Enceladus DEM: Combining stereo and crude shape from shading, Early attempts Options

[Bjorn Jonsson]

After seeing Nirgal's highly spectacular results in creating DEMs of Mars from HiRISE images using shape from shading (SFS; see this thread) I got really interested in combining DEMs created using stereo imagery and DEMs created using shape from shading. The reason of course is that I already have software for creating stereo based DEMs and it's working very well. Why I want to combine these two approaches is obvious when looking at this image of Enceladus created using a stereo DEM:



The large scale topography is correct but smaller features are missing (the small scale stuff in this image is spurious). This doesn't look realistic (not too bad at much larger distances than here though).

I have an extremely simple and crude SFS program that simply scans the input image in the direction from which the illumination is coming and treats each 'line' independently. The SFS software assumes the illumination is from the left and rotates the input image if it isn't. Since this was a true quick-and-dirty experiment I simply assumed the illumination came exactly from the west and used the Steve Albers map as a source image. This wasn't too inaccurate for the region I was processing. The resulting DEM looked absolutely horrible with *lots* of extremely ugly dark and bright horizontal stripes so I'm not even showing it here; the total elevation range was ~250 km (!). The result would have been similar (perhaps a bit better) even if I had used an exactly correct illumination geometry. However, after I combined this with the stereo derived DEM by taking the low frequency stuff from the stereo DEM and the high frequency stuff from the SFS DEM I got this test render:



This is an enormous improvement over the stereo-only DEM above. Some east-west stripes are visible though that become more apparent if I change the illumination geometry:



Despite the east-west stripes this is probably the best DEM I have ever created and certainly the highest resolution one; there is no loss of resolution from the SFS source image. The problem is those damn stripes even though they are far more subdued than in earlier SFS DEMs I have created. I have some ideas for automatically detecting and fixing them at negligible loss of resolution but I don't know if they'll work. Another possibility is writing more sophisticated SFS software in an attempt to get DEMs approaching 'Nirgal quality' but this is a *huge* amount of work. Still, after seeing the test renders above I want a global DEM of Enceladus like the one above - but without the stripes. Whether I eventually succeed at this is uncertain at this time but I'm getting moderately optimistic.

And in fact I want similar DEMs for all of Saturn's large icy satellites...

[JohnVV]

a continuation on Enceladus
just some trial and error at the moment
i just ( a few min ago) exported the 3d mesh to a isis cub
from the new Enc map
"6197_14573_4Enceladus.tiff"
cropped from 13600 over
and 4100 down

the orig cropped image

a bump map made from using cyclops > exporting a mesh > converting to the Z data a cub

then a simple "emboss " ( light from the upper left 45 deg. )

still needs some work . but not to bad for two nights since i looked as the program