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Unmanned Spaceflight.com > Outer Solar System > Saturn > Cassini Huygens > Cassini PDS
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Bjorn Jonsson
Following discussions in the Image Processing Techniques subforum (see in particular this thread but also this one) I have now managed to create DEMs of acceptable quality of Enceladus using shape from shading and extensive post processing (mainly destriping). I now have a DEM mosaicked together from 5 images obtained during Cassini's first flyby of Enceladus in 2005. This will eventually become a global 23040x11520 pixel DEM but finishing it is going to be a lot of work (I will probably be using 50-100 images or more). Not all of Enceladus has been imaged at this resolution but there are many high resolution patches and I want a DEM big enough for these.

This 5 image DEM was big enough for me to really want to see what an Enceladus DEM animation would look like. So here we go:

Click to view attachment

The field of view is 50 degrees. Most of the animation is at an altitude of 25-30 km. This is similar to Cassini's altitide during the closest flybys and the speed is not far from Cassini's speed either. However, the animation starts and ends at higher altitudes and we also swoop down to an altitude of ~10 km where the resolution of the DEM is highest.

This is the Cassini image I used for the highest resolution part of the DEM:

Click to view attachment

And a single frame from the animation showing a part of this terrain:

Click to view attachment

The DEM should be fairly accurate - in particular the animation should give a very good general idea of what Enceladus looks like even though some details are inaccurate. Also a higher resolution DEM is really needed for these low altitudes - the surface should look less smooth than it does here. Most of the striping is real though as there are lots of parallel ridges and grooves on Enceladus. There may be some spurious stripes but these are very subtle - the obvious ones are real.

I'll do a new animation once I have a significantly bigger DEM. It will probably have better optimized illumination. Shadows are really needed in the first half of this one because I optimized the illumination for the highest resolution part of the DEM. We fly over that part of the DEM at roughly 00:30.

EDIT: To play the animation you need to have an H.264 codec installed (if you are using Windows you can find one here for example).
charborob
I must be missing something in my version of Quicktime because I can't play your .avi file. I'll try to fix that. In the meantime, can you tell me how much vertical exaggeration you have in your rendering?
Bjorn Jonsson
I forgot to mention that to play the animation you need to have an H.264 codec installed (if you are using Windows you can find one here for example).

There is no vertical exaggeration but the true vertical range was rather difficult to estimate accurately. I ended up repeatedly adjusting it until the rendered images approximately matched Cassini's images when using identical illumination and viewing geometry.
Floyd
Very nice! And thanks for the directions to the codec. When I first just tried to open it, my Real player tried but fiailed. When I saved it and opened with Windows Media player all went well.
lyford
Beautiful - thank you!
nprev
blink.gif ...outstanding, Bjorn, thank you!!!
Ian R
Very well done!
JohnVV
very nice

it is time consuming isn't it

by the way what program are you using to make the vid .
Bjorn Jonsson
Yes, finishing the DEM is time consuming - it's going to be a lot of work (I'm not even sure I'll finish it this year).

The individual frames are rendered using software written by myself and then assembled into an AVI file using VideoMach.
Bjorn Jonsson
After seeing machi's anaglyphs of Titania I decided to see what an anaglyph of my Enceladus DEM looked like - actually my first ever anaglyph. This first experiment turned out way better than I expected so here it is:

Click to view attachment

Now I really want to do an anaglyph animation of Enceladus.
machi
Very nice!
I'm glad, that my work is inspirational. smile.gif

"Now I really want to do an anaglyph animation of Enceladus."
That would be really wonderful and I think, it would be first such Enceladus' animation.
Phil Stooke
Right... approaching the south pole with the plumes rising above the horizon, and then weaving between the plumes... cool!

Phil
Bjorn Jonsson
QUOTE (Phil Stooke @ Apr 19 2011, 03:14 PM) *
Right... approaching the south pole with the plumes rising above the horizon, and then weaving between the plumes... cool!

This would be cool once I have finished a DEM of the south polar region (I'm working on a global DEM of Enceladus). The DEM I currently have is near the equator only.

And here we go, an anaglyph animation of a Enceladus:

Click to view attachment

This is the same general area as in the earlier animation but the flight path is different and shorter (the altitude is constant at ~25 km). Needless to say you'll need red-blue glasses to view this properly.
machi
Superb work!

Can you make this animation in reverse direction (opposite view, from flat terrain to mountainous terrain) and approx 2× slower (it's so nice and so quick smile.gif )?
Bjorn Jonsson
As I have mentioned, I'm working on a DEM of Enceladus using images from the PDS. Using these images can result in considerably higher quality than using the raw JPGs. This is a by-product of the DEM processing, a 12 frame mosaic of images obtained during Cassini's first close flyby of Enceladus back in February 2005:

Click to view attachment

North is up. This is the first Cassini image product where I used ISIS to a significant extent - for the processing I used various software including ISIS, Photoshop and software written by myself. I used ISIS mainly for correcting the camera pointing angles (this turned out to be suprisingly easy to do once I got past some initial problems using ISIS). The more accurate pointing makes it easier and faster to get the images properly aligned and also yields more accurate results. Soon I should also have a DEM of most of this terrain (the main exceptions are terrain near the terminator and near the limb).

And here is a wide angle context image:

Click to view attachment

I may post more image or mosaics here later. Needless to say, anyone is welcome to post Enceladus-related PDS work here.
volcanopele
Not bad, not bad at all. You did better at blending the high res frame in with the rest than I did:

http://www.ciclops.org/view/2456/Enceladus...ling_Hemisphere
Ian R
That's top-drawer, Bjorn. Simply top-drawer. blink.gif
machi
Feast for the Eyes! tongue.gif
tedstryk
Wow...Bjorn, that is all I can say, wow. Great work!
ElkGroveDan
Bjorn knows more than a little bit about ice.
Bjorn Jonsson
QUOTE (ElkGroveDan @ Jul 2 2011, 03:35 AM) *
Bjorn knows more than a little bit about ice.

Yes, a bit smile.gif.

Regarding Enceladus, more mosaics are coming in the next several weeks, possibly better than this one. And the DEM I now have of most of the terrain visible in the mosaic I posted turned out awesome - I even managed to confuse a rendered image with a Cassini image for a few seconds, the first time this has happened to me. Needless to say I was happy.

BTW ISIS is turning out to be easier to use than I had expected. I used ISIS 2 a bit several years ago but ISIS 3 (which I'm using now) is considerably easier to use in my opinion.
elakdawalla
Are you using ISIS on a Mac or running Linux?
Bjorn Jonsson
QUOTE (elakdawalla @ Jul 4 2011, 02:13 PM) *
Are you using ISIS on a Mac or running Linux?

Linux on a machine with a dual boot configuration (Windows 7 and Linux).
djellison
On a Mac, apart from having to use the terminal to set some path variables before you use it - it's actually fairly easy. You can run it all from the terminal ( Mac version of a dos prompt ) or you can have actual programs for each app in turn.
ugordan
Calibrated NAC RGB view of Enceladus from Nov 30, 2010:

machi
Beautiful!
Phil Stooke
agreed!

Phil
ngunn
An all time classic. That deserves wide circulation. smile.gif smile.gif smile.gif
ugordan
Thanks.

BTW, if that image looks slightly "foggy" to you, it's not an imaging artifact, it's the dense bulk of E ring around the moon revealing its presence. If Enceladus happened to split the ring optical density along Cassini's line of sight precisely in half, you would expect the background beyond Enceladus' dark limb to be twice as bright as the foreground. Here it's not quite that, but reasonably close. A rough measurement shows the foreground portion at about 60-ish percent brightness of the background.
Stu
Absolutely beautiful. Seriously, why your images aren't *everywhere* - in books and magazines, and on NASA's own websites - is a mystery to me.
djellison
QUOTE (Stu @ Oct 5 2011, 04:21 PM) *
and on NASA's own websites


Yeah, someone should do something about that.


ph34r.gif

eoincampbell
Wondrous !
ugordan
Subject: Enceladus plume temporal variance. 3 NAC clear frames taken roughly at 50 second intervals, unsharped and contrast enhanced:

Click to view attachment

Can you pick up material from a couple of vents going up in "puffs"? I don't think this can be explained by parallax/rotation, the observed rotation of Enceladus is too small for that. I strongly believe this is a genuine variation in output flux on a timescale of a minute.
ugordan
Here's a ratio flicker gif. First frame is frame #2 divided by #1, second frame is frame #3 divided by #2. Shows subtle change in plume appearance from one frame to another better.

Click to view attachment

Notice alternating dark/bright clouds in the plume to the left and to the right. At least two distinct puffs seem to be present in each plume. There's a hint of variation in a third plume at around 12 o'clock but it's much less convincing than these two.

I tried to do a (very) rough measurement of the displacement in the right hand plume during the 50-ish seconds between snapshots and I got a radial velocity of ~250 m/s. I haven't double-checked this. In reality the flow is not in the viewing plane so any number would probably underestimate the real speed.

I've been looking to see if anything like this could be noticed in past plume images and I don't recall seeing anything convincing before.
ngunn
I'm not sure if it's two variable vents or just one that is changing direction, but yes, I agree there is real variation there. A nice obsevation! It's easy to believe - there's no reason why they shouldn't be variable. Perhaps the vent has an ice boulder stuck in its throat. Even in the absence of a mobile obstruction rapid flow is often accompanied by instability/turbulence. I wonder if it has a regular periodicity? Maybe it's singing a low lunar note.
machi
QUOTE (ugordan @ Oct 10 2011, 10:33 PM) *
Subject: Enceladus plume temporal variance. ....
Can you pick up material from a couple of vents going up in "puffs"? I don't think this can be explained by parallax/rotation, the observed rotation of Enceladus is too small for that. I strongly believe this is a genuine variation in output flux on a timescale of a minute.


It's very interesting, but I think, that it's game of shadows.
eoincampbell
Has the long shadow been explained?
john_s
QUOTE (ugordan @ Oct 10 2011, 02:33 PM) *
Subject: Enceladus plume temporal variance.


Awesome find! It looks pretty convincing to me.

Congratulations Gordan!
John
nprev
Re the long shadow: Looks to me like that's probably an effect of the shadow of Enceladus itself; parts of the plumes are in sunlight, some aren't. There are other plumes in the foreground of the shadowed region, which makes it look a little weird but that's a perspective effect.
hendric
Isn't that mostly Saturnshine lighting up the surface? It looks like the rightmost pixels are blown out, so that's where the sunlight terminator is located. The multiple shadow-lines are caused by the mostly-linear nature of the plumes; the further ones are more "down" I guess.
Bjorn Jonsson
This is a 21 frame mosaic of images obtained during Cassini's targeted flyby of Enceladus back in March 2005:

Click to view attachment

North is up and the resolution of the images I used ranges from ~35 m/pixel to ~350 m/pixel. This image is actually a by-product from a different image processing project; I should soon have a shape from shading DEM of most of this terrain.

The images were reprojected to simple cylindrical projection. The resulting map was then rendered with subspacecraft latitude=-1.4 and longitude=203.8 without applying any illumination.

Processed using mainly a 'mix' of ISIS, Photoshop and software written by myself.
Juramike
blink.gif Wow! The detail in that image is fantastic! Bravo!
tedstryk
QUOTE (Bjorn Jonsson @ Nov 15 2011, 09:54 PM) *
This is a 21 frame mosaic of images obtained during Cassini's targeted flyby of Enceladus back in March 2005:


I saw it and thought, "Oh, that's pretty." Then I zoomed in- AMAZING!!!
Guillermo Abramson
Amazing. Thanks for sharing it.
Guillermo
dilo
Congratulations to Gordan for today's APOD mosaic, it is really stunning!
http://apod.nasa.gov/apod/ap120208.html
(I would like to see more in the plume region but I guess wasn't photographed).

ugordan
QUOTE (dilo @ Feb 8 2012, 09:19 AM) *
Congratulations to Gordan for today's APOD mosaic, it is really stunning!
http://apod.nasa.gov/apod/ap120208.html
(I would like to see more in the plume region but I guess wasn't photographed).

Thanks, but that doesn't really belong to this thread. The image (not a mosaic) was taken a year ago.

Thanks for pointing this out. Posts moved to the correct thread - moderator
scalbers
Greetings - thought I'd post my latest Enceladus feature map here:

Click to view attachment

(Note to mod, technically this includes some PDS and older raw images, so the best thread/forum for this might be considered)
elakdawalla
These are cool, Steve! Thanks for sharing. Regarding where they should be put -- the point of the "raw" threads is to discuss ongoing mission in real time (the way the MER threads work), "PDS" threads are about manipulation of data sets. You've posted in the right place.
scalbers
Thanks Emily. Here's an updated version where more of the feature labels are rotated and offset for the Dorsa, Fossae, Sulci and such...

Click to view attachment

Full Resolution here: http://laps.noaa.gov/albers/sos/features/c..._180_center.png

That's the latest,

Steve
Bjorn Jonsson
My latest animation:

Flight over Enceladus

This is an almost 7 minute animation featuring a digital elevation model (DEM) covering roughly 50 percent of Enceladus' surface. It is the most complex and by far the biggest animation I have ever done. The DEM is created from 55 of the images Cassini obtained during its three close flybys of Enceladus back in 2005. The flight path, viewing and illumination geometry is carefully selected to completely hide the fact that the DEM is not global. The DEM's resolution varies from ~70 to ~350 m/pixel. The field of view is 50 degrees.

The DEM is created using a very simple shape from shading algorithm (SFS) followed by 'destriping' and extensive post processing. A significant amount of the processing is based on (or some processing ideas were indirectly triggered by) various tips posted in several threads here (in particular, some of JohnVV's posts were helpful). All of this processing was done using a mix of ISIS 3, Photoshop and software written by myself. The individual frames were rendered using a renderer written by myself. The first frames were rendered in early December but due to the size of the DEM and this animation project several things have changed since then. The most significant change is that I finally built a 64 bit version of the renderer in early January (the DEM is too big to be easily manageable at close range using the old 32 bit version).

Since the DEM is created using SFS, vertical exaggeration is variable across the DEM. I tried to keep it uniform and close to 1 but this really is impossible to do accurately without combining the SFS DEM with another DEM created using stereo imaging. A lot of stereo coverage is available but I haven't done this yet since it takes a lot of time - I may do it later. Vertical exaggeration probably tends to be greater in the highest resolution patches than in the lower resolution areas. It should be noted that for Enceladus I used a uniformly white texture map, i.e. all of the details visible are from the DEM. Compared to the source images, resolution loss is minimal in the DEM.

There is probably sufficient medium to high resolution data available to make a global DEM with one exception: The north polar region. Hopefully Cassini manages to completely image the NPR at 300-500 m/pixel (or better - preferably 100-300 m/pixel) later in its mission.

A few sample frames:

Click to view attachmentClick to view attachment
Click to view attachmentClick to view attachment

Needless to say I recommend fullscreen viewing (and a biased comment: Looks awesome on a large TV screen).
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