[X] My Assistant

[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:

 enceladus_sfs_umsf.avi ( 7.74MB ) Number of downloads: 1335


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:



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



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).

[scalbers]

Very nice animation Bjorn. It's fun to try and recognize various features as you fly over. One example is the sequence starting at 4:55 when the crater Sabur is centered in the view. Then from 5:00 to 5:12 we are flying northbound alongside Anbar Fossae. At 5:21 we're transitioning from Samarkand Sulci to Hamah Sulci (note unnamed crater at that time), then about 5:30 when flying from Hamah Sulci down to Ebony Dorsum.

Earlier at 2:23 we come upon a double crater, the one on the right side being Al-Mustazi. We approach the northern part of Bishangarh Fossae at 2:26. Then we catch the western part of Al-Yaman Sulci (oriented from left to right) around 2:33. By 2:43 we swing to look at the southern end of Harran Sulci (towards the west). At 2:49, we are looking westward at the northern end of Khorasan Fossa. At 3:00 we spot the intersection of Harran Sulci and Kaukaban Fossae near the limb. Then by 3:07 the crater Harun is located above the center. The southbound canyon fly through at 3:30 looks like we're going back through the southern end of Harran Sulci.

Perhaps the makings of a narrated sound track?

Things like the serrated limb help to make this look very realistic. Might be interesting to consider texture and even some slight color at some point?

Steve

[ugordan]

Might be interesting to consider texture and even some slight color at some point?

On the contrary, I think Bjorn nailed the color here.

Interesting to watch the phase angle effects as well, it's clear right from the initial frame that the photometric modelling of the disc is more realisic than what one would expect from just illuminating a ball in a commercial 3D renderer. About the only thing that gives away the fact this is a rendering is the lack of secondary illumination of shadowed slopes near the terminator by the opposing sunlit slopes. Other than that, add some point spread function and this could pass under an actual Cassini image.