What do you mean, I spend too much time on Saturn?

Okaaaay ... draw a couple of points around the fully-illuminated limb, solve for the circle that passes through them best, estimate the diameter of Dione as 575 ± 10 kilometres using the optics specification, unwrap the map from spherical polar coordinates to cartesian, construct an enormously-blurred negative image and alpha-blend it in to remove the phase effect, and we have something resembling a map of Dione. I'm really impressed that the craters actually come out circular.

Next: get actual latitudes and longitudes for the features from here,
get a Voyager-era map marked up with the location names and figure out which crater is which, at which point I should be able to deproject the larger images, even the ones which don't show a limb.

Unfortunately, I can't convince myself that the Voyager-era map (the place names are mostly from Aeneas) and the deprojected map show the same planet. Maybe the crater pair in the top left of my map are Romulus and Remus.

There are moments when I wonder if I might have ended up in the wrong job, but I'm sure astrophysics gets as tiresome as civil service with long exposure.

Reprojection works better than it has any right to

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.