Reprojection works better than it has any right to

[fivemack]

Y'know, if testing an algorithm which turns out to rely absolutely critically on precise to-the-pixel identification of surface features between images, maybe I should have chosen something other than Titan, an object all of whose surface features have critically fuzzy edges.

To obtain this image (click on it! it grows bigger!), I took the four photos that I photo-mosaiced incompetently yesterday, then solved for the best-fit circle to the ones showing limbs, then solved for the circle parameters for the ones not showing limbs by requiring the features to map to the same places as features whose positions I knew by reference to the limbs. I've then cropped off the bits that were black, or so close to a pole as to be absurdly fuzzy. I'm impressed at the continuity of scale and of colour.

The scale on this map is slightly too small to see the Mysterious Scratch without the eye of faith, but it's visible at the terminator on the big image.



This is a cylindrical projection, nothing like as good even as Mercator's, and with arbitrarily chosen equator and poles.

It is an odd feeling to be producing what I think may be the first maps of unexplored parts of a new world. I wonder if anyone will bother to name these craters. There are enough hundreds of them to drain the name-stocks of the Aeneid many times over.

Comments

[shimgray.livejournal.com]

The Mysterious Scratch is interesting; rift of some form? It does seem to be fairly recent - it overlays all but one of the features it passes through, I think. (But it's hard to say)

There's a couple of sharp linear features on the Moon that might be useful comparisons, but none that directly map as far as I can recall.

(also: um. hi. saw the pretty pictures on your comments to a post of James', and wandered over...)

[fivemack.livejournal.com]

The Mysterious Scratch is on the order of twice as long as the Straight Wall on the Moon, and significantly straighter.

http://legault.club.fr/alpinevalley_w.jpg and http://legault.club.fr/mur_m.jpg look like the same sort of thing, but the surroundings on Luna are clearly mariae, which Dione doesn't seem to have.

Glad someone likes the pictures. I should probably have gone to bed some hours ago.

[shimgray.livejournal.com]

There's also other rift features running at an angle to this, on the upper right-hand side. Not sure what that might indicate, except that they're "rougher", which gives the impression that those are more likely to be real / there's multiple processes at work.

A friend suggested ice-cracking? Apparently there's analogies on Ganymede, but I haven't chased that up.

Hmmm

[ellarien]

Seeing the remapping, and the way it goes across image boundaries, I'm leaning more towards believing that the Mysterious Scratch is real.

Thanks for the images!

[scottscidmore.livejournal.com]

The scratch is in the center, running upper left to lower right? It appears to ave a bright spot wherever it cross the illuminated side of a crater? If that is it, seems to be paired light and dark 'lines'.

[emperor]

Are you going to publish these images?

[papersky.livejournal.com]

On Ganymede, there's thought to be ice under the rock which causes odd effects a bit like your Mysterious Scratch.

This is very cool. Also gorgeous.

There are a lot of names in the Aeneid, all those sailors and spear-carrying Carthaginians. What I think would be beyond weird would be calling one of those craters Aeolus -- opener of the bag of the winds -- who appears in book 1 to cause a storm at Juno's behest and then have an argument with Neptune. If there's one thing Dione doesn't have more than anything else it's wind. It might have ice, which is like an ocean, sort of, but you can just tell looking at those images that there was never any wind, not even once.

[fivemack.livejournal.com]

Where do you suggest? Doubtless the Cassini Imaging Science team have done much the same thing for publication, using better tools, and even if they don't get the results as quickly as J Random Blogger, they deserve the priority through the fifteen years prior to today they've spent getting Cassini built and launched.

[shimgray.livejournal.com]

It's also possible it's on the back-burner; the next Dione flyby is in October (a close one, though - 500km!), and they may be wanting to keep this back until they have some detail imagery to attatch it to, help make sense of the broader picture. (If this is what comes out of a flyby at 80,000km, when they've their hands full with Titan two days earlier, a dedicated approach/close-pass will be wonderful)