. I see a lot of improvements clearly evident even in the 1024x512 version. The very large crater in the bright terrain of the southern hemisphere looks great in your new texture, but it's barely visible in the current version.

--Chris

Nice work Fridger, although I personally like Steve Albers' version of the Iapetus map better. That map is also available in an 8k version.



imho this map looks more like Cassini sees Iapetus. The ciclops map is too bright I think. Ofcourse you could think Steve's map is too much like a chocolate icecream

CAP-Team wrote:Nice work Fridger, although I personally like Steve Albers' version of the Iapetus map better. That map is also available in an 8k version.

iapetus.jpg

imho this map looks more like Cassini sees Iapetus. The ciclops map is too bright I think. Ofcourse you could think Steve's map is too much like a chocolate icecream

For the Celestia distribution, I certainly prefer the official reprojections of the iapetus photographic images done by Ciclops rather than those done (in part) by Steve Albers. Reprojections are a very delicate matter and we want very accurate textures....

There is presently NO official 8k iapetus texture released by Ciclops. Steve is using preliminary, non-certified data...Also his mosaic transitions are often pretty "rough" to say the least. My colorations are ALWAYS done by quantitatively mapping from a true color template photo with GIMP, while Steve seems to invoke subjective colorations by hand. So I never need to ask whether I "like the color" . Such arguments are not part of a scientific approach that we adopt in Celestia...

Since I made this texture for the final Celestia 1.6.0 distribution, 4k is the maximum anyway that we have agreed on. Anything bigger will have to be part of a future hires pack...

Please NOTE: My new Iapetus texture has been substantially darkened relative to the Ciclops original.

Fridger

Fridger:

The texture is very nice. Thanks for taking the effort to prepare it for Celestia use.

Is the raised ridge running through the equatorial region real, or is it an artifact of the photographic process used to combine all the Ciclops images? If real, what is the current theory of how it formed?

Frank

fsgregs wrote:Fridger:

The texture is very nice. Thanks for taking the effort to prepare it for Celestia use.

Is the raised ridge running through the equatorial region real, or is it an artifact of the photographic process used to combine all the Ciclops images? If real, what is the current theory of how it formed?

Frank

It's real. In some places, the equatorial ridge is as high as 20km. It can be easily seen in images of Iapetus from Cassini:

http://ciclops.org/view_media/3428/Encountering_Iapetus

The currently favored theory for the origin of the ridge seems to be that it's a leftover from when Iapetus was spinning much faster and drawn into an oblate shape. As the rotation of the moon slowed, it cooled fast enough to preserve the equatorial bulge, yet slow enough for the rest of Iapetus to relax into a spherical form.

--Chris

fsgregs wrote:Fridger:

The texture is very nice. Thanks for taking the effort to prepare it for Celestia use.

Is the raised ridge running through the equatorial region real, or is it an artifact of the photographic process used to combine all the Ciclops images? If real, what is the current theory of how it formed?

Frank

Frank,

as a supplement to Chris' reply (with which I agree), here is a magnified portion from the rendering of my new 4k Iapetus texture for Celestia 1.6.0 that beautifully exhibits details of the equatorial ridge. From the displayed new hires mosaic, you can clearly make out the shape of the ridge that is partly ice-covered . That hires mosaic was added in the latest Ciclops map, and I have much improved it's smooth embedding into the lower-res environment.



Fridger

As ever, Good Doctor, just wanted to thank you for this
improvement. Magnifique...

I have now committed my Iapetus update to SVN (4k, 1k, 0.5k). It is based on a new Ciclops map dated Oct 2008.

The affected files are

hires/iapetus.jpg medres/iapetus/jpg lores/iapetus.jpg
ChangeLog

Fridger

t00fri wrote:

CAP-Team wrote:Nice work Fridger, although I personally like Steve Albers' version of the Iapetus map better. That map is also available in an 8k version.

iapetus.jpg

imho this map looks more like Cassini sees Iapetus. The ciclops map is too bright I think. Ofcourse you could think Steve's map is too much like a chocolate icecream

For the Celestia distribution, I certainly prefer the official reprojections of the iapetus photographic images done by Ciclops rather than those done (in part) by Steve Albers. Reprojections are a very delicate matter and we want very accurate textures....

There is presently NO official 8k iapetus texture released by Ciclops. Steve is using preliminary, non-certified data...Also his mosaic transitions are often pretty "rough" to say the least. My colorations are ALWAYS done by quantitatively mapping from a true color template photo with GIMP, while Steve seems to invoke subjective colorations by hand. So I never need to ask whether I "like the color" . Such arguments are not part of a scientific approach that we adopt in Celestia...

Since I made this texture for the final Celestia 1.6.0 distribution, 4k is the maximum anyway that we have agreed on. Anything bigger will have to be part of a future hires pack...

Please NOTE: My new Iapetus texture has been substantially darkened relative to the Ciclops original.

Fridger

Hello Fridger,

I think the official maps are generally good for reprojections, though there are cases where mine appear to be more accurate in terms of consistency in matching some of the local features. One can see the types of errors present both in NASA's and in mine by comparing successive versions of each. For example south of the crater Naimon (~40 E longitude) there are some mismatches in the NASA version where several features appear to be duplicated. I agree that reprojection can be tricky (with some inherent inaccuracies) with a satellite like Iapetus when we have images taken from different angles given the irregular (and incompletely known) figure of the satellite.

Out of curiosity, are true color templates always available for most of Iapetus? Many of the color images I've seen are in IR-G-UV, though I suppose one can dig into the PDS and find a few that are in RGB. How many RGB images have you used?
The color of Iapetus may change according to locale, so a single color template (if that is what you are using) may be incomplete. For example a shadowed area in the icy section would be grayer than a sunlit section in the dark terrain. Overall though I do like the general appearance and blending from what I've seen so far in your map, except that Cassini Regio should perhaps be darkened a bit further (thus more consistent with its "scientifically" determined albedo ). To be fair perhaps a bit of art is required when representing the real satellite on a computer monitor having limited dynamic range.

I think I've relied too much on IR-G-UV imagery to get my color so I should perhaps tone it down a bit to produce the best estimation of what RGB coverage would produce (if it were available). My maps have often been produced rather quickly to be as up to date as possible with new imagery. It is thus worth taking a second look at what can be improved including comparisons with the more recently produced official versions. I have started to include improved navigation info from the PDS in my latest Iapetus map (and some others).

FWIW, in my general defense, my maps enjoy some behind the scenes use within NASA as can be seen on various NASA web sites (along with various personal communications). I'd also suggest that real-world science often has some art mixed in to help fill gaps in the data along with a dash of politics for good measure .

Steve